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Since Cactoblastis cactorum appeared in Florida in 1989, via importation of infested horticultural Opuntia plants and/or natural spread from the Caribbean, there has been a concern about the moth’s threat to native and economic North American and Mexican Opuntia. The moth’s occurrence in the Caribbean is due to its introduction to Nevis Island in 1957 for the control of native Opuntia that were pasture weeds. We assessed the abundance of C. cactorum in target and non-target Opuntia species and the persistence of these Opuntia species on the small islands of Nevis and St. Kitts 50 years after the moth’s introduction. C. cactorum occurred at 10/16 sites on the two islands and attacked 22.7% of total plants. Of the four Opuntia sensu lato species found, three were attacked, including the native targets Opuntia triacantha (with 15.6% of plants and 8.9% of pads attacked) and Opuntia stricta (with 44.4% plants and 8.1% pads attacked), and the non-target cultivated and naturalized Opuntia cochenillifera (with 19.1% plants and 1.2% pads attacked). The native nontarget tree pear, Consolea (= Opuntia) rubesens, was not attacked. Larger and wild plants had significantly higher percentages of attack. Based upon our data, it appears that biological control of O. triacantha and O. stricta persists and these natives have survived 50 years of C. cactorum attack on these small islands, despite fears that the moth could have caused their extinction. Our analysis of this historical biological control effort suggests that the potential impact of C. cactorum on native North American and Mexican Opuntia will be significant and variable, but not necessarily catastrophic.

The reproductive system of adult male Cactoblastis cactorum, the cactus moth, was examined to determine whether the mating status of males could be ascertained. In unmated males, the posterior portion of the primary ductus ejaculatorius simplex is opaque yellow in color and contains many small football-shaped hyaline granules 3-5 x 5-10 {mu}m in size. In mated males, the posterior simplex is clear and contains no granules. The presence or absence of these characters was found to be highly reliable and should be of value in determining mating status in marked-recaptured males of this species in a sterile insect release program directed against Cactoblastis. (author)

The cactus moth, Cactoblastis cactorum (Lepidoptera: Pyralidae: Phycitinae), is a non-native species threatening a variety of native cacti, particularly endangered species of Opuntia (Zimmerman et al. 2001), on the coast of the Gulf of Mexico. Cactoblastis cactorum populations have expanded from Florida northward along the Atlantic coast as far as Charleston, SC, and westward along the Gulf of Mexico to Dauphin Island, south of Mobile, AL. It is feared that further movement to the west will allow C. cactorum to enter the US desert Southwest and Mexico, particularly the latter. Numerous cactus species, especially those of the genera Opuntia and Nopalea, are native to the U.S. and Mexico. Local economies based on agricultural and horticultural uses of cacti could be devastated by C. cactorum (Vigueras and Portillo 2001). A bi-national control program between the US and Mexico is being developed, utilizing the sterile insect technique (SIT). In the SIT program, newly emerged moths are irradiated with a {sup 60}Co source and released to mate with wild individuals. The radiation dose completely sterilizes the females and partially sterilizes the males. When irradiated males mate with wild females, the F1 progeny of these matings are sterile. In order for the SIT programmore » to succeed, large numbers of moths must be reared from egg to adult on artificial diet in a quarantined rearing facility (Carpenter et al. 2001). Irradiated insects must then be released in large numbers at the leading edge of the invasive population and at times which coincide with the presence of wild individuals available for mating. Mortality from disease in the rearing colony disrupts the SIT program by reducing the numbers of insects available for release.« less

The cactus moth, Cactoblastis cactorum mainly distributed throughout central and northeastern Argentina was intentionally introduced in the Caribbean region in 1957 as a biological control agent of cacti species of the genus Opuntia. This moth invaded during the last 20–30 years the North American continent, threatening the major center of biodiversity of native Opuntia species. Although human induced and natural dispersal have been invocated to explain its expansion in the non-native distribution range, there is still no evidence to support natural dispersal. In particular, hurricanes are one of the major environmental factors affecting species dispersal in the region. In this study we used mitochondrial DNA to examine whether the spatial distribution of haplotype variation of C. cactorum is at least partially explained by hurricane trajectories within the Caribbean region. DNA sequences for the mitochondrial gene cytochrome oxidase I were obtained for a sample of 110 individuals from the Antillean islands. This information was combined with existing sequences in the GenBank for the same gene for the Caribbean and Florida (N = 132 sequences). Genetic diversity descriptors, a haplotypic network, a spatial analyses of molecular variance and a landscape genetic analysis of migration conditioned by hurricane tracks were conducted to test our hypothesis. Our results revealed a significant spatial grouping of haplotypes consistent with the more frequent hurricane trajectories in the Caribbean region. Significant isolation by distance conditioned by hurricane tracks was detected. Populations of Florida were genetically closer to those of Cuba than to the rest of the population sampled. Within the region, Cuba appears as a reservoir of genetic diversity increasing the risk of invasion to Mexico and the US. Despite commercial transportation of Opuntia promoted dispersal to Florida, our results support the hypothesis that natural disturbances such as hurricanes played a role dispersing this invasive insect. Future conservation programs of North American Opuntia species requires taking into account hurricane mediated dispersal events and permanent whole regional monitoring and international control policies to prevent future range expansions of C. cactorum. Fil: Andraca Gómez, Guadalupe. Universidad Nacional Autónoma de México; México Fil: Ordano, Mariano Andrés. Fundación Miguel Lillo; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Boege, Karina. Universidad Nacional Autónoma de México; México Fil: Domínguez, César A.. Universidad Nacional Autónoma de México; México Fil: Piñero, Daniel. Universidad Nacional Autónoma de México; México Fil: Pérez Ishiwara, Rubén. Universidad Nacional Autónoma de México; México Fil: Pérez Camacho, Jacqueline. Ministerio de Ciencia, Tecnología y Medio Ambiente. Instituto de Ecología y Sistemática; Cuba Fil: Cañizares, Maikel. Ministerio de Ciencia, Tecnología y Medio Ambiente. Instituto de Ecología y Sistemática; Cuba Fil: Fornoni, Juan. Universidad Nacional Autónoma de México; México

The cactus moth, Cactoblastis cactorum (Berg), is an invasive pest of Opuntia spp. Since its arrival in the Florida Keys in 1989, it has moved rapidly up the east and west coasts of Florida, threatening to invade the southwestern United States and Mexico. Female moths produce a sex pheromone that attracts male moths. In this study, we report on mating behavior observed in the laboratory and the identification of putative pheromonal chemical components based on mass spectral analysis of volatiles collected from virgin female moths and from solvent extraction of excised glands. Three candidate components, formulated on rubber septa in different release rates and ratios, were tested in laboratory olfactometer and flight tunnel experiments, and in field tests in areas with known feral populations of cactus moths. Lures formulated with the three-component blend of 54% (Z,E)-9,12 tetradecadien-1-ol acetate, 42% (Z,E)-9,12 tetradecadien-1-ol, and 4% (Z)-9- tetradecen-1-ol acetate were the most effective, although changes in the ratio of these components had little effect on lure efficacy. For field deployment, traps baited with synthetic lures with a 1 mg load of the three component blend captured equal or higher numbers of males than traps baited with two virgin females. Trapping systems using this pheromone-based attractant will be useful for population delineation in areas currently infested.

