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Interactions between earwigs and entomopathogens, such as Bacillus thuringiensis (Bt), are still poorly understood. This study tested whether Bt-based bioinsecticides have any effect on the predation of Euborellia annulipes (Lucas) (Dermaptera: Anisolabididae) on Plutella xylostella (L.) (Lepidoptera: Plutellidae), one of the pests with the largest number of cases of use and resistance to Bt. Fourth instar larvae were Bt infected by feeding on collard green leaves treated with Dipel®WG and XenTari®WG at the manufacturer-recommended doses. We used one no-choice condition, in which the predator had access to uninfected or Bt-infected larvae separately, and four free-choice conditions: uninfected vs Dipel®-infected larvae, uninfected vs XenTari®-infected larvae, Dipel®-infected vs XenTari®-infected larvae, and uninfected vs Bt-infected larvae with both bioinsecticides. Uninfected larvae were less consumed than those infected by both Bt-bioinsecticides in the no-choice condition. There was a higher consumption of uninfected over Dipel®-infected larvae in the free-choice condition. Overall, uninfected larvae were preferred over both Bt-based bioinsecticides infected larvae. We also used six different prey densities. The ringlegged earwig's predation rate enhanced as the prey population density increased, but the functional response was not affected by Bt-infection, being type II. The predator invested a low amount of handling time on Bt-fed prey and increased the maximum predation rate. Bt-based bioinsecticides cause effects on E. annulipes predation by altering their feeding preference and some aspects of its predatory behavior. The results of our study provide an important background for understanding interactions between earwigs and Bt. In addition, they can be used for decision making during approaches to integrated P. xylostella management.

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BACKGROUND: Selective insecticides and insecticide-resistant natural enemies are components of chemical and biological methods that can be compatible in an integrated pest management (IPM) program. Many insecticides that are labeled for treatment against insects in Brassica crops have lost their efficacy because of the development of resistance. However, natural enemies can provide an important role in regulating the population of these pests. RESULTS: Survival of Eriopis connexa populations was >80% when exposed to insecticides, except for EcFM exposed to indoxacarb and methomyl. Bacillus thuringiensis, cyantraniliprole, chlorfenapyr and spinosad caused high mortality of P. xylostella larvae, but neither affected E. connexa survival nor its predation upon L. pseudobrassicae. Cyantraniliprole, chlorfenapyr, deltamethrin and methomyl caused high mortality of L. pseudobrassicae, but did not affect E. connexa survival nor its predation upon P. xylostella larvae. According to the differential selectivity index and the risk quotient, chlorfenapyr and methomyl were more toxic to P. xylostella larvae than to E. connexa, whereas indoxacarb was more toxic to E. connexa. CONCLUSION: This study demonstrates that the insecticides B. thuringiensis, cyantraniliprole, chlorantraniliprole, deltamethrin, chlorfenapyr, spinosad, azadiracthin and spiromesifen are compatible with insecticide-resistant adult E. connexa within an IPM program in Brassica crops. © 2023 Society of Chemical Industry.

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Plutella xylostella is the main pest of cruciferous crops worldwide. To reduce P. xylostella populations, better integration of natural control and chemical control (dominant tactic used) is needed. This work analyzed the compatibility of nine insecticides with the parasitoid Diadegma insulare, outlining them as complementary tools in an integrated pest management strategy. The acute toxicity of spinosad, imidacloprid, indoxacarb, flonicamid, naled, pyridalyl, emamectin benzoate, and spinetoram against the parasitoid was assessed. Residual activity (persistence) was also evaluated over time; the mortality of the parasitoid in contact with leaf tissue of plants treated with insecticides was analyzed. According to the International Organization of Biological Control, all nine insecticides were toxic to D. insulare; the lowest mortality was recorded with spirotetramat (64%) and pyridalyl (48%), while the rest of the insecticides caused 100% mortality at 72 h after application. In terms of persistence, by days 14, 16, 16, 17, 17, 21, and 22 after application, flonicamid, naled, spirotetramat, spinosad, piridalyl, imidacloprid, and indoxacarb caused mortality of less than 25%, respectively, so they were considered harmless (Category 1). Nonetheless, some insecticide toxicity and residual activity must be regarded within integrated pest management programs for conserving the role of D. insulare field populations.

