Search

Plutella xylostella (Plutellidae: Lepidoptera) is the one of most destructive and critical cosmopolitan insect herbivores of brassica crops. Globally efforts have been undertaken to develop integrated management strategies for its control, based principally on manipulation of its parasitoids including Diadegma insulare. The research study was conducted to investigate the effects of two cabbage varieties on fitness parameters (i.e. percent parasitism, offspring sex ratio and developmental periods) of Diadegma insulare, a larval parasitoid of Plutella xylostella. All experiments were carried out under controlled conditions maintained at 23±2 °C, 60±5% RH and 16L: 8D photoperiod. The findings revealed that developmental period was lower on Asha while higher on Golden acre whenever both second and third instars larvae were released on cabbage varieties. Parasitism efficacy was lower on third instars larvae as compared to the second. Higher parasitism (53.53%) was assessed on Asha while lower parasitism (44.95%) was observed on Golden acre when second instars larvae were exposed. Parasitism was higher (61.17%) on Asha while lower (50.1%) on golden acre when third instars larvae were exposed. Offspring sex ratio differed on stages of parasitized larvae. Higher male offspring emerged when second instars larvae were parasitized while more female offspring were emerged when third instars larvae were parasitized by D. insulare reared on both varieties. It was concluded that Asha was recognized as most suitable variety, as developmental period of D. insulare was shorter as well as parasitizing efficacy was also recorded higher on Asha. [ABSTRACT FROM AUTHOR]

Abstract Background Diadegma insulare (Cresson) is the most efficient parasitoid of Plutella xylostella (L.) in cruciferous crops. Considering its effectiveness, the present study was performed to investigate the impacts of cauliflower and cabbage cultivars under 3 different temperature regimes on the parasitism efficiency and offspring sex ratio of D. insulare. Main body This study revealed that D. insulare remained active at all the 3 temperatures (i.e., 19, 23, and 27 °C) and on all selected cruciferous cultivars. However, 23 °C (along with 65±5% RH and 16L: 8D hours) was the most suitable temperature, whereas relatively preferred host plant cultivars were the “White marble” (cauliflower) and “Asha” (cabbage) at which comparatively higher parasitism rates (79.39 and 73.31%, respectively) were recorded. Moreover, non-significant differences were observed in the offspring sex ratios of the parasitoid at different temperature regimes; however, minute differences were found among studied cruciferous cultivars. Conclusion Overall, “White marble” (cauliflower) and “Asha” (cabbage) were recommended to be used as potential host plant cultivars for mass rearing of D. insulare.

Many parasitoids and their herbivorous hosts forage on the same floral resources in agroecosystems. Floral resources that benefit natural enemies without supporting pests can improve the efficacy of biological control agents. Here, we report the results of a study on selective effects of floral and non-floral food sources on the life-history traits of the parasitoid Diadegma insulare (Cresson) (Hymenoptera: Ichneumonidae) and its host Plutella xylostella (L.) (Lepidoptera: Plutellidae). Under standard laboratory conditions, insects were exposed to four flowering plant species, 10% honey solution, and water. All food sources increased the longevity of the herbivore and its parasitoid by as much as four- to nine-fold, respectively, compared to the water control diet. Diadegma insulare survived the longest on Thlaspi arvense L. (Brassicaceae) and P. xylostella on Sinapis arvensis L. (Brassicaceae). However, none of the food sources tested was beneficial to the parasitoid alone, though Lobularia maritima L. (Brassicaceae) was found to selectively favor the longevity of D. insulare. Diadegma insulare adults were heavier when fed on S. arvensis, whereas feeding on the honey solution led to higher body weights of P. xylostella. In conclusion, we demonstrated that floral and non-floral food sources varied in their suitability and acted differently on life-history traits of a host-parasitoid system. The selective characteristics of nectar-producing plants and their influence on the herbivorenatural enemy combination can, therefore, be employed to increase their impact in integrated P. xylostella management. [ABSTRACT FROM AUTHOR]

