Efeito de inseticidas usados na cultura do milho (Zea mays L.) sobre ninfas e adultos de Doru luteipes (Scudder) (Dermaptera: forficulidae) em semicampo

Abstract

Doru luteipes (Scudder) (Dermaptera: Forficulidae) is one of the major agents of natural biological control of Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) in Brazil, feeding on eggs and small larvae in maize (Zea mays L.) plants. This predator shares the same habitat of the pest, laying their eggs inside the whorl of the plant. Therefore, any application of insecticide to control the pest population affects the predator. The objective of this study was to evaluate the selectivity of insecticides on nymphs (first and third instars) and adults of D. luteipes, in a semi-field condition. Insects were placed inside the plant whorl and sprayed with backpack equipment (pressure 2.6 lb in-2, nozzle type quick Jet 8003 and 282 liters ha-1). After the application of insecticides, maize plants were covered with cages made of wire frame and tissue. The assessments were done at 24, 48 and 72 hours after spraying. The insecticides were classified according to international standards (IOBC). The insecticides triflumuron (24 g a.i. ha-1) and etofenprox (30 g a.i. ha-1) were slightly harmful (class 2) to nymphs and adults of D. luteipes; the chlorfenapyr (180 g a.i. ha-1) was moderately harmful (class 3) for nymphs and slightly harmful (class 2) for adults; teflubenzuron/α-cypermethrin (12.7/12.7 g a.i. ha-1) was toxic to nymphs (class 4). Tiamethoxan/λ-cyhalothrin (26.5/32.5 g a.i. ha-1) was moderately harmful to third instar nymphs and adults and harmful to first instar nymphs. The insecticide spinosad (48 g a.i. ha-1) was moderately harmful to first instar nymphs, slightly harmful to third instar nymphs and harmless to adults. Triflumuron (24 g a.i. ha-1) was slightly harmful to nymphs and adults of D. luteipes, making it more selective since its toxicity is the same regardless of the developmental stage of the predator.