The oligophagous cactus moth, Cactoblastis cactorum (Berg), has been recognized as a serious and immediate threat to Opuntia cacti in Florida and the southeastern United States. The moth has successfully colonized new geographical ranges with lower annual temperatures north of the Florida Keys where it was first detected in the continental United States in 1989. This study evaluated the effect of temperature on egg development and egg hatch of C. cactorum by utilizing various treatment temperatures, exposure times, and egg ages. The temperatures used in this study ranged from a low of -20°C to a high of 50°C, thus encompassing the potential range of temperatures that eggsticks may be exposed to in potential new host areas. One-d-old eggs held at a constant temperature of 30°C resulted in the highest percent hatch and shortest time to egg hatch. Eggs did not hatch when held at constant temperatures ≤15°C or ≥35°C. Furthermore, one d of exposure at -10°C and 4 d of exposure at -5°C were 100% lethal...

We conducted laboratory assays of nine products registered for use on ornamental plants in Florida for their ovicidal and larvicidal activity against the invasive cactus moth Cactoblastis cactorum. One-hundred percent mortality (or 0% survival) of 1-day-old eggs was obtained when eggstick sections were treated with cypermethrin, spinosad, or imidacloprid. These products were equally as effective when assayed against eggs that were fully embryonated (28 days old), when cladodes of Opuntia stricta were exposed to neonates 24 hours after dipping, or to cladodes that were dipped and stored for 30 days before exposure. When Bacillus thuringiensis (Dipel®) was used to prevent neonate penetration into treated cladodes of O. stricta, 100% mortality (or 0% survival) was recorded in the laboratory.

Moths can detect changes in environmental carbon dioxide (CO2) with extremely high sensitivity, but the role of CO2 in the biology of these and other insects is not well understood. Although CO2 has been demonstrated to influence egg-laying (oviposition) behavior of the pyralid moth Cactoblastis cactorum and nectar foraging of the sphingid moth Manduca sexta, information about the generalized role of CO2 in the behavioral biology of these species is lacking. Comparative data are necessary to properly assess how the behaviors of different species may be modified by steadily rising levels of greenhouse gases in the environment. Experiments carried out in Biosphere 2 addressed whether changes in ambient CO2 levels play a role in the oviposition behaviors of M. sexta moths. In the first series of experiments, oviposition was measured inside a flight cage with different levels of nearly ambient or elevated CO2 (400, 800 or 1200ppm). For each concentration, hostplants used as oviposition sites were grown from seed at a CO2 level that matched the environment inside the flight cage. Under homogenous levels of CO2, we observed no significant difference in oviposition behavior at the concentrations tested. In a second series of experiments, two groups of hostplants, each surrounded by a mini free-air CO2 enrichment (FACE) ring, were assembled inside a flight cage. In this choice test, a dynamic plume of artificially high CO2 was generated around one group of test plants, while ambient CO2 was released around the second (control) group. After eggs were counted on both plant groups, M. sexta females showed a small preference for ovipositing on the control plants. Therefore, in contrast to C. cactorum females tested under similar dynamic flow conditions, M. sexta female oviposition was not strongly inhibited by elevated CO2. To investigate this phenomenon further, we used electrophysiological recording and found that the CO2 receptor cells in M. sexta, unlike those in C. cactorum, are not readily affected by elevated levels of ambient CO2. These findings therefore suggest that elevated background levels of CO2 affect the physiology of the CO2 detection system of M. sexta to a lesser extent than that of C. cactorum, and this correlates well with the observed differences in oviposition behavior between the two species under elevated levels of environmental CO2. Hostplants of C. cactorum are crassulacean acid metabolism plants that generate nocturnal CO2 sinks on the cladode surfaces, whereas, M. sexta hostplants are nocturnal sources of respiratory CO2. We hypothesize that the abrupt and continuing increase in global ambient CO2 levels will differentially alter the behavior and physiology of moths that use CO2 sinks and sources as sensory cues to find hostplants.

In an effort to continue the development of a sterile insect release program against the invasive cactus moth, Cactoblastis cactorum (Berg), we released partially sterile males alone or in combination with fully sterile females at a 5:1 or 10:1 (treated:fertile) overflooding ratio inside large field cages containing Opuntia stricta Haworth (Haworth) host plants. Insects were allowed to mate and lay eggs, and all eggsticks were collected daily. Percent egg hatch and reduction in F1 fertile larvae were used to ascertain the effectiveness of each release combination. In addition, limited field release-recapture experiments were conducted to examine the dispersal ability of untreated and treated cactus moth males. Results suggest that an overflooding ratio as low as 5:1 can effectively suppress C. cactorum in field cages and that releasing both genders together is more effective than releasing males only. In open field releases, the dispersal ability of C. cactorum was not significantly affected by treating the adults with gamma radiation.

Our study characterized host searching and oviposition ability of T. fuentesi . In general, female wasps walked to a C. cactorum egg, drummed over the surface, drilled into the chorion, and deposited an egg. Grooming and resting behaviors were observed infrequently and host feeding was never recorded. In a typical observation period of 60 min with eggs of the exotic C. cactorum , female parasitoids spent 16% of their time drumming, 4% drilling, and 8% egg laying into the selected host. Most of the oviposition behaviors happened in the first hour. Nuestro estudio caracterizo la busqueda de hospedero y la capacidad de oviposicion de Trichogramma fuentesi . En general, las avispas hembras caminaron hacia los huevos de Cactoblastis cactorum, pegaron sus antenas sobre la superficie de los huevos como un tambor (en tamboreo), perforaron el corion y depositaron su huevo adentro. Los comportamientos de aseo y de descanso fueron observados con poca frecuencia y la alimentacion sobre el hospedero no fue registrada. En un periodo de observacion tipica de 60 min con los huevos de la especie exotica C. cactorum , los parasitoides hembras pasaron el 16% de su tiempo en tamboreo, el 4% perforando y el 8% poniendo huevos dentro de los hospederos seleccionados. La mayoria del comportamiento de oviposicion ocurrio en la primera hora. View this article in BioOne

