Insecticidal activity of extracts of handroanthus impetiginosus on Plutella xylostella (Lepidoptera: plutellidae) larvae.

Plutella xylostella is considered the main pest of cabbage in Brazil and the world, causing damage of up to 100%. Thus, this study evaluated the insecticidal activity of extracts obtained from the fruits, seeds, bark, leaves, and flowers of Handroanthus impetiginosus against the diamondback moth, P. xylostella larvae. The seed extract showed the highest mortality (97.0%) compared to the control treatment. The LC50 values indicated that the seed and flower extracts (0.01003 and 0.01288 mg/L respectively) assumed the highest toxicity to P. xylostella larvae after 24 h of exposure. The results of this study indicated that the seeds extract is the most promising toxic extract, with measured mortality of approximately 97.0% for P. xylostella larvae after 144 h of exposure in kale plants. Seed extract showed the best insecticidal activity. Thus, this extract can be applied to develop an insecticide based on H. impetiginosus seed.

Efficacy and Residual Toxicity of Insecticides on Plutella xylostella and Their Selectivity to the Predator Solenopsis saevissima.

We evaluated the efficacy and residual toxicity of nine commercial insecticides on Plutella xylostella and their selectivity to the predator ant Solenopsis saevissima under laboratory and field conditions. First, to test the insecticides' effectiveness and selectivity, we conducted concentration-response bioassays on both species and the mortalities were recorded 48 h after exposure. Next, rapeseed plants were sprayed following label rate recommendations in the field. Finally, insecticide-treated leaves were removed from the field up to 20 days after application and both organisms were exposed to them as in the first experiment. Our concentration-response bioassay indicated that seven insecticides caused mortality ≥80% of P. xylostella: bifenthrin, chlorfenapyr, chlorantraniliprole, cyantraniliprole, indoxacarb, spinetoram, and spinosad. However, only chlorantraniliprole and cyantraniliprole caused mortality ≤30% of S. saevissima. The residual bioassay indicated that four insecticides had a long-lasting effect, causing mortality of 100% to P. xylostella 20 days after application: chlorantraniliprole, cyantraniliprole, spinetoram, and spinosad. For S. saevissima, bifenthrin caused mortality of 100% during the evaluated period. Additionally, mortality rates below 30% occurred four days after the application of spinetoram and spinosad. Thus, chlorantraniliprole and cyantraniliprole are safe options for P. xylostella management since their efficacy favor S. saevissima.

Economic Benefits from the Use of Mass Trapping in the Management of Diamondback Moth, Plutella xylostella, in Central America.

The diamondback moth, Plutella xylostella (L.), is a worldwide pest of brassica crops, resistant to a large number of insecticides. As an alternative, the use of pheromone-baited traps has been proposed but farmers are yet to be convinced. In the present study, we aimed to validate the benefits of the use of pheromone-baited traps for monitoring and mass trapping in cabbage production in Central America as means of Integrated Pest Management (IPM) in comparison to calendarized insecticide sprays, which are the farmers' current practices (FCP). Mass trapping was established in nine selected plots of cabbage in Costa Rica and Nicaragua. Average captures of males/trap/night, plant damage and net profits of these IPM plots were compared to simultaneously evaluated or historically reported FCP plots. The results indicate that in Costa Rica, trap captures did not justify the application of insecticides and average net profits increased by more than 11% when the trapping methods were implemented. In Nicaragua, IPM plots were able to reduce insecticide applications to one third of those in FCP plots. These results confirm the economic and environmental benefits of pheromone-based management of DBM in Central America.

Antifeeding and Oviposition Deterrent Effect of Ludwigia spp. (Onagraceae) against Plutella xylostella (Lepidoptera: Plutellidae).

Plants produce a wide variety of bioactive compounds with insecticidal properties, such as secondary metabolites capable of interfering with the nutrition and reproduction of pest species such as Plutella xylostella. Thus, the objective of this study was to evaluate the effects of aqueous and ethanolic extracts of Ludwigia spp. (Onagraceae) on the feeding and oviposition of P. xylostella. Choice bioassays were performed using aqueous and ethanolic extracts. The aqueous extract of L. tomentosa resulted in an approximately 81% reduction in larval feeding compared to that in the control, with an antifeedant index (AI) of 52%. The aqueous and ethanolic extract of L. nervosa acted by stimulating larval feeding. The oviposition was significantly reduced in the kale leaves treated with aqueous and ethanolic extracts of Ludwigia spp. The aqueous extracts promoted an average 90% reduction in oviposition when compared to that in the control, and an oviposition deterrent index (ODI) above 61% was classified as an oviposition deterrent. In addition, ethanolic extracts affected 81% of oviposition, with an ODI above 41%. Bioassays should be performed to clarify the use of aqueous and ethanolic extracts of L. nervosa as they acted as phagostimulants in the feeding tests and as deterrents in the oviposition tests. The phenolic compounds-flavonoids, condensed tannins, and alkaloids-were more abundant in L. nervosa, L. tomentosa, L. sericea, and L. longifolia. The extracts of L. longifolia and L. tomentosa showed the best results, interfering with the host choice for feeding and oviposition in P. xylostella and representing an alternative for the control of diamondback moths.

