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Anthonomus santacruzi Hustache (Coleoptera: Curculionidae) was released in South Africa in 2008 to curb the spread of the invasive alien weed Solanum mauritianum Scopoli (Solanaceae) and is widely ...

Despite potential negative interactions between biological control agents, the release of multiple agents against invasive alien weeds is often justified. The leaf-feeding beetle Mada polluta Mulsant (Coleoptera: Coccinellidae), released against Tecoma stans (L.) Juss ex Kunth var. stans in South Africa, has so far been unable to contain the weed. Consequently, the root-feeding flea beetle Heikertingerella sp. (Coleoptera: Galerucinae) was introduced to complement M. polluta. The effects of the interaction between the two beetles on their performance and on the target weed were studied on potted T. stans plants in a quarantine glasshouse to assess whether they were additive, synergistic or negative. There was no significant difference in the percentage survival of the P1 adults of either beetle when tested alone or in combination. Mada polluta produced significantly more F1 adult progeny than Heikertingerella sp. when tested alone, while both beetles produced significantly fewer offspring when tested in combination. Leaf damage by M. polluta alone was higher than that caused by Heikertingerella sp. alone, but in combination was not significantly higher than damage by M. polluta alone. Although both beetles on their own caused a significant reduction in leaf density relative to the control, leaf density was significantly lower when in combination. Despite significant reductions in plant height relative to the control, the differences between the three beetle treatments were not significant. Although competitive interactions caused a trade-off between agent proliferation and their impact on the growth of T. stans, these data need to be confirmed in the field.

Tithonia rotundifolia (Mill.) S.F. Blake (Asteraceae) is among the three Tithonia species from Mexico that are invasive in South Africa. To curb its invasiveness and negative impact in South Africa, two chrysomelid beetles, Zygogramma signatipennis (Stål) and Zygogramma piceicollis (Stål), from Mexico were investigated as candidate biological control agents. The life histories and host ranges of these beetles were studied under laboratory conditions to determine their suitability for release. The two beetle species displayed very similar life histories, including a short pre-oviposition period (13–14 days), incubation period (4–5 days) and lifecycle (40–45 days). The longevity of Z. signatipennis and Z. piceicollis was 113 and 125 days, while their fecundities were 1146 and 1133 eggs per female, respectively. Feeding, oviposition and development of both beetle species were confined within the tribe Heliantheae, but showed a very strong preference for the invasive T. rotundifolia. The only non-target species that supported development to adulthood was the exotic weed Tithonia diversifolia (Hemsl.) A. Gray, itself a target for biocontrol. Although some sunflower (Helianthus annuus L.) cultivars were partially utilized during host-specificity tests, none supported complete development, suggesting that both Zygogramma species are suitable for release in South Africa.

Delairea odorata Lemaire, Cape ivy (Asteraceae: Senecioneae), is native to South Africa but invasive in several countries. The plant is a target for biological control in the USA (California and Ha...

Native to southern Africa, Senecio madagascariensis Poir. (fireweed, Asteraceae) has invaded agricultural lands and disturbed areas in several countries worldwide and is currently a target ...

Introduced from Central America for agroforestry, Leucaena leucocephala (Lam.) De Wit (Fabaceae) has become invasive in several tropical and subtropical regions worldwide. The seed beetle Acanthoscelides macrophthalmus (Schaeffer) (Coleoptera: Chrysomelidae: Bruchinae) was released in South Africa in 1999 to curb the plant’s high seed production. Monthly sampling was conducted during 2011/2012 at four sites in KwaZulu-Natal Province to determine the reproductive phenology of L. leucocephala populations, the levels of seed damage inflicted by A. macrophthalmus, and the extent to which the beetle has recruited native parasitoids. There were typically two podding cycles annually, with variations in peak pod production between sites and periods of very low seed availability. The levels of pre-dispersal seed damage on canopy-held pods were erratic, fluctuating greatly between months and sites, and seldom exceeding 50%. Levels of post-dispersal damage on soil-surface seeds were substantially lower, seldom exceeding 5%. Parasitism of the larval/pupal stages of A. macrophthalmus also varied between months and sites, reaching a maximum of 45%. There was a moderate but significant negative correlation between percentage seed damage and seed availability, indicating higher damage during periods of seed scarcity. In contrast, there was no significant correlation between percentage parasitism and seed infestation by A. macrophthalmus. These trends suggest that neither A. macrophthalmus nor its recruited parasitoids are tracking resource availability, ensuring a negligible impact on seedling recruitment. Additional seed-reducing agents, particularly insects that exploit green pods, are required to regulate L. leucocephala populations in South Africa.

The florivorous weevil Anthonomus santacruzi Hustache (Coleoptera: Curculionidae) was first released in South Africa in 2009 to reduce fruiting by the invasive Solanum mauritianum Scopoli (Solanaceae). Additional releases during 2011–2014 achieved widespread establishment in KwaZulu-Natal Province, notably in its warmer coastal regions. The aims of this study were to determine whether A. santacruzi abundance: (i) varied monthly at coastal versus inland sites; (ii) was influenced by floral availability and the numbers of ants associated with S. mauritianum inflorescences and; (iii) negatively affected the weed’s fruit production. Sampling over a 12-month period indicated that A. santacruzi abundance varied seasonally across coastal and inland sites, with populations consistently peaking in the austral autumn months and declining during winter. Although A. santacruzi numbers were significantly positively correlated with floral availability in the previous month

