2013 ASHS Annual Conference

Lewis spider mite, Eotetranychus lewisi (Acari: Tetranychidae), is a new emerging pest in California strawberries.  The predatory mite Phytoseiulus persimilis (Acari: Phytoseiidae), typically used for biocontrol of the twospotted spider mite, Tetranychus urticae (Acari: Tetranychidae), provided growers little to no control of Lewis spider mite.  We evaluated the efficacy of four commonly used phytoseiid predatory mites: P. persimilis, Neoseiulus californicus, N. fallacis, and Amblyseius andersoni.  We also investigated the interactions between the twospotted spider mite and Lewis spider mite and in relation to phytoseiid efficiency given the potential for indirect effects of biocontrol.  When Lewis spider mite and twospotted spider mite are present on the same leaf, twospotted spider mite populations began displacing Lewis spider mite.  P. persimilis did not feed on Lewis spider mite, but the other three predatory mites consumed this spider mite and lowered their populations from 40 to near zero in 14 days.  When both Lewis spider mite and twospotted spider mite are present on the same leaf, N. fallacis and A. andersoni fed on both types of mites equally.  N. californicus showed preference toward Lewis spider mite and allowed twospotted spider mite populations to increase from 20 to 180 in 14 day period.  The reproduction rate of Lewis spider mite and twospotted spider mite on three popular strawberry varieties (Ventana, Benicia, and San Andreas) were also evaluated.  Lewis spider mite reproduced best on Ventana and Benicia, while twospotted spider mite reproduced equally on all three varieties.