Studying competitive interactions among natural enemies is important to elucidate the success and non-target impact of candidate biological control agents. Increased regulation of new introductions requires that studies on non-target species be carried out in confined conditions. Hypotheses about potential impacts of biological control agents in the field are based on data from Petri dish or small cage experiments conducted in the laboratory. This study compared the performance of the diamondback moth,Plutella xylostella(L.) (Lepidoptera: Plutellidae), parasitoidsDiadegma insulare(Cresson) (Hymenoptera: Ichneumonidae) andMicroplitis plutellae(Muesebeck) (Hymenoptera: Braconidae) in experiments conducted in small cages in the laboratory and in large cages in the field. Results showed no significant differences between laboratory and field outcomes forD. insularealone and whenD. insulareandM. plutellaewere combined. ForM. plutellaealone, parasitism in the laboratory cages was significantly less than in the field cages. These results demonstrate that laboratory studies may be useful to develop hypotheses on competitive interactions of candidate parasitoid biological control agents. [ABSTRACT FROM PUBLISHER]

Barbarea vulgaris R. Br. and B. verna (Mill.) Asch (Brassicaceae) have been proposed as trap crops for the diamondback moth, Plutella xylostella L. (Lepidoptera: Plutellidae). In bloom, these plants could also be used to attract beneficial insects. In this study, we tested the attractiveness of flowering Barbarea to P. xylostella and to two of its parasitoids, Diadegma insulare Cresson (Hymenoptera: Ichneumonidae) and Diadromus collaris Gravenhorst (Hymenoptera: Ichneumonidae). We also tested whether the presence of flowering Barbarea planted in the field border could affect densities of 10 insect pests and two beneficial coccinellids in adjacent cauliflower plants. Flowering Barbarea did not change the densities of insects found in adjacent cauliflower, except for Eurydema ornata L. (Hemiptera: Pentatomidae), which densities on cauliflower were reduced by flowering B. vulgaris. Coccinellids were more abundant on flowering Barbarea than on cauliflower plants. Chrysomelids were also more abundant on flowering Barbarea than on cauliflower plants, while hemipteran and lepidopteran pests were often more abundant on cauliflower than on Barbarea plants. In plots with flowering B. vulgaris, P. xylostella pupae suffered 1.7 and 4.0 times more parasitism by D. insulare and D. collaris, respectively, than in plots without flowering B. vulgaris. Flowering reduced the attractiveness of Barbarea to P. xylostella, making it lose its effectiveness as a trap crop. However, being biennial, Barbarea could be used as a trap crop for P. xylostella the first year, and to lower the populations of E. ornata and increase parasitism of P. xylostella when it flowers the second year. [ABSTRACT FROM AUTHOR]

Natural enemies of herbivores function in a multitrophic context, and their performance is directly or indirectly influenced by herbivores and their host plants. Very little is known about tritrophic interactions between host plants, pests and their parasitoids, particularly when the host plants are under any stress. Herbivores and their natural enemies' response to plants under stress are diverse and variable. Therefore, in this study we investigated how diamondback moth, Plutella xylostella ( L.), reared on water-stressed host plants ( Brassica napus L. and Sinapis alba L.) influenced the development of its larval parasitoid, Diadegma insulare ( Cresson). No significant differences were observed in development of P. xylostella when reared on water-stressed host plants. However, all results indicated that water stress had a strong effect on developmental parameters of D. insulare. Development of D. insulare was delayed when the parasitoid fed on P. xylostella, reared on stressed host plants. Egg to adult development of D. insulare was faster on non-stressed B. napus than non-stressed S. alba followed by stressed B. napus and S. alba. Female parasitoids were heavier on non-stressed host plants than stressed counterparts. Furthermore, the parasitoid lived significantly longer on stressed B. napus. However, body size was not affected by water treatment. Most host plant parameters measured were significantly lower for water-stressed than non-stressed treatments. Results suggest that development of this important and effective P. xylostella parasitoid was influenced by both water stress and host plant species. [ABSTRACT FROM AUTHOR]

