Density-related volatile emissions and responses in the red flour beetle, Tribolium castaneum

Intraspecific attraction depends both on the cues provided by the attracting individual and the response of the attracted individual. These attracting cues are related not only to current conditions, but also are a reflection of individual and population life history. These relationships were examined by placing red flour beetle, Tribolium castaneum (Herbst.), adults in flasks at increasing densities and monitoring the changes in volatile chemical emission over time. Only certain chemicals were quantified: methyl benzoquinone, ethyl benzoquinone and 4,8-dimethyldecanal, all of which are known to impact the biology of T. castaneum. The flasks were used as sources for both quantification of the chemicals and for bioassays. Additional bioassays were conducted with synthetic 4,8-dimethyldecanal, a known aggregation pheromone component, to evaluate attraction with respect to population density. Tribolium castaneum density affected both the release of volatile chemicals and the responses of conspecifics to those chemicals. The results indicated that while there were important effects of beetle density on chemical emission and response, none of the chemicals evaluated emerged as promising synergists to the current aggregation pheromone 4,8-dimethyldecanal. The benzoquinones released in response to stress and density acted as anti-aggregation pheromones along with their accepted defensive function.