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BACKGROUND: The application of synthetic insecticides is the main strategy used to reduce the damage caused by the diamondback moth Plutella xylostella in commercial Brassica crops. However, incorrect insecticide use can cause biological and ecological disturbances in agroecosystems. Cycloneda sanguinea is a generalist voracious predator and is distributed widely in cultivated and noncultivated ecosystems. This study investigated the efficiency of four insecticides for the control of P. xylostella and the lethal and sublethal effects of these insecticides on C. sanguinea. RESULTS: Spinosad (92% mortality) and chlorfenapyr (76% mortality) were highly toxic to P. xylostela. However, chlorantraniliprole (10% mortality) and methomyl (no mortality) were ineffective against this pest. Chlorantraniliprole was the only insecticide that was highly toxic to C. sanguinea by contact (90% mortality), however, it was nontoxic following the ingestion of chlorantraniliprole-contaminated aphids. Interestingly, ingestion of prey contaminated with methomyl and chlorfenapyr was highly toxic (100% mortality) to C. sanguinea. Spinosad was nontoxic to C. sanguinea via exposure to contaminated surfaces and following ingestion of contaminated prey. However, direct contact of the insects with both methomyl and spinosad significantly affected C. sanguinea flight activity (vertical flight and free-fall flight), whereas chlorfenapyr impacted vertical flight only. CONCLUSION: These findings showed that chlorantraniliprole was not only ineffective for the control of P. xylostela, but was also highly toxic to C. sanguinea. The results indicated that spinosad was efficient against P. xylostela and was of low toxicity to C. sanguinea; however, the deleterious effects of this insecticide on flight behavior could result in reduced predatory efficiency. © 2022 Society of Chemical Industry.

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The diamondback moth (DBM), Plutella xylostella (L.) (Lep.: Plutellidae), is an important pest of broccoli (Brassica oleracea L. var. italica Plenck). Few studies have focused on the real DBM impact on broccoli yield. We performed greenhouse studies to assess the effect of DBM densities and infestation timing (at pre-heading, heading, or during the entire cycle) on broccoli head weight. Polynomial trend analysis revealed a downward linear response of head weight to DBM densities, indicating that broccoli is susceptible to DBM attack. As for the infestation timing, infestations during the pre-heading stage significantly impacted head weight, whereas the same did not occur for infestations during the heading stage. DBM density did not affect plant height or total leaves but was upward-related to plant defoliation, and head weight correlated negatively with plant defoliation. These findings indicate that pre-heading is the determining stage for head weight loss of plants under DBM attack. In order to prevent quantitative losses, efforts for DBM management should be focused on this particular stage.

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The present study aimed to explore some simple ways to optimize the mass rearing of Cotesia vestalis (Haliday) (Hymenoptera: Braconidae), one of the most important biocontrol agents of the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae). The effects of host and parasitoid initial densities on the quantity and quality of produced wasps were investigated. In particular, a factorial experiment was established using three different host densities (20, 50, and 100 P. xylostella larvae per cage) in presence of C. vestalis at three different densities (2, 5, and 7 females, with a 24-h exposure) in well-ventilated cages. There was a significant effect of wasp's initial density on the percentage parasitism (measured based on the cocoon and emerged adult wasps); comparatively the greatest percentage parasitism was obtained with five wasps per cage. Initial host density had no significant effects on the percentage parasitism, sex ratio, and larval period, but it influenced the survival rate (measured based on the cocoon and adult emerged) and pupal period of produced wasps, and also percentage host mortality. The density of 20 host larvae was the best in this regard. These findings were discussed in the contexts of optimum mass rearing, life history, and potential of C. vestalis as a biological control agent.

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Recently generated high-throughput sequencing data sets have shed light on the important regulatory roles of noncoding RNA (ncRNA) molecules in the development of higher organisms. Nowadays it is well-known that regulatory ncRNAs can bind complementary RNA or DNA sequences and recruit chromatin remodelers to selectively modulate gene expression. Consequently, genome sequencing and transcriptomics technologies are now being used to reveal hidden associations among ncRNAs and distinct biological mechanisms. This is the case for the diamondback moth Plutella xylostella, a worldwide pest known to infest cruciferous crops and to display resistance to most insecticides, including Bacillus thuringiensis (Bt) based biopesticides. In P. xylostella, it is thought that ncRNAs could play important roles in both development and insecticide resistance. This review will highlight recent insights into the roles of ncRNAs in P. xylostella and related lepidopterans, and will outline genetic engineering technologies which might be used to design efficient ncRNA-based pest control strategies. This article is categorized under: Regulatory RNAs/RNAi/Riboswitches > Regulatory RNAs.