Mortality of Plutella xylostella (Lepidoptera, Plutellidae) by parasitoids in the Province of Santa Fe, Argentina. Plutella xylostella (Linnaeus, 1758) (Lepidoptera, Plutellidae) larvae cause severe economic damage on cabbage, Brassica oleracea L. variety capitata (Brassicaceae), in the horticultural fields in the Province of Santa Fe, Argentina. Overuse of broad spectrum insecticides affects the action of natural enemies of this insect on cabbage. The objectives of this work were to identify the parasitoids of P. xylostella and to determine their influence on larva and pupa mortality. Weekly collections of larvae and pupae were randomly conducted in cabbage crops during spring 2006 and 2007. The immature forms collected were classified according to their developmental stage: L1 and L2 (Ls = small larvae), L3 (Lm = medium larvae), L4 (Ll = large larvae), pre-pupae and pupae (P). Each individual was observed daily in the laboratory until the adult pest or parasitoid emergence. We identified parasitoids, the number of instar and the percentage of mortality of P. xylostella for each species of parasitoid. Parasitoids recorded were: Diadegma insulare (Cresson, 1875) (Hymenoptera, Ichneumonidae), Oomyzus sokolowskii (Kurdjumov, 1912) (Hymenoptera, Eulophidae), Cotesia plutellae (Kurdjumov, 1912) (Hymenoptera, Braconidae) and an unidentified species of Chalcididae (Hymenoptera). Besides parasitoids, an unidentified entomopathogenic fungus was also recorded in 2006 and 2007. In 2006, the most successful parasitoids were D. insulare and O. sokolowskii, while in 2007 only D. insulare exerted a satisfactory control and it attacked the early instars of the pest.Mortalidade de Plutella xylostella (Lepidoptera, Plutellidae) por parasitóides na Província de Santa Fé, Argentina. Plutella xylostella (Linnaeus, 1758) (Lepidoptera, Plutellidae) causa danos econômicos severos em repolho, Brassica oleracea variedade capitata L. (Brassicaceae), na área de horticultura localizada na Província de Santa Fé, Argentina. O uso excessivo de inseticidas de largo espectro afeta a ação dos inimigos naturais de P. xylostella em repolho. O presente trabalho teve como objetivo identificar os parasitóides de P. xylostella e determinar sua influência na mortalidade de larvas e pupas em Santa Fé, Argentina. Coletas semanais de larvas e pupas em culturas de repolho foram realizadas aleatoriamente na área durante a primavera de 2006 e 2007, registradas pelo estágio de desenvolvimento: L1 e L2 (Ls = larvas pequenas), (Lm = larvas médias) L3, L4 (Ll = larvas grandes) pré-pupa e pupa (P). Cada indivíduo foi observado diariamente no laboratório até a emergência dos adultos da praga ou dos parasitóides. Foram identificadas as espécies de parasitóides o número de instars e a porcentagem de mortalidade. Os parasitóides registrados foram: Diadegma insulare (Cresson, 1875) (Hymenoptera, Ichneumonidae), Oomyzus sokolowskii (Kurdjumov, 1912) (Hymenoptera, Eulophidae), Cotesia plutellae (Kurdjumov, 1912) (Hymenoptera, Braconidae) e uma espécie não identificada pertencente à família Chalcididae. Além dos parasitóides, um fungo entomopatogênico não identificado foi registrado. Em 2006, os parasitóides mais bem sucedidos foram D. insulare e O. Sokolowskii; enquanto que em 2007 apenas D. insulare exerceu um controle satisfatório, atacando os instares iniciais da praga.