A biotype of the flower-galling mite, Aceria lantanae (Cook) (Trombidiformes: Eriophyidae) collected in Florida (U.S.A.) was released in South Africa in 2007 against Lantana camara L. (Verbenaceae) but has displayed patchy establishment. The occurrence of different L. camara varieties and their susceptibility to A. lantanae were assessed across four provinces with dense infestations. Surveys were undertaken at 113 sites during the mite’s peak infestation period (April–May) in 2013–2015. The occurrence of 13 recorded L. camara varieties differed substantially across and within these provinces. Overall, five varieties accounted for 7–45% of the sampled plants at 9–51% of the surveyed sites. The remaining eight varieties accounted for

The invasive tree Solanum mauritianum Scopoli remains one of the world’s most widespread environmental weeds. Despite biocontrol providing one of the few viable long-term solutions to tackling S. mauritianum invasions globally, only South Africa and, more recently, New Zealand, have programmes in place. Ongoing biocontrol efforts against S. mauritianum are reviewed here with particular reference to South Africa. The South African programme has suffered a troubled history, with considerable research efforts culminating in the eventual release and establishment of only two insect agents, Gargaphia decoris Drake and Anthonomus santacruzi Hustache. The difficulties experienced have hindered research into new agents, causing apprehension in using biocontrol internationally. However, recent studies have demonstrated that biocontrol may be deserving of renewed investment, particularly within an integrated management context. In this review, we advocate for the revival of the S. mauritianum biocontrol programme in South Africa, and discuss possible avenues for future research internationally.

Senecio madagascariensis Poiret (Asteraceae) is a target for biological control in Australia and Hawaii, with several candidate insect agents recorded in KwaZulu-Natal, South Africa, the confirmed origin of the invasive populations. Although the root-feeding Longitarsus basutoensis Bechyne (Chrysomelidae: Galerucinae: Alticini) was prioritised for assessment, similar flea beetle taxa were also considered. We first investigated the seasonal abundance of L. basutoensis and related taxa on S. madagascariensis populations in the KwaZulu-Natal Midlands. Second, we assessed their host-plant affinities by surveying 17 non-target native Senecio species in the region. We used DNA CO1 barcoding to differentiate flea beetle taxa and their root-feeding larvae in both studies. Monthly sampling revealed three root-feeding taxa associated with S. madagascariensis, with L. basutoensis the most abundant. Longitarsus basutoensis was recorded throughout the year, with no clear patterns in seasonal abundance but significantly higher numbers at sites with deep, well drained soils that have high water holding capacity. Two unidentified flea beetle taxa, represented by larval specimens only, were recorded infrequently and in low numbers. The host-range study revealed 18 flea beetle taxa on 11 Senecio species, with L. basutoensis the most abundant species and recorded mostly on S. madagascariensis. Longitarsus basutoensis was also detected on four non-target Senecio species which, together with the results of preliminary host-specificity tests, indicated insufficient host-range restriction for countries like Australia that host a diverse Senecio flora. However, L basutoensis may have potential for release in Hawaii, due to a lack of native Senecio species on any of its islands.

Several invasive Asteraceae have been targeted for biological control worldwide, with variable success. Senecio madagascariensis Poiret, which invades agricultural lands in Australia and Hawaii, is a recent target. Since several potential insect agents were recorded in the plant’s native range in South Africa, we assessed biocontrol efforts against asteraceous weeds to determine those most likely to deliver success. Some 108 insect species, from five orders and 23 families, were deployed against 38 weed taxa, mostly in the mainland USA, Canada, Australia and New Zealand. Coleoptera (mainly Curculionidae and Chrysomelidae), Diptera (Tephritidae) and Lepidoptera (Tortricidae) featured the most. Despite high establishment success (73% of releases across countries), only 37% of successful releases achieved meaningful impact. Although root-feeding and stem-feeding insects appeared to be the best candidates, neither insect family nor feeding guild significantly influenced the probability of success. This synthesis of the global contribution of different guilds of specialist herbivores to the management of invasive Asteraceae is guiding the selection of candidate agents for the biocontrol of S. madagascariensis in Australia.

The biology and host range of the defoliating beetle Physonota maculiventris Boheman (Chrysomelidae: Cassidinae) were studied in quarantine to determine its suitability for release as a biological control agent against Mexican sunflower, Tithonia diversifolia (Hemsl.) A. Gray (Asteraceae), in South Africa. Females laid 5.25 ± 0.25 (mean ± SE) egg batches during their lifetimes, with each batch consisting of approximately 33 eggs. Larvae were highly gregarious as early instars and both larvae and adults fed voraciously, often defoliating the plants completely. The life cycle of the beetle was completed in 67.5 ± 7.5 days under quarantine conditions. Among the 58 test plant species subjected to no-choice tests, P. maculiventris developed successfully on T. diversifolia and some sunflower (Helianthus annuus L.) cultivars. However, only minor damage was recorded on non-target species, notably the exotic weed Xanthium strumarium L. and some H. annuus cultivars. Also, survival to adulthood was considera...