Bioactivity of aqueous extract of Jacaranda spp. (Bignoniaceae) on Plutella xylostella L. 1758 (Lepidoptera: Plutellidae) / Bioatividade do extrato aquoso de Jacaranda spp. (Bignoniaceae) em Plutella xylostella L. 1758 (Lepidoptera: Plutellidae)

The high consumption rate of vegetables stimulates the cultivation and increases the demand regarding the adequacy of the production processes. The attack of the pest Plutella xylostella causes high losses by reducing product quality, typifying a phytosanitary problem. This study aimed to verify the bioactivity of aqueous extracts of leaves of Jacaranda decurrens and Jacaranda mimosifolia at concentrations of 5, 10, and 15% on the insect. The choice test was carried out at the laboratory to determine the food effect of plant extracts and evaluate changes in the life cycle of insects exposed to active compounds through the analysis of biological parameters. Plant extracts of J. decurrens and J. mimosifolia presented with phagodeterrent classification in the choice experiments. The three J. decurrens extract concentrations promoted a prolongation of larval and pupal duration, while the duration of individuals treated with J. mimosifolia at 10% was significantly reduced. Occurred reduction in larval survival of individuals treated with aqueous extracts of J. decurrens and J. mimosifolia. Eggs from treatments with aqueous extract of J. decurrens and J. mimosifolia had reduced survival. Pupal survival of individuals treated with extract at 15% showed a significant reduction compared to the treatments at 5% and 10%. Pupae from the treatment with aqueous extract of Jacaranda mimosifolia showed a reduction in biomass in the treatment at 15% differing from the control e 5%. Thus, the aqueous extracts of the species J. decurrens and J. mimosifolia show insecticidal potential in the tests performed on P. xylostella.

O alto índice de consumo de hortaliças estimula o cultivo e aumenta a demanda quanto à adequação dos processos produtivos. O ataque da praga Plutella xylostella causa grandes perdas por reduzir a qualidade do produto, caracterizando um problema fitossanitário. Este trabalho teve como objetivo verificar a bioatividade de extratos aquosos de folhas de Jacaranda decurrens e Jacaranda mimosifolia nas concentrações de 5, 10 e 15% sobre o inseto. O teste de escolha foi realizado em laboratório para determinar o efeito alimentar de extratos vegetais e avaliar alterações no ciclo de vida de insetos expostos a compostos ativos por meio da análise de parâmetros biológicos. Os extratos vegetais de J. decurrens e J. mimosifolia apresentaram classificação fagodeterrente nos experimentos de escolha. As três concentrações de extrato de J. decurrens promoveram um prolongamento da duração larval e pupal, enquanto a duração dos indivíduos tratados com J. mimosifolia a 10% foi significativamente reduzida. Ocorreu redução na sobrevivência larval de indivíduos tratados com extratos aquosos de J. decurrens e J. mimosifolia. Ovos dos tratamentos com extrato aquoso de J. decurrens e J. mimosifolia tiveram sobrevivência reduzida. A sobrevivência pupal dos indivíduos tratados com extrato a 15% apresentou redução significativa em relação aos tratamentos a 5% e 10%. Pupas do tratamento com extrato aquoso de J. mimosifolia apresentaram redução de biomassa no tratamento a 15% diferindo do controle e 5%. Assim, os extratos aquosos das espécies J. decurrens e J. mimosifolia apresentam potencial inseticida nos testes realizados em P. xylostella.

