Toxicity of Bacillus thuringiensis at different larval ages of Agrotis ipsilon (Lepidoptera: Noctuidae).

Toxicidade de Bacillus thuringiensis a diferentes idades de lagartas de Agrotis ipsilon (Lepidoptera: Noctuidae).

The black cutworm Agrotis ipsilon (Hufnagel) (Lepidoptera: Noctuidae) is a cosmopolitan and polyphagous pest that attacks diverse crops and weed. One of the alternatives to insecticides may be the use of bioinsecticides based on Bacillus thuringiensis Berliner (Bt). Thus, the objective of the present study were evaluating the toxicity of Agree® and Dipel® bioinsecticides based on Bt on different larval ages of A. ipsilon. For the experiments, five larval ages were used (0-24, 48-72, 96-120, 144-168, and 192-216 h). The A. ipsilon caterpillars were individualized in acrylic tubes containing an artificial diet and 50 µL of each biopesticide in the concentration 1 × 108 spores mL-1. Mortality was assessed for seven days. The two bioinsecticides evaluated promoted mortality at all larval ages of A. ipsilon. The age of 0-24 h had mortality above 90%. The values of LC50 and LC90 were 9.8 × 105 and 7.4 × 106 spores mL-1 for Agree® and 1.3 × 106 e 1.4 × 107 spores mL-1 for Dipel®, respectively, without difference between LC50 and LC90 values of the bioinsecticides. The results indicate that younger caterpillars are more susceptible to Bt-based bioinsecticides. [ABSTRACT FROM AUTHOR]

A lagarta rosca Agrotis ipsilon (Hufnagel) (Lepidoptera: Noctuidae) é uma praga cosmopolita e polífaga que ataca diversas culturas e plantas daninhas. Uma das alternativas de manejo ao uso de inseticidas químicos pode ser o uso de bioinseticidas à base de Bacillus thuringiensis Berliner (Bt). Deste modo, o presente trabalho teve por objetivo avaliar a toxicidade dos bioinseticidas Agree® e Dipel® à base de Bt sobre diferentes idades de lagartas de A. ipsilon. Para os experimentos, lagartas de cinco idades foram utilizadas (0-24, 48-72, 96-120, 144-168 e 192-216 horas). As lagartas de A. ipsilon foram individualizadas em tubos de acrílico contendo dieta artificial e 50 µL de cada bioinseticida na concentração 1 × 108 esporos mL-1. A mortalidade foi avaliada durante sete dias. Os dois bioinseticidas avaliados promoveram mortalidade em todas as idades das lagartas de A. ipsilon. Lagartas com idade 0-24 h apresentaram mortalidade acima de 90%. Os valores de CL50 e CL90 foram 9,8 × 105 e 7,4 × 106 esporos mL-1 para Agree® e 1,3 × 106 e 1,4 × 107 esporos mL-1 para Dipel®, respectivamente, sem diferença entre os valores de CL50 e CL90 dos bioinseticidas. Os resultados indicam que lagartas mais jovens são mais suscetíveis aos bioinseticidas à base de Bt. [ABSTRACT FROM AUTHOR]

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