Use of alternative host fruit and overwintering biology of spotted wing Drosophila (Drosophila suzukii) in California

Spotted wing drosophila (SWD), Drosophila suzukii Matsumura is a newly invasive pest that attacks cherries and other various soft- and thin-skinned fruits. Adult flies are highly mobile and may move among different host plant species as they seek out susceptible fruit. Current control programs rely on multiple insecticide sprays, in attempt to kill the adult SWD as they enter the field to search for susceptible host fruit and to lay eggs.  Because a wide range of crop and landscape plant species serve as SWD refuges for overwintering or ‘off-fruit’ seasonal habitats, there will always be untreated SWD populations nearby to re-infest the cash crop and thus repeating the need for future insecticide sprays. It is therefore crucial to suppress source populations on non-crop hosts and post-harvest cash crops at the landscape level in order to reduce pest pressure in susceptible crops (e.g., cherries). Any reduction in the sizes of source populations surrounding the crop fields would greatly improve the efficiency of other control strategies, such as biological controls. Currently, the details of the sources and movement patterns of SWD populations in California agricultural landscapes are not completely understood. In particular, its overwintering hosts and habitats in California. In order to elucidate these details of SWD landscape ecology, we first investigated SWD seasonal occurence in an agricultural landscape, use of host plant species, and possible movement among those species. Secondly, we investigated the survial and development of various immature stages in the winter months in a citrus orchard and the effects of various fruit juices on adult longevity and fecundity. We finally discussed where, when, and how the fly might continually infests fruit crops year to year in California’s central valley.