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This study aimed to evaluate the effects of three solvent extractors (water, ethanol and hexane) of grounded seeds of soursop, Annona muricata L. (Annonaceae), in the mortality, biology and oviposition of Plutella xylostella L. (Lepidoptera: Plutellidae). The results showed that the LC50 and LC99 were 0.0133 and 0.084%, 0.025% and 0.196%, 2.33 and 35.22% for the ethanolic, hexanic and aqueous extracts, respectively. The organic extracts affected only the larval phase and reduced viability in more than 60%, but did not affect pupal stage of the remaining larvae. Furthermore, the ethanolic extract at lethal concentraction also affected negatively the embryonic phase. The results lead to the conclusion that the ethanolic extract of soursop grounded seeds is a viable alternative to control diamondback moth on vegetables.

O presente trabalho teve como objetivo avaliar o efeito de extratos de sementes de graviola, Annona muricata L. (Annonaceae) obtidos com diferentes solventes sobre Plutella xylostella L. (Lepidoptera: Plutellidae). Foram estimadas as concentrações letais de três solventes extratores (água, hexano e etanol) e seus efeitos na biologia e oviposição. Os valores estimados das concentrações letais foram de 0,013 e 0,084%; 0,025 e 0,196%; 2,33 e 35,22%, para as CL50 e CL99 do extrato etanólico, hexânico e aquoso, respectivamente. Os extratos orgânicos afetaram apenas a fase larval e reduziu a viabilidade em mais de 60%, mas não afetou a fase pupal das lagartas remanescentes. Além disso, o extrato etanólico na concentração letal se mostrou eficiente afetando negativamente a fase embrionária. Conclui-se que o extrato etanólico da graviola é uma alternativa viável no controle da traça.

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Successive applications of insecticides to control Plutella xylostella L. (Lepidoptera: Plutellidae) have resulted in the emergence of resistant populations of this insect. A novel control measure for this target insect could be the use of botanical insecticides derived from plant tissues. Hence, we experimentally tested aqueous extracts of Alibertia edulis (Rich.), Alibertia intermedia (Mart.), and Alibertia sessilis (Vell.) K. Schum. found in the Brazilian savannah in order to investigate their potential to disrupt the life cycle of P. xylostella. Aqueous extracts of the leaves of A. intermedia and A. sessilis negatively affected the development of P. xylostella in all stages of the life cycle, prolonging the larval stage and causing mortality in the larval or pupal stages. Treatments with A. intermedia and A. sessilis extracts caused the lowest fecundity and the number of hatched larvae. The harmful effects of these aqueous extracts on the life cycle of P. xylostella may be attributable to the flavonoids and other phenolic compounds present in A. intermedia and A. sessilis. These aqueous botanical extracts are low in toxicity when compared to non-aqueous pesticides, and may emerge as an effective approach for control of populations of P. xylostella.

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The diamondback moth Plutella xylostella (Linnaeus, 1758) (Lepidoptera: Plutellidae) is an herbivorous specialist on Brassicaceae species. Brassicas spp. plants developed a range of defenses (chemical, physical, and morphological) to prevent herbivores attack. In this study, we reported the antixenotic and antibiotic effects of outermost layer of two species of epicuticular wax of Brassicaceae, Brassica oleracea L. var. "Santo Antônio," and Hybrid Kope F1 100MX, on larvae and adult of P. xylostella. In the choice experiment, P. xylostella adults showed an oviposition preference for collard cultivars Santo Antônio (control) and Hybrid Kope F1 100MX with wax removal. In the no-choice experiment, oviposition was 6.4 times higher in the Hybrid Kope F1 100MX with wax removal than without wax removal. There were significant differences among larvae feeding on leaf disks of Hybrid Kope F1 100MX in the treatments with (65.3 mg) and without wax removal (23.5 mg). The net reproduction rate (R 0 ), and intrinsic (rm) and finite rates of increase (λ) of P. xylostella in the cv. Santo Antônio were bigger in the treatment without wax removal (R 0  = 50.4, rm = 0.23 and λ = 1.26) than treatment with wax removal (R 0  = 28.5, rm = 0.20 and λ = 1.22). However, only the R 0 value was affected by mechanical wax removal in the Hybrid Kope F1 100MX (with wax removal R 0  = 43.3 and without wax removal R 0  = 30.8). In conclusion, the results indicate that collard's wax is important to accessibility and development of P. xylostella, and its removal changes the resistance of collard's varieties to P. xylostella.

