Efeito de Bacillus thuringiensis var. kurstaki sobre Podisus nigrispinus Dallas, 1851 (Heteroptera Pentatomidae: Asopinae) em laboratório

Abstract

Methodologies to evaluate potential risks of microbial biological control agents refers only to mortality in a determined period of time. The objective of the present study was to evaluate the effect of B. thuringiensis var. kurstaki on the predator P. nigrispinus through comparative analyses of fertility life tables. The experiment was conducted in the Entomology Laboratory at CNPMA/EMBRAPA, in Jaguariúna., State of São Paulo, at 25 ± 2 °C, 70 ± 10% RH and photophase of 12 h. There were two treatments; in the first, predators were fed healthy larvae of Bombyx mori whereas in the second, predators were fed larvae infected with the pathogen. The biological parameters Ro, rm , X, T and Td were evaluated in two consecutive generations, and the values were corrected through an estimationprogram "Jackknife". Ro for the first generationwas 243.9 females/female in the course ofone generation for the control treatment (ti), and 94.6 for the treatment with infected larvae (t2). Ro for the second generation was 223.9 for (ti) and 53.3 for (t2). The infinitesimal rate ofpopulation increase (rm) in the first and second generations were 0.17 (ti); 0.12 (t2) and 0.14 (ti) and 0.10 (t2), respectively. The finite rates of population increase (X) inthe first generation were 1.19 (ti) and 1.12 (t2) females/females/day; in the second generation, these were 1.15 (ti) and 1.10 (t2) females/females/day, respectively. The values ofthe mean interval (T) between generations were 32.3 days (ti) and 39.4 days (t2) in the first generation, respectively. For the second generation, (T) values were 39.2 days for ti and 39.3 days for t2. Daily and total oviposition rates were higher for the control treatment (ti) in both generations. In the first generation, the mean duration ofthe immature phase ofP.nigrispinus was 18.4 ± 1.0 days for ti and 20.3 ± 2.0 days for t2. Egg hatching in the two treatments was 100%; immature survivorship was 80% for ti and 56% for t2. In the second generation, the mean duration ofthe immature phase was 19.7 ±1.7 for ti and 21.2 ± 1.0 for t2. Egg hatching rates were 100% for ti and 64% for t2; immature survivorship was 64% for ti and 42% for t2. P.nigrispinus did not show any difference between preferences to feed on healthy larvae or larvae infected with B.thuringiensis var. kurstaki. Spores ofB.thuringiensis were not detected in the haemolymph ofthe predator which suggests that this bacterium does not multiply in this insect. Viable spores were detected in the feeces ofP.nigrispinus, leading to the conclusion that these pass intact through the digestive tract and disseminate in the environment. The results suggest that the observed adverse effects were caused by the inert compounds present in the formulation ofthe commercial B.thuringiensis var. kurstaki product.