The flower-galling mite, Aceria lantanae (Cook) (Acari: Trombidiformes: Eriophyidae), was released as a biological control agent of Lantana camara L. (Verbenaceae) in the Limpopo, Mpumalanga, Gauteng and KwaZulu-Natal provinces of South Africa, between 2007 and 2012. Flower galls were subsequently observed at several sites where the mite had not been released, providing evidence of dispersal. This study was therefore conducted to determine the establishment, seasonal performance and dispersal rate of A. lantanae in the aforementioned South African provinces and neighbouring Swaziland. The effect of A. lantanae along with the other previously-established biological control agents on inflorescence and seed production of susceptible L. camara varieties was determined by insecticide exclusion experiments in the field. Aceria lantanae became established at 58.6% of the original release sites located in the four provinces. The mite has also established widely within the geographic range of L. camara in South Africa and Swaziland, with dispersal rates of up to 40.6 km per annum. Infestations of inflorescences varied substantially between sites, provinces and seasons and ranged from 2.7% to 97%. Inflorescence and seed production declined significantly by up to 97% and 94%, respectively, on untreated biological control stands compared to the insecticide-treated exclusion stands. Although A. lantanae has become widespread within the geographic range of L. camara in South Africa, different L. camara plants appeared to vary in their susceptibility to A. lantanae, suggesting that genetic differences among plants may have affected the performance of the mite. If this is true, additional mite strains will be required to control resistant varieties.

The flowerbud-feeding weevil Anthonomus santacruzi Hustache (Coleoptera: Curculionidae) was released in South Africa in 2008 for the biological control of the invasive tree Solanum mauritianum Scopoli (Solanaceae). The weevil was widely deployed throughout KwaZulu-Natal province, which supports large S. mauritianum infestations, and has become well established in its warmer coastal regions. The aim of this study was to provide field evidence that climate is constraining the weevil’s distribution in South Africa. Solanum mauritianum populations were sampled at 23 sites across an altitudinal gradient in KwaZulu-Natal to determine A. santacruzi densities in relation to food availability and climatic variables. Despite significantly higher amounts of floral material on S. mauritianum at the higher altitude inland sites, A. santacruzi numbers were significantly higher at the lower altitude coastal sites. There was thus a significant negative relationship between A. santacruzi numbers and altitude and s...

The flower-galling mite Aceria lantanae (Cook) (Trombidiformes: Eriophyidae) was released for the biological control of Lantana camara L. (Verbenaceae) in South Africa in 2007, but has displayed variable and patchy establishment throughout the weed's range. Surveys were undertaken in 2013-2014, both seasonally and during the mite's peak infestation periods, to determine the influence of climatic factors on its performance. Although there were seasonal differences in the percentages of mite-infested inflorescences, these did not differ significantly between altitudinal zones. There were also no significant relationships between the percentages of mite-infested inflorescences and either of annual rainfall, temperature or relative humidity. A field inoculation trial revealed significant differences between 10 common South African L. camara varieties in their susceptibility to A. lantanae. Only three varieties displayed appreciable susceptibility (50-61% of inflorescences infested), whereas six displayed only slight to moderate susceptibility (8-21%) and one displayed a lack of susceptibility (no infestation). These data support the contention that differential varietal susceptibility and not climate is responsible for the variable performance of A. lantanae on L. camara in South Africa. Complementing the current biotype of A. lantanae, originally sourced from Florida (USA), with other biotypes from different L. camara genotypes in Central and South America could increase the mite's impact on the weed.

The South American herb Campuloclinium macrocephalum (Less.) DC. (Asteraceae; pompom weed), which invades grasslands, savannas, and wetlands in South Africa, is a recent target for biological control. A foliage‐deforming thrips, Liothrips tractabilis Mound & Pereyra (Thysanoptera: Phlaeothripidae), was released in South Africa in 2013, following confirmation of its host specificity and damage potential in quarantine. However, weed biocontrol agents sometimes fail to establish or have the desired impact because they are poorly suited to the climate of the new range. Thermal tolerance trials, within the range of 15–32.5 °C, were conducted prior to the thrips’ release to determine its developmental threshold and to generate a degree‐day model to highlight areas best suited for its establishment in South Africa. These laboratory data were validated by outdoor trials. The thrips completed development from egg to adulthood at all except the lowest and highest laboratory test temperatures, with developmental duration decreasing with increasing temperature. The lower developmental threshold was estimated at 9.6 °C with 546.9 degree days required to complete development. Within the regions invaded by C. macrocephalum in South Africa, the thrips was predicted to complete 3–9 annual generations. Developmental times in the outdoor trials were largely consistent with those in the laboratory. Liothrips tractabilis is largely compatible with the broader South African climate and seems likely to establish and proliferate on C. macrocephalum populations throughout the country. These predictions have partially been verified in that L. tractabilis has become established at several sites in South Africa, many of these in colder, high‐altitude areas which were predicted to support fewer annual generations.

The foliage-deforming thrips Liothrips tractabilis Mound and Pereyra (Thysanoptera: Phlaeothripidae) was recently released in South Africa as the first classical biological control agent against the invasive South American herb, Campuloclinium macrocephalum (Less.) DC. (Asteraceae). The impact of the thrips on young plants and regrowth of C. macrocephalum was assessed under outdoor conditions, and the results were compared to those of earlier laboratory trials that were conducted while the agent was still under investigation in quarantine. The outdoor trials revealed that feeding by L. tractabilis reduced the growth and biomass accumulation of C. macrocephalum, particularly in young plants and to a lesser extent in regrowth, which was largely consistent with the results of the earlier laboratory trials. Thrips-infested young plants were significantly shorter, produced fewer leaves and displayed significantly lower wet root masses and lower below- and above-ground dry masses, compared to the contro...

