Efeito do tratamento de sementes de sorgo sacarino sobre o predador Podisus nigrispinus (Dallas, 1851) (Hemiptera: Pentatomidae)

Abstract

Sorghum bicolor (L.) Moench is a promising alternative for supplementation of raw material for the sugarcane industry, but a series of insect pest damage to this crop, wich seed treatment with insecticides have been widely used in the control of early season insect pests. Natural enemies such as Podisus nigrispinus (Dallas, 1851) (Hemiptera: Pentatomidae) has been shown an alternative to chemical control, although P. nigrispinus can usually feed on plants to supplement its diet, where studies have suggested side effects of insecticides used in seed treatment on natural enemies when using plant as a food supplement. The objective was to evaluate the effect of sorghum seeds treatment on the predator P. nigrispinus, when it feeds on plants grown from treated seeds and comparative exposure of the predator with Spodoptera frugiperda (Lepidoptera: Noctuidae) to insecticides. There was no difference between the treatments on survival within each instar, females weight and egg incubation period, however the survival of the nymphal period, number of eggs per female and number of postures per female were affected by bifenthrin + pirimiphos-methyl treatments and fipronil + pyraclostrobin + thiophanatemethyl. Number of eggs per posture was reduced in treatment with bifenthrin + pirimiphos-methyl, and this treatment together with the treatment imidacloprid + thiodicarb reduced egg viability. The sex ratio was lower in the treatments with imidacloprid + thiodicarb and fipronil + pyraclostrobin + thiophanate-methyl. Adults kept in sorghum plants with collection immersed in insecticide solution were only affected in the treatment with imidacloprid + thiodicarb, for S. frugiperda all the treatments differed from the control, emphasizing that the insecticides were more harmful to the pest than to the predator. Lethal and sublethal effects were observed in the predator P. nigrispinus, when it fed on sorghum plants from seeds treated with insecticides.