• Both hosts and parasitoids develop faster at higher temperatures. • Higher temperatures reduce survival of the parasitoid, but not the host. • Parasitism rates decrease at higher temperatures. • Parasitoid-mediated biocontrol is likely to be compromised under climate warming. • Temperature for biocontrol disruption reduced when warming spans entirety of host development. A primary facet of climate change is an increase in average temperatures which can have immense consequences for ectotherms, organisms that cannot physiologically regulate their own body temperatures, such as insects. Moreover, thermal stress can influence species interactions across trophic levels, especially if members of different trophic levels show differential responses. In agricultural systems, parasitoids are frequently used as biocontrol agents to reduce crop damage by regulating populations of insect herbivores, but climate change can potentially threaten this ecosystem service. In this study, we investigated the effects of diurnally fluctuating temperature regimes (average treatment temperatures = 23 °C, 25 °C, 27 °C) on the relationship between the common agricultural pest Plutella xylostella and its larval parasitoid Diadegma insulare. We found that at higher temperatures, both the host and the parasitoid developed faster. Host survival was not influenced by temperature, but higher temperatures resulted in increased parasitoid mortality in the pupal stage. Realized parasitism rates were also significantly decreased at higher temperatures, suggesting that D. insulare may become a less efficient biocontrol agent of P. xylostella as temperatures continue to increase. [ABSTRACT FROM AUTHOR]

The currently accepted lower threshold temperature for the development of diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae), the world's most destructive insect pest of cruciferous crops, is around 6.0°C, and there is no known upper threshold temperature. Neither are there established threshold temperatures for diamondback moth's major natural enemy, Diadegma insulare (Hymenoptera: Ichneumonidae). Laboratory studies were undertaken to determine the survival and development of a North American diamondback moth population and its parasitoid D. insulare at 20 constant temperatures ranging from 2.0 to 38.0°C. Diamondback moth completed development from second instar to adult within a temperature range of 4.0-37°C, and D. insulare completed its life cycle from egg to adult within a temperature range of 4.0-33°C. The developmental data were fitted into one linear and four nonlinear models. Using goodness-of-fit and the ability to estimate parameters of biological significance as selection criteria, the Wang model was the most acceptable among the nonlinear models to describe the relationship between temperature and development of both species. According to this model, the lower and upper threshold temperatures for diamondback moth were 2.1 and 38.0°C, respectively, and for D. insulare they were 2.1 and 34.0°C, respectively. Based on the Degree Day model, diamondback moth required 143 d above the lower threshold of 4.23°C to complete the life cycle, while D. insulare required 286 d above the lower threshold of 2.57°C. This study suggests that temperatures during the crop-growing seasons in North America are not limiting factors for development of either diamondback moth or D. insulare. [ABSTRACT FROM AUTHOR]

Parasitism levels by Diadegma insulare (Muesebeck) (Hymenoptera: Ichneumonidae) and Microplitis plutellae (Haliday) (Hymenoptera: Braconidae) at various densities of their host, Plutella xylostella (L.) (Lepidoptera: Plutellidae), were assessed. Cages with densities of 10 hosts, 20 hosts, and 40 hosts were set up, with the cage volume (40 500 cm³) and number of wasps (2 females) remaining constant. The host populations were also exposed to the wasps for two different exposure times: I day and 3 days. The study showed that D. insulare was a better parasitoid overall, achieving a level of parasitism equal to or higher than M. plutellae at all densities. Microplitis plutellae performed best at a lower host density (76% ± 9% of 10 hosts vs. 43% ± 3% of 40 hosts). Diadegma insulare performed similarly at all densities tested (75% ± 5% of 10 hosts, 83% ± 4% of 20 hosts, and 79% ± 6% of 40 hosts). This suggests that D. insulare may be the better parasitoid overall and should be applied in severe, large-scale infestations, while M. plutellae may be better for small-scale infestations. [ABSTRACT FROM AUTHOR]

The prevalence of the diamondback moth and its larval parasitoids, was explored across Saskatchewan, Canada. Higher numbers of diamondback moths were recorded early in the season than later and in the Mixed Grassland compared to three other ecoregions. The highest proportion of parasitism was observed in the Boreal Transition ecoregion in early season. [ABSTRACT FROM PUBLISHER]