Senecio madagascariensis Poiret (Asteraceae), an invasive herb from southern Africa that inflicts high economic losses in several countries worldwide, is currently a target for biological control in Australia and Hawaii. Several candidate insect agents were identified from the weed’s native range in South Africa. Confirmation of narrow host ranges, prior to agent importations into quarantine, is important for Australia given its rich native Senecio flora. In particular, surveys for candidate agents on closely related non-target plants in the native range can differentiate between host specific and unsuitable agents at an early stage. This study focused on endophagous insects from families that were deployed in biocontrol programmes against other weedy Asteraceae. The host-plant affinities of stem-boring Coleoptera and stem-boring and capitulum-feeding Lepidoptera and Diptera were assessed across 18 native herbaceous Senecio species in KwaZulu-Natal, South Africa. Since larval morphology is typically unable to confirm insect identity, DNA barcoding was used to differentiate between insect species associated with different Senecio species to determine their host-plant affinities. COI phylogenies revealed that stem-boring Curculionidae and Tortricidae and capitulum-feeding Pterophoridae and Tephritidae that are associated with S. madagascariensis were restricted to plants in the S. madagascariensis species complex. In contrast, none of the stem-boring Agromyzidae were restricted to S. madagascariensis or its species complex. This study has supported the selection of several potentially host-specific agents for S. madagascariensis that could be imported for quarantine testing in Australia and Hawaii.

Senecio madagascariensis Poir. (Asteraceae), which is native to southern Africa, has invaded agricultural lands in several countries, reducing pastoral productivity and poisoning livestock. Severe infestations in Australia and Hawaii have prompted investigations into the feasibility of biological control. Surveys in KwaZulu-Natal, South Africa, considered to be the origin of the plants that have invaded Australia and Hawaii, revealed several insect herbivore taxa that attack the plant's floral and structural tissues. However, their potential as candidate agentsmaybe influenced by the extent of their association with the plant throughout the year. Populations of S. madagascariensis around Pietermaritzburg were sampled four times over one year (i.e. across seasons) to determine the presence and abundance of the major herbivore taxa relative to the plant's phenology. Similar amounts of foliar and floral material were available to the various insect herbivore guilds throughout the year. The sampled plant populations supported 84 % of the insect herbivore taxa known to be associated with S. madagascariensis in KwaZulu-Natal. Nine of the 10 taxa that were deemed promising as candidate agents were recovered and included three capitulum feeders, four stem borers and two foliage feeders. Of these nine taxa, four were recovered during all four sampling occasions, while two were recovered on three occasions, two on two occasions and one on one occasion only. There were significant differences across seasons in the abundance of these candidate agents. The release of combinations of agents, that attack the same or different tissues, may be required to compensate for differences in abundance and ensure that herbivore pressure is sustained throughout the year.

Solanum mauritianum Scop. (bugweed, woolly nightshade; Solanaceae), a small perennial tree from South America, is a major environmental weed in South Africa and elsewhere in the world (see review by Olckers 2011). Bugweed populations persist in a variety of habitats in South Africa, ranging from sunny, exposed habitats (e.g. grasslands, savanna and roadsides) to partially shaded and fully shaded habitats (e.g. forest/plantation margins and understoreys, respectively). The lace bug Gargaphia decoris Drake (Hemiptera: Tingidae) was released in South Africa in 1999, and later in New Zealand in 2010, for the biological control of S. mauritianum (Olckers 2000, 2011; Olckers & Borea 2009). As is typical of lace bugs (e.g. Buntin et al. 1996), high levels of sap-sucking by the adults and nymphs can reduce the plant's growth rate as a result of leaf chlorosis, reduced rates of photosynthesis and transpiration, as well as premature leaf abscission.

The Neotropical tree Leucaena leucocephala (Lam.) de Wit (Fabaceae), which was introduced worldwide for agroforestry, has become invasive in several countries. In an attempt to reduce its invasiveness in South Africa, the seed-feeding beetle Acanthoscelides macrophthalmus (Schaeffer) (Chrysomelidae: Bruchinae) was released in 1999 as a biological control agent. The beetle oviposits on seed pods and on loose seeds of its host. Hatching larvae burrow into the seeds to consume the contents, emerging as adults. Since L. leucocephala seeds and seed pods display considerable variation in size (i.e. resource quality) in the field, a laboratory study was conducted to determine whether size affects utilization by A. macrophthalmus. A seed-switching trial was also carried out to determine whether seed pod or seed size was the most consistent oviposition cue. The beetles displayed strong oviposition preferences for larger resources, with significantly higher egg loads on the largest seeds and seed pods. The seed-switching trials suggested that seed pod size was a more important oviposition cue than seed size. These results were verified by field surveys which revealed significant positive relationships between egg loads and seed pod size at two of the three sites surveyed. Since seed size is positively correlated with germination success and seedling fitness in leguminous plants, these oviposition patterns suggest that, in situations where dehisced seeds are utilized, A. macrophthalmus may be targeting the fittest seeds in L. leucocephala populations. This may have positive, albeit subtle, implications for biological control.

The leaf-mining fly Calycomyza eupatorivora Spencer (Diptera: Agromyzidae) has become widely established in the eastern regions of South Africa, following its release for the biological control of the invasive shrub Chromolaena odorata (L.) King and Robinson. This study was conducted to gain some insight into the impact of C. eupatorivora populations, by assessing their seasonal activity, habitat preferences, levels of leaf exploitation and extent of larval mortality in the field over a 1-year period. Leaf mining intensity was poorly synchronised with leaf availability, with leaf exploitation peaking at the end of the growing season of C. odorata. Although significantly more mines were recovered on plants growing in shaded situations, the percentage of available leaves that were exploited for mining was not significantly different between plants growing in shaded versus open situations. Overall, the levels of leaf damage were trivial with mines recovered from

The leaf-mining fly Calycomyza eupatorivora Spencer (Diptera: Agromyzidae) was released in the eastern coastal regions of South Africa for the biological control of the invasive shrub Chromolaena odorata (L.) King and Robinson. Despite widespread establishment, its ability to inflict sufficient foliar damage has been questioned. This laboratory study was initiated to provide some insight into how increasing fly populations (represented by 1, 5 and 10 mating pairs per plant) are likely to influence leaf-mining intensity and the levels of damage. On average, individual plants exposed to five mating pairs displayed significantly more larval mines (248) than those exposed to single pairs (69), while plants exposed to 10 mating pairs were intermediate (125). Similarly, at densities of five mating pairs per plant, the percentages of available leaves that were exploited peaked at 36%, while the percentages of available leaf area that were removed by larval leaf mining peaked at 22%. The non-linear relationship b...