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Abstract Diamondback moth (DBM), Plutella xylostella (Linnaeus), is a notorious pest of brassica crops worldwide and is resistant to all groups of insecticides. The insect system harbors diverse groups of microbiota, which in turn helps in enzymatic degradation of xenobiotic-like insecticides. The present study aimed to determine the diversity of gut microflora in DBM, quantify esterase activity and elucidate their possible role in degradation of indoxacarb. We screened 11 geographic populations of DBM in India and analyzed them for bacterial diversity. The culturable gut bacterial flora underwent molecular characterization with 16S rRNA. We obtained 25 bacterial isolates from larvae (n = 13) and adults (n = 12) of DBM. In larval gut isolates, gammaproteobacteria was the most abundant (76%), followed by bacilli (15.4%). Molecular characterization placed adult gut bacterial strains into three major classes based on abundance: gammaproteobacteria (66%), bacilli (16.7%) and flavobacteria (16.7%). Esterase activity from 19 gut bacterial isolates ranged from 0.072 to 2.32 µmol/min/mg protein. Esterase bands were observed in 15 bacterial strains and the banding pattern differed in Bacillus cereus – KC985225 and Pantoea agglomerans – KC985229. The bands were characterized as carboxylesterase with profenofos used as an inhibitor. Minimal media study showed that B. cereus degraded indoxacarb up to 20%, so it could use indoxacarb for metabolism and growth. Furthermore, esterase activity was greater with minimal media than control media: 1.87 versus 0.26 µmol/min/mg protein. Apart from the insect esterases, bacterial carboxylesterase may aid in the degradation of insecticides in DBM.

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Diamondback moth (DBM), Plutella xylostella (Linnaeus), is a notorious pest of brassica crops worldwide and is resistant to all groups of insecticides. The insect system harbors diverse groups of microbiota, which in turn helps in enzymatic degradation of xenobiotic-like insecticides. The present study aimed to determine the diversity of gut microflora in DBM, quantify esterase activity and elucidate their possible role in degradation of indoxacarb. We screened 11 geographic populations of DBM in India and analyzed them for bacterial diversity. The culturable gut bacterial flora underwent molecular characterization with 16S rRNA. We obtained 25 bacterial isolates from larvae (n = 13) and adults (n = 12) of DBM. In larval gut isolates, gammaproteobacteria was the most abundant (76%), followed by bacilli (15.4%). Molecular characterization placed adult gut bacterial strains into three major classes based on abundance: gammaproteobacteria (66%), bacilli (16.7%) and flavobacteria (16.7%). Esterase activity from 19 gut bacterial isolates ranged from 0.072 to 2.32 µmol/min/mg protein. Esterase bands were observed in 15 bacterial strains and the banding pattern differed in Bacillus cereus KC985225 and Pantoea agglomerans KC985229. The bands were characterized as carboxylesterase with profenofos used as an inhibitor. Minimal media study showed that B. cereus degraded indoxacarb up to 20%, so it could use indoxacarb for metabolism and growth. Furthermore, esterase activity was greater with minimal media than control media: 1.87 versus 0.26 µmol/min/mg protein. Apart from the insect esterases, bacterial carboxylesterase may aid in the degradation of insecticides in DBM.(AU)