Laboratory studies were conducted to determine the effects of constant temperatures (7, 22, and 30°C) and corresponding fluctuating temperatures (0-14, 15-29, and 23-37°C) on the development of diamondback moth, PluteUa xylostella (L), and its North American parasitoid Diadegma insulare (Hellén). Parasitized third-instar diamondback moth larvae were reared until adult mortality in individual thermal gradient cells at different temperature regimes. Larval mortality, parasitism success, pupal mortality, larval and pupal developmental time, adult longevity, and pupal and adult dry weight were recorded. Overall diamondback moth larval mortality was low. The pupal mortality of D. insulare increased with increasing temperature; however, diamondback moth did not show such a response. Greatest parasitism success (67%) was found at constant and fluctuating 22°C and fluctuating 7°C, and the lowest (30%) at fluctuating 30°C. Longer development times and greater pupal body masses occurred at lower temperatures for both insects. Significant differences occurred between constant and fluctuating temperature regimes for most parameters of both insects. Fluctuating compared with constant temperatures caused shorter development times, similar body mass, and higher adult longevity for both insects at optimal and lower temperature ranges. Both insects experienced 0°C at fluctuating 7°C (0-14°C) and survived. These results have important implications for extrapolating temperature effects on insects in laboratory studies with constant temperatures. Comparing successful parasitism capacity of the wasp and pupal survival and body mass of both host and parasitoid, we conclude that D. insulare is a more effective parasitoid at lower temperatures. [ABSTRACT FROM AUTHOR]

Intensive use of pesticides is common and increasing despite a growing and historically well documented awareness of the costs and hazards. The benefits from pesticides of increased yields from sufficient pest control may be outweighed by developed resistance in pests and killing of beneficial natural enemies. Other negative effects are human health problems and lower prices because of consumers' desire to buy organic products. Few studies have examined these trade-offs in the field. Here, we demonstrate that Nicaraguan cabbage (Brassica spp.) farmers may suffer economically by using insecticides as they get more damage by the main pest diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), at the same time as they spend economic resources on insecticides. Replicated similarly sized cabbage fields cultivated in a standardized manner were either treated with insecticides according common practice or not treated with insecticides over two seasons. Fields treated with insecticides suffered, compared with nontreated fields, equal or, at least in some periods of the seasons, higher diamondback moth pest attacks. These fields also had increased leaf damage on the harvested cabbage heads. Weight and size of the heads were not affected. The farmers received the same price on the local market irrespective of insecticide use. Rates of parasitized diamondback moth were consistently lower in the treated fields. Negative effects of using insecticides against diamondback moth were found for the density of parasitoids and generalist predatory wasps, and tended to affect spiders negatively. The observed increased leaf damages in insecticide-treated fields may be a combined consequence of insecticide resistance in the pest, and of lower predation and parasitization rates from naturally occurring predators that are suppressed by the insecticide applications. The results indicate biological control as a viable and economic alternative pest management strategy, something that may be particularly relevant for the production of cash crops in tropical countries where insecticide use is heavy and possibly increasing. [ABSTRACT FROM AUTHOR]

