Predation of Pterostichus melanarius on cocoons of soybean gall midge, Resseliella maxima

The soybean gall midge, Resseliella maxima Gagné (Diptera: Cecidomyiidae), feeds on soybean, Glycine max (L.) Merrill (Fabales: Fabaceae), causing significant injury and yield losses. Pterostichus melanarius Illiger (Coleoptera: Carabidae), a generalist predator introduced to North America, has been reported to prey on R. maxima larvae under laboratory conditions. Understanding the feeding preference of P. melanarius on different prey life stages is important to evaluate its role in the biological control of R. maxima. Three laboratory experiments were conducted to assess predatory behaviors. In a no-choice test, P. melanarius adults fed on both R. maxima free (i.e., not cocooned) larvae and cocooned larvae, showing significant differences in prey consumption between R. maxima developmental stages over time. A choice test revealed a preference of P. melanarius adults for free larvae over cocooned larvae within the first hour, although this preference was not significant after 24 h. In an experiment examining the effect of soil on predation rates, P. melanarius adults consumed larvae and cocooned pupae placed either without soil, on the soil surface, or at a 1 cm depth, and predation rates were influenced by prey stage and the presence and depth of soil. These findings indicate that P. melanarius adults can feed on cocooned life stages, but that the presence of soil may hinder predation.