Sex-specific foraging response to interspecific interactions in carabid beetles

Abstract

Carabids beetles are considered important biocontrol agents of weeds, but predicting levels of weed seed consumption and regulation is difficult. Olfactory cues from predators or potential competitors alter the selection and consumption of particular food resources by foraging individuals. Whether this leads to changes in consumption levels or simply to changes in the rate at which consumption takes place over time is not yet known. Identifying and understanding the factors that drive the seed foraging behaviour of carabid beetles, in the context of interspecific interaction, is essential for predicting consumption levels in different carabid communities and hence improve the ecosystem service of weed regulation by carabid beetles.We tested the response of 119 Harpalus affinis individuals foraging for Viola arvensis or Taraxacum officinale seeds, to encounters with individuals of another carabid species, Pterostichus melanarius. Their foraging behaviour (i.e. total consumption, latency to first seed acceptance and position in the arena) was recorded for 72 h and the consumption rates were reported in detail for the first 7 h of the experiment for all treatments.Even though the total number of seeds consumed after 24 h did not differ, the dynamic of seed consumption by H. affinis changed significantly in the presence of P. melanarius. The attraction of individuals to the seeds diminished over time, indicating a probable state of satiety being reached. This suggests that looking at the total number of seeds consumed after a long period of time may be misleading and that a greater focus on of the temporal dynamics of consumption is needed if we are to understand carabids interest in specific weed species in a specific foraging context. We found that only females seemed to react to the presence of P. melanarius individuals, indicating that the perception of the level of risk may be sex-specific in carabid beetles.