Trophic-egg producing strategies in subsocial cydnid bugs

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Trophic eggs, which are inviable and usually function as a food supply for offspring, have been regarded as extended parental investment or the outcome of parent-offspring conflict in sibling oophagy. Adomerus triguttulus and Parastrachia japonensis (Heteroptera : Cydnidae) are subsocial bugs showing a complex pattern of maternal care, including defense against predators, progressive provisioning of host fruit and trophic-egg production.To investigate the functions of trophic eggs, we conducted experimental removal of trophic eggs from clutches and compared performance, including the incidence of viable-egg cannibalism, of nymphs with trophic eggs and those without trophic eggs. Trophic-egg feeding enhances offspring survival and/or development in A. triguttulus and P.japonensis. In A.triguttulus, some viable eggs were also fed upon by sibling nymphs. However, there was no difference in the proportion of viable eggs consumed between clutches with and without trophic eggs. The body size of A.triguttulus females affected their relative investment in trophic eggs : larger females produced more viable eggs with relatively fewer trophic eggs.To investigate the effects of food-resource environments that A.triguttulus females experience on trophic-egg production, we reared females under different resource conditions prior to oviposition and then compared the subsequent allocations of trophic eggs. Females that had been supplied with less-developed seeds produced fewer viable eggs than those supplied with well-developed seeds. However, there was no difference in the number of trophic eggs between them, and thus the number of trophic eggs per viable egg was higher in females supplied with less-developed seeds.The functions and adaptive allocation of trophic eggs are discussed in light of the two hypotheses mentioned above and the adaptive maternal effects under fluctuating resource environments