Interspecific Chemical Competition Between Tribolium castaneum and Tribolium confusum (Coleoptera: Tenebrionidae) Reduces Fecundity and Hastens Development Time

The flour beetles Tribolium castaneum (Herbst) and Tribolium confusum (du Val) are model organisms for studying the effects of intra- and interspecific competition. Both species are known to compete directly through egg cannibalism and indirectly through the density-dependent release of allelopathic chemicals. To better characterize these indirect interactions, recent work has focused on quantifying the per-capita effects of intraspecific chemical competition. However, the effects of interspecific chemical competition in this system have not previously been estimated. We used experimental microcosms to examine how interspecific chemical secretions affected the reproductive activity and development time of laboratory populations of T. castaneum and T. confusum. We created replicated habitats containing flour medium that had been occupied and chemically 'conditioned' by one of the two beetle species across a range of densities, then examined how beetles of the other species responded in terms of the number of eggs laid by females and, separately, the development time of offspring. We found that T. castaneum fecundity was reduced when beetles experienced flour conditioned by T. confusum. In contrast, fecundity of T. confusum was largely unaffected by flour conditioned by T. castaneum. Additionally, we found that interspecific conditioning decreased development times for beetles of both species, particularly the development of larvae to pupae. Our results indicate that interspecific chemical competition impacts the life history of Tribolium species and suggests that models incorporating chemical competition may more accurately describe the biology of flour beetle communities.