RESUMO: O uso de cultivares de soja resistente a insetos-praga é uma alternativa de controle que diminui os custos de produção e não causa desequilíbrio no agroecossistema. Assim, objetivou-se com este trabalho avaliar se diferentes densidades de plantio influenciam a suscetibilidade de cultivares de soja a Cerotoma arcuata Oliver (Coleoptera: Chrysomelidae) no estado do Tocantins. Para tanto, foram conduzidos ensaios de preferência com chance de escolha em laboratório utilizando os cultivares de soja P98Y70, M8766RR e M9144RR. A preferência dos insetos variou em função da cultivar. Os tricomas desempenham papel importante na proteção das plantas ao ataque da C. arcuata, de forma que o cultivar M8766RR apresenta resistência do tipo não-preferência para alimentação deste desfolhador. PALAVRAS-CHAVE: defesas morfológicas, manejo de resistência, relação inseto-planta.

ABSTRACT. The objective of this study was to evaluate the impact of oil extract of neem, Azadirachta indica, on the watermelon aphid Aphis gossypii and its natural enemy Cycloneda sanguinea. Toxicity bioassays were conducted with the commercial product DalNeem (1,475 g L -1 azadirachtin) at 0.0037 μg a.i. mL -1 , 0.0074 μg a.i. mL -1 and 0.0148 μg a.i. mL -1 , Malathion at 1 μg a.i. mL -1 and distilled water as a control treatment. The products were sprayed to watermelon leaf discs, and the insects were exposed to the product residues. The instantaneous population growth rate of A. gossypii and the survival of C. sanguinea larvae exposed to the different treatments were calculated. A decrease in the instantaneous population growth rate of A. gossypii with increasing concentrations of neem was observed, and the aphids did not reproduce on the leaf discs treated with malathion during the first 24 hours of exposure due to its rapid lethal effect on adult insects. The larvae of the predator C. sanguinea exposed to malathion survived only for 24 hours. The survival of the predator exposed to different concentrations of neem was also significantly reduced compared to the predators exposed only to water. However, laboratory experiments may overestimate the effect of neem on predators because the individuals cannot employ escape behavior caused by neem repellency.Keywords: Citrullus lanatus, Azadirachta indica, Coccinellidae, Aphididae.Efeito letal e subletal do nim em Aphis gossypii e Cycloneda sanguinea na cultura da melancia RESUMO. O objetivo deste estudo foi avaliar o impacto de extrato oleoso de nim, Azadirachta indica, no afídeo Aphis gossipii e em seu inimigo natural Cycloneda sanguinea, na melancia. Ensaios de toxicidade foram conduzidos com o produto comercial (DalNeem®) (1.475 g L -1 de azadirachtina) 0,0037 μg i.a. mL -1 , 0,0074 μg i.a. mL -1 and 0,0148 μg i.a. mL -1 , Malathion 1 μg i.a. mL -1 , e água destilada como tratamento controle. Os produtos foram aplicados em discos de folhas de melancia e os insetos foram expostos ao resíduo dos produtos. Foram calculados padrão de crescimento instantâneo da população de A. gossypii e sobrevivência das larvas de C. sanguinea expostos aos diferentes tratamentos. Houve uma diminuição no padrão de crescimento instantâneo da população de A. gossypii com aumento da concentração de nim. Afídeos não se reproduziram nos discos de folhas tratadas com malathion, devido ao rápido efeito letal em adultos, menor que 24 horas após a exposição. Larvas de C. sanguinea expostas ao malathion sobreviveram por 24 horas. Sobrevivência do predador exposto a diferentes concentrações de nim também foi significativamente reduzida quando comparada a exposição à água. Entretanto, experimentos de laboratório podem ter superestimado o efeito do nim em predadores porque eles não mostraram comportamento de escape causado pela repelência do nim.

