Experiments with Elasmucha grisea L. (Heteroptera: Acanthosomatidae): does a female parent bug lay as many eggs as she can defend?

Arja Kaitala Department of Zoology, University of Stockholm, S-10691 Stockholm, Sweden Females of the parent bug Elasmucha grisea L. (Acanthosomatidae, Heteroptera) defend eggs and small nymphs against invertebrate predators. Predation is the main mortality factor affecting offspring numbers in this species. Since we found a positive correlation between female size and clutch size we tested the hypothesis that a female parent bug lays as many eggs as she can defend. We manipulated clutch size by removing small and large females from their own eggs and giving them another clutch. Small females guarding large clutches lost significantly more eggs than large females guarding small clutches or females in the two control groups. Large females could defend, on average, 16% more eggs against invertebrate predators (mainly ants) than could small females. We conclude that an ecological factor (predation) limits clutch size in this species and the parent bug lays an optimal clutch size as determined by the defending ability of the female.