The moth Cactoblastis cactorum (Berg), the poster child of weed biological control in Australia, has recently invaded the United States and threatens native cacti. Concern is greatest for the endangered semaphore cactus, Opuntia corallicola, of which only two known populations exist in the wild. We made three separate outplantings of O. corallicola, designed to bolster the number of extant cacti and to test the effectiveness of three different treatments to protect the cacti from Cactoblastis. In one outplanting, we tested the associational susceptibility hypothesis and found that cacti planted more than 20 m away from the common prickly pear cactus, Opuntia stricta, which act as a reservoir of Cactoblastis, were just as frequently attacked and killed by Cactoblastis as cacti planted within 5 m. In addition, Cactoblastis attack was greater in the shade than in the sun. In the second outplanting, we minimized the attack from Cactoblastis by using protective cages planted at least 500 m from O. stricta in areas not inhabited by cacti. Cages attracted the attention of local animals, which destroyed the cages and trampled the cacti inside to death. Crown rot caused high mortality in this outplanting. In the third outplanting, again conducted at least 500 m away from O. stricta, fertilization did not reduce crown rot mortality. We suggest that increasing populations of O. corallicola in Florida, by means of outplantings, will remain a challenge because of death from Cactoblastis when planted in areas where cacti normally grow and because of death from crown rot in areas where they do not. Because Cactoblastis is moving rapidly northward and westward and has already reached Charleston, South Carolina, rare cacti in the rest of the U.S. Southeast may be in danger. Eventually, many cactus species in the U.S. South, Southwest, and Mexico will likely be threatened by this moth.

The Strength of Biological Control in the Battle against Invasive Pests: a Reply MARK S. HODDLE Department of Entomology, University of California–Riverside, Riverside, CA 92521, U.S.A., email mark.hoddle@ucr.edu Nontarget Impacts of Biological Control Louda and Stiling (2004 [this issue]) state that biological control is not a simple matter of community re-assemblage because deliberate introductions of exotic natural ene- mies for suppression of exotic pest populations can have reticulate impacts that are difficult, if not impossible, to predict a priori. In an insightful retrospective study, Hawkins et al. (1999) analyzed 68 life-table studies of native insects and introduced insect pests to determine whether biological control is analogous to naturally oc- curring control (i.e., the action of native natural enemies on native hosts). Hawkins et al. (1999) show that suc- cessful biological control programs result in less reticulate trophic relationships than those seen in natural food webs of native insects. The most successful biological control programs are those that do not have “natural” food-web structures because biological control food webs consist of short, linear food chains that are devoid of complex reticulate trophic interactions. This result occurs because biological control systems often consist of exotic species that share few ecologi- cal or evolutionary links with native biota. Furthermore, control is enhanced in simplified habitats characteristic of agroecosystems and, arguably, native systems invaded by exotic plants because both often consist of vast mono- typic stands of exotic vegetation. Host-specific natural en- emies that cause population declines of the target pest are themselves subject to density-dependent population regulation as the biological control agent’s food source is depleted, and they are unable to adequately exploit other hosts in the environment to maintain high population densities because they lack significant trophic linkages to other hosts. The more specialized the natural enemy the less likely it is to infiltrate native communities and attack nontarget native species (Hennemen & Memmott 2001). Generalist natural enemies that have low levels of host and habitat fidelity and exploit a wide range of hosts in a vari- ety of habitats are more likely to cause unwanted collat- eral damage to nontarget species either directly through direct attack or indirectly through apparent competition because of reticulate food-web linkages. Two plant-feeding insects (Rhinocyllus conicus [inten- tionally released; Gassmann & Louda 2001] and Larinus planus [an accidental arrival in the United States that was eliminated as a potential biological control agent because of broad host breadth on Carduinae thistles in its home range; Louda & O’Brien 2002]) mentioned by Louda and Stiling as having “unexpected levels of nontarget feeding” were anticipated from host-specificity tests because both weevils were known to feed and reproduce on a variety of thistle species in their home and introduced range. As Louda and Stiling point out, both insects are “thistle specialists,” but thistles are a speciose group with repre- sentatives in genera that occur in Europe and North Amer- ica, and these weevils, due to their broad dietary breadth within the thistle group, have greater numbers of signif- icant food-web linkages than desirable, thereby making significant nontarget impacts more likely. The real issue here concerns legislation (i.e., redistribution of L. planus and R. conicus) and changing social values (i.e., what con- stituted acceptable damage to nontarget species, and the value of native flora and fauna in the 1960s versus 2003), as opposed to an inherent flaw in the theoretical prin- ciples underlying concepts of host specificity and host range assessment as they pertain to biological control. The moth Cactoblastis cactorum, a native of Argentina and “poster child” of biological control (Stiling 2002) has invaded the continental United States from the Caribbean and is attacking native cactii. Louda and Stiling consider C. cactorum a “specialist” on the cactus genus Opuntia, a group with approximately 200 species in the new world but no representatives in Australia, making C. cactorum a specialist on this continent when it was released in Paper submitted April 15, 2003; revised manuscript accepted May 23, 2003. Conservation Biology, Pages 61–64 Volume 18, No. 1, February 2003

Cactoblastis cactorum (Berg) (Lepidoptera: Pyralidae) is renown for its control of invasive cacti (Opuntia spp.). Its accidental arrival in Florida and its rapidly expanding range along the Gulf coast pose an imminent threat to native Opuntia spp., especially in the southwestern U.S. and Mexico. Adequate survey techniques are crucial in order to delineate the rate of spread of this invasive species. Virgin female-baited sticky traps have been effective in detecting C. cactorum adult males in areas where visual surveys failed to detect larval damage. However, the use of fertile females in traps placed beyond the currently infested area is discouraged because an escaped fertile female might establish a breeding population and expand the infested area. In this study we compare the attractiveness and the longevity of fertile and irradiated (sterile) females deployed as bait in traps. Traps baited with females sterilized with gamma radiation were as effective as traps baited with unirradiated (fertile) females in detecting populations of feral C. cactorum male moths.

Cactoblastis cactorum (Berg) has become an invasive pest of Opuntia spp. along the coastal areas of southeastern United States from the panhandle of Florida to South Carolina. Spread of this insect into cactus dominated natural areas of the United States and Mexico and into agricultural opuntia fields of Mexico is raising concerns within international governments and conservation organizations. Interest is growing in using the Sterile Insect Technique (SIT) to manage C. cactorum populations. Information on courtship and mating behaviors of this insect is important in the development and application of SIT. We conducted mating table studies and determined that this moth exhibits simple rather than elaborate mating behaviors and that courtship and mating take place briefly during morning twilight. Typically, females initiate calling, males respond to females, and copulation are complete before sunrise. Successfully mated females attract males within a short period (mean of 5.2 min), while unsuccessful females continue calling for about 40 minutes. Mating pairs remain in copula for a mean of 31.8 min. Generally, mated females are busy ovipositing the first few nights after mating, not exhibiting additional mating behaviors. A release of marked males revealed that males stay near the release site and can be recovered and identified for subsequent population estimate studies. This study on courtship/mating behavior is helpful to the ongoing C. cactorum research to develop a successful SIT program, identify the female calling pheromone, improve monitoring traps, and develop a technique to estimate adult moth population abundance.