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Diamondback moth (DBM), Plutella xylostella (Linnaeus), is a notorious pest of brassica crops worldwide and is resistant to all groups of insecticides. The insect system harbors diverse groups of microbiota, which in turn helps in enzymatic degradation of xenobiotic-like insecticides. The present study aimed to determine the diversity of gut microflora in DBM, quantify esterase activity and elucidate their possible role in degradation of indoxacarb. We screened 11 geographic populations of DBM in India and analyzed them for bacterial diversity. The culturable gut bacterial flora underwent molecular characterization with 16S rRNA. We obtained 25 bacterial isolates from larvae (n=13) and adults (n=12) of DBM. In larval gut isolates, gammaproteobacteria was the most abundant (76%), followed by bacilli (15.4%). Molecular characterization placed adult gut bacterial strains into three major classes based on abundance: gammaproteobacteria (66%), bacilli (16.7%) and flavobacteria (16.7%). Esterase activity from 19 gut bacterial isolates ranged from 0.072 to 2.32µmol/min/mg protein. Esterase bands were observed in 15 bacterial strains and the banding pattern differed in Bacillus cereus - KC985225 and Pantoea agglomerans - KC985229. The bands were characterized as carboxylesterase with profenofos used as an inhibitor. Minimal media study showed that B. cereus degraded indoxacarb up to 20%, so it could use indoxacarb for metabolism and growth. Furthermore, esterase activity was greater with minimal media than control media: 1.87 versus 0.26µmol/min/mg protein. Apart from the insect esterases, bacterial carboxylesterase may aid in the degradation of insecticides in DBM.

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The widespread and sustainable exploitation of the entomopathogen Bacillus thuringiensis (Bt) in pest control is threatened by the evolution of resistance. Although resistance is often associated with loss of binding of the Bt toxins to the insect midgut cells, other factors have been implicated. Here we used suppressive subtractive hybridization and gene expression suppression to identify additional molecular components involved in Bt-resistance in Plutella xylostella. We isolated transcripts from genes that were differentially expressed in the midgut of larvae from a resistant population, following ingestion of a Bt kurstaki HD1 strain-based commercial formulation (DiPel), and compared with a genetically similar susceptible population. Quantitative real-time polymerase-chain reaction (RT-PCR) analysis confirmed the differential basal expression of a subset of these genes. Gene expression suppression of three of these genes (P. xylostella cyclin-dependent kinase 5 regulatory subunit associated protein 1-like 1, stromal cell-derived factor 2-like 1 and hatching enzyme-like 1) significantly increased the pathogenicity of HD1 to the resistant population. In an attempt to link the multitude of factors reportedly influencing resistance to Bt with the well-characterized loss of toxin binding, we also considered Bt-resistance models in P. xylostella and other insects.

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A estimativa da área foliar, em função da sua redução causada pelo consumo por insetos filófagos, é uma metodologia básica em várias áreas da Entomologia, como, por exemplo, em estudos sobre resistência de plantas, entomologia econômica e ecologia nutricional. Um dos fatores que pode interferir na quantidade de área foliar consumida pelo fitófago é a presença de certos químicos nas folhas, como a sinigrina em brassicáceas. Dessa forma, foram aplicadas em folhas de couve e brócolis diversas concentrações de sinigrina (0,2, 0,4, 0,8, 1,6, e 3,2 mg/mL em solução a 5% de Tween20(r)), medindo-se o consumo da área foliar por lagartas de P. xylostella, o qual foi aferido pela porcentagem de redução da área, diferença de peso e escala visual de notas. Os resultados mostraram que as concentrações 0,2, 0,4 e 3,2 mg/mL de sinigrina aumentam o consumo em folhas de couve e diminuem em folhas de brócolis por lagartas de P. xylostella. As metodologias utilizadas proporcionam resultados similares, sendo as estimativas de peso fresco e nota visual mais práticas.(AU)

Leaf area estimation, based on their reduction due to consumption by phytophagous insects, is a basic methodology in several areas of Entomology, for instance, in studies about plant resistance, economic entomology and nutritional ecology. One of the factors that can affect the amount of leaf area consumed by insects is the presence of certain chemicals in the leaves, such as sinigrin in Brassicaceae. Thus, several concentrations of sinigrin were applied on the leaves of cabbage and broccoli (0.2, 0.4, 0.8, 1.6, and 3.2 mg/mL in 5% Tween20(r) solution) in order to measure leaf area consumption by larvae of P. xylostella, estimated by the percentage of area reduction, weight loss and visual scale of notes. The results show that the concentrations of 0.2, 0.4 and 3.2 mg/mL of sinigrin increase larvae consumption of P. xylostella on kale leaves and decrease it on broccoli leaves. The methodologies used provide similar results, and fresh weight measurements and visual grades are more practical.(AU)

