Effects of Aphid (Homoptera) Abundance and Surrounding Vegetation on the Encounter Rate of Coccinellidae (Coleoptera), Chrysopidae (Neuroptera), and Nabidae (Hemiptera) in Alfalfa

Abstract

Predaceous insect encounter rate was measured in 21 southeast Nebraska alfalfa fields through weekly sweep net sampling during 2002–03. The most frequently encountered predaceous insect families were Coccinellidae (Coleoptera), Nabidae (Hemiptera), and Chrysopidae (Neuroptera). The study used multiple regression analysis to examine the effect of aphid abundance and the surrounding vegetative patch composition on predaceous insect abundance. In 2002, Hippodamia parenthesis Say was encountered more frequently in fields with lower aphid abundances, and Hippodamia convergens Guerin-Meneville, Coccinella septem-punctata L., and Nabis americoferus Carayon were encountered more frequently in fields with higher aphid abundances. In 2003, Coleomegilla maculata DeGeer was encountered more frequently in fields with higher aphid abundance. The remaining two species of coccinellids and Chryoperla spp. did not exhibit significant correlations with aphid abundance in either year. It was determined that in 2002, H. parenthesis was encountered more frequently in alfalfa surrounded by a higher percentage of unfarmed land, and C. maculata, C. septempunctata, N. americoferus, and Chrysoperla spp. were encountered more frequently in alfalfa surrounded by a higher percentage of farmed land. In 2003, N. americoferus was again encountered more frequently in alfalfa fields surrounded by a higher percentage of farmed land. The remaining three coccinellid species collected did not exhibit significant relationships between vegetative patch composition and encounter rate in either year.