Nonconsumptive Harmonia axyridis (Coleoptera: Coccinellidae) induces stage-dependent dispersal, development, and diapause investment in Periphyllus koelreuteriae (Hemiptera: Chaitophoridae)

In predator-prey systems, nonconsumptive effects can influence prey behavior and physiological states. Prey encountering enemies exhibit adaptive responses to reduce predation risk, with these responses often tied to their current life stages. Here, we experimentally investigated the adaptive changes in Periphyllus koelreuteriae (Takahashi) across different life stages in response to short-term exposure to the nonfeeding Harmonia axyridis (Pallas) in the laboratory, focusing on aphid dispersion, development, and fecundity. Upon receiving signals from H. axyridis, aphids at all instars except the early nymphs (first instar and second instar) showed enhanced dispersal ability, with antipredatory dispersion intensifying as either ladybeetles or aphids matured. When facing predation risk, aphid nymphs respond by prolonging the developmental duration of their current instar, and once the risk is eliminated, the nymphs resume normal development. Furthermore, shortened adult longevity is observed only in the fourth-instar nymphs and adults, which reduces the total lifespan, whereas the lifespan of the first- to third-instar nymphs remains unchanged. In addition, fourth-instar nymphs and adults, facing predation risk, significantly decreased reproductive output and had a higher proportion of diapause offspring. This study demonstrates that transient predation pressure from H. axyridis induces stage-dependent adaptive changes in aphid populations, including enhanced dispersal, prolonged preadult duration, and reduced fecundity. The results provide insights for optimizing biological control of aphid populations using predatory ladybeetles.