Description

Adults of this species are small, robust flies 0.07-0.11 inches (2-3 mm) in length. Both sexes are reddish-brown in overall color, with dark cross bands on the abdomen. The eyes in live individuals are bright red. They are similar in appearance to other members of the family Drosophilidae, including the well-known laboratory “fruit fly” (Drosophila melanogaster), to which they are closely related. Males of the spotted wing drosophila are distinctive and easily separated from most similar species by the dark spot near the end of each wing. The females lack the dark spot but possess a distinctly saw-toothed egg-laying apparatus (ovipositor) that extends out of the tip of the abdomen. The latter is only visible under magnification of 10 times or higher. The species also goes by the common names cherry vinegar fly and Asian vinegar fly.

Larvae are small (up to 4 mm), elongated maggots that spend their development inside soft fruits.

Spotted wing drosophila female on a fig. Photo Jong-Seok Park, Louisiana State Arthropod Museum.

Spotted wing drosophila male on a fig. Photo Jong-Seok Park, Louisiana State Arthropod Museum.

Life Cycle

Adults are attracted to soft-skinned fruits, where they congregate and mate. The female pierces the skin of the fruit using her ovipositor and inserts eggs that hatch into minute maggots. The latter burrow into the flesh of the fruits in large numbers and undergo three developmental growth stages (instars) before emerging and transforming into a pupa (the developmental stage between larva and adult). After emerging from the pupae, adults require a few days for maturation and mating, and the cycle is repeated. Development is highly dependent on temperature, but in Louisiana during summer it may require as few as 10 days from egg to adult, with many generations during a typical growing season in the southern U.S.

Fig infested with spotted wing drosophila. Photo Jong-Seok Park, Louisiana State Arthropod Museum.

Ecological Significance and Pest Status

Fruit growers in Louisiana began to notice infestations of spotted wing drosophila about 2012. Fig trees in Baton Rouge were particularly hard hit, rendering ripening figs inedible within two weeks of first observations of infestations. The species is a pest of many types of thin-skinned fruits, including figs, grapes, strawberries, blueberries, cherries, blackberries, and peaches and other stone fruits. Wild hosts in Louisiana include elderberries (Sambucus sp.), pokeweed (Phytolacca americana) and muscadines (Vitis sp.). The stout, saw-toothed ovipositor of the females allows penetration of the skin of these fruits, unlike most other drosophilids that possess simple tubular ovipositors. Pome and citrus fruits are less susceptible unless the skin is broken, providing an access point for egg laying. The species spread rapidly across the North American continent beginning about 2008 and has spread to many other parts of the world from its native range in Asia. It is now present in virtually every fruit-growing region in the Northern Hemisphere, South America and North Africa. Aggressive biosecurity measures have thus far kept it out of Australia and New Zealand.

Control

Developing successful control strategies of spotted wing drosophila has proven difficult. Chemical control has limited efficacy, may not be practical on small fruit crops and may result in resistance in this rapidly reproducing species. Cultural controls such as screening, burying fruit harvest residues and elimination of nearby wild hosts may be effective on high-value crops. Careful monitoring of orchards and residential fruit trees may prompt rapid harvesting before infestations build up. In short, if spotted wing drosophila are observed, enjoy your figs as soon as they start ripening. You have more than birds and squirrels that are competing for them.

References

Asplen, M. K., G. Anfora, A. Biondi, D.-S. Choi, D. Chu, K. M. Daane, P. Gibert, A. P. Gutierrez, K. A. Hoelmer, W. D. Hutchison, R. Isaacs, Z.-L. Jiang, Z. Karpati, M. T. Kimura, M. Pascual, C. R. Philips, C. Plantamp, L. Ponti, G. Vetek, H. Vogt, V. M. Walton, Y. Yu, L. Zappala, and N. Desneux. 2015. Invasion biology of spotted wing Drosophila (Drosophila suzukii): a global perspective and furture priorities. Journal of Pest Science 88: 469-494.