Chromolaena odorata (L.) King & H.E. Robins. (Asteraceae) threatens several economic and environmental activities in the eastern subtropical regions of South Africa and is a target for biological control. Three populations of Pareuchaetes insulata (Walker) (Lepidoptera: Erebidae) originating from Florida (USA), Cuba and Jamaica were released at 30 separate sites in KwaZulu-Natal, South Africa. Subsequent overlapping of two of these populations in the field and the likelihood of interbreeding posed a potential risk of establishment failure. To explore the genetic diversity of the different P. insulata populations and test for the existence of pre- and post-zygotic reproductive isolation between them, molecular analyses and cross-mating experiments were conducted. Mitochondrial DNA sequences revealed significant genetic similarity between them. Cross-mating trials between Floridian and Jamaican populations of P. insulata revealed no significant pre- and post-zygotic isolation, with no demonstrable differences in measured parameters between the ‘parental’ populations, the F1 ‘hybrids’ and the backcrosses. These results suggest that P. insulata populations released in South Africa are part of the same ‘parental’ population. Genetic incompatibility is, therefore, relatively unlikely to be the cause of any failure in establishment of P. insulata at any of the release sites.

Solanum mauritianum Scop. (bugweed, woolly nightshade, Solanaceae), a perennial small tree that is native to South America, threatens several commercial and conservation activities in the eastern higher rainfall regions of South Africa and has thus been targeted for biological control (see review by Olckers 2011). The flowerbud-feeding weevil Anthonomus santacruzi Hustache (Coleoptera: Curculionidae), which has the potential to reduce the weed's excessive fruit set, was first released in South Africa in late 2008 (Olckers 2003, 2008) and is currently the subject of extensive release efforts to promote its establishment and distribution. Mass-rearing by the South African Sugarcane Research Institute since 2011 has so far facilitated the release of several thousand weevils in the province of KwaZulu-Natal (D. Gillespie, pers. comm.).

Following widespread introduction for agroforesty, the Central American tree Leucaena leucocephala (Lam.) de Wit (Fabaceae) (leucaena) has become invasive, largely through excessive seed production, in several countries worldwide, including South Africa (Olckers 2011 and references therein). The seed beetle Acanthoscelides macrophthalmus (Schaeffer) (Chrysomelidae: Bruchinae) was released in South Africa in 1999 to increase seed mortality and thereby reduce further invasion, without compromising the plant's utilization (Shoba & Olckers 2010; Olckers 2011). The beetles lay their eggs on the outside surfaces of seed pods, or loose seeds that have been dehisced, and each larva burrows into a single seed which it destroys in completing its development (Shoba & Olckers 2010). Although the beetle has become widely established in South Africa (Olckers 2011), the levels of seed damage recorded so far have been erratic and relatively modest (Sharratt & Olckers 2012).

The florivorous weevil Anthonomus santacruzi is being released in South Africa to reduce the reproductive capacity of the invasive tree, Solanum mauritianum. Initiated to allay concerns about biotic interference, our study suggests that inflorescence-inhabiting spiders pose no risk to the survival and proliferation of A. santacruzi populations in the field.

Introduced into several countries worldwide for agroforestry, Leucaena leucocephala (Lam.) de Wit is a typical ‘conflict species’ that invades several riparian, forested and disturbed habitats in South Africa. The seed beetle Acanthoscelides macrophthalmus (Schaeffer) (Chrysomelidae: Bruchinae) was subsequently deployed as a seed-reducing agent to offset its excessive seed output. However, exploratory egg-exposure trials, in which native Acacia s.l. trees were used as ‘surrogate host plants’, suggested that high egg mortality is reducing the beetle's impact. The aims of this study were to (1) verify this suspicion by comparing the mortality of eggs exposed in L. leucocephala and Acacia nilotica (L.) Willd ex Del. stands and (2) determine whether height of exposure in the canopy (i.e. oviposition site selection) influences the different mortality factors. Although lower than in the exploratory trials, egg mortality was considerable, ranging from 30 to 50% in most instances. While unaffected by hei...

The invasive tree Solanum mauritianum Scop. has been targeted for biological control in South Africa and New Zealand, by deploying insect agents that could constrain its excessive reproductive output. The flower-feeding weevil Anthonomus santacruzi (Curculionidae) was approved for release in South Africa in 2007 but following the loss of the original culture in quarantine, new stocks were introduced from Argentina in 2008–2009. This study was initiated to confirm that the host range of the new culture was the same as that of the previous one, but also to assess the risks associated with the weevil's release in New Zealand. Different testing procedures, including no-choice tests and multi-choice tests in different arenas, produced inconsistent and ambiguous results. During no-choice tests, oviposition and larval development to adulthood occurred on three non-target species including two native South African and one native New Zealand Solanum species. However, subsequent multi-choice tests and a ri...

