Many organisms often rely on chemical defenses to deter predators. However, the way in which invertebrates utilize chemical defenses has been relatively understudied. Darkling beetle species of the Eleodes and Coelocnemis genera exhibit defensive posturing followed by malodorous chemical secretions to signal their unpalatability towards potential predators. However, the metabolic costs and trade-offs associated with these mechanisms are unknown. It is also unclear whether certain beetle species utilize chemical defenses more readily than others. We examined the defensive displays and secretions of four darkling beetles species. We also examined the effect of captivity on defensive behavior by comparing responses in beetles challenged in situ versus beetles that were held captive. We found that beetles challenged in captivity exhibited defensive posturing for a significantly shorter time than beetles challenged in situ. In addition, one species, Eleodes armatus, required a significantly longer period of agitation before odor release compared to the other three species. Our results suggest that prior stress can cause the beetles to choose evasion over defensive posturing and that different species utilize different strategies in their defensive secretions.

CEC Research Volume 1, Issue 2