Spotted wing drosophila (SWD) is a new invasive pest of fleshy fruit in California. It was first collected on the Central Coast in late 2008 and was officially identified and recognized as being established as a pest in California during 2009. In 2009 it also spread to and became established throughout much of California, Oregon, Washington, British Colombia and a few other locations.
SWD is a newly-introduced species of Drosophila fruit flies, also known as vinegar flies, which are nothing new to citrus producers worldwide. Drosophilas are the common, small fruit flies that can be found hovering around rotting fruit underneath citrus trees. Spotted wing drosophila is similar to these common vinegar flies, except that it can also attack fleshy fruit prior to harvest. Some of the favorite hosts are cherries, blueberries, blackberries, raspberries and strawberries. Intact citrus fruit are not a host. However, rotting citrus fruit on the ground are excellent hosts, especially in the shade where leaf litter and microsprinklers provide a moderate, humid environment.
What this means is that citrus itself is at absolutely no risk due to SWD. However, citrus growers should be aware that neighbors that grow cherries, blueberries or caneberries are extremely concerned about SWD and in 2009 will be putting in place aggressive programs to keep this pest out of their fruit. These neighbors will be very concerned about the role of rotting citrus fruit as an ideal host for the early-season buildup of SWD populations that could migrate to their crops. As good participants of the agricultural community, citrus growers should be aware of this concern until more information either discredits or validates the role of citrus within the landscape-scale biology of this new exotic pest.