Parasitism rate of Plutella xylostella (Lepidoptera: Plutellidae) larvae in greenhouse by Tetrastichus howardi (Hymenoptera: Eulophidae) females at different densities / Taxa de parasitismo de lagartas Plutella xylostella (Lepidoptera: Plutellidae) em estufa por fêmeas de Tetrastichus howardi (Hymenoptera: Eulophidae) em diferentes densidades

Parasitoids control insect pests, but their number per host affects their efficiency. The objective of this work was to evaluate the best density of Tetrastichus howardi (Olliff, 1893) (Hymenoptera: Eulophidae) individuals parasitizing fourth instar Plutella xylostella (Linnaeus, 1758) (Lepidoptera: Plutellidae) larvae in greenhouse conditions. These larvae were exposed to parasitism by T. howardi females with 1:1, 3:1, 6:1, 9:1, 12:1, 15:1 and 18:1 parasitoid/host ratios with 10 replications during 96 hours. After this period the larvae were kept on host plants (Brassica oleracea) until pupa formation. Tetrastichus howardi parasitized and reproduced in P. xylostella larvae at all its densities tested, but with higher values, 84% and 10 ± 2.4 individuals, respectively, with 9:1 parasitoids/host. Nine T. howardi females per P. xylostella larvae are the adequate number to manage this insect pest.

Os parasitoides controlam os insetos pragas, mas o seu número por hospedeiro afeta a sua eficiência. O objetivo deste trabalho foi avaliar a melhor densidade de Tetrastichus howardi (Olliff, 1893) (Hymenoptera: Eulophidae) parasitando o quarto instar de larvas de Plutella xylostella (Linnaeus, 1758) (Lepidoptera: Plutellidae) em condições de estufa. Estas lagartas foram expostas ao parasitismo por fêmeas T. howardi com densidades 1:1, 3:1, 6:1, 9:1, 12:1, 15:1 e 18:1 de parasitoide/hospedeiro com 10 repetições durante 96 horas. Após este período, as lagartas foram mantidas em plantas hospedeiras (Brassica oleracea) até à formação de pupas. Tetrastichus howardi parasitaram e reproduziram em lagartas P. xylostella em todas as suas densidades testadas, mas com valores mais elevados de 84% e 10 ± 2.4 indivíduos, respectivamente, com 9:1 parasitoides/hospedeiro. Nove fêmeas de T. howardi por lagarta de P. xylostella são o número adequado para controlar está praga de inseto.

Acute and Chronic Toxicity of Indoxacarb in Two Populations of Plutella xylostella (Lepidoptera: Plutellidae).

The diamondback moth, Plutella xylostella (Linnaeus, 1758), is one of the main pests of brassicas, and various insecticides, such as indoxacarb, are used to control it. However, frequent insecticide applications favor the selection of resistant individuals. Thus, the residual and sublethal effects of indoxacarb in two populations of P. xylostella, one collected in the field (FP) and one from the laboratory (LP), were evaluated and compared. The objective of this research was to investigate the toxicity of indoxacarb at residual and sublethal levels in a field population of P. xylostella from Brazil and a population from the laboratory. Leaf-dip bioassays showed high toxicity, with LC50 values after 48 h of 3.7 and 6.9 mg/liter for the LP and FP, respectively. Sublethal effects were indicated by significant reduction in the survival of larvae, pupae, and offspring. There was an increase in foliar consumption and a decrease in adult survival in the LP, and a decrease in fecundity in the FP. For the LP and FP population, the mean values for R0, rm, and λ for the control treatment were significantly higher than for the treatment groups (CL15 and CL25). Exposure of larvae to sublethal indoxacarb concentrations significantly reduced larval and pupal survival. Larval and pupal survival decreased as the indoxacarb concentration increased. Fecundity was significantly lower for the FP at LC15 (96.2 eggs per female) and LC25 (69.2 eggs per female) concentrations compared with the other treatments.

Phytochemical Screening and Bioactivity of Ludwigia spp. in the Control of Plutella xylostella (Lepidoptera: Plutellidae).

We tested the bioactivity of aqueous extracts of Ludwigia spp. (Myrtales: Onagraceae) on the biological cycle of Plutella xylostella. We assessed the duration of and viability during the larval, pupal and adult phases, as well as the influence of the extracts on the fecundity and hatching of P. xylostella eggs. Subsequently, we phytochemically screened the extracts. The extracts of L. tomentosa and L. longifolia reduced the pupal weight instead of prolonging the larval stage of P. xylostella. The L. tomentosa effect caused higher larval mortality and reduced the fecundity and hatching of P. xylostella eggs, and L. sericea reduced the egg survival. The phenolic compounds-flavonoids, condensed tannins and alkaloids-were more abundant in L. nervosa, L. tomentosa, L. sericea and L. longifolia. The L. tomentosa, L. longifolia and L. sericea extracts were bioactive, and these species showed the best results regarding their ability to control P. xylostella populations, because these plants produce substances able to inhibit food consumption and interfere with the morphological and physiological transformations of the offspring and the oviposition of adults.

