Reproduction of Ooencyrtus submetallicus (Hymenoptera: Encyrtidae) in egg densities of Euschistus heros (Hemiptera: Pentatomidae)

Knowledge about the ideal host ratio per female parasitoid reared in glass tubes is important for obtaining descendants with better biological quality. The study aimed to evaluate the reproduction of Ooencyrtus submetallicus (Hymenoptera: Encyrtidae) females in egg densities of Euschistus heros (Hemiptera: Pentatomidae) to find the most adequate relationship between parasitoids and hosts aiming at the parasitoid multiplication. The experiment was conducted with E. heros eggs at densities (parasitoid:host) of 1:3, 1:6, 1:9, 1:12, 1:15, or 1:18 with 24 hours of parasitism by O. submetallicus. The parasitoid females and the egg carton were placed in glass tubes and kept in a climate-controlled chamber. The percentage of parasitism was affected by the nonparasitised eggs. The emergence of adult parasitoids, number of parasitised eggs, number of individual parasitoids emerging per egg, the length of the parasitoids’ posterior tibiae, and the parasitoids’ longevity, life cycle, and sex ratio were not affected by the different densities of nonparasitised eggs subjected to treatments. Ooencyrtus submetallicus parasitised and developed in E. heros eggs in all evaluated densities, with 1:6 presenting the best combination of parasitoid and host.

Characterization and Comparison of Intestinal Bacterial Microbiomes of Euschistus heros and Piezodorus guildinii Collected in Brazil and the United States

Background: Herbivorous insects are one of the main biological threats to crops. One such group of insects, stink bugs, do not eat large amounts of tissue when feeding on soybean, but are damaging to the quality of the seed yield as they feed on green developing seeds leading to poorly marketable harvests. In addition to causing physical damage during sucking-feeding activities, the insects can also transmit microbial pathogens, leading to even greater yield loss. Conducting surveys of the insect intestinal microbiome can help identify possible pathogens, as well as detail what healthy stink bug digestive systems have in common.Methods: We used the conserved V4 region of the 16S rRNA gene to characterize the bacterial microbiome of the red-banded stink bug Piezodorus guildinii collected in Brazil and the United States, as well as the neotropical brown stink bug Euschistus heros collected in Brazil.Results: After quality filtering of the data, 192 samples were kept for analyses: 117 samples from P. guildinii covering three sites in Brazil and four sites in the United States, and 75 samples for E. heros covering 10 sites in Brazil. The most interesting observations were that the diversity and abundance of some bacterial families were different in the different ecoregions of Brazil and the United States.Conclusion: Some families, such as Acetobacteraceae, Bacillaceae, Moraxellaceae, Enterobacteriaceae, and Rhodocyclaceae, may be related to the better adaptation in some localities in providing nutrients, break down cellulose, detoxify phytochemicals, and degrade organic compounds, which makes it difficult to control these species.

Aspectos principais sobre a biologia e o controle químico do percevejo marrom na cultura da soja

O percevejo marrom (Euschistus heros) era uma praga secundária da soja até meados dos anos 70. Entretanto, com o a expansão dos cultivos da região sul para as áreas mais centrais do país, este inseto mudou seu status e atualmente é considerado a principal praga da cultura. Os danos causados pelo E. heros decorrem do ataque às vagens da planta, principalmente na fase de enchimento, reduzindo a produtividade e a qualidade da produção. O inseto é bastante adaptado às regiões de clima mais quente e pode alcançar densidade populacional bastante elevada, principalmente nas fases finais do ciclo da cultura. A praga também é favorecida pelo sistema de plantio direto, que facilita a obtenção de abrigo e alimento nos restos culturais, pela sucessão de cultivos, já que culturas como milho, feijão e algodão também podem ser atacadas; e pelo uso inadequado de pesticidas que reduzem a população de inimigos naturais. O manejo da praga tem se baseado predominantemente no controle químico. Há 67 inseticidas comerciais registrados no país para este fim, os quais se dividem em apenas 4 modos de ação e 6 grupos químicos, com destaque para os organofosforados, piretróides e neonicotinóides que são os mais utilizados. Essa limitação desperta preocupações quanto ao desenvolvimento de populações resistentes da praga. Vários estudos já indicam a ocorrência de resistência a alguns dos inseticidas mais utilizados em certos locais. A implementação do manejo integrado de pragas é essencial para evitar o uso excessivo dos inseticidas, preservar a população dos inimigos naturais e, assim, atenuar a pressão de seleção para a resistência da praga. Neste sentido, deve-se também evitar o uso repetitivo de produtos com o mesmo princípio ativo, dando preferência pela rotação de inseticidas com diferentes modos de ação. Além disso, é importante avaliar a eficiência do controle realizado para identificar possíveis casos de resistência. Como muitos episódios de falha de controle podem ser consequência de problemas na tecnologia de aplicação ou de condições meteorológicas inadequadas, em caso de suspeita de resistência, amostra representativa da população local da praga deve ser enviada para avaliação em laboratório qualificado. Se confirmada a resistência, o inseticida em questão deverá ser excluído do programa de manejo e substituído por outro, preferencialmente com um modo de ação diferente.

