Egg parasitoid assemblages and their effectiveness on soybean defoliator Lepidoptera in the subtropical producing area of Argentina

Abstract

Soybean is one of the most important crops worldwide; However, its annual yield is strongly affected by lepidopteran caterpillar. Nowadays, the main control for this pest species is based on the use of broad-spectrum insecticides affecting human health and increasing environmental contamination. Therefore, others sustainable methods of control, such as biological control are in demand. Hence, the present study aimed to identify the egg parasitoids guild for the soybean defoliator lepidopteran species in the subtropical areas of South America and to determine its effectiveness during three consecutive soybean seasons. Soybean A-8000 RG (GM VIII) variety was sown in a commercial soybean field (80 ha.) located in Leales, Tucumán, Argentina. Every week, 20 soybean plants were randomly collected and carried out to laboratory, to search lepidopteran eggs. During the three crop seasons, soybeans were attacked by Anticarsia gemmatalis, Rachiplusia nu, and Chrysodeixis includens. Six egg parasitoid species were identified, but only three of them were important (by frequency and abundance). Trichogramma pretiosum has the higher effectiveness in control all lepidopteran pest across soybean phenological stages. In contrast, E. porteri prefers to parasitize R. nu eggs while T. cyamophylax parasitized no C. includens eggs. The defoliating Lepidoptera eggs showed high levels of parasitism despite applying insecticides in soybean fields. Therefore, using conservative tactics leads to higher rates of natural control.