Effects of a Bt-based insecticide on the functional response of Ceraeochrysa cincta preying on Plutella xylostella.

Plutella xylostella, is the main pest infesting Brassica crops, and products based on Bacillus thuringiensis (Bt) are frequently used in strategies for its biocontrol. The present study aimed to evaluate whether a Bt-based bioinsecticide affects the predation behavior of Ceraeochrysa cincta when preying on P. xylostella. Three larval instars of the predator and the eggs and second-instar larvae of the moth were used, with the prey either untreated or treated with a Bt-based product (Xentari®). Results showed that, the first larval instar of C. cincta presented a type II functional response when preying upon untreated eggs, and a type III response when preying upon Bt-treated eggs, while the second and third instars presented type II and III responses, respectively, in both situations. The predator's first and third larval instars presented a type II functional response when preying upon untreated larvae and a type III response when preying upon Bt-treated larvae. However, the predator's second-instar larvae showed a type II response in both treatments. The results obtained allowed us to conclude that the Bt-based insecticide tested affects the predation behavior of the first-instar larvae of C. cincta on eggs and of both the first- and third-instar larvae of this predator on P. xylostella larvae.

Interactions of Bacillus thuringiensis strains for Plutella xylostella (L.) (Lepidoptera: Plutellidae) susceptibility.

Bacillus thuringiensis (Bt) biopesticides are an environmentally safe alternative to the management of Plutella xylostella pesticide resistance evolution. We evaluated P. xylostella susceptibility to six Bt strains cultivated and applied individually, and 15 combinations of Bt strains mixed after cultivation. Three combinations resulted in synergism and one in antagonism. Promising results of larval mortality with synergistic effects were obtained with the combinations Bt var. thuringiensis strain HD-2 + Bt finitimus strain HD-3, Bt var. thuringiensis strain HD-2 + Bt dendrolimus strain HD-7 and Bt var. thuringiensis strain HD-2 + Bt var. aizawai strain HD-11.

Evaluation of Leaf Consumption and Determination of Economic Injury Level Caused by Plutella xylostella (L.) (Lepidoptera: Plutellidae) in Brassica oleracea var. acephala (Brassicales: Brassicaceae).

Plutella xylostella (L.) is a microlepidopteran found in all brassica-producing regions of the world. However, no economic injury level (EIL) has been established for this pest in collard greens. Therefore, studies evaluating the EIL of P. xylostella in this crop based on the number of caterpillars per plant can assist pest monitoring and the most effective time for pest control, ensuring profits and the use of pesticides only when required. The present study assessed leaf consumption of caterpillars at different levels of infestation and determinined the EIL for P. xylostella in collard greens. Based on the yield reduction index of collard greens for P. xylostella, EIL was estimated for different scenarios of pest control costs, setting the market value of the bunch of collard greens, and, alternatively, with prices varying and the control cost fixed. In simulated scenarios for 7 d after infestation, the number of caterpillars per plant was always below 1.38, whereas for 10 d, the maximum number was 1.25 caterpillars per plant. When simulating scenarios with different market values for the bunch of collard greens the lower the price of the collard greens bunch, the higher the mean number of caterpillars per plant to compensate the application cost. The mean number of caterpillars per plant ranged from 4.59 to 0.38 in the evaluation for 7 d, and from 4.17 to 0.35 caterpillars per plant for 10 d according to the price of the bunch of collard greens.

Is the spider a good biological control agent for Plutella xylostella (Lepidoptera: Plutellidae)?

Spiders, as predators of insects and other invertebrates, are an important part of the natural enemies, and they are recognized as an important biological control agent. Plutella xylostella (Linnaeus, 1758), the diamondback moth (DBM), is a well-known and destructive insect pest of brassicaceous crops worldwide. Here, we analyzed the functional responses of four spiders (Araneae) - Ebrechtella tricuspidata (Fabricius, 1775) (Thomisidae), Pardosa laura (Karsch, 1879) (Lycosidae), Pardosa astrigera (Koch, 1878) (Lycosidae), and Pardosa pseudoannulata (Bõsenberg & Strand, 1906) (Lycosidae) - on P. xylostella larvae. We also analyzed intraspecific disturbances in the predation reaction and the intensity of scrambling competition of the spiders to P. xylostella larvae. Our results demonstrated that the functional responses of four spiders of different genera were in line with the Holling II model. Two Lycosidae spiders (P. astrigera and P. pseudoannulata) had the potential to control P. xylostella, and female and male spiders that belonged to the same species had different functional responses to P. xylostella. The functional responses of female predation of P. astrigena, P. laura, and P. pseudoannulata was stronger than the males, but male E. tricuspidatus had stronger functional responses to predation than females. We used the Hassell model to describe the intraspecific disturbance experiments of four spiders. There were intraspecific disturbances in the predation reactions of spiders, indicating that the predation ratio of spiders decreased in relation to the increase of its density, and with the increase of spider density, the intensity of scrambling competition of the spider increased.(AU)