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A estimativa da área foliar, em função da sua redução causada pelo consumo por insetos filófagos, é uma metodologia básica em várias áreas da Entomologia, como, por exemplo, em estudos sobre resistência de plantas, entomologia econômica e ecologia nutricional. Um dos fatores que pode interferir na quantidade de área foliar consumida pelo fitófago é a presença de certos químicos nas folhas, como a sinigrina em brassicáceas. Dessa forma, foram aplicadas em folhas de couve e brócolis diversas concentrações de sinigrina (0,2, 0,4, 0,8, 1,6, e 3,2 mg/mL em solução a 5% de Tween20(r)), medindo-se o consumo da área foliar por lagartas de P. xylostella, o qual foi aferido pela porcentagem de redução da área, diferença de peso e escala visual de notas. Os resultados mostraram que as concentrações 0,2, 0,4 e 3,2 mg/mL de sinigrina aumentam o consumo em folhas de couve e diminuem em folhas de brócolis por lagartas de P. xylostella. As metodologias utilizadas proporcionam resultados similares, sendo as estimativas de peso fresco e nota visual mais práticas.(AU)

Leaf area estimation, based on their reduction due to consumption by phytophagous insects, is a basic methodology in several areas of Entomology, for instance, in studies about plant resistance, economic entomology and nutritional ecology. One of the factors that can affect the amount of leaf area consumed by insects is the presence of certain chemicals in the leaves, such as sinigrin in Brassicaceae. Thus, several concentrations of sinigrin were applied on the leaves of cabbage and broccoli (0.2, 0.4, 0.8, 1.6, and 3.2 mg/mL in 5% Tween20(r) solution) in order to measure leaf area consumption by larvae of P. xylostella, estimated by the percentage of area reduction, weight loss and visual scale of notes. The results show that the concentrations of 0.2, 0.4 and 3.2 mg/mL of sinigrin increase larvae consumption of P. xylostella on kale leaves and decrease it on broccoli leaves. The methodologies used provide similar results, and fresh weight measurements and visual grades are more practical.(AU)

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Plutella xylostella is a recurring pest on cruciferous crops around the world. In Brazil, it typically requires large number of insecticide sprays, which may lead to fast evolution of resistance. The aim of this study was to assess the susceptibility of Brazilian diamondback moth populations to the insecticides abamectin, deltamethrin, and spinosad. Leaf dip bioassays were used to determine mortality data obtained after 48 h of exposure to insecticides and subjected to Probit analysis. The population from Bonito, state of Pernambuco, Brazil, had the highest toxicity ratio (20.2 - fold) to abamectin compared to the reference population. The LC50 values for deltamethrin ranged from 85.2 to 360.1 mg L-1, demonstrating a high survival of populations in relation to this insecticide field dose rate (7.5 mg L-1). The toxicity ratios of the estimated LC50s, however, were very low (varying from 2.2 - to 4.2 - fold). Most populations exhibited toxicity ratios for spinosad, ranging from 2.3 - to 5.1 - fold, while both the LC50 and LC95 values reflected a high susceptibility to the spinosad field dosage (120 mg L-1). Only the Bonito - PE population resisted to abamectin, while all P. xylostella populations were resistant to deltamethrin, but particularly susceptible to spinosad because of the absence of selection pressure with it in these areas.

Plutella xylostella é uma praga recorrente em brássicas de todo o mundo. No Brasil, normalmente exige grande número de pulverizações de inseticidas, que pode levar à rápida evolução da resistência. Avaliou-se a suscetibilidade de populações brasileiras da traça das crucíferas aos inseticidas abamectina, deltametrina e espinosade. Bioensaios de imersão de folhas foram utilizados para determinar a mortalidade, sendo os dados obtidos após 48 h de exposição aos inseticidas e submetidos à análise de Probit. A população de Bonito-PE apresentou a maior razão de toxicidade (20,2 vezes) para abamectina em relação à população de referência. Os valores de CL50s para deltametrina variaram entre 85,2 - 360,1 mg L-1, demonstrando alta sobrevivência das populações a este inseticida com relação à dose de campo (7,5 mg L-1). Entretanto, as razões de toxicidade das CL50 estimadas foram muito baixas (variando de 2,2 a 4,2 vezes). A maioria das populações apresentou razões de toxicidade para espinosade, variando de 2,3 para 5,1 vezes, embora os valores de CL demonstram alta suscetibilidade delas à dose de campo para espinosade (120 mg L-1). Apenas a população de Bonito PE apresentou resistência a abamectina, enquanto todas as populações de P. xylostella estão resistentes a deltametrina, mas suscetíveis ao espinosade particularmente devido à ausência de pressão de seleção com este nestas áreas.

