Larval feeding types shape the predation aggression of predatory mites in both intraspecific and interspecific encounters

Abstract Cannibalism (intraspecific predation) and intraguild (interspecific) predation are widely observed phenomena in the animal kingdom, including amongst predatory mites of the Phytoseiidae family. While the larval stage of phytoseiids is a vulnerable and important life stage, it has received less attention than the adult stage. The larvae of phytoseiid species can be categorised into three types based on their feeding behaviour: non-feeding, facultative feeding, and obligatory feeding. This study aimed to investigate the occurrence of cannibalism and intraguild predation among the larval stages of three generalist predatory phytoseiids: Amblydromalus limonicus (Garman & McGregor), Amblyseius herbicolus (Chant), and Neoseiulus cucumeris (Oudemans). We hypothesised that the larval feeding type could influence the aggressiveness of the predators in intraspecific and interspecific encounters, with obligatory-feeding larvae being the most aggressive and non-feeding larvae being the least aggressive. To test this hypothesis, we conducted a no-choice experiment under laboratory conditions using larvae to observe the prevalence of predation among conspecifics and heterospecifics in these three predatory mite species. In addition to observing predation outcomes, we measured larval body size, cheliceral size, and cheliceral morphology to investigate these parameters' correlation with predation success. Our study revealed significant differences in the prevalence of cannibalism and intraguild predation among the three predatory species in agreement with our hypothesis: N. cucumeris larvae did not engage in predatory behaviours, while A. herbicolus displayed the highest predation success. Our findings suggest that cheliceral morphology may be a better indicator than body size of the aggressiveness of larval predation against conspecifics and heterospecifics. Our results provide valuable insights into the importance of larval behaviour in population dynamics and the development of effective pest management strategies. The study also highlights the need for further research on the larval stage of phytoseiids and emphasises the significance of considering larval behaviour when studying and managing these important predatory mites.