Sublethal effects of a neonicotinoid insecticide on the sharpshooter vectors of Xylella fastidiosa

The neonicotinoid insecticide imidacloprid, applied in soil to grape seedlings in a series of doses, was tested on two major vectors of the bacterium Xylella fastidiosa in California: Homalodisca vitripennis (glassy-winged sharpshooter (GWSS), Hemiptera: Cicadellidae) and Graphocephala atropunctata (blue-green sharpshooter (BGSS), Hemiptera, Cicadellidae) for effects on longevity, possible repellency, and flight ability. The insecticide greatly reduced feeding of both insects at doses where mortality was not significantly different from untreated control insects. Imidacloprid did not affect the ratio of insects on the plant to that of off the plant, and G. atropunctata were found on the leaves rather than on the stems, whereas H. vitripennis was more frequently found on the stems. However, insecticide treatment reduced the rate of both G. atropunctata and H. vitripennis present on the stems. Sublethal doses did not reduce flight ability markedly and did not measurably reduce transmission of X. fastidiosa to grape beyond reductions in transmission ascribable to vector mortality.