Characterization of populations of natural enemies of Piezodorus guildinii (Westwood) (Hemiptera: Pentatomidae)

Abstract

Piezodorus guildinii (Westwood) affects soybean and forage legumes and determine one or two insecticide applications in soybean, every year. The objective of this work was to determine the behavior of populations of the natural enemies and their efficacy on the pentatomid. Samplings were carried out weekly in the Experimental Station «Dr. Mario A. Cassinoni» (Paysandú) on soybeans (6 ha) and lucerne (5 ha) without insecticide sprayings. Collects on three borders of the soybean field, on three lines and five sites per line, each one with two or three plants, depending on egg masses abundance, were done to determine the fluctuations of parasitoids. The fluctuation of predators, was studied with weekly samples of 100 passes of an entomological sweep-net in soybean. Samplings were also taken in soybeans for P. guildinii with a vertical beat sheet. Mortality of nymphs and adults was determined in the laboratory, from the samples taken fortnightly with sweep net in soybean and in lucerne. Average parasitism of egg masses was 66.54 %. Telenomus podisi Ashmead accounted for 99.65 %. Egg predation was 10.52 %. Geocoris pallipes, Tropiconabis capsiformis, Orius tristicolor, Orius insidiosus, Eriopis connexa, Harmonia axiridis and larvae of Chrysopidae were the predators found. Adults and nymphs were affected by nematodes in 1.71 % and 0.09 %, respectively. Natural enemies did not prevent P. guildinii from reaching economical damage thresholds.