Legacies from mom: cryptic maternal effects on progeny life histories in Hippodamia convergens

Aphidophagaous coccinellids exploit ephemeral resources (aphid blooms) and gravid females must target an 'oviposition window' midway through an aphid cycle to maximize offspring survival. Competition for aphids, by conspecific and heterospecific predators, becomes increasingly intense as the population cycle advances. We hypothesized that female H. convergens should increase their egg size over a sequence of clutches so as to improve offspring survival as environmental conditions deteriorate. We produced females of three different sizes by controlling larval access to food (eggs of Ephestia kuehniella), and tracked their reproductive activity. We collected the 2nd, 12th and 24th clutches laid by these females, measured the eggs, and reared a sample of 12 larvae per clutch on E. kuehniella. The development of offspring was followed, and the dry weight of the resulting adults was obtained. Although only large females were able to increase egg size over time, this was not the only factor influencing offspring adult weight. Insects developing from later clutches of mid-sized females grew to emerge as larger adults than those from earlier clutches even though they hatched from eggs of similar size. These results indicate that egg size is only one factor affecting potential offspring size, and that other phenotypically cryptic maternal signals mediate larval growth rates according to clutch sequence. Progeny of later clutches tended to hatch earlier and pupate in a shorter period, but larvae spent longer in the 4th instar where most weight is gained, suggesting that these maternal signals may influence larval voracity in a stage-specific manner.