Provision of small sterile eggs is a circumstance-dependent maternal investment in sibling cannibalism in the ladybird beetle Harmonia axyridis (Coleoptera: Coccinellidae)

Abstract

Many aphidophagous ladybird beetles lay clusters of eggs and sibling cannibalism occurs at hatching. Larvae that hatch early tend to cannibalize undeveloped eggs and those that hatch late. The cannibalized eggs, especially those that are sterile, represent a maternal investment in the cannibal and are regarded as "trophic" eggs, which increase their chances of surviving. The characteristics of cannibalized eggs, however, are poorly studied. In this study, I determined the sizes of eggs that developing and undeveloped eggs within egg clusters of Harmonia axyridis (Coleoptera: Coccinellidae). Developing eggs were significantly larger (on average 3.45% larger) than the undeveloped sterile ones, which were mainly small. Furthermore, the hatchability of eggs was also significantly associated with their size, inclusive of the maternal effects. These results indicate that the production of relatively small sterile eggs functions as circumstance-dependent maternal investment in improving the survival of the first instar larvae to hatch in each egg cluster.