Cactoblastis cactorum (Berg) (Lepidoptera: Pyralidae), the poster child of biological control, has recently invaded the United States. The first US record was at Big Pine Key, Florida, in 1989. Since then it has moved rapidly northward into South Carolina. Fears are high that it will disperse, either on its own, or with human help, into the US desert southwest and Mexico. There are at least 31 species of prickly pear in the US that are likely to be attacked by Cactoblastis and 56 species in Mexico. As well as the threat to wild cacti, there are over 250,000 ha of Opuntia plantations in Mexico that support a thriving agricultural industry, most of which is centered on harvesting fruits or pads. Possible control measures include classical biological control using parasitoids or pathogens from South America, chemical control or F1 sterility, as has been used successfully for the codling moth. However, most of these options appear to have insurmountable difficulties. Classical biological control raises the fear of further non-target effects of natural enemies on native cactus herbivores. Chemical control has potential non-target effects on other (rare) insects and is expensive. F1 sterility is also expensive and is not self-sustaining, requiring considerable and continual human input. Nevertheless, research on control options is vital as is further work on the rate of spread and impact of Cactoblastis in the United States Southeast, so that we can be as well prepared as possible to deal with this threat when it arrives in Arizona, California, and Mexico.

As part of sterile insect technique (SIT) programs, irradiation can effectively induce sterility in insects by damaging genomic DNA. However, irradiation also induces other off-target side effects that reduce the quality and performance of sterilized males. Thus, treatments that reduce off-target effects of irradiation on male performance while maintaining sterility can improve the feasibility and economy of SIT programs. Exposure to ionizing radiation induces the formation of damaging free radicals in biological systems that may reduce sterile male performance. Here, we test whether exposure to an anoxic environment for 1 h before and during irradiation improves male performance, while maintaining sterility in males of the cactus moth, Cactoblastis cactorum (Berg). We show that exposure to 1 h of anoxia increases the moth's antioxidant capacity and that irradiation in anoxia after 1 h of anoxic conditioning decreases irradiation-induced oxidative damage to the moth's lipids and proteins. Anoxia treatment that reduced oxidative damage after irradiation also produced moths with greater flight performance, mating success, and longevity, while maintaining F1 male sterility at acceptable levels for SIT. We conclude that anoxia pretreatment followed by irradiation in anoxia is an efficient way to improve the quality of irradiated moths and perhaps lower the number of moths needed for release SIT moth operations.

In Australia, fungi associated with larvae of the biological control agent Cactoblastis cactorum may contribute to the control of the exotic weed pricklypear (Opuntia inermis). C. cactorum larvae were assessed for their ability to vector pathogenic fungi into O. inermis by the infestation of larvae with fungal suspensions. Six fungal isolates caused disease after being carried into the host on external surfaces of larvae, and propagules of one isolate (UQ5109) initiated disease after being transferred from the cladode epidermis into the host by larvae feeding on the plant. Scanning electron microscopy revealed extensive hyphal growth on the external surfaces of larvae infested with several of the isolates. Fungi isolated from field-grown O. inermis cladodes were tested for pathogenicity to this plant in an in vivo plant assay. In total, 152 isolates were screened, 22 of which infected the host in pathogenicity tests. Only 1 (UQ5115) infected undamaged host tissue, whereas the remainder required the host to be wounded before infection could proceed. The majority of isolates were only weakly pathogenic, even when inoculated via wounds, suggesting that most were either saprophytes or weak parasites. This study demonstrates that it is possible for larvae of C. cactorum to transmit fungal pathogens into O. inermis tissue and it has provided a sound basis for future field work to determine the contribution that fungi make to the control of O. inermis.

The cactus moth, Cactoblastis cactorumn (Berg) (Phycitidae) is native to South America. It was released as a biological control agent against alien Opuntia-cacti in Australia in the 1920s, then in southern Africa, and latterly on several islands, including those in the Caribbean. In 1989, the cactus moth was discovered in Florida, in the United States of America, where it is now threatening the survival of indigenous Opuntia species. In this paper we identify some of the attributes that have contributed to the success of C cactorumn as a weed biological control agent. Many of these same qualities account for the problems that C cactorum has caused in Florida and pre- dispose it as a major threat to the speciose, native Opuntia-floras of Central and North America. An estimated 79 platyopuntia (prickly pear) species are at risk: 51 species endemic to Mexico; nine species endemic to the United States; and 19 spe- cies common to both countries. Many cultivated and wild Opuntia species, that are used in various ways, are also vulnerable to attack by C cactorurm, including at least 25 species in Mexico and three species in the United States, particularly the widely exploited and culturally important cultivars of 0. ficus-indica. Some control strategies are sug- gested that may minimize the risk and consequences of invasion by the cactus moth. The wider implica- tions of this threat to the practice of weed bio- logical control and to conservation are discussed.

The Florida Semaphore cactus, Opuntia corallicola, is a rare species with a distribution currently limited to one island in the Florida Keys. The only 12 mature, flowering individuals known to exist in 1989 were threatened by the arrival of an exotic cactus feeding moth, Cactoblastis cactorum. Cages were erected in 1990 around these cacti to protect them from Cactoblastis. From 1990 to 1998 the O. corallicola population was monitored and number of new recruits were measured. In May 1996, we made an outplanting of 96 small, new cacti derived from fallen pads, in an experimental regime designed to bolster the number of extant cacti and to test for the effectiveness of cages as a protection against Cactoblastis. Both the natural and the outplanted population declined by over 30% during our monitoring periods. In both the natural population and the experimental outplanting most individuals died because of what appeared to be stem browning, probably by a plant pathogen. The next largest cause of mortality in the outplanting was by trampling, probably by Key deer. Cactoblastis destroyed one mature cactus but killed no individuals in the outplanting. A hurricane in 1998 was a minor cause of death for outplanted individuals but killed two mature cacti.

1. Until recently, neither the phycitid moth Cactoblastis cactorum nor the cochineal insect Dactylopius opuntiae have been satisfactory biological control agents of Opuntia stricta in South Africa. 2. In marked contrast, both of these agents have kept O. stricta under biological control for many decades in Australia. 3. In an attempt to improve the situation in South Africa, a stock of D. opuntiae was obtained from O. stricta in Australia during 1996. 4. Host-specificity tests confirmed that the newly imported D. opuntiae from Australia is a different biotype to the one already established in South Africa. 5. The Australian (‘stricta’) biotype thrives on O. stricta but is unable to develop satisfactorily on O. ficus-indica, while the converse is true for the South African (‘ficus’) biotype, which thrives on O. ficus-indica but fares poorly on O. stricta. 6. The integrity of the host-plant specificity of the two biotypes of D. opuntiae has important implications for biological control of Cactaceae in South Africa, and has greatly enhanced prospects that O. stricta can be brought under biological control successfully.