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Plutella xylostella is a recurring pest on cruciferous crops around the world. In Brazil, it typically requires large number of insecticide sprays, which may lead to fast evolution of resistance. The aim of this study was to assess the susceptibility of Brazilian diamondback moth populations to the insecticides abamectin, deltamethrin, and spinosad. Leaf dip bioassays were used to determine mortality data obtained after 48 h of exposure to insecticides and subjected to Probit analysis. The population from Bonito, state of Pernambuco, Brazil, had the highest toxicity ratio (20.2 - fold) to abamectin compared to the reference population. The LC50 values for deltamethrin ranged from 85.2 to 360.1 mg L-1, demonstrating a high survival of populations in relation to this insecticide field dose rate (7.5 mg L-1). The toxicity ratios of the estimated LC50s, however, were very low (varying from 2.2 - to 4.2 - fold). Most populations exhibited toxicity ratios for spinosad, ranging from 2.3 - to 5.1 - fold, while both the LC50 and LC95 values reflected a high susceptibility to the spinosad field dosage (120 mg L-1). Only the Bonito - PE population resisted to abamectin, while all P. xylostella populations were resistant to deltamethrin, but particularly susceptible to spinosad because of the absence of selection pressure with it in these areas.

Plutella xylostella é uma praga recorrente em brássicas de todo o mundo. No Brasil, normalmente exige grande número de pulverizações de inseticidas, que pode levar à rápida evolução da resistência. Avaliou-se a suscetibilidade de populações brasileiras da traça das crucíferas aos inseticidas abamectina, deltametrina e espinosade. Bioensaios de imersão de folhas foram utilizados para determinar a mortalidade, sendo os dados obtidos após 48 h de exposição aos inseticidas e submetidos à análise de Probit. A população de Bonito-PE apresentou a maior razão de toxicidade (20,2 vezes) para abamectina em relação à população de referência. Os valores de CL50s para deltametrina variaram entre 85,2 - 360,1 mg L-1, demonstrando alta sobrevivência das populações a este inseticida com relação à dose de campo (7,5 mg L-1). Entretanto, as razões de toxicidade das CL50 estimadas foram muito baixas (variando de 2,2 a 4,2 vezes). A maioria das populações apresentou razões de toxicidade para espinosade, variando de 2,3 para 5,1 vezes, embora os valores de CL demonstram alta suscetibilidade delas à dose de campo para espinosade (120 mg L-1). Apenas a população de Bonito PE apresentou resistência a abamectina, enquanto todas as populações de P. xylostella estão resistentes a deltametrina, mas suscetíveis ao espinosade particularmente devido à ausência de pressão de seleção com este nestas áreas.

RESUMO

Plutella xylostella (L.) é uma praga de difícil controle em virtude de seu alto potencial reprodutivo e de causar danos, e ampla distribuição geográfica, além de apresentar resistência a inseticidas. No entanto, as fases de larva e pupa dessa praga são naturalmente parasitadas por Oomyzus sokolowskii (Kurdjumov), favorecendo o incremento do parasitismo natural. Este estudo investigou o efeito da idade do parasitóide, disponibilidade de hospedeiro e fotoperíodo no comportamento reprodutivo de O. sokolowskii. O número de encontros entre parasitóide e hospedeiro e a taxa de parasitismo aumentaram com a idade das fêmeas até 96h. O parasitismo foi maior quando fêmeas do parasitóide receberam diariamente um número constante de hospedeiros comparado à disponibilidade randômica (13,3 versus 8,9 lagartas). A atividade de parasitismo ocorreu até 20 dias de idade e com longevidade semelhante entre os tratamentos (constante = 33,5 d; randômico = 34,7 d). O número de descendentes por fêmea, no entanto, decresceu com a sua idade, sendo o mesmo observado para o número de parasitóides emergidos por lagarta parasitada. A exposição contínua do hospedeiro à luz ou ao escuro por 12h não afetou a taxa de parasitismo; porém, parasitóides apresentaram maior atividade após 3h de exposição à luz. Assim, futuros estudos e possível utilização de O. sokolowskii, em campo, devem considerar a liberações de parasitóides com idade entre 48h e 72h e, preferencialmente, na madrugada para maiores chances de sucesso de parasitismo.

