Abundance and Developmental Stability ofPterostichus melanarius(Coleoptera: Carabidae) in Organic and Integrated Pest Management Orchards of Québec, Canada

Abstract

This study evaluated the agricultural impacts of organic and integrated pest management (IPM) orchards in Quebec, Canada on the carabids Pterostichus melanarius Illiger (Coleoptera, Carabidae), with two biomonitors, population density and fluctuating asymmetry (FA) of morphologic and meristic characters. The carabids were trapped between May and August 1999 and 2000 in 20 pitfall traps on four organically certified orchards and five IPM farmlands located in two farming communities 100 km apart. Numbers of P. melanarius and total trap catch were assessed for each year. We measured the length of two segments of the right and left antennae, the length of first tarsae, and the number of tibiae spines on the mesothoracic leg of 50–100 individuals per site/yr. These measurements were used to calculate two fluctuating asymmetry indices to evaluate individual developmental stability. No differences in fluctuating asymmetry were found between organic and IPM orchards although total catch of P. melanarius was higher in IPM orchards in 1999. The use of fluctuating asymmetry analysis in these fields seem inadequate to assess the impact of pesticides. Density analysis give a slightly response in the opposite of the predictions because IPM orchards seem to be a more adequate habitat for this carabid species. There is a need for evaluating the impacts of natural products used in the organic cultures.