Prey preference of Orius sauteri between Western Flower Thrips and spider mites

Prey preference of polyphagous predators plays an important role in the suppression of various species of pest insects. In this study, the prey preference of Orius sauteri (Poppius) (Heteroptera: Anthocoridae) between deutonymphs of Tetranychus urticae Koch (Acari: Tetranychidae) and second instars of Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), and the influence of spider mite density on the preference were examined in the laboratory in three-dimensional set-ups at 25 +/- 1 degrees C and 70 +/- 5% r.h. The results showed that the predatory bug in the presence of equal densities of the two prey species had a clear preference for thrips (preference index beta: 0.86 +/- 0.02), consuming 7.2 thrips larvae and 1.5 spider mite deutonymphs during the experimental periods of 6 h. The number of thrips consumed by O. sauteri did not change when the density ratio of thrips to spider mites was decreased from 1:1 to 1:5. Predation on spider mites increased when their ratio to thrips increased, but the disproportionate predation (i.e., the functional response) of O. sauteri towards spider mites resulted in a linear increase in the preference for F. occidentalis. The possible implications of these findings for the suppression of spider mites by O. sauteri in relation to the recent invasion of F. occidentalis into China are discussed.