Predation Risk Effects of Lady Beetle <em>Harmonia axyridis</em> (Pallas) on the Development and Fecundity of <em>Periphyllus koelreuteriae</em> Takahashi

In biological control of pests using predatory natural enemies, predators not only prey on pests directly but also can affect the population fitness of pests through indirect non-consumptive effects (predation risk effects). However, the impact of predation risk effects varies depending on the mode of stress imposed by natural enemies and the state of the stressed pests. Herein, we exposed aphids (Periphyllus koelreuteriae) at different stages to various cues from the multicolored Asian lady beetle (Harmonia axyridis) to assess the effects of different predation risks on P. koelreuteriae development and reproduction. We found that the effect of predation risk on aphid developmental time was clearly stage-dependent. When 1st instar nymphs were exposed to predator cues, their developmental time was prolonged only in the early stages (1st-3rd instar). Similarly, when 3rd instar nymphs were stressed, only the current stage (3rd instar) showed a developmental delay, while 4th instar nymphs and adult aphids were not significantly affected. Additionally, aphids at different stages perceive predation risk differently. Nymphs cannot recognize visual cues from predators but can perceive odor cues. In contrast, adult aphids are sensitive to a variety of predator cues, including visual ones. Predation risk caused aphids to shorten their adult lifespan and reduced reproductive output, but it increased the proportion of diapause offspring. This study highlights the importance of considering how predation risk affects multiple life stages and physiological changes, which are important for gaining insights into the mechanisms of predator-prey interactions and for comprehensively assessing the ability of lady beetles to regulate aphid populations.