Predator-parasitoid interaction between Harmonia axyridis (Coleoptera: Coccinellidae) and Pyemotes zhonghuajia (Prostigmata: Pyemotidae) in aphid control.

Intraguild predation (IGP) is a crucial ecological interaction that influences the dynamics of natural enemies and affects the effectiveness of biological control. Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae), an invasive predator, significantly impacts native predators through IGP in certain countries. Pyemotes zhonghuajia (Yu, Zhang & He) (Prostigmata: Pyemotidae), a small ectoparasitoid, parasitizes various pests from the orders Lepidoptera, Coleoptera, and Hemiptera. Although both natural enemies are essential in controlling pests like Neotoxoptera formosana (Takahashi) (Hemiptera: Aphididae), their interactions and effects on pest management remain poorly understood. The study investigates the functional response of H. axyridis to N. formosana, the lethal ability of P. zhonghuajia against N. formosana, and how intraguild interactions affect the mortality rates of both N. formosana and H. axyridis when exposed to P. zhonghuajia. Our findings revealed that H. axyridis exhibited a Holling type II functional response to N. formosana, with female adults being the most effective predators. Pyemotes zhonghuajia demonstrated significant lethality against N. formosana, particularly at higher mite densities. However, the presence of P. zhonghuajia also increased the mortality rate of H. axyridis, highlighting a parasitism-driven intraguild interaction in which the mite dominates the predator. These results challenge conventional views of predator-parasitoid dynamics and highlight the complexity of interactions among natural enemies in pest control systems.