Deliberately introduced for agroforestry, the invasive tree Leucaena leucocephala (Lam.) de Wit (Fabaceae) is naturalized in several countries worldwide, including parts of South Africa. The seed beetle Acanthoscelides macrophthalmus (Schaeffer) (Chrysomelidae: Bruchinae) was inadvertently introduced to several countries via contaminated seed, but was released as a biological control agent in South Africa. Although widely established in South Africa, its efficacy may be curtailed because damage is reputed to be confined to canopy-held seeds, with dehisced seeds escaping damage on the ground. To clarify the beetle's potential, we investigated: (i) its selection of oviposition sites when presented with pods bearing seeds, loose seeds and empty pods in different locations (canopy-versus ground-held); and (ii) the effect of seed location on egg mortality. The beetles oviposited on pods bearing seeds, loose seeds and empty pods in both locations but showed significant preferences for pods bearing seeds, regard...

Cat's claw creeper, Macfadyena unguis-cati (L.) Gentry (Bignoniaceae), introduced as an ornamental plant, has invaded several ecologically sensitive habitats in the higher rainfall regions of South Africa. Biological control was initiated with the release of the leaf-feeding tortoise beetle Charidotis auroguttata (Boheman) (Coleoptera: Chrysomelidae) in 1999. Although established at several field sites, population densities of the beetle have remained low with no assessment of impact to date. However, simulated herbivory studies in Australia revealed that severe and repeated defoliations could slow the weed's growth rate and its accumulation of biomass in the subterranean tubers. The aim of this study was to quantify the impact of medium (50 %) and high-intensity (100 %) defoliations by C. auroguttata, in relation to equivalent simulated damage, on the growth and biomass accumulation of M. unguis-cati. The trials were monitored for 16 weeks with repeated defoliations at two-week intervals. Despite considerable variation in the response variables, plants that were defoliated by C. auroguttata, but not those defoliated mechanically, displayed reduced growth rates. However, significant decreases in stem length and numbers of nodes were demonstrated only after high-intensity beetle defoliations. Despite reductions in tuber biomass in the beetle-defoliated treatments, the differences were not significant, while only high-intensity beetle defoliations caused a significantly lower accumulation of total plant biomass. Simulated herbivory was a poor predictor of insect damage in this study which suggested that C. auroguttata could prove damaging to M. unguis-cati, but only at high population densities. However, in field situations, synergism with a range of additional environmental stressors may increase the negative impact of feeding damage.

The eucalyptus snout beetle, Gonipterus scutellatus (Gyllenhal), introduced to South Africa from Australia, causes extensive damage to eucalyptus plantations in colder regions where biological control is less effective. A cytogenetic study was undertaken to assess the weevil's genetic recombination potential and thereby its ability to adapt to changing environmental conditions. During this study we investigated: (i) the sequence of meiosis; (ii) the weevil's karyotype; and (iii) the number and position of chiasmata on the bivalents. Squashes of male testes revealed a normal, chiasmate meiosis, a sex chromosome complement of Xyp and an autosome complement of three large, and two medium-sized, sub-metacentric pairs and seven small acrocentric pairs. The diploid chromosome number (2n = 26) is marginally higher than the ancestral chromosome number of the Curculionidae (2n = 22). Chiasmata were absent from the proximal regions of the bivalents, occurring mostly in the distal regions and less frequently in the ...

Leucaena leucocephala (Lam.) de Wit (Fabaceae) is a typical ‘conflict species’, possessing both useful and damaging attributes, that has become naturalized in several countries worldwide, following deliberate introductions for agroforestry. Considered one of the ‘World’s 100 Worst Invaders’, the plant in South Africa is an incipient or ‘emerging weed’, with infestations mostly occurring in the eastern subtropical regions of the country. Deliberate biological control efforts have been confined to South Africa, although these have been opportunistic, unfunded and, given the plant’s propensity for prolific seed production, have focused exclusively on the seed beetle, Acanthoscelides macrophthalmus (Schaeffer) (Chrysomelidae: Bruchinae). Following confirmation of host specificity, and after several low-intensity releases, the beetle has become widely established in KwaZulu-Natal, where releases were mostly made, but also in Gauteng, Mpumalanga and the North West provinces. A sap-sucking psyllid, Heteropsylla cubana Crawford (Psyllidae), was inadvertently introduced into South Africa, but has not had any impact on weed infestations. The biological control programme against L. leucocephala in South Africa is reviewed, including: (i) aspects of the target plant that are pertinent to its invasiveness and management; (ii) details pertaining to the two natural enemies that have featured so far; (iii) progress that has been achieved; and (iv) the direction of future research efforts.

Solanum mauritianum Scop. (Solanaceae), a fast-growing tree with a high reproductive capacity, threatens several commercial activities and natural habitats in the higher rainfall regions of South Africa. Biological control efforts spanning 26 years have previously been confined to South Africa, but have recently been extended to New Zealand. The weed is a particularly challenging target for biological control, largely because of its taxonomic relatedness to economically important and native plant species which resulted in the rejection or shelving of the majority of candidate agents tested thus far. Despite these problems, two insect agents, the sap-sucking Gargaphia decoris Drake (Hemiptera: Tingidae) and flowerbud-feeding Anthonomus santacruzi Hustache (Coleoptera: Curculionidae), have been released in South Africa. Gargaphia decoris was first released in 1999 and has become established in several regions of the country. Although large outbreaks and extensive damage have been observed in the field, to date these have been erratic and insufficient to inflict meaningful damage on the weed populations. Anthonomus santacruzi was released in early 2009 and so far appears to have established at two sites in KwaZulu-Natal. This paper is a review of the biological control programme against S. mauritianum in South Africa, including (i) aspects of the weed that are pertinent to its invasiveness and management, (ii) the current status of the two prominent insect agents, and (iii) the direction of future research efforts.

