Predatory mites Amblydromalus limonicus and Amblyseius herbicolus (Acari: Phytoseiidae) as potential biocontrol agents of Eotetranychus sexmaculatus (Acari: Tetranychidae) in avocado: examining predation on different prey life stages.

The six-spotted spider mite, Eotetranychus sexmaculatus (Riley) (Acari: Tetranychidae), is a severe pest of avocado trees, causing excessive leaf drop and reduced yield. Two predators found to be sympatric with E. sexmaculatus in surveys, Amblydromalus limonicus (Garman & McGregor) and Amblyseius herbicolus (Chant) (Acari: Phytoseiidae), may serve as potential biological control agents. We examined their potential in 2 laboratory experiments. (i) In no-choice tests, each predator was presented with 40 eggs, 40 larvae, 40 nymphs, or 20 female adults of E. sexmaculatus, and predation and oviposition rates (per day) were measured. (ii) In choice tests, predators were given a mixture of 10 eggs, 10 larvae, 10 nymphs, and 10 female adults, and the same parameters were measured, but with prey stage preference also assessed using Manly's preference index. Our results showed both A. limonicus and A. herbicolus fed and reproduced on all stages of E. sexmaculatus. Significantly higher predation rates were observed for A. limonicus on E. sexmaculatus than A. herbicolus. Both predator species preferred earlier life stages of E. sexmaculatus, with the preference more pronounced in A. herbicolus than in A. limonicus. In both choice and no-choice experiments, the oviposition rate (one criterion for determining whether artificially released biological control agents can use the nutrients of the new prey to reproduce) was higher in A. limonicus than A. herbicolus. This study is the first to report on the biological control potential of these two predatory mite species for use against E. sexmaculatus in avocado plantations.