1. The use of floral resource subsidies to improve herbivore suppression by parasitoids requires certain trophic interactions and physiological changes to occur. While the longevity and fecundity of parasitoids are positively affected by nectar subsidies in laboratory studies, the impacts of floral subsidies on the fecundity and longevity of freely foraging parasitoids have not been studied. 2. We studied the longevity and per capita fecundity of naturally occurring Diadegma insulare foraging in cabbage plots with and without borders of flowering buckwheat, Fagopyrum esculentum, as well as relationships between longevity, fecundity, sugar feeding and parasitism rates on larvae of the diamondback moth, Plutella xylostella. 3. Relative longevity was estimated by counting broken setae on the fringe of the forewing. Floral borders increased the longevity of males and females in adjacent cabbage plots. 4. The egg maturation rate of D. insulare was estimated by comparing egg loads of females collected early in the day with egg loads of females held without hosts in field cages throughout the day. Females in buckwheat cages matured 2·7 eggs per hour while females in control cages resorbed 0·27 eggs over the same time period. 5. The fecundity of females collected in the afternoon was estimated by comparing their actual egg load to the estimated egg load in the absence of oviposition for females in a given plot. Females foraging in buckwheat plots had marginally fewer eggs remaining in their ovaries, and laid marginally more eggs than females in control plots. Females from both treatments carried 30–60 eggs by the afternoon and therefore were time-limited rather than egg-limited. 6. Plots where a greater proportion of females had fed on sugar had longer-lived females. This suggests that feeding enhanced longevity of D. insulare. However, plots with longer-lived and more fecund females did not exhibit higher parasitism rates, although the power of these tests were low. [ABSTRACT FROM AUTHOR]

Abstract: In summer and fall 2004, insecticide toxicity bioassays were conducted on adults of Diadegma insulare and Oomyzus sokolowskii, two important parasitoids of diamondback moth, Plutella xylostella in the southeastern United States. The toxicity bioassay utilized a cabbage leaf dip method and serial dilution concentrations of various labeled insecticides on crucifer crops. Results showed that all insecticide treatments, including spinosad, indoxacarb, esfenvalerate, methomyl, acetamiprid, acephate, emamectin benzoate, and methoxyfenozide were toxic to the adult stage of D. insulare or O. sokolowskii or both. The broad-spectrum insecticides esfenvalerate, methomyl, and acephate as well as the more IPM-compatible insecticides, spinosad, indoxacarb, and emamectin benzoate at their field rate concentrations resulted in 100% mortality to either D. insulare or O. sokolowskii or both after 72h of exposure. Moreover, LC50 values for all of these insecticides were only a fraction (<2%) of the actual field rate concentration. The neonicotinoid, acetamiprid was less toxic than the other insecticides but still killed 77% of D. insulare adults and 91% of O. sokolowskii adults after 72h of exposure. The insect growth regulator, methoxyfenozide, though considerably less toxic than the other insecticides based on LC50 levels, still resulted in substantial (62%) mortality of O. sokolowskii adults after 72h. Results of these studies suggest that field applications of any of the aforementioned insecticides would impact biological control of diamondback moth. [Copyright &y& Elsevier]

Adding sugar to agricultural habitats is expected to enhance pest control by improving the longevity and physiological status of parasitoids. How a sugar diet and physiological parameters affect the host-foraging behaviour of Diadegma insulare, a parasitoid of diamondback moth larvae ( Plutella xylostella), is investigated in the laboratory. Newly-emerged females are given water or sucrose-water ad libitum for 1 day, and then monitored for movement onto and away from a single cabbage leaf infested with 30 host larvae for 1 h. A significantly lower percentage of sucrose-fed females enter the host patch than those with access to only water (starved) females (60% vs. 91%). Of the females that enter the patch, fed wasps spend significantly less time in the patch than starved wasps (32.2 vs. 25.7 min) but feeding does not significantly affect oviposition rate. Fed and starved females sting six to seven larvae, and 19–29% of females superparasitize host larvae. Wasps with higher levels of fructose are less likely to enter the host patch than wasps with lower fructose levels. The lower proportion of fed wasps entering the patch may be due to a period of inactivity after sugar feeding. [ABSTRACT FROM AUTHOR]

The article explains the procedure of constructing life tables of randomly collected insects of unknown age and how it may be used to determine ageing patterns of wild populations. Broken wing fringe setae is used as a relative estimate to know insects' age. Breakage rates are affected by age and sex of wasp and treatment and experimental conditions. Various experimental observations prove that older insects tend to have more broken setae on the fringe of the forewing.