Is the spider a good biological control agent for Plutella xylostella (Lepidoptera: Plutellidae)?

Spiders, as predators of insects and other invertebrates, are an important part of the natural enemies, and they are recognized as an important biological control agent. Plutella xylostella (Linnaeus, 1758), the diamondback moth (DBM), is a well-known and destructive insect pest of brassicaceous crops worldwide. Here, we analyzed the functional responses of four spiders (Araneae) - Ebrechtella tricuspidata (Fabricius, 1775) (Thomisidae), Pardosa laura (Karsch, 1879) (Lycosidae), Pardosa astrigera (Koch, 1878) (Lycosidae), and Pardosa pseudoannulata (Bõsenberg & Strand, 1906) (Lycosidae) - on P. xylostella larvae. We also analyzed intraspecific disturbances in the predation reaction and the intensity of scrambling competition of the spiders to P. xylostella larvae. Our results demonstrated that the functional responses of four spiders of different genera were in line with the Holling II model. Two Lycosidae spiders (P. astrigera and P. pseudoannulata) had the potential to control P. xylostella, and female and male spiders that belonged to the same species had different functional responses to P. xylostella. The functional responses of female predation of P. astrigena, P. laura, and P. pseudoannulata was stronger than the males, but male E. tricuspidatus had stronger functional responses to predation than females. We used the Hassell model to describe the intraspecific disturbance experiments of four spiders. There were intraspecific disturbances in the predation reactions of spiders, indicating that the predation ratio of spiders decreased in relation to the increase of its density, and with the increase of spider density, the intensity of scrambling competition of the spider increased.

Gamma irradiation on canola seeds affects herbivore-plant and host-parasitoid interactions.

As an agricultural modernization, gamma irradiation is an important method for enhancing crop yield and quality. Nevertheless, its use can alter other plant traits such as nutrition and resistance to different biotic/abiotic stresses that consequently affect plant-insect interactions. A tritrophic system was utilized based on two canola mutant lines produced through gamma irradiation (RGS 8-1 and Talaye 8-3). Plutella xylostella (L.), as a worldwide pest of Brassicaceae and Cotesia vestalis (Holiday) as a key biocontrol agent of P. xylostella were examined for the potential indirect effects of canola seed irradiation on the experimental insects' performance when acting on the respective mutant lines. This study showed that physical mutation did not affect plant nitrogen and herbivore-damaged total phenolics; however, phenolic compounds showed greater concentration in damaged leaves than undamaged leaves of both mutant and control plants. The relative growth rate and pupal weight of P. xylostella reared on RGS 8-1 were significantly higher than those reared on the control RGS. There was no significant difference by performance parameters of the parasitoid, C. vestalis, including total pre-oviposition period, adult longevity, adult fresh body weight of males and females, pupal weight, forewing area, and total longevity of both sexes on tested canola cultivars in comparison with their mutant lines. Life table parameters of C. vestalis on mutant lines of both cultivars, RGS and Talaye, were not significantly different from their control treatments. Comprehensive studies should be conducted to find out the mechanisms under which gamma rays affect plant-insect interactions.

