Toxicicity and histological changes caused by insecticides in Spodoptera frugiperda (Lepidoptera: Noctuidae) eggs
Abstract
Insecticides typically are used to control Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) larvae in corn crops; however, both eggs and larvae are affected by these applications. The purpose of this study was to evaluate the effects of 9 insecticides commonly used on corn crops in Brazil on ovicide and embryonic development of S. frugiperda. The insecticides were applied with an airbrush to the outer surface of eggs at 72, 96, 120, 144, and 168 h after oviposition. Larval emergence rates then were calculated. Eggs in the control and the alpha-cypermethrin and methomyl + novaluron treatment were evaluated by light microscopy to investigate possible histological changes in the embryos. The insecticides methomyl + novaluron, chlorantraniliprole + lambda-cyhalothrin, and deltamethrin reduced the emergence rate of S. frugiperda larvae. A mixture of alphacypermethrin and methomyl + novaluron did not affect the embryonic development of S. frugiperda; however, methomyl + novaluron-treated larvae did not emerge. Therefore, the insecticides methomyl + novaluron, chlorantraniliprole + lambda-cyhalothrin, and deltamethrin have an ovicidal effect and may be recommended for managing S. frugiperda.
Resumo
Na cultura do milho, inseticidas são usados no controle de larvas de Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), embora, os ovos e larvas são expostos à ação química. O objetivo de este estudo foi avaliar o efeito ovicida e o desenvolvimento embrionário de S. frugiperda de nove inseticidas usados na cultura de milho. Inseticidas foram aplicados com um aerógrafo sobre a superfície externa dos ovos desse inseto com idades de 72, 96, 120, 144, e 168 horas após a oviposiçao. Posteriormente, a taxa de emergência de larvas foi calculada. Ovos do controle e tratados com inseticida alfa-cipermetrina e metomil + novaluron foram analizados por microscopia de luz para observar as possíveis mudanças histológicas sobre os embriões. Os inseticidas metomil + novaluron, clorantraniliprole + lambda-cialotrina, e deltametrina reduziram a taxa de emergencia de larvas de S. frugiperda. A mistura da alfa-cipermetrina e metomil + novaluron não afetaram o desenvolvimento embrionário de S. frugiperda, no entanto, larvas tratadas por metomil + novalurom não emergiram. Portanto, os inseticidas metomil + novaluron, clorantraniliprole + lambda-cialotrina, e deltametrina tem efeito ovicida e podem se recomendados no manejo das populações de S. frugiperda.
Key Words: fall armyworm; neurotoxic insecticide; growth regulator; ovicidal effect; Zea mays
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