1. To investigate how floral resources impact feeding and nutrient dynamics of parasitoids, the ichneumonid Diadegma insulare (Cresson) was monitored in cabbage fields with and without buckwheat Fagopyrum esculentum Moench borders. Biochemical analyses of field-collected wasps determined whether sugar feeding occurred, and whether it enhanced nutrient levels and increased parasitism of diamondback larvae Plutella xylostella (L.) from 2000 to 2003. The effects of experimental spatial scale on sugar feeding dynamics were also evaluated in 2001. 2. The majority of D. insulare foraging on cabbage had fed upon sugar, but floral borders did not consistently increase the proportion of sugar-fed wasps or their levels of glycogen and lipid over all 4 years. Floral borders increased sugar storage by females in 2001. More females fed on sugar when experimental plots were separated by at least 800 m compared with 67 m. 3. Feeding on buckwheat nectar vs. honeydew produced by the soybean aphid Aphis glycines Matsumura in surrounding fields was distinguished using the ratio of fructose to total sugars, which was higher in nectar- than in honeydew-fed parasitoids. Floral borders increased the probability that females collected from adjacent crops were nectar-fed in 2002, demonstrating that floral resources were utilised by foraging parasitoids. Diadegma insulare that fed upon any sugar source had higher levels of sugar and glycogen than unfed wasps, and feeding on honeydew appeared to enhance nutrient storage. 4. The prevalence of sugar or nectar feeding by female D. insulare was not correlated with parasitism rates over the 4 years from all plots, but nectar feeding was positively correlated with parasitism rates within floral plots. [ABSTRACT FROM AUTHOR]

Abstract: We assessed the potential of annual buckwheat, Fagopyrum esculentum Moench, to lead to improved parasitism of lepidopteran cabbage pests over four years. Pest, parasitism, and hyperparasitism rates were monitored in replicated cabbage plots (12×20m) with or without 3m wide buckwheat borders from 2000 to 2003. Floral borders did not significantly increase egg, larval, or pupal densities of cabbage looper, Trichoplusia ni (Hübner), imported cabbageworm, Pieris rapae (L.), or diamondback moth, Plutella xylostella (L.). Buckwheat increased parasitism rates by Voria ruralis (Fallen) on T. ni larvae and Cotesia rubecula (Marshall) on P. rapae larvae over four years. Parasitism by Diadegma insulare (Cresson) on P. xylostella larvae was higher in buckwheat than control plots in the first year, and parasitism by Euplectrus plathypenae (Howard) on T. ni larvae was lower in buckwheat than control plots in the second year. The hyperparasitoid Conura side (Walker) attacked D. insulare all four years, but buckwheat did not affect hyperparasitism rates. The effect of spatial scale on pest densities and parasitism in 2001 was evaluated by comparing plots separated at least 67m (nearby) versus 800m apart (isolated). T. ni pupae and P. rapae eggs and pupae were more abundant in plots in closer proximity, whereas P. xylostella densities did not vary by the spatial separation of plots. Tachinids and Pteromalus puparum (L.) attacked more P. rapae in nearby plots. E. plathypenae responded to the treatment×scale interaction, parasitizing more in control than buckwheat when plots were isolated but not when plots were nearby. [Copyright &y& Elsevier]