Bioactivity of microencapsulated soursop seeds extract on Plutella xylostella / Bioatividade de extrato microencapsulado de sementes de graviola sobre Plutella xylostella

The aim of this study was to evaluate the bioactivity of microencapsulated extract from the soursop seeds, Annona muricata L. ( Annonaceae ), on diamondback moth, Plutella xylostela L. (Lepidoptera: Plutellidae ). Microencapsulation was performed in a Mini Spray Dryer model B-290 using 50mL of ethanolic and hexanic extracts plus 150mL of ethanol and 150mL of ultrapure water, mixed with aerosil (first polymer) or arabic gum (second polymer). It was possible to microencapsulate the ethanolic extract of soursop seeds only by using the polymer arabic gum at 20%. The microencapsulated extract caused significant acute toxicity (LC50=258mg L-1) and chronic effects, especially reduction of larval viability and increased larval stage. We concluded that the microencapsulation of the ethanolic extract of soursop seeds can be a viable alternative for controlling diamondback moth with possible gains for the environment.(AU)

O objetivo deste estudo foi avaliar a bioatividade do extrato microencapsulado das sementes de graviola, Annona muricata L. ( Annonaceae ), sobre a traça-das-crucíferas, Plutella xylostella L. (Lepidoptera: Plutellidae ). A microencapsulação foi realizada em um Mini Spray Dryer modelo B-290 utilizando-se 50mL dos extratos etanólico e hexânico mais 150mL de álcool etílico e 150mL de água ultrapurificada, misturado com aerosil (primeiro polímero) ou com goma arábica (segundo polímero). Só foi possível microencapsular o extrato etanólico de sementes de graviola com a utilização do polímero goma arábica a 20%. O extrato microencapsulado causou significativa toxicidade aguda (CL50=258mg L-1) e efeitos crônicos, especialmente redução da viabilidade larval e aumento da duração do estágio larval. Conclui-se que a microencapsulação do extrato etanólico da semente de graviola pode ser uma alternativa viável no controle da traça com possíveis ganhos para o meio ambiente.(AU)

Bioactivity of microencapsulated soursop seeds extract on Plutella xylostella / Bioatividade de extrato microencapsulado de sementes de graviola sobre Plutella xylostella

ABSTRACT: The aim of this study was to evaluate the bioactivity of microencapsulated extract from the soursop seeds, Annona muricata L. (Annonaceae), on diamondback moth, Plutella xylostela L. (Lepidoptera: Plutellidae). Microencapsulation was performed in a Mini Spray Dryer model B-290 using 50mL of ethanolic and hexanic extracts plus 150mL of ethanol and 150mL of ultrapure water, mixed with aerosil (first polymer) or arabic gum (second polymer). It was possible to microencapsulate the ethanolic extract of soursop seeds only by using the polymer arabic gum at 20%. The microencapsulated extract caused significant acute toxicity (LC50=258mg L-1) and chronic effects, especially reduction of larval viability and increased larval stage. We concluded that the microencapsulation of the ethanolic extract of soursop seeds can be a viable alternative for controlling diamondback moth with possible gains for the environment.

RESUMO: O objetivo deste estudo foi avaliar a bioatividade do extrato microencapsulado das sementes de graviola, Annona muricata L. (Annonaceae), sobre a traça-das-crucíferas, Plutella xylostella L. (Lepidoptera: Plutellidae). A microencapsulação foi realizada em um Mini Spray Dryer modelo B-290 utilizando-se 50mL dos extratos etanólico e hexânico mais 150mL de álcool etílico e 150mL de água ultrapurificada, misturado com aerosil (primeiro polímero) ou com goma arábica (segundo polímero). Só foi possível microencapsular o extrato etanólico de sementes de graviola com a utilização do polímero goma arábica a 20%. O extrato microencapsulado causou significativa toxicidade aguda (CL50=258mg L-1) e efeitos crônicos, especialmente redução da viabilidade larval e aumento da duração do estágio larval. Conclui-se que a microencapsulação do extrato etanólico da semente de graviola pode ser uma alternativa viável no controle da traça com possíveis ganhos para o meio ambiente.

Reliability of Degree-Day Models to Predict the Development Time of Plutella xylostella (L.) under Field Conditions.

The diamondback moth, Plutella xylostella (L.), is a cosmopolitan pest of brassicaceous crops occurring in regions with highly distinct climate conditions. Several studies have investigated the relationship between temperature and P. xylostella development rate, providing degree-day models for populations from different geographical regions. However, there are no data available to date to demonstrate the suitability of such models to make reliable projections on the development time for this species in field conditions. In the present study, 19 models available in the literature were tested regarding their ability to accurately predict the development time of two cohorts of P. xylostella under field conditions. Only 11 out of the 19 models tested accurately predicted the development time for the first cohort of P. xylostella, but only seven for the second cohort. Five models correctly predicted the development time for both cohorts evaluated. Our data demonstrate that the accuracy of the models available for P. xylostella varies widely and therefore should be used with caution for pest management purposes.