Opuntia strictais an increasing problem in South Africa's premier wildlife reserve, the Kruger National Park, where the weed continues to disperse and has formed many dense, impenetrable thickets, some of which extend over several hectares. Although herbicidal control measures are being used to help control the weed, a biological control program was initiated in 1988 whenCactoblastis cactorumwas introduced into the park. A primary objective in the control ofO. strictais to prevent fruit production by the plants so that long-range dispersal and recruitment of the weed is minimized.Opuntia strictaplants begin to fruit after approximately six years when they reach a size of 28 cladodes.Cactoblastis cactorumhas become well established in the park and has had a striking effect on both the density and average size of theO. strictaplants in both dense and sparse infestations of the weed. The average size of the plants has declined as the damage caused byC. cactorumlarvae has fragmented the large plants; however, simultaneously, the density of plants has escalated as the fragments have taken root and produced new plants. The net effect has been that the few large plants have been replaced by many smaller plants, but this has not resulted in a significant decline in fruit production. Unlike the situation in Australia and elsewhere in the world, the population densities ofC. cactorumhave not reached the levels required for satisfactory control of the weed. While the reasons for this have not yet been determined, ant predation ofC. cactorumeggs, along with baboon predation of larvae, may contribute to the lack of adequate control.

A cactus, Opuntia stricta, has invaded almost 16 000 ha of conserved, natural habitat and has become a major weed problem in Kruger National Park (KNP), South Africa. The main objectives in the control of O. stricta are to reduce the density of the weed and to curb long-range dispersal of seeds by preventing young plants from reaching the size (28 cladodes) at which they start to produce fruits. Herbicides have failed to provide satisfactory control of O. stricta because the weed infestations are replenished from seeds in the soil and from small plants that are overlooked during spraying. A phycitid moth, Cactoblastis cactorum, was released in KNP during 1988 in an attempt to control O. stricta biologically. Population counts of the biological control agent and of the weed over a 5-year period showed that, even though C. cactorum has not provided complete control of O. stricta in KNP, the moderate levels of larval damage have stunted the growth of O. stricta and have considerably extended the time that the young plants take to reach sexual maturity. Comparisons of modelled (i.e. with no C. cactorum) and actual populations of O. stricta showed that C. cactorum is making a substantial contribution to the control of O. stricta in residual infestations of the weed that have been treated with herbicides. The need for long-term evaluation studies in biological weed control is demonstrated by the development of an integrated management programme for effective control of O. stricta.

A partir de la amenaza que constituye Cactoblastis cactorum para la industria de la tuna y labiodiversidad de cactus de México y Estados Unidos, se está desarrollando un enfoqueintegrado de control de esta plaga. Las investigaciones básicas sobre esta especie invasora ysus enemigos naturales son imprescindibles para minimizar los efectos nocivos en áreasinvadidas. El objetivo principal de este trabajo es estudiar la bioecología de C. cactorum en Argentina para favorecer la implementación de una estrategia de manejo integrado queincluya al control biológico. A partir de la estructura genética descripta de C. cactorum y laexistencia de cuatro clados en Argentina, se determinó su distribución geográfica, se estudióel patrón de uso de plantas hospedadoras (Opuntia spp. nativas y exóticas), la preferencia deoviposición (en campo y laboratorio), el rendimiento en el desarrollo y adaptación local asus hospedadoras, y el grado de compatibilidad reproductiva. Además, se realizaronrelevamientos de enemigos naturales y se seleccionó un nuevo candidato del que se estudiósu biología, especificidad y se diseñó un método de cría. Se encontró que la utilización de lasespecies de Opuntia en el campo fue proporcional a su abundancia para todos los clados. Enlaboratorio, C. cactorum utilizó casi todas las Opuntia spp. ofrecidas para oviponer, aunquealgunas especies fueron preferidas. El rendimiento en el desarrollo fue mejor sobrealgunas Opuntia spp., no coincidiendo con la preferencia de oviposición. No se observóningún patrón de adaptación local a sus plantas hospedadoras ni incompatibilidadreproductiva entre los clados. Ninguno de estos dos factores estarían determinando laestructura genética de C. cactorum. Las rutas y dinámica de la invasión se verán influidas porla calidad y disponibilidad de hospedadoras encontradas que ofrecerán espacios libres dedefensa antiherbívoro. Apanteles opuntiarum fue el parasitoide más común sobre C.cactorum y estuvo restringido a dos especies del género. Se desarrolló una técnica de cría enlaboratorio que maximiza su éxito reproductivo y se realizó su primera exportación a unacuarentena en Florida, EE. UU. An integrated control approach is being developed for Cactoblastis cactorum, a threat for theprickly pear industry and the biodiversity of cactus of Mexico and the United States. Thebasic investigations on this invading species and its natural enemies are essential tominimize harmful effects on invaded areas. The primary goal of this work is to study thebioecology of C. cactorum in Argentina to favor the implementation of an integratedmanagement strategy that includes the biological control. Based on the genetic structuredescribed for C. cactorum and the existence of four clades, their geographic distribution in Argentina, the host use pattern (native and exotic Opuntia spp.), oviposition preference (inthe field and the laboratory), the larval performance and the local adaptation to their hostplants, and the reproductive compatibility were studied. In addition, natural enemies wereidentified and biology and specificity were studied, and a rearing technique developed. Forall the clades, the use of Opuntia spp. in the field was proportional to the hosts abundance. Inthe laboratory, C. cactorum used almost all the Opuntia spp. offered to oviposit, althoughsome species were preferred. The larval performance was higher on some Opuntia spp., butnot in concordance with the oviposition preference. Pattern of local adaptation to the hostplants or reproductive incompatibility between the clades were not observed. None of thelatter factors studied seemed to determine the genetic structure of C. cactorum. The rates,routes and dynamics of the invasion will be influenced by the quality and availability ofhosts found that would offer antiherbivore defense-free space. Apanteles opuntiarum wasthe most common parasitoid on C. cactorum and was restricted to two species of the genus. A rearing technique was developed that maximized the reproductive success; the firstexport of the parasitoid was conducted to quarantine in FL, United States. Fil: Varone, Laura. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.

The recent arrival of the cactus moth, Cactoblastis cactorum (Berg) in Florida in 1989 has raised concern for the native Opuntia cacti. At particular risk is Opuntia spinosissima , whose entire U.S. population consists of 12 plants in the Florida Keys. We examined host choice of both C. cactorum larvae and ovipositing females to determine if any species of native Opuntia are preferred by C. cactorum . In addition, larval performance among Opuntia hosts was examined. Ovipositing moths showed no host preference in interspecific host choice experiments. Although larvae significantly preferred O. spinosissima over the other Opuntia species, larval survivorship on O. spinosissima was less than on O. stricta and O. humifusa . We also examined intraspecific host choice between pads of O. spinosissima to see if any of the 12 remaining plants is more resistant to attack than others. Such information is valuable for future restoration efforts to protect O. spinosissima . No adult or larval host choice was demonstrated in the intraspecific experiments.