The high reproduction rate, potential to cause damage, wide geographic distribution and resistance to insecticides of Plutella xylostella (L.) makes difficult its efficient control. However, larvae and pupae of this pest are naturally parasitized by Oomyzus sokolowskii (Kurdjumov), providing opportunities to improve the natural parasitism. This study investigated the effects of the age of adult parasitoids, host availability and time of exposure on O. sokolowskii parasitism behavior. The number of larvae encounters by parasitoid females and the parasitism rate increased with parasitoid age up to 96h. The parasitization was higher when wasps received a constant number of hosts daily in comparison with a random number (13.3 versus 8.9 larvae parasitized). Female parasitization activity was maintained up to the age of 20 days in both treatments and exhibited similar longevity (constant host = 33.5 d; and random host = 34.7 d). The progeny produced per female and the number of parasitoids emerged per host significantly decreased as wasps aged. There was no significant effect of the light regime (12h darkness or 12h light exposure) on the parasitization, although parasitoid was more active after 3h of light exposure. Therefore, further studies on field application of O. sokolowskii should consider the release of 48h- to 72h-old parasitoids at dawn as a way to increase the success of host parasitization.

Assuntos

RESUMO

A traça-das-crucíferas, Plutella xylostella (L.) (Lepidoptera: Yponomeutidae), é uma das principais espécies de inseto-praga de plantas da família Brassicaceae no Brasil e no mundo. A utilização de extratos de plantas inseticidas no controle desse inseto é uma alternativa promissora. O presente trabalho teve como objetivo avaliar, em laboratório, o efeito de extratos de plantas na oviposição e na mortalidade de P. xylostella. Para análise do efeito sobre a oviposição, pedaços de folhas de couve foram expostos, em gaiola, aos seguintes tratamentos: extratos aquosos (10 por cento p/v) de folha de cinamomo (Melia azedarach), de ramo de cinamomo, de pó-de-fumo (Nicotiana tabacum), além de DalNeem (produto comercial à base de Azadirachta indica), a 10 por cento v/v. No interior da gaiola, foram liberados 50 adultos de P. xylostella e, após 48h, foi contado o número de ovos por folha, em sete repetições. Um segundo ensaio constou da exposição de três larvas aos extratos referidos anteriormente em tubos de vidro com um pedaço de folha de couve previamente tratado. Foram utilizados três tubos por tratamento, com quatro repetições. O número de larvas mortas foi avaliado diariamente. Os extratos aquosos de folha de cinamomo, de ramo de cinamomo e de pó-de-fumo, além de DalNeem, reduzem a oviposição de P. xylostella e a utilização de extrato de pó-de-fumo, de DalNeem e de ramo de cinamomo resultam em controle eficiente de larvas de P. xylostella a partir do segundo, do quinto e do sexto dias após a aplicação, respectivamente.

The diamondback moth, Plutella xylostella (L.) (Lepidoptera, Yponomeutidae), is one of the most important insect pest species of the Brassicaceae family plants in Brazil and in the world. The use of insecticidal plants extracts in the control of this insect is a promising alternative. Therefore, this research goal is to evaluate, in laboratory, the plants extracts effect on the oviposition and mortality of P. xylostella. In order to analyze the effect on the oviposition, kale leaf pieces were treated, in cage, as following: aqueous extracts (10 percent p/v) of leaf of chinaberry (Melia azedarach), of branch of chinaberry, of tobacco powder (Nicotiana tabacum), besides DalNeem (commercial product, based on Azadirachta indica), at 10 percent v/v. Inside the cage, 50 adults of P. xylostella were put and, 48h later, the egg number per leaf was counted, in seven repetitions. A second assay was consisted of the exposition of three larvae to the same cited extracts, in glass tube with a kale leaf piece previously treated. Three glass tubes were used per treatment, with four repetitions. The number of death larvae was evaluated daily. The aqueous extracts of chinaberry leaf, chinaberry branch and tobacco powder, besides DalNeem, reduce the oviposition of P. xylostella and the use of tobacco powder extract, DalNeem and chinaberry branch extract result in efficient control of P. xylostella larvae after the second, fifth and sixth days after application, respectively.