Susceptibility of Plutella xylostella (Lepidoptera: Plutellidae; Linnaeus 1758) to Beauveria bassiana Bb9205, Metarhizium anisopliae Ma9236 and Heterorhabditis bacteriophora HNI0100 / Susceptibilidade de Plutella xylostella (Lepidoptera: Plutellidae; Linnaeus 1758) a Beauveria bassiana Bb9205, Metarhizium anisopliae Ma9236 e Heterorhabditis bacteriophora HNI0100 / Susceptibilidad de Plutella xylostella (Lepidoptera: Plutellidae; Linnaeus 1758) a Beauveria bassiana Bb9205, Metarhizium anisopliae Ma9236 y Heterorhabditis bacteriophora HNI0100

The diamondback moth (Plutella xylostella) is a major pest of broccoli worldwide. It mainly causes leaf defoliation and generates annual losses of 80%. In this study we evaluated the susceptibility of P. xylostella to entomopathogens Heterorhabditis bacteriophora HNI0100, Beauveria bassiana Bb9205 and Metarhizium anisopliae Ma9236. The methodology was based on the inoculation of third instar larvae of P. xylostella with 5x10/ 1x10², 3x10², 6x10² and 1,2x10³ IJs/cm² of H. bacteriophora HNI0100 and evaluated them after 24, 48 and 72 h and 1x10(4), 1x10(5), 1x10(6), 1x10(7) and 1x10(8) con/cm² of B. bassiana Bb9205 and M. anisopliae Ma9236, which were evaluated during two weeks. At a dose of 1,2 x10³ JIs/cm², P. xylostella had a susceptibility to H. bacteriophora HNI0100 of 91,66%. Similarly, B. bassiana Bb9205 and M. anisopiae Ma9236 had a mortality of 95,33 and 99,67% at 1x10(5) con/cm². The results suggest that the use of strains of entomopathogenic nematodes and fungi is an innovative alternative for the control of P. xylostella. However, studies on the interaction of nematodes and fungi and Plutella xylostella are necessary.

La palomilla dorso de diamante (Plutella xylostella) es una de las principales plagas del cultivo de brócoli (Brassica oleracea) en el mundo. El principal daño es la defoliación de las hojas, generando pérdidas anuales del 80%. El objetivo de este estudio fue evaluar la susceptibilidad de P. xylostella a los entomopatógenos Heterorhabditis bacteriophora HNI0100, Beauveria bassiana Bb9205 y Metarhizium anisopliae Ma9236. La metodología se basó en la inoculación de 5x10¹, 1x10², 3x10², 6x10² y 1,2x10³ JIs/cm² en larvas de tercer instar de P. xylostella evaluada a las 24, 48 y 72 h y 1x10(4), 1x10(5), 1x10(6), 1x10(7) y 1x10(8) con/cm² de B. bassiana y M. anisopliae evaluadas durante dos semanas. Los resultados mostraron que P. xylostella fue susceptible a H. bacteriophora HNI0100 con una tasa de mortalidad del 91,66% a dosis de 1,2x10³ JIs/cm². Así mismo, B. bassiana Bb9205 y M. anisopliae Ma9236 generaron 95,33 y 99,67% de mortalidad con la dosis de 1x10(5) con/cm². El uso de nematodos y hongos entomopatógenos es una alternativa innovadora para el control de P. xylostella, sin embargo, se requiere estudiar su interacción para el control de este insecto plaga.

A mariposa dorso de diamante Plutella xxylostella é uma das principais pragas do cultivo dos brócolos (Brassica oleraceà) no mundo. O principal dano é o desfolhamento das folhas, gerando perdas anuais de 80%. O objetivo deste estudo foi avaliar a suceptibilidade da P. xylostella aos entomopatógenos Heterorhabditis bacteriophora HNI0100, Beauveria bassiana Bb9205 e Metarhizium anisopliae Ma9236. A metodologia baseou-se na inoculação de 5x10¹, 1x10², 3x10², 6x10² y 1,2x10³ JIs/cm² em larvas do terceiro instar de P. xylostella avaliada às 24, 48 e 72 h e 1x10(4), 1x10(5), 1x10(6), 1x10(7) e 1x10(8) con/cm² de B. bassiana e M. anisopliae avaliadas durante 2 semanas. Os resultados mostraram que P. xylostella foi susceptível a H. bacteriophora HNI0100 com uma taxa de mortalidade de 91,66% com a dose de 1,2x10³ JIs/ cm². Desta forma, B. bassiana Bb9205 e M. anisopliae Ma9236 geraram 95,33 é 99,67% de mortalidade com a dose de 1x10(5) con/cm². O uso de estirpes colombianas de nematóides e fungos entomopatógenos é uma alternativa inovadora para o controlo de P. xylostella. Ainda se requer estudar a interação entre fungos e nematóides em Plutella xylostella.