The interaction between the moth, Cactoblastis cactorum, and the cactus, Opuntia stricta, is used as a model to examine the question of whether the CO2 sense of a herbivorous insect can detect the CO2 gradients associated with a plant's metabolic activity. Both the anatomical and the electrophysiological characteristics of CO2-sensitive receptor neurons in C. cactorum indicate an adaptation to the detection of small fluctuations around the atmospheric background. Evidence is provided that further rises in background will impair the function of the sensory organ. In the habitat of the plant, during the diurnal window of the moth's activity, two types of CO2 gradients occur that are detectable by the moth's sensors. The first gradient, associated with soil respiration, is vertical and extends from the soil surface to an altitude of approximately 1 m. Its magnitude is well above the detectability limit of the sensors. The notion that this gradient provides, to a flying insect, a cue for the maintenance of a flight altitude favourable for host detection is supported by field observations of behaviour. The second gradient, associated with CO2 fixation by the plant, extends from the surfaces of photosynthetic organs (cladodes) over a boundary layer distance of approximately 5 mm. Again, its magnitude is well above the detectability limit. The notion that this gradient provides, to a walking insect, a cue to the physiological condition of the plant is supported by the observation that females of C. cactorum, prior to oviposition, actively probe the plant surface with their CO2 sensors. In a simulation of probing, pronounced responses of the sensors to the CO2-fixing capacity of O. stricta are observed. We propose that by probing the boundary layer, females of C. cactorum can detect the healthiest, most active O. stricta cladodes, accounting for earlier observations that the most vigorous plants attract the greatest density of egg sticks.

Environmental niche models (ENMs) have gained enormous popularity as tools to investigate potential changes in species distributions resulting from climate change and species introductions. Despite recognition that species interactions can influence the dynamics of invasion spread, most implementations of ENMs focus on abiotic factors as the sole predictors of potential range limits. Implicit in this approach is the assumption that biotic interactions are relatively unimportant, either because of scaling issues, or because fundamental and realized niches are equivalent in a species' native range. When species are introduced into exotic landscapes, changes in biotic interactions relative to the native range can lead to occupation of different regions of niche space and apparent shifts in physiological tolerances. We use an escaped biological control organism, Cactoblastis cactorum (Berg.), to assess the role of the environmental envelope as compared with patterns of host-herbivore associations based on collections made in the native range. Because all nonnative populations are derived from a single C. cactorum ecotype, we hypothesize that biotic interactions associated with this ecotype are driving the species' invasion dynamics. Environmental niche models constructed from known native populations perform poorly in predicting nonnative distributions of this species, except where there is an overlap in niche space. In contrast, genetic isolation in the native range is concordant with the observed pattern of host use, and strong host association has been noted in nonnative landscapes. Our results support the hypothesis that the apparent shift in niche space from the native to the exotic ranges results from a shift in biotic interactions, and demonstrate the importance of considering biotic interactions in assessing the risk of future spread for species whose native range is highly constrained by biotic interactions.

The unintentional introduction of the cactus moth, Cactoblastis cactorum, a successful biological control agent formerly employed in the control of invasive prickly pear cactus species (Opuntia spp.) in Australia, Hawaii, South Africa, and various Caribbean islands, has posed great concern as to the possible threat to native, endangered species of cactus in the southeastern USA as well as with the potential to cause a major infestation of commercial and agricultural cactus crops in Mexico. A number of control measures have been investigated with varying degrees of success including, field exploration for cactus moth-specific parasitoids, insecticides, fungal, bacterial, and nematode agents. Current tactics used by the USA–Mexico binational program to eradicate cactus moth from Mexico and mitigate its westward movement in the USA include host plant removal, the manual removal and destruction of egg sticks and infected cacti stems, and the Sterile Insect Technique. One other approach not taken until now is the development of a cactus moth cell line as a tool to facilitate the investigation of baculoviruses as an alternative biocontrol method for the cactus moth. Consequently, we established C. cactorum cell lines derived from adult ovarian tissue designated as BCIRL-Cc-AM and BCIRL-Cc-JG. The mean cell population doubling time was 204.3 and 112 h for BCIRL-Cc-AM and BCIRL-Cc-JG, respectively, with weekly medium change, while the doubling time was 176.6 and 192.6 h for BCIRL-Cc-AM and BCIRL-Cc-JG, respectively, with a daily change of medium. In addition, the daily versus weekly change in medium was reflected in the percentage viability with both cell lines showing higher levels with a daily medium change. Of the three baculoviruses tested, only the recombinant AcMNPV-hsp70Red and GmMNPV at a multiplicity of infection (MOI) of 1.0 were able to demonstrate significant production of extracellular virus (ECV) in each of the cell lines, whereas both cell lines were refractive to an HzSNPV challenge at an MOI of 10. In this study, we have demonstrated both the successful development of a C. cactorum cell line and its ability to support a complete baculovirus infection. The potential is also there to pursue further investigations to determine the susceptibility of the cactus moth cell line to other viruses. Additionally, the availability of a cactus moth cell line will facilitate the analysis of viruses prior to using the more expensive bioassay test. Finally, it is hoped with the knowledge presented here that baculoviruses may also be considered as an alternative biocontrol method for the cactus moth.

— Scanning electron microscopy was used to study the morphology of the chorionic surface of two pyralids that feed on Opuntia cactus. The chorionic surface of Cactoblastis cactorum has a reticulate pattern due to the ridges on the surface and aeropyles. The chorionic surface has a granular appearance at low magnifications and rugose at high ones. The micropylar area has a central depression with the micropyles and is surrounded by irregularly shaped polygonal cells. The tertiary cells have aeropyles associated with the cells, and these aeropyles have mesh-like extensions that cover their openings. The general appearance of the chorionic surface of Melitara prodenialis is similar to C. cactorum, but the micropylar region differs in that primary cells surrounding the micropylar depression are looping cells of varying sizes. Also, no aeropyles are associated with the looping cells around the micropylar region.

Dactylopius opuntiae reduced an Opuntia stricta var. stricta population in the Central Tablelands of New South Wales, an area where Cactoblastis cactorum has little impact. Cactoblastis cactorum was bivoltine at the experimental site. The proportion of C. cactorum eggs hatching and larvae penetrating segments was much greater for the generation commencing between November and January compared with that commencing between February and June. Failure of first instar C. cactorum to establish during the latter generation appeared to prevent C. cactorum from having a significant impact on the cactus population. Dactylopius opuntiae released at the site decreased new growth of O. stricta var. stricta and caused direct damage to segments. This damage led to a decline in the cactus population in the area. The use of D. opuntiae for biological control of O. stricta var. stricta in similar areas is discussed.