The sap-sucking lace bug, Gargaphia decoris Drake (Tingidae), was released in South Africa, and is pending release in New Zealand, for the biological control of Solanum mauritianum Scopoli (Solanaceae). Most releases were carried out with stocks imported from northeastern Argentina in 1995, but these were later augmented using stocks imported from southern Brazil in 2002 that were deemed to be better suited to the colder regions of South Africa. While the Argentinean stocks were subjected to extensive host-range testing prior to release, the Brazilian stocks were not tested prior to release. In retrospect, this was risky because of the possibility that distinct populations of the same insect species could comprise biotypes (strains) that display either major or subtle differences in host range, thus raising the possibility of non-target effects in the field. In this study, the host ranges of the two G. decoris populations were compared on an identical set of test plants, to rule out the possibility of within-species host-range variation prior to the insect’s release in New Zealand. Standard host-range tests, involving seven ‘indicator’ Solanum species, failed to demonstrate any significant differences between the Argentinean and Brazilian populations in their response to the test plants in both no-choice and multi-choice arenas. Adults and nymphs from both populations performed considerably better on S. mauritianum and adults consequently displayed strong feeding and oviposition preferences for this species. There is thus no evidence of host-range variation between the two populations and we conclude that either is suitable for release

Introduced for agroforestry, Leucaena leucocephala (Lam.) de Wit (Fabaceae) has become naturalized in several countries worldwide and constitutes an ‘emerging weed’ in South Africa. The seed beetle Acanthoscelides macrophthalmus (Schaeffer) (Chrysomelidae: Bruchinae) was inadvertently introduced to many of these countries via contaminated seeds, but was deliberately introduced into South Africa for biological control. Following an isolated report of non-target feeding in the field in southeastern Asia, this study was aimed at re-evaluating aspects of the beetle’s biology, in particular the likelihood of non-target attacks on native mimosoid Fabaceae that are closely related to L. leucocephala. A preliminary field assessment of the beetle’s susceptibility to native parasitoids was also undertaken. The beetle’s life cycle includes several attributes (e.g. rapid reproductive maturation, high rates of oviposition) that favour high population densities in the field. Although adults oviposited on the seeds of all test plant species during no-choice tests, oviposition was significantly higher on L. leucocephala. While several hatching larvae survived to adulthood on L. leucocephala, single adult individuals were reared from the seeds of each of three non-target species. Also, during multichoice tests, the beetles displayed strong oviposition preferences for L. leucocephala. Two hymenopteran parasitoid species were reared from seeds containing larvae which were exposed in the field, but overall levels of parasitism were low. These results confirm that the host range of A. macrophthalmus is largely restricted to the genus Leucaena, that native mimosoid Fabaceae are unlikely to be at risk and that the decision taken in 1999 to release the beetle was justified.

The South American tree Solanum mauritianum Scopoli (Solanaceae), a major environmental weed in South Africa and New Zealand, has been targeted for biological control, with releases of agents restricted to South Africa. The leaf-sucking lace bug, Gargaphia decoris Drake (Tingidae), so far the only agent released, has become established in South Africa with recent reports of severe damage at a few field sites. To evaluate the insect’s suitability for release in New Zealand, host-specificity testing was carried out in South Africa in laboratory and open-field trials, with selected cultivated and native species of Solanum from New Zealand. No-choice tests confirmed the results of earlier trials that none of the three native New Zealand Solanum species are acceptable as hosts. Although the cultivated Solanum muricatum Aiton and S. quitoense Lam. also proved unacceptable as hosts, some cultivars of S. melongena L. (eggplant) supported feeding, development and oviposition in the no-choice tests. Although eggplant was routinely accepted under laboratory no-choice conditions in this and previous studies, observations in the native and introduced range of G. decoris, open-field trials and risk assessment based on multiple measures of insect performance indicate that the insect has a host range restricted to S. mauritianum. These results strongly support the proposed release of G. decoris in New Zealand because risks to non-target native and cultivated Solanum species appear to be negligible. An application for permission to release G. decoris in New Zealand will be submitted to the regulatory authority.

The South American tree Solanum mauritianum, a major environmentalweed in the high-rainfall regions of SouthAfrica, has proved to be a difficult target forbiological control. Artificially expanded hostranges of candidate agents during quarantinehost-specificity tests, have resulted in therelease of only one agent species which has sofar had a negligible impact on the weed. Thenecessity for additional agents resulted in theimportation of a leaf-mining flea beetle, anunidentified species of Acallepitrix,from Brazil in 1997. No-choice tests inquarantine showed that potential host plantsare confined to the genus Solanum.Although several non-target plants, includingcultivated eggplant (aubergine) and some nativeSouth African Solanum species, sustainedfeeding, oviposition and the development oflarval leaf mines, most of these were inferiorhosts. These results were confirmed by pairedchoice tests, where Acallepitrix sp. nov.displayed significant feeding and ovipositionpreferences for S. mauritianum and where,with few exceptions, more larval leaf mineswere initiated on S. mauritianum.Interpretation of the host-specificity testswas facilitated by a risk assessment matrixwhich suggested that the risk of feeding andoviposition on non-target Solanum plants,including eggplant cultivations, was relativelylow. These and other considerations, such asthe lack of evidence of damage inflicted oncultivated Solanaceae in South America, suggestthat Acallepitrix sp. nov. could beconsidered for release against S. mauritianum in South Africa. However, the results of the host-specificity tests remain ambiguous and until more compelling evidence is obtained from field surveys and open-field trials in Brazil, an application for permission to release the flea beetle in South Africa will not be considered.

