Stage-specific predation and functional response of predatory mites to greenhouse thrips (Heliothrips haemorrhoidalis) on avocado.

The greenhouse thrips Heliothrips haemorrhoidalis is a major pest of avocado (Persea americana), causing significant leaf damage and yield losses worldwide. Biological control using predatory mites offers a potentially sustainable alternative to chemical management, yet the effectiveness of different mite species and the role of prey developmental stage remain poorly understood. In this study we compared the predation capacity of four phytoseiid mites-Amblydromalus limonicus, Amblyseius herbicolus, Amblyseius lentiginosus, and Neoseiulus cucumeris-on first- and second-instar larvae of H. haemorrhoidalis under controlled laboratory conditions. No-choice experiments revealed significant differences (p < 0.001) among predator species and thrips stages, with A. limonicus exhibiting the highest predation rates and a strong bias towards first-instar thrips, while the other mite species showed negligible thrips consumption. Choice experiments further demonstrated that A. limonicus exclusively preyed on first-instar thrips when both larvae instars were simultaneously available, confirmed by Manly's preference index (Manly's α = 1). Functional response analysis indicated a Type II functional response of A. limonicus feeding on first-instar thrips, characterised by a high attack rate at low prey densities and saturation at higher densities due to handling time constraints. These preliminary 24 h laboratory results indicate pronounced stage-specific predation under the conditions tested and show that A. limonicus performed better than the other predatory mite species examined. However, because the experiments included no predator-free controls, the findings should be interpreted cautiously and future studies under field or orchard conditions are needed to demonstrate the effectiveness of A. limonicus in H. haemorrhoidalis biocontrol.