Invasive pests, such as the cactus moth, Cactoblastis cactorum (Berg) (Lepidoptera: Pyralidae), have not reached equilibrium distributions and present unique opportunities to validate models by comparing predicted distributions with eventual realized geographic ranges. A CLIMEX model was developed for C. cactorum. Model validation was attempted at the global scale by comparing worldwide distribution against known occurrence records and at the field scale by comparing CLIMEX "growth indices" against field measurements of larval growth. Globally, CLIMEX predicted limited potential distribution in North America (from the Caribbean Islands to Florida, Texas, and Mexico), Africa (South Africa and parts of the eastern coast), southern India, parts of Southeast Asia, and the northeastern coast of Australia. Actual records indicate the moth has been found in the Caribbean (Antigua, Barbuda, Montserrat Saint Kitts and Nevis, Cayman Islands, and U.S. Virgin Islands), Cuba, Bahamas, Puerto Rico, southern Africa, Kenya, Mexico, and Australia. However, the model did not predict that distribution would extend from India to the west into Pakistan. In the United States, comparison of the predicted and actual distribution patterns suggests that the moth may be close to its predicted northern range along the Atlantic coast. Parts of Texas and most of Mexico may be vulnerable to geographic range expansion of C. cactorum. Larval growth rates in the field were estimated by measuring differences in head capsules and body lengths of larval cohorts at weekly intervals. Growth indices plotted against measures of larval growth rates compared poorly when CLIMEX was run using the default historical weather data. CLIMEX predicted a single period conducive to insect development, in contrast to the three generations observed in the field. Only time and more complete records will tell whether C. cactorum will extend its geographical distribution to regions predicted by the CLIMEX model. In terms of small scale temporal predictions, this study suggests that CLIMEX indices may agree with field-specific population dynamics, provided an adequate metric for insect growth rate is used and weather data are location and time specific.

Jointed cactus, Opuntia aurantiaca Lindley, has been a problem weed in South Africa for nearly a century. Its taxonomic status, history of introduction, and chemical and biological control were reviewed in 1979. The present account updates this information and deals with recent South African research on the ecology of O. aurantiaca and its biological control agents, and on the management of the weed. This review places some emphasis on the primary agent, the cochineal insect Dactylopius austrinus De Lotto (Homoptera: Dactylopiidae), with a shorter commentary on the phycitid moth Cactoblastis cactorum (Bergroth) that has also become established on jointed cactus. Research on three other introduced moths, Tucumania tapiacola Dyar (Phycitidae), Mimorista pulchellalis Dyar (Pyraustidae) and Nanaia sp. Heinrich (Phycitidae), is abstracted. Of the latter three species, only M. pulchellalis has become established, but its role in biological control is insignificant. It is concluded that: (i) the utility of insects as biological agents against jointed cactus has probably been fully exploited; (ii) the importance and threat of O. aurantiaca as a weed in South Africa may have been overestimated; (iii) future research emphases should be on the role of pathogens as biocontrol agents and on the formulation of area-specific integrated management procedures involving D. austrinus and herbicides.

The outstanding success of a cochineal insect, Dactylopius opuntiae (Cockerell), and, to a far lesser extent, a phycitid moth, Cactoblastis cactorum (Bergroth), in biocontrol of the prickly pear, Opuntia ficus-indica (L.) Miller, in South Africa was fully reviewed in 1978. The present account updates this information. Today, the weed infests less than 100 000 ha (of the 900 000 ha originally colonized) in the cooler, higher rainfall areas where D. opuntiae is relatively ineffective. Cactoblastis cactorum is able to kill only the small prickly pear plants and suffers lossess because of ant predation, climatic extremes and, partly, to host plant incompatibility. Integrated chemical and biological control methods are described which allow O. ficus-indica to be managed as necessary and also to be exploited as a drought fodder for stock, as a fruit and vegetable source for humans, and as a host plant for the commercial production of dye stuff from the cochineal, Dactylopius coccus O. Costa. As a result of successful biological control over the past 50 years, the public has forgotten the former severity of the prickly pear weed problem in South Africa. The residual O. ficus-indica populations are now highly valued and the biological control agents themselves are regarded as pests. The consequences of these changed perceptions are discussed.

Cactoblastis cactorum (Berg) is an invasive pest that represents an economic and ecological threat to native cacti in the U. S. and Mexico and that is currently the object of an eradication/control program in both countries. One tactic used to mitigate the threat of this species involves the SIT (Sterile Insect Technique), in which large numbers of larvae are reared on artificial diet or cactus cladodes, preferably the former, and released as sterile adults to mate with wild individuals at or near the leading edge of invasion. We studied combinations of 3 different rearing temperatures (22, 26, and 29°C) and 3 different crowding levels (50, 215, and 500 eggs) to determine percent survival to the adult stage, pupal size of each gender, and fecundity of C. cactorum reared on a factitious meridic diet. Temperature and crowding levels affected survival. The lowest rearing temperature and the low and high crowding levels adversely affect survival. Female pupae were larger than male pupae, and pupal si...

The biological control literature is filled with the terms ‘success’ and ‘failure’ used in various guises but in very few cases is the meaning clearly defined. The implicit assumption is that agents generally have failed unless they have caused a substantial decline in the overall abundance of the target weed. This perception is probably a legacy of the early outstanding biological control programmes against cactus weeds, St. John’s wort and, more recently, against floating aquatic weeds. These examples have raised expectations that almost-complete extermination of the target should be the objective of every biological control programme. Consequently, the other types of benefits conferred by biological control are undervalued. One way of ensuring that agents are properly credited is to ask the crucial question: ‘What would the situation have been without any biological control?’ This question provides the focus for assessing the biological control programme against Opuntia stricta (Haworth) Haworth in South Africa, using the cactus moth, Cactoblastis cactorum Berg., and a cochineal insect, Dactylopius opuntiae (Cockerell), which demonstrates how prolonged monitoring can reveal subtle but very real benefits that accrue from otherwise seemingly ineffective agents.

During the 1930s and 1940s the idea of releasing insects of pest species to introduce sterility (sterile insect technique or SIT) into wild populations, and thus control them, was independently conceived in three extremely diverse intellectual environments. The key researchers were A. S. Serebrovskii at Moscow State University, F. L. Vanderplank at a tsetse field research station in rural Tanganyika (now Tanzania), and E. F. Knipling of the United States Department of Agriculture. Serebrovskii’s work on chromosomal translocations for pest population suppression could not succeed in the catastrophic conditions in the USSR during World War II, after which he died. Vanderplank used hybrid sterility to suppress a tsetse population in a large field experiment, but lacked the resources to develop this method further. Knipling and his team exploited H. J. Muller’s discovery that ionizing radiation can induce dominant lethal mutations, and after World War II this approach was applied on an area-wide basis to eradicate the New World screwworm Cochliomyia hominivorax (Coquerel) in the USA, Mexico, and Central America. Since then very effective programmes integrating the SIT have been mounted against tropical fruit flies, some species of tsetse flies Glossina spp., the pink bollworm Pectinophora gossypiella (Saunders), and the codling moth Cydia pomonella (L.). In non-isolated onion fields in the Netherlands, the onion maggot Delia antiqua (Meigen) has since 1981 been suppressed by the SIT. In the 1970s there was much research conducted on mosquito SIT, which then went into “eclipse”, but now appears to be reviving. Development of the SIT for use against the boll weevil Anthonomus grandis grandis Boheman and the gypsy moth Lymantria dispar (L.) has ended, but it is in progress for two sweetpotato weevil species, Cylas formicarius (F.) and Euscepes postfasciatus (Fairmaire), the false codling moth Cryptophlebia leucotreta (Meyrick), the carob moth Ectomyelois ceratoniae (Zeller), the cactus moth Cactoblastis cactorum (Berg), the Old World screwworm Chrysomya bezziana (Villeneuve), additional Glossina spp., other Anastrepha spp. and Bactrocera spp. fruit flies, and other pest insects.

