Invertebrate weed seed predation is an important component of weed seed loss in agricultural fields. This study investigated the role of environmental temperature and soil moisture on the selection and consumption of the seeds of seven common agricultural weed species by Harpalus pensylvanicus De Geer, a widespread granivorous carabid beetle (Coleoptera: Carabidae). Y-tube bioassays were conducted to determine if H. pensylvanicus individuals responded to volatile compounds released from weed seeds at different temperature-moisture gradients. Cafeteria studies were then conducted at these same temperature-moisture gradients to determine if correlations existed between detectability and the amount of seed consumed.
H. pensylvanicus individuals were found to detect and consume significantly more seeds of each seed species in high temperature and high moisture environments when compared to low moisture and low temperature environments (p < 0.05). Larger seeded species had the greatest differences in detection and mass consumption between these two extreme gradients. The detectability of the seeds and the mass consumed varied significantly (p < 0.05) by seed species across the different temperature-moisture gradients. These results support previous work stating that both temperature and moisture are important determinates in the mass of seeds that invertebrate granivores consume. Moreover, it suggests that different soil moisture-gradients may affect which seeds are found and preferentially consumed. As such, these results illustrate that an agricultural field is not static to an invertebrate granivore, and field conditions are quite important in predicting what agricultural weeds are more or less likely to be consumed in a given area.