Effects of eight insecticides on Diadegma insulare (Cresson), a parasitoid of the diamondback moth, Plutella xylostella L., were evaluated under the laboratory conditions. The insecticides were three azadirachtin-based products (Ecozin, Agroneem and Neemix), two Bacillus thuringiensis (Bt) products (Xentari and Crymax), indoxacarb, spinosad, and λ-cyhalothrin. When D . insulare pupae were treated, none of the insecticide treatments except λ-cyhalothrin significantly reduced adult emergence, with 76-90% adults emerged from the treated pupae. In the λ-cyhalothrin treatment, only 10% D . insulare pupae produced adult wasps. Indoxacarb, spinosad, and λ-cyhalothrin caused 100% D . insulare adult mortality in 24 h in Petri dishes sprayed with insecticides in the contact bioassays, and 95.8, 100 and 95.8% adult mortality in 24 h in the ingestion bioassays, respectively. In contrast, all three azadirachtin-based insecticides and the two Bt-insecticides caused only 0-10.4% mortality of D . insulare adults after ingestion. The surviving D . insulare from ingestion treatments with Bt- and azadirachtin-insecticides parasitized 50.8-67.6% of P. xylostella larvae, respectively, compare to 72.1% for the water control. After ingesting indoxacarb, spinosad and λ-cyhalothrin mixed in honey-water, both the females and the males lived significantly shorter than those ingesting Bt- and azadirachtin-insecticides and the non-insecticide honey-water. Effects of leaf residues of indoxacarb, spinosad and λ-cyhalothrin varied significantly. The leaf residues of spinosad had the least effects on D . insulare adults, and 7- and 10-day-old residue only caused 5.6 and 7.4% mortality in 24 h, whereas 10-day-old leaf residues of indoxacarb and λ-cyhalothrin caused 40.7 and 57.4% mortality in 24 h, respectively. [ABSTRACT FROM AUTHOR]

We compared the effects of floral nectar from buckwheat, Fagopyrum esculentum Moench, and honeydew produced by the soybean aphid, Aphis glycines Matsumura (Homoptera: Aphididae), on longevity, nutrient levels, and egg loads of the parasitoid Diadegma insulare Cresson (Hymenoptera: Ichneumonidae). Diadegma insulare lived for 2 days in control treatments of water or clean soybean leaves, for 6–7 days with honeydew, and in excess of 2 weeks with buckwheat nectar. Potential reasons for the superiority of buckwheat nectar over soybean aphid honeydew for extending the longevity of parasitoids include: (i) parasitoids ingest more sugars from floral sources, (ii) oligosaccharides in honeydew have a lower nutritional value than nectar sugars, and (iii) honeydew has antagonistic compounds. Overall sugar levels were lower in honeydew- vs. nectar-fed female wasps, suggesting a lower feeding rate, but other explanations cannot be excluded. Diadegma insulare eclosed with high levels of lipids and glycogen, and low levels of gut and storage sugars. All carbohydrates increased over the life of both nectar- and honeydew-fed wasps, but remained low or decreased in starved wasps. Lipid levels declined over the lifespan of female wasps, but females fed floral nectar showed the slowest rate of lipid decline. Diet did not affect egg load, probably because the females were not given hosts in the experiment. [ABSTRACT FROM AUTHOR]

Six field populations of the parasitoid Diadegma insulare (Cresson) were collected from Mexico and the United States and tested for their susceptibility to permethrin by using a glass-vial residue bioassay. Significant differences existed in susceptibility, with one population significantly more susceptible than the other five. Susceptibility of D. insulare increased when they were reared for several generations in the greenhouse in the absence of selection. D. insulare was less suceptible to permethrin than the adult stage of its host, Plutella xylostella (L.), from a laboratory colony, but more susceptible than those hosts collected from a commercial field. Our data suggest that a field population of D. insulare appeared to increase its tolerance to permethrin much more slowly than P. xylostella. [ABSTRACT FROM PUBLISHER]

We studied interactions among collards, Brassica oleracea var. acephala, the diamondback moth (DBM), Plutella xylostella (Lepidoptera: Yponomeutidae) and its parasitoid Diadegma insulare (Hymenoptera: Ichneumonidae) by manipulating plant nitrogen (N) concentrations in field and laboratory experiments. Parasitoid abundance strongly reflected DBM abundance and was related to total leaf N. Parasitism rates were high (70.7%) and density-independent. Wasp sex ratios varied markedly (3-93% female) in response to the herbivores, the plants, or both. Higher proportions of female wasps emerged from DBM larvae on plants with high leaf N than on unfertilized plants. More female wasps also emerged from larvae parasitized as larger instars. We suggest that wasps have the potential to control DBM populations through long-term numerical responses mediated by variable sex ratios. [ABSTRACT FROM AUTHOR]