Resistance and behavioural response of Plutella xylostella (Lepidoptera: Plutellidae) populations to Bacillus thuringiensis formulations.

BACKGROUND: Insecticide resistance is probably the major cause of control failure of Plutella xylostella (L.) in Brazil. In most production regions, the use of chemicals has been the prevalent method of control, with reduced efficacy through cropping seasons, even for the most recent use of products based on Bacillus thuringiensis (Bt). The current status of the resistance to these products was assessed, as well as the behavioural response of P. xylostella populations to Bt sprays. RESULTS: Most populations of P. xylostella were resistant to Bt products, particularly to Xentari®WDG (2-54-fold). Differences in walking characteristics of larvae were variable for most populations, for both Dipel®WP and Xentari®WDG, but not associated with resistance. Most females preferred to lay eggs on untreated surfaces and showed a reduced proportion of oviposition on treated surfaces that only correlated with resistance to Dipel®WP (r = -0.74, P = 0.02). CONCLUSION: Broad and indiscriminate use of Bt-based products has selected Brazilian P. xylostella populations to resistance. Larval movement appears to be a resistance-independent mechanism. Most populations of P. xylostella preferred to lay eggs on Bt-free surfaces, which might be a result of growers' practice of spraying the cabbage head. Reduced oviposition on treated surfaces correlated with physiological resistance, suggesting a behavioural response among the Bt-resistant colonies to Dipel®WP.

Insecticide activity of Beauveria bassiana and castor bean oil against Plutella xylostella under greenhouse / Atividade inseticida de Beauveria bassiana e óleo de mamona sobre Plutella xylostella em casa telada

The diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), one of the principal pests of brassicas, can reduce productivity and thus cause losses for brassica farmers. Alternative controls, such as biological agents and plant extracts, may be used to reduce insect populations, either alone or in conjunction with pest management programs. The objective was to evaluate the insecticidal activity of Beauveria bassiana (Bals.) Vuill. and castor bean oil and mixtures of both components against the diamondback moth. To do so, we separately used castor bean oil (at 2% concentration), the isolate ESALQ-447 and a commercial formulation (Boveril® WP), and a mixture of castor bean oil with the isolate and the B. bassiana product formulation, totaling six treatments with a control. Assays were carried out under greenhouse with the respective treatments sprayed on cabbage plants infested with four second instar larvae of P. xylostella. The evaluated parameters were larval mortality and pupal and larval viability. All treatments reduced larval viability in relation to the control, however, only the ESALQ-447 isolate or a mixture of the isolate with castor bean oil reduced pupal viability, significantly reducing the pest population levels in the next generation. Castor bean oil mixed with B. bassiana, however, does not augment pest mortality.

A traça-das-crucíferas, Plutella xylostella (L.) (Lepidoptera: Plutellidae), uma das principais pragas das brássicas, pode ocasionar redução na produtividade e consequentemente prejuízos aos produtores rurais destas culturas. A busca por alternativas de controle, como o uso do controle biológico e extratos de plantas são métodos de redução populacional de insetos que podem ser usados isoladamente ou associados em programas de manejo fitossanitário. Dessa forma, o objetivo foi avaliar a atividade inseticida de Beauveria bassiana (Bals.) Vuill., do óleo de mamona e a associação destes, visando ao controle da traça-das-crucíferas. Para isso, foram utilizados isoladamente o óleo de mamona (na concentração de 2%), o isolado ESALQ-447 e um formulado comercial (Boveril® WP) e a mistura do óleo de mamona com o respectivo isolado e com o produto formulado de B. bassiana, totalizando assim seis tratamentos com a testemunha. Os ensaios foram realizados em casa telada, onde plantas de repolho infestadas com quatro larvas de segundo ínstar de P. xylostella foram pulverizadas com os respectivos tratamentos mencionados. Os parâmetros avaliados foram mortalidade larval, viabilidade larval e pupal. Todos os tratamentos reduziram a viabilidade larval em relação à testemunha, no entanto apenas o isolado ESALQ-447 ou a sua associação com o óleo de mamona reduziram a viabilidade pupal, diminuindo significativamente o nível populacional da praga na próxima geração. Contudo, o óleo de mamona misturado com B. bassiana não aumenta a mortalidade da praga.