Pest control by use of ‘natural enemies’ is the basis for biological control, which may involve the introduction and release of exotic predators and parasites of pests, or enhancement of naturally occurring species that fulfil these roles. Concerns over the former (classical biological control) involve the invasive effects of such introduced species to attack native, non-target biota, and have led to development of convincing protocols to help affirm their specificity (and, hence, safety) in their new environment. Many of the concerns of conservationists over biological control devolve on the difficulties of predicting what introduced species may do after release. Introduction Biological control involves the use and manipulation of the so-called ‘natural enemies’ of pests (that is, most frequently, their predators, parasitoids and pathogens) in the management of those pests. It was developed largely as the major alternative or complementary strategy to insecticide use, and earlier work involved predominantly ‘classical biological control’ (CBC). This approach dealt with the numerous cases in which the pest (usually an arthropod, and most commonly an insect) is exotic (that is, it has been introduced or arrived naturally but is non-native) to the area in which it causes damage, and that high levels of abundance and invasibility resulted – at least in part – because it is no longer regulated by the complex of associated natural enemies that are associated with it within its natural area of distribution and evolution.

Miami APHIS–Plant Protection ' Quarantine records showed 13 Cactoblastis cactorin Bergroth interceptions in commercial nursery imports of Opuntia from the Dominican Republic between 1981 and 1986. These interceptions and the large volume of underinspected cacti that have been imported from the Dominican Republic and other countries with C. cactorum suggest that the moth may have entered Florida as an unintended commercial introduction. The present problem with C. cactorum relates the difficulty of preventing pest introductions with commercial plant imports and, to a lesser degree, the historical introduction of the moth to the Caribbean and habitat destruction that has contributed to the rarity of some American Opuntia .

A systematic review focused by plant on non-target impacts from agents deliberately introduced for the biological control of weeds found significant non-target impacts to be rare. The magnitude of direct impact of 43 biocontrol agents on 140 non-target plants was retrospectively categorized using a risk management framework for ecological impacts of invasive species (minimal, minor, moderate, major, massive). The vast majority of agents introduced for classical biological control of weeds (>99% of 512 agents released) have had no known significant adverse effects on non-target plants thus far; major effects suppressing non-target plant populations could be expected to be detectable. Most direct non-target impacts on plants (91.6%) were categorized as minimal or minor in magnitude with no known adverse long-term impact on non-target plant populations, but a few cacti and thistles are affected at moderate (n = 3), major (n = 7) to massive (n = 1) scale. The largest direct impacts are from two agents (Cactoblastis cactorum on native cacti and Rhinocyllus conicus on native thistles), but these introductions would not be permitted today as more balanced attitudes exist to plant biodiversity, driven by both society and the scientific community. Our analysis shows (as far as is known), weed biological control agents have a biosafety track record of >99% of cases avoiding significant non-target impacts on plant populations. Some impacts could have been overlooked, but this seems unlikely to change the basic distribution of very limited adverse effects. Fewer non-target impacts can be expected in future because of improved science and incorporation of wider values. Failure to use biological control represents a significant opportunity cost from the certainty of ongoing adverse impacts from invasive weeds. It is recommended that a simple five-step scale be used to better communicate the risk of consequences from both action (classical biological control) and no action (ongoing impacts from invasive weeds).

Chemical control efforts, the introduction of Cactoblastis cactorum and attempted releases of Dactylopius opuntiae Cockerell into the expanding infestation of Opuntia stricta in the Skukuza region of the Kruger National Park (KNP) have had limited suc- cess in preventing the spread and densification of 0. stricta. To boost the biological control component, a new strain of D. opuntiae was introduced into KNP during 1997. The new strain established readily and has destroyed large clumps of plants in the vicin- ity of the release site. A large-scale redistribution programme with D. opuntiae is now needed to exploit this biological control agent to the full. In order to match the frequency of manual releases with the natural rates of spread of the insects, surveys were conducted under field conditions to determine the dispersal abilities ofD. opuntiae, with regard to rate and direction of movement. Dispersal of D. opuntiae was found to be slow and restricted and that the insects need to be redistributed by placing them onto plants at approximately 10 m intervals to ensure that they become quickly and evenly distributed on the weed. This information will be crucial in the revision of the integrated management plan for 0. stricta in the KNP, in integrating the cochineal and other control mechanisms.

The ribosomal DNA of the cactophilic yeast species Clavispora opuntiae was studied in order to clarify the global distribution of the yeast. Over 500 strains, including isolates from several new localities worldwide, were characterized by rDNA restriction mapping. An unusual restriction pattern previously encountered only in one strain, from Conception Island in the Bahamas, was found in several Brazilian isolates. Sequences of the D1/D2 and D7/D8 divergent domains of the large subunit (LSU) and of the intergenic spacers (IGS) confirmed that these strains represent a genetically distinct variety of Clavispora opuntiae. This divergence had previously been hypothesized on the basis of reduced genetic recombination in inter-varietal crosses and the presence of a polymorphic ApaI restriction site located in the LSU. The exact position of the ApaI site in the D8 divergent domain and the nature of the variation that it reveals were determined. The complete sequences of 12 intergenic spacers clarified the significance of the species-wide variation uncovered by restriction mapping. Most of the polymorphic sites occur in the IGS1 and IGS2 regions, on either side of the 5S gene, and the variation is largely due to differences in the numbers and the sequences of internal repeats. Two other polymorphic sites are located in the external transcribed spacer (ETS) region. The reliability of various sites as indicators of overall spacer sequence divergence differed from one case to another. Variety-specific probes were devised and used to screen 120 strains for the presence of recombinant rDNA spacers. Three strains gave ambiguous results, but these did not constitute evidence that inter-varietal recombination has taken place in nature. The hypothesis that the global movement of Clavispora opuntiae has been influenced by the worldwide biological control of prickly pear with Cactoblastis cactorum, a moth of Argentinian origin, has received additional support from the demonstration that Argentinian strains have rDNAs similar to those found where the moth has been introduced. A dramatic founder effect was identified in a yeast population collected in cacti (Maui, Hawaii) in a site where the moth had been recently introduced.Key words: Clavispora, ribosomal DNA, biogeography, speciation.