Spatial and temporal patterns of carabid beetle (Coleoptera: Carabidae) assemblages in winter wheat factor into their potential as biocontrol agents

Abstract

An alternative to pesticide use in agriculture is the use of natural enemies such as predators as a pest control technique, also known as biocontrol. This technique requires an understanding of the enemies and their interactions with the environment. In order for a predator to be an effective biocontrol agent in agriculture it must be present throughout the field for the entire season, especially early in the season when the first pest colonizers appear. This study looks at the spatial and temporal abundances of carabid beetles (Coleoptera: Carabidae) in winter wheat over a growing season to assess their potential as biocontrol agents of grain aphids. Carabids were collected for eight weeks by pitfall traps placed in the edges and centers of wheat fields. The total abundance of carabids and the abundance of the three most common species of carabid beetles were analyzed as a factor of time and location. A total of 54 carabid species were identified out of the 3,437 individual carabid beetles collected. The three most abundant carabid species were Amara aenea, Pterostichus melanarius, and Agonum placidum in descending order. The general carabid population inhabited the entire wheat field (center and edge) however the population did not inhabit wheat in great abundances during the first half of the season. Separately, each species had its own distributional pattern. A. placidum individuals were found in the center more often than the edge. During the early season P. melanarius were more abundant in the edge, but were more abundant in the center late in the season. A. aenea showed a more even distribution throughout the wheat fields. All three species peaked in the late season, however A. placidum also peaked at the beginning of the growing season. Although each individual species would not be very effective at controlling grain aphids alone, each species’ unique density patterns complements the other to provide better control of pest populations. A diverse assemblage of carabid beetles has the potential for successful biocontrol especially with the addition of climbing predators such as lady beetles and habitat modifications providing overwintering sites for predators.