Factors affecting oviposition rate in the flour beetle Tribolium castaneum and the origin of the population regulation mechanism

Abstract

SummaryThe effects of egg cannibalism, conditioned medium and the presence of quinone secretions on oviposition rate were studied using single pairs of adults to eliminate any direct crowding effects. Most measurements were made on beetles confined to the surface of the flour medium in plastic towers. Oviposition rate was decreased by about 58% when pairs were transferred from fresh to conditioned medium; lowered about 25% when only quinones were present and the medium was still fresh; and enhanced 35% in dry conditions when beetles were provided with eggs to eat. Both the lowered oviposition rate in confined cultures and egg‐eating may be explained by natural selection at the individual level. Cannibalizing eggs boosts a female's oviposition rate. The presence of quinones or conditioned medium indicates high population densities and acts as a signal for ceasing oviposition and dispersing to avoid high egg mortality. In confined populations, this results in population regulation, while in open populations, this strategy is a mechanism to avoid competition. It implies that the resource shortages normally experienced by such organisms are relative, not absolute.