The recent infestation of local crops by the spotted wing drosophila, Drosophila suzukii, is serious.
Vinegar flies normally are associated with rotting and over-ripe fruit and have not been thought of as being anything beyond a nuisance. However, the spotted wing drosophila is different from other vinegar flies in that it lays eggs into fruit which are yet to be harvested. The larvae then feed within the fruit and exit to pupate. The feeding of the larvae, while damaging in itself, also exposes the fruit to fungal and bacterial infection.
To growers, a pest such as the spotted wing drosophila presents several challenges. The first is that three of the four stages of fly development, namely the egg, larva and pupa are generally inaccessible to conventional pest management methods. Secondly, the very high numbers of flies frequently found in production fields and the apparently high breeding potential of the individual female make it very difficult to reduce a population quickly to economically acceptable levels once it is established.
While apparently new to Santa Cruz County and other areas of California, the situation of the spotted wing drosophila is not unique. Serious infestations of fruit flies (not vinegar flies) in Hawaii, California and Florida have been successfully brought under control by multi-faceted management programs, which can guide us in our approach to managing the spotted wing drosophila.
A successful management program for spotted wing drosophila will quite likely consist of three essential parts:
1. Use of attractant bait sprays, although this has not yet been fully tested for control of spotted wing drosophila. Attractant based sprays, such as the GF 120, utilizing environmentally safe toxicants used in low volumes across the production field and border areas can be useful in reducing fly populations while minimizing effects on predators, parasitoids and honeybees. However, since the efficacy of any bait and toxicant decreases over time, these materials need to be re-applied, perhaps at weekly or bi-weekly intervals to be effective.
2. Field sanitation. Infested fruit which remains in the field allows eggs and larvae to fully develop and serve as a source of more flies. All infested, ripe fruit should be removed from the field and destroyed, either by burial or disposal in a closed container.
3. Looking at other successful programs of fruit or vinegar fly management, it is clear that using management practices over a wide area was essential. It is important for every grower within a fly infested area to participate, since a single, unmanaged field will serve as a source of infestation to surrounding fields.