Insecticide impacts on the native predaceous mite Euseius hibisci (Acari: Phytoseiidae) in southern California avocados

Avocado thrips, Scirtothrips perseae Nakahara, was first reported in 1996 damaging foliage and fruit of Hass avocados. Avocado thrips feeding can scar the entire fruit surface leading to economic losses when fruit are culled or downgraded. In years when thrips pressure is high in southern California avocados, insecticide use also increases. The native predaceous mite, Euseius hibisci (Chant) is particularly common in avocado orchards and is considered a significant generalist predator. Euseius hibisci is capable of building to high densities in the absence of mite prey and can successfully survive and reproduce on a diet of pollen among other food sources. We evaluated four insecticides currently registered for avocado thrips management in southern California avocados; Agri-Mek (abamectin), Danitol (fenpropathrin), Delegate (spinetoram), Veratran-D (sabadilla) and a control (water) against E. hibisci. Individual leaves were flagged, treated, and allowed to weather in the field on the tree until their use in laboratory bioassays at various times post insecticide application (1, 3, 7, 14, 21, etc. days post-treatment). Bioassay mortality readings were taken 1, 2, 3, 4, and 5 days post bioassay setup. Each insecticide evaluated caused mortality to E. hibisci, with fenpropathrin causing mortality for the longest period of time (111 d); abamectin caused mortality for the shortest period of time (7 d). These results will be discussed further.