Short-term spatial niche partitioning between the larger grain borer and the maize weevil with implications for management of stored maize

Prostephanus truncatus (Horn), the larger grain borer, is endemic to southern North America and Central America, but invaded Africa with severe economic consequences for maize and cassava production. Its main competitor is the cosmopolitan Sitophilus zeamais (Motschulsky), the maize weevil. These insects co-occur in many regions of the world and both are threats to maize. While interspecific competition between these two species has been studied for several decades, there is little information on spatial partitioning in bulk storages of grain. In order to evaluate potential overlap in their realized niche, the aims of our study were to evaluate the short-term niche partitioning behavior of P. truncatus and S. zeamais when placed in a monolayer of grain for one day versus seven days. We used a response surface design with nine different densities, representing large, medium, and small population densities for P. truncatus and S. zeamais either alone or in combination with one another. The monolayers were visually divided into 24 equally sized vertical and horizontal zones to track location of the insects on maize. After one day and then seven days, monolayers were placed on their side, and the grain and insects from each zone were removed. The number of insects per species and damage was recorded per zone. We found that the both species generally aggregated together with heterospecifics and preferred the bottom of the grain mass. These data may help improve targeting of pest control tactics by identifying the position of these insects in the grain mass.