Pollen availability for predaceous mites on apple: spatial and temporal heterogeneity

It has been suggested that an abundance of alternate food early in the spri ng may be critical to the ability of generalist predaceous mites to suppres s spider mite pests. One alternate food that is typically very abundant in spring is wind-dispersed pollen. Here we investigate, at several spatial sc ales, the heterogeneity in the availability of pollen to predaceous mites o n apple. We found pollen to be abundant on apple leaves very soon after the y opened (> 100 grains/cm(2)), and that the dominant pollen types at this t ime were wind-dispersed tree pollens (Betulaceae and Pinaceae). We found th at most of the spatial variation in pollen abundance occurred at either sma ll spatial scales (within trees) or very large spatial scales (among orchar d blocks). Variability among orchards was clearly influenced by the surroun ding vegetation, and probably also by the management regime (frequency of m owing). Spatial heterogeneity in pollen availability may affect the build-u p of predatory mite populations in the spring, as we found early season abu ndances of Typhlodromus pyri (Phytoseiidae) and Zetzellia mall (Stigmaeidae ) to be better correlated with early season pollen density than with abunda nce of mite prey (Aculus schlechtendali).