Thermal Requirements of Ooencyrtus submetallicus (Hym.: Encyrtidae) and Telenomus podisi (Hym.: Platygastridae) Parasitizing Euschistus heros Eggs (Hem.: Pentatomidae)

Temperature is one of the abiotic factors that strongly influences the biology and behavior of insects. In this study, we assessed the development of egg parasitoids Ooencyrtus submetallicus and Telenomus podisi parasitizing Euschistus heros eggs at different temperatures, and estimated the average number of generations for seven representative soybean-producing regions in Brazil. A comparative biology study was conducted, where the percentage of parasitism and emergence, life cycle duration (egg–adult), and longevity were found to be similar between O. submetallicus and T. podisi. The sex ratio and the number of individuals emerged from parasitized egg were higher in O. submetallicus in all regions. In the study of thermal requirements, temperatures of 16, 19, 22, 25, 28, 31, and 33 °C were tested. O. submetallicus and T. podisi developed at temperatures between 16 and 31 °C. The base temperature (Tb) for O. submetallicus and T. podisi was 9.3 and 6.7 °C, respectively; the thermal constant (K) was 336.9 and 272.7 degree-days, respectively. The estimated average number of annual generations of both parasitoids was higher than the host. O. submetallicus and T. podisi have the same ability to parasitize and develop in eggs of E. heros under the conditions studied. Both parasitoids exhibited satisfactory development and parasitism at temperatures between 19 and 31 °C. The development of both parasitoids was faster than their host, and the number of generations was higher for the seven studied localities.

Sublethal Concentration of Pyriproxyfen Reduces Testicular Connective Tissue Thickness in Euschistus heros Fabr. (Hemiptera: Pentatomidae)

The aim of this study was to determine the effect of the insecticide pyriproxyfen (Tiger™ 100 CE), juvenile hormone analogue, when applied in a sublethal LC30 concentration (0.668 mL a. i. L-1), on the morphological and morphometric parameters of external and internal connective tissue (CT) of the Neotropical-brown stink bug Euschistus heros testicles. The insecticide was applied on nymphs from the 4th instar using a Potter tower with a working pressure of 82.73 kPa (12 lb pol-²) and 1 mL of the emulsion per replicate. A completely randomized experimental design was used, consisting of two treatments (control and pyriproxyfen-treated), five repetitions, and 10 adults of E. heros per experimental unit. The insects were maintained under controlled conditions until the emergence of adults. After 48 h of emergence of adults, the testicles were collected, fixed, and processed for morphological and morphometric analyses. A change was observed in the collagen fibers of the CT of treated insects when compared with those of controls. It was also observed that both types of CT (dense irregular and loose) over the internal tunic of the treated insect were thinner than those in control insects. The analysis showed that pyriproxyfen significantly reduced the external and internal CT width and the conformation of its fibers in all the observed regions when compared with the controls; this may affect the production of the three different types of sperm present in this species.

New Records of Egg Parasitoids of Stink Bugs (Hemiptera: Pentatomidae) on Rice in Piauí, Brazil: Rate Parasitism, Incidence and Seasonality

This study was conducted to investigate parasitism of naturally occurring pentatomid eggs in rice crops in a Cerrado-Caatinga ecosystem during the rainy and dry seasons in Teresina, Piauí, Brazil. Also, it provides information on the incidence and seasonality of parasitoid species. Parasitism was registered only during the rainy season, where Telenomus podisi (Ashmead, 1893) parasitized Oebalus poecilus (Dallas, 1851), Tibraca limbativentris (Stal, 1860) and Euschistus heros (Fabricius, 1798) eggs. Additionally, Trissolcus urichi (Crawford, 1913) was collected from O. poecilus and T. limbativentris eggs. Ooencyrtus anasae (Ashmead, 1887) was found in O. poecilus eggs. Such findings provide information that can be used to supplement the management of pentatomid pests in the rice agroecosystems, in Piauí, Brazil.