The parental effects of body size on developmental phenotype in Harmonia axyridis.

Body size is a trait with many potential impacts on fitness. Adult body size can affect the strength of condition-dependent parental effects that determine offspring phenotypes, with potentially important transgenerational consequences. In a preliminary experiment, larval food deprivation (30 min daily access) created Harmonia axyridis Pallas (Coleoptera: Coccinellidae) females that weighed <50% of controls reared on ad libitum food (eggs of Ephestia kuehniella Zeller). Although only 1/3 of larvae survived to adulthood in the 30 min treatment, adult pairs produced eggs that were not significantly different in size from those of pairs fed ad libitum as larvae. Less extreme larval food deprivation (4 h daily access) was used to create a cohort of H. axyridis that weighed <60% of controls reared on ad libitum food. Small couples had lower 20-day fecundities and reduced egg fertility relative to large couples. Both egg and pupal periods were shortest when both parents were small, and longest when both parents were large, with reciprocal crosses intermediate. There were no consistent effects of parental body size on larval development time, but the progeny of small females mated to large males pupated later than other treatments. Progeny of large pairs had the heaviest adult weights at emergence, and progeny of small pairs, the lightest, with the progeny of reciprocal crosses intermediate. Small females produced the lightest female offspring, whereas small males sired the lightest male offspring, suggesting stronger responses to epigenetic signals from parents of the same sex. These results indicate that H. axyridis cohorts maturing with abundant food will produce progeny with larger potential body size and fitness, whereas those experiencing food limitation will confer size and fitness limitations to the subsequent generation, with potentially important implications for short-term population dynamics.

No nutritional benefits of egg cannibalism for Coleomegilla maculata (Coleoptera: Coccinellidae) on a high-quality diet.

Egg cannibalism serves various functions in the Coccinellidae. Here we examined the fitness consequences of egg cannibalism by neonates, fourth instar larvae, and prereproductive adults of Coleomegilla maculata DeGeer, with beetles fed a diet of Ephestia kuehniella Zeller eggs. Cannibalism of two eggs by neonates had no effect on development, and cannibalism of five eggs by fourth instars did not benefit any aspect of reproduction, but delayed pupation slightly. Cannibalism of eggs by pre-reproductive adults had no effect on reproductive success in any combination of reciprocal crosses of cannibals and non-cannibals. Females did not recognize, nor avoid consuming, their own clutches, and cannibalism propensity did not change following mating and onset of oviposition in either sex. These results contrast with those for more strictly aphidophagous species in which larvae gain developmental benefits, and females may recognize and avoid filial egg clusters while using cannibalism to interfere with conspecific females, whereas males reduce egg cannibalism after mating because they cannot recognize filial clusters. Egg cannibalism may confer developmental benefits to C. maculata when diet is suboptimal, as previously shown, but no such benefits were evident on the high-quality E. kuehniella egg diet. Female C. maculata do not require aphids to reproduce and distribute their eggs broadly in the environment, given that larvae can develop on pollen and non-aphid prey. Thus, C. maculata is not subject to the intraspecific competition that selects for cannibalism in more aphidophagous species, and also lacks many secondary adaptations associated with the behaviour.