Termination of parental care in male giant waterbugs, Belostoma flumineum Say (Heteroptera: Belostomatidae) is associated with breeding season, egg pad size, and presence of females

Reproductive effort and/or success sometimes increase with the age of a parent. We found that reproductive effort was greatest in older egg-brooding male giant waterbugs, Belostoma flumineum Say. Consistent with previous studies, males with large egg pads were unlikely to discard them unhatched under any condition. However, males with small egg pads were significantly more likely to discard the eggs unhatched in the autumn (when breeding adults are young) than in the spring. By brooding smaller pads, older males invested more heavily in each offspring. Males bearing small egg pads were also significantly less likely to discard them in the presence of females. Three kinds of hypotheses have previously been proposed to explain why reproductive investment and/or success might increase with age: selection hypotheses predict differential survival of better parents; experience hypotheses predict that more experienced parents achieve greater success without additional cost per offspring; and residual reproduction hypotheses predict that older parents invest more per offspring. It is difficult to experimentally untangle these hypotheses, but the results of this study provide cautious support for a residual reproduction hypothesis that older males with few remaining reproductive opportunities invest more heavily per offspring by retaining small egg pads.