Light‐dependent effects of feeding timing on the daily timing of ecdysis in the water strider Aquarius paludum (Hemiptera: Gerridae)

Abstract The timing of ecdysis in insects is often gated to particular phases of the daily cycle; however, this diel gating has only been documented in few hemimetabolous species, and whether the timing of feeding modulates its expression remains unknown. As newly moulted individuals are especially vulnerable to predation and cannibalism, the precise timing of ecdysis is a plausible target of selection. In this study, we tested whether feeding timing affects the daily distribution of nymphal ecdysis events in the water strider Aquarius paludum (Fabricius) (Hemiptera: Gerridae), and whether this effect depends on the light regime. Newly hatched nymphs were reared under either a 15.5 h light:8.5 h dark cycle (15.5 L:8.5 D) or continuous light (24 L), with four feeding regimens (food thrice daily, or once at the beginning, middle or end of the light phase), and ecdysis events were recorded thrice daily throughout all five nymphal instars. A hierarchical log‐linear model revealed a significant three‐way interaction between the light regime, feeding regimen and observation time ( G 2 = 29.68, df = 6, p < 0.001): the timing of feeding modified the distribution of ecdysis only under the light–dark cycle. Within each instar, a consistent temporal shift, namely, ecdysis events concentrated in the evening on the first major day and shifting to the morning on subsequent days, was observed under both light regimes, consistent with diel gating. The synchrony index was significantly higher under 15.5 L:8.5 D than under 24 L ( p = 0.030), indicating reduced temporal precision of ecdysis in the absence of a light–dark cycle. These results provide the first evidence that feeding timing interacts with the photic environment to shape the diel timing of ecdysis in a hemimetabolous insect, extending the evidence for diel/circadian gating of ecdysis beyond the small number of species in which it has so far been described.