Flour beetles (genus Tribolium) compete directly through egg cannibalism and indirectly due to shared resource usage. They may also compete indirectly through the release of chemicals which change the suitability of the local environment for other beetles. However, many current ecological models of flour beetle competition do not account for the potential effects of such chemically-mediated, indirect competition. We tested the effects of chemical secretions in “conditioned” experimental habitats of both Tribolium castaneum and Tribolium confusum to quantify indirect competition. We asked whether chemical conditioning alters reproductive activity (egg-laying), development time and adult longevity.
We created a gradient of chemical secretions in the flour using 6 densities of T. confusum beetles. Beetles were allowed 48 hours to condition flour, then adults and eggs were completely removed. 50 beetles of T. casteneum or 50 of T. confusum were then added to the conditioned flour. After 24 hours these beetles were removed and the total number of eggs present were counted. 75 eggs from each patch were put back onto the conditioned flour and their development was watched over a 5 week period. Finally, the 50 adults were transferred to fresh flour where their success was tracked over the next 5 weeks.
Results/Conclusions
We found that both T. confusum and T. castaneum beetles mating in flour previously inhabited by high densities of beetles – and therefore high amounts of chemical secretions - exhibited significantly lower fecundity (25% fewer eggs at the highest densities). Further, eggs developing in conditioned flour were on average slower to develop (+5 days or 16% longer), and reached maturity less often.
These results highlight the importance of chemically-mediated competition in these model organisms and will allow future studies to incorporate chemical interference into quantitative ecological models.