Population dynamics of Chrysoperla externa (Hagen) (Neuroptera: Chrysopidae) in a silvopastoral system

Abstract

In this study we investigated lacewings (Neuroptera: Chrysopidae) in a silvopastoral system. The study was conducted between July, 2006 and June, 2008 in a pasture with Brachiaria decumbens and trees. Adult specimens were caught twice a month by using a malaise trap, while the larvae were caught in the shoots of fodder and by visual observation. Flowering panicles were also observed for the presence of immature specimens. All adult lacewings (1186) belonging to one species Chrysoperla externa (Hagen, 1861). The adult population peaked between April and June, but this occurrence was significantly affected by temperature and rainfall. We only captured 8 adult lacewings by using the malaise traps. There was a significant correlation between the number of immature specimens and relative humidity and the number of captured adults. A higher population density of larval and adult lacewings was associated with the flowering of signalgrass, leading to the inference that pollen was used as a source of protein. This strategy ensures that these predators remain on crops during periods of prey scarcity.