Transgenic Bt maize, seed treatment and foliar insecticides against fall armyworm and a stink bug

• Ano de defesa: 2020
• Autor(a) principal: Santos, Camila Oliveira
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Universidade Federal de Viçosa
• Palavras-chave em Português: Plantas - Doenças e pragas; Plantas - Proteção; Spodoptera frugiperda; Dichelops melacanthus; Entomologia Agrícola
• Link de acesso: https://locus.ufv.br//handle/123456789/28918

Maize is one of the most important cereal crops in the world, and the high infestation by insect pests is one of the main yield-loss factors in the crop, especially when occurring in the early growth stages. In these, the fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith, 1797) (Lepidoptera: Noctuidae), and the green- belly stink bug (GBS), Dichelops melacanthus (Dalas, 1851) (Hemiptera: Pentatomidae), can be great a challenge, particularly if the maize crop is preceded by soybeans or grown using minimal tillage over the preceding-crop residues. In this dissertation, the integrated use of Bacillus thuringiensis (Bt) transgenic maize, seed treatment and foliar insecticides was tested for efficacy against these two insect species. Because some Bt-resistant FAWs can have altered response to stressors, the susceptibility of Bt-resistant populations of FAW to seed treatment and foliar insecticides was also determined. In bioassays of cumulative effects of control measures against FAW and GBS, the seed treatment using neonicotinoid (clothianidin) was effective against FAW and GBS; the diamide (chlorantraniliprole) was effective only for FAW until seven days after emergence in optimal edaphoclimatic conditions. After 21 days of emergence, the mortality effect of the seed treatment was no longer present and foliar insecticides may be needed to provide plant protection. In bioassays using field-rate sprayed maize plants, all foliar insecticides were efficacious (mortality > 80%) in controlling the Bt-resistant FAWs feeding on Cry1A.105+Cry2Ab Bt maize, except acephate. In contrast, acephate killed 100% of the stink bugs as did methomyl. Imidacloprid+beta-cyfluthrin also caused more than 80% mortality of GBS adults. The other insecticides (thiamethoxam+lambda-cyhalothrin, chlorantraniliprole and flubendiamide) had less than 80% mortality. Diamides as foliar insecticides or in seed treatment caused high mortality of FAWs, but not of GBSs. Regarding seed treatments, in concentration- mortality bioassays the larvae of a recently-isolated Bt-resistant FAW population showed resistance to diamides (43 fold for chlorantraniliprole and 17 fold for cyantraniliprole). In concentration-response bioassays with foliar insecticides, at least one FAW population resistant to Cry Bt toxins showed resistance to the insecticides tested (chlorantraniliprole, spinetoram, indoxacarb, flubendiamide, bifenthrin+carbosulfan, methomyl) when compared to the susceptible population; however, only to indoxacarb the larvae showed moderate-to-high resistance ratios. The LC 90 values for the insecticides introduced more recently (e.g., chlorantraniliprole, spinetoram) were 300-900 fold lower than their field label rates, indicating a high likelihood of control success; for the insecticides introduced long ago (carbamates, pyrethroids) these values were only 10 fold, indicating a smaller safety margin for control success in the field. Therefore, the use of clothianidin to treat seeds of transgenic Bt maize may be a efficacious combination against FAWs and GBSs; if needed, foliar insecticides such as methomyl and imidacloprid+beta- cyfluthrin are likely to have high efficacy against both of these pest species and may be useful for integrated management in maize. These results are useful in decision- making and recommendations for integrated resistance management to important pest control technologies used against FAW and GBS, including Bt maize, seed treatment and foliar insecticides. Keywords: Spodoptera frugiperda. Dichelops melacanthus. Zea mays. Resistance. Integrated pest management. Crop protection.