Biological control of Solanum mauritianum Scopoli, a major environmental weed in the high-rainfall regions of South Africa, is dependent on the establishment of agents that can reduce fruiting and limit seed dispersal. The flowerbud weevil, Anthonomus santacruzi Hustache, is a promising fruit-reducing agent, despite ambiguous results obtained during host-specificity evaluations in quarantine. Adult no-choice tests showed that although feeding is confined to Solanum species, normal feeding and survival occurred on the foliage (devoid of floral material) of cultivated eggplant (aubergine), potato, and several native South African Solanum species. During paired-choice tests, involving floral bouquets in 10-liter containers, A. santacruzi oviposited in the flower buds of 12 of the 17 test species, including potato and eggplant, although significantly more larvae were recovered on S. mauritianum than on eight other species. Larvae survived to adults on all 12 species, with survival significantly lower on only four species than on S. mauritianum . However, during multi-choice tests, involving potted plants in a large walk-in cage, A. santacruzi consistently displayed significant feeding and oviposition preferences for S. mauritianum over all of the 14 Solanum species tested. Analyses of the risk of attack on nontarget Solanum plants suggested that, with the possible exception of two native species, none is likely to be extensively utilized as a host in the field. Also, host records and field surveys in South America have suggested that A. santacruzi has a very narrow host range and that the ambiguous laboratory results are further examples of artificially expanded host ranges. These and other considerations suggest that A. santacruzi should be considered for release against S. mauritianum in South Africa, and an application for permission to release the weevil was submitted in 2003.

Woolly nightshade Solanum mauritianum (Solanaceae) is a serious environmental and forestry weed in New Zealand The leaffeeding lace bug Gargaphia decoris (Tingidae) was released in South Africa in 1999 after rigorous host specificity testing revealed that natives and crops in the genus Solanum were unlikely to be attacked All three New Zealand native Solanum spp were similarly tested in South Africa Neither Solanum laciniatum Solanum aviculare (poroporo) nor Solanum americanum (smallflowered nightshade) supported feeding by nymphs or adults of G decoris in nochoice tests During multichoice tests 97 of adults selected S mauritianum while 2 selected eggplant cv Black Beauty (S melongena) Oviposition occurred only on S mauritianum The risks of nontarget attack are therefore low enough to warrant further evaluation of G decoris as a biocontrol agent in New Zealand

Solanum mauritianum Scopoli and Solanum sisymbriifolium Lamarck are major exotic weeds in South Africa, while Solanum viarum Dunal is similarly problematic in the United States of America. All three species are native to northeastern Argentina and southeastern Paraguay, where they were surveyed for natural enemies in February 1998. Insect agents for Solanum weeds have a tendency to extend their host ranges to include non-target Solanum species, in particular cultivated eggplant (S. melongena L.), during laboratory trials, making it difficult to promote their release. To facilitate the interpretation of such results, other native and cultivated Solanum species that grew in close proximity to the target species were also surveyed to give an indication of the insects’ field host ranges. During the survey period, 19 insect herbivore species were recorded on S. mauritianum, while 8 species were recorded on each of S. sisymbriifolium and S. viarum. Based on the insects’ occurrence, abundance and damage...

The search for natural enemies of the South American tree Solanum mauritianum Scop., a major environmental weed in the high-rainfall regions of South Africa, created the opportunity to observe and study several leaf-feeding beetles from the genus Platyphora Gistel. Data on the biology and host range of three species from southern Brazil, Platyphora biforis (Germar), Platyphora conviva (Stal) and Platyphora nigronotata (Stal), and one from northeastern Argentina, Platyphora paraguana (Jacoby), were collected during their evaluation as potential biological control agents. All four species displayed similar, highly specialized biologies in the field, including viviparity, monophagy and sensitivity to host plant quality and microhabitat. Despite this, considerably broader host ranges were observed in captivity, including both cultivated and native South African species of Solanum L. Certain of these non-target plants were suitable hosts for the beetles, because there were no consistent differences in...

The South American tree Solanummauritianum is a major environmental weed in thehigh-rainfall regions of South Africa and has beentargeted for biological control since 1984. Althoughhost ranges of imported agents determined duringquarantine tests have resulted in the rejection ofeight of the 11 candidate agents tested so far, theleaf-sucking lace bug Gargaphia decoris,imported from Argentina in 1995, displayed anacceptably narrow host range in captivity. No-choicetests showed that G. decoris is confined to Solanum species and cannot survive on solanaceouscrops outside that genus. Although these tests alsoindicated that G. decoris colonies could surviveand reproduce on cultivated eggplant (aubergine) andat least five native South African Solanumspecies, all but one native species proved to beinferior hosts in terms of adult survival andoviposition potential. During paired choice andmultichoice tests in small and larger cagesrespectively, G. decoris displayed very strongfeeding and oviposition preferences for S. mauritianum. Analyses of the risk of attack onnon-target Solanum plants revealed that, withone possible exception, none were likely to suffermore than incidental damage in the field. Host recordsfrom South America have also indicated that G. decoris has not been recorded on any Solanumspecies other than S. mauritianum, providingfurther evidence of its host specificity. The resultsof this study were accepted by the regulatoryauthorities and in February 1999, G. decorisbecame the first agent to be released in South Africafor the biological control of S. mauritianum.