Watermelon Citrullus lunatus (Thunberg, Matsumura & Nakai) is an ecosystem having a variety of arthropods, each one playing a specific role. Although some of them are considered pest to crops, some others are responsible for soil aeration, nutrient release and predation of pest species and are, therefore, considered beneficial to crops. The intensive farming practiced for watermelon cultivation in Brazil is based on the use of tiamethoxam and deltamethrin, which may not only kill target but also nontarget organisms such as beneficial arthropods. Research data regarding the influence of insecticides on arthropods in watermelon cropping is scarce. This study aimed to evaluate the effect of the insecticides deltamethrin and thiamethoxam on soil surface and watermelon canopy arthropod community. The study was carried out in the State of Tocantins, Brazil. Although the application of thiamethoxam and deltamethrin was efficient in controlling populations of Aphis gossypii (Glover), as we expected, they negatively affected non-target arthropods such as detritivores insects in the canopy and soil surface. Ecological implications of the impact of such pesticides on beneficial arthropod species are discussed. Key words: Citrullus lanatus, neonicotinoids, pyrethroids, non-target arthropods ResumoA cultura da melancia Citrullus lunatus (Thunberg, Matsumura & Nakai) abriga uma grande diversidade de artrópodes, cada um desempenhando um papel específico. Apesar de alguns desses artrópodes serem considerados pragas, outros são responsáveis pela aeração do solo, liberação de nutrientes e predação das espécies-praga, sendo, dessa forma, considerados benéficos às culturas. A agricultura intensiva praticada no Brasil para o cultivo da melancia é baseada no uso dos inseticidas como tiamethoxam e deltametrina, que pode não só matar as pragas, mas também organismos não-alvo. Pesquisas relacionadas à influência de inseticidas sobre artrópodes benéficos na cultura da melancia são escassas. Este estudo foi realizado com o objetivo de avaliar o efeito dos inseticidas deltametrina e thiamethoxam na comunidade de artrópodes existentes na superfície do solo, bem como naqueles artropópodes que habitam o dossel das plantas na cultura da melancia. Este estudo foi realizado no Estado do Tocantins, Brasil. Embora as aplicações de thiamethoxam e deltametrina foram eficientes no controle de populações de Aphis gossypii, como era esperado, os inseticidas afetaram negativamente artrópodes não-alvo como insetos detritívoros, insetos de dossel e da superfície do solo. Implicações ecológicas do impacto dos pesticidas sobre as espécies de artrópodes benéficos são discutidos.

Tropical biomes such as Brazilian Cerrado and Amazon Forest have a great diversity of fungi and insects. Interactions between these organisms can be beneficial to both partners. In streams, these interactions contribute to litter decomposition. Studying the digestive tract (DT) of shredder insects as a habitat for fungal microorganisms is an opportunity to obtain fungal strains with biotechnological potential, which may help to understand the symbiotic relationships between these organisms in tropical forests. This study investigated the fungal community in the DT of larvae of Triplectides (Trichoptera: Leptoceridae) collected in low-order streams in the Cerrado and Amazon Forest biomes in Brazil. Forty-nine fungal isolates were obtained and identified among 32 species and 12 genera. The genus Roussoella was only found in the DT of insects in Amazon Forest streams, while 7 genera only occurred in the DT of insects in Cerrado streams. The genus Penicillium (40%) was the most frequent. In the Cerrado, 78% were producers of CMCase, more than two-fold that in the Amazon Forest (35%). And 62% were producers of xylanase, in the Cerrado and 71% in the Amazon Forest. In this context, the fungal community in the DT of Triplectides larvae may play an important role in the insect diet by breaking down lignocellulosic material.

The study of the relationship between fungi and insects brings important contributions to the knowledge of fungal biodiversity and to the understanding of mutualistic ecological interactions. This study reports the occurrence of a community of filamentous fungi in the digestive tract (DT) of mining insect larvae belonging to genus Stenochironomus in streams of two Brazilian biomes. Fungi were obtained from the digestive tract of larvae found on trunks and leaves of low-order streams in the Amazon Forest and Cerrado in the north of Brazil. The fungal community was screened for xylanolytic and cellulolytic activities. The diversity of fungal species in the DT of larvae is possibly related to the diversity of diets of species of that genus and the diversity of substrates in the ecosystems. The diversity and richness of fungal species were influenced by ecological differences between locations more than by the types of substrates in which they were collected (trunk and leaf). Most fungi in the DT of Stenochironomus larvae sampled in leaves exhibited cellulolytic enzyme activity. Such results stress that the mycobiomes of the DT of Stenochiromonus larvae produce enzymes that contribute to the process of breaking down plant remains in their hosts.

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