The spotted wing drosophila (SWD) is an invasive insect first reported in California in 2008. It has since spread throughout the US including in the southeast. In Alabama, SWD was first observed on yellow sticky traps in 2011 in Coosa and Chilton counties and was later found in Elmore County. Spotted wing drosophila will infest a broad range of edible crops such as tree fruit, berry, nut, and vegetable crops. Raspberry, blackberry and blueberry crops are highly susceptible to SWD infestation. For more information on SWD, please go to www.aces.edu/timelyinfo/Horticulture/2011/July/july2011.pdf.
The African fig fly, Zaprionus indianus Gupta (Diptera: Drosophilidae), is another invasive fruit pest that has spread rapidly through much of the eastern United States. The Zaprionus genus contains 59 species. The genus is closely related to Drosophila. The African Fig Fly (AFF) was first found in the U.S. in Florida in 2005. The insect spread rapidly and now can be found throughout much of the North American continent. Though AFF can be found in ripe fruit on trees, researchers question whether they can infest intact, tree-ripening fruit as they are mainly found in rotten fruit on the ground. Conversely, in certain types of figs, the AFF will lay eggs in the ostiole (Figure 1) which is a small orifice at the distal end of the fruit (not all fig varieties have an ostiole) giving developing larvae access to the interior of the fruit.
The AFF infests a broad range of edible crops, as is the case with its close relative SWD. The SWD female can lay eggs in developing fruit mainly because of the serrated ovipositor, which gives her the ability to penetrate intact fruit. The AFF on the other hand lacks a serrated ovipositor, which purportedly limits laying of eggs to decaying or damaged fruit or in fig varieties that have an ostiole. The eggs of the AFF are creamy white and develop into larvae that are white to light yellow and less than 1 mm in length. A single AFF female can produce 58 offspring.
At 3.5 mm in length the adult AFF is considerably larger than the SWD. It is also distinguishable from the SWD because s a prominent pair of white stripes that run the length of the body from the antennae to the tip of the thorax.
Management of fruit flies should not begin until they have been caught in monitoring traps. Monitoring traps can be containers that are partially filled with bait or specialized, yellow sticky cards. Container traps are often the preferred method for monitoring and can either be ordered online (Marginaldesign.com) or constructed from household materials. For more information on construction, please go to www.aces.edu/timelyinfo/Horticulture/2011/July/july2011.pdf). If you suspect SWD or AFF infestation, please contact your Regional Extension Agent for identification confirmation.
Once SWD or AFF has been properly identified, a spray program can begin. Insecticidal sprays used to control SWD also work in the control of AFF. As always, consult with your Regional Extension Agent and refer to the product label for proper application. Additional control can be achieved through proper sanitation, which involves removal of fruit from the ground and overripe or decaying fruit from the plant. In the case of small or home orchards, specially designed bags used to cover individual fruit can serve as a barrier to these pests. Application of these bags will be time consuming and impractical for most commercial operations. Frequent harvests will also reduce the potential for infestation of ripening fruit.
Monitoring traps were deployed at a local tree and fruit crop nursery in Chilton County. The first captures were recorded on May 31. The first six weeks of monitoring are presented below (Figure 2). Currently, the number of captures have increased compared to the first four weeks but increasing. Number of male SWD (blue bars) are low and have not increased during the four-week period. The number of AFF were highest during the first three weeks but were substantially lower than the number of female SWD by week 4. However, the population may increase. Last season, the number of AFF increased later than SWD but vastly outnumbered SWD throughout most of the season. Additionally, as the number of AFF increased the number of SWD decreased.
Spotted wing drosophila continues to be an important pest in fruit operations in the Southeast and across the nation. Research investigating the most effective monitoring and pest management strategies are currently underway at various institutions. Less is known about AFF. Since the female does not have a serrated ovipositor, infestation of healthy developing fruit seems unlikely. However, for fig, particularly those types that have an ostiole, AFF is a greater concern. Last season, a farmer in Alabama reported that an entire fig crop was affected by AFF. Calls reporting damage due to AFF in figs are increasing.
Researchers are concerned about the increased population of AFF. Rarely would an AFF be observed in monitoring traps in 2016. This status was elevated from a rare observation to an almost exclusive observation in 2017. Monitoring of AFF as well as SWD will continue. More information will be presented as it made available.