Nov 16, 2012

New invasive fruit fly discovered in Pennsylvania

Zaprionus indianus Gupta, commonly known in Brazil as the African fig fly (AFF), is an invasive species that was recently found in Pennsylvania for the first time, according to Penn State University.

First discovered by the Pennsylvania Department of Agriculture (PDA) in early October in survey traps, it was found immediately after by David Biddinger at the Penn State Fruit Research and Extension Center in Biglerville. Adult flies were found in apple cider vinegar traps used for the seasonal monitoring of spotted wing drosophila (SWD), another recently introduced invasive pest of small fruit crops.

Reviewing SWD samples from 2011, Biddinger also found the fig fly had been present in Adams County in the fall of 2011, so it has been in Pennsylvania for at least two seasons. For what is considered to be a tropical pest, this is important because they not only survived the extremely mild winter of 2011-12, but also the more typical winter of 2010-11. Of note, however, is that while SWD trap catches have greatly increased in the last two weeks despite heavy frosts, the same vinegar traps are no longer catching AFF. AFF is now recorded from Adams, York, Dauphin, and Clearfield counties, according to PDA.

African fig fly adults are easily distinguished from all other fruit flies in the region because of a pair of silvery-white stripes, from antennae to thorax tip, that are outlined along both sides by black stripes. Adults of this species are slightly larger in size than the spotted wing drosophila, according to Penn State.

Native to Africa, the Middle East and Eurasia, it is now found in much of South and Central America, where it is mainly a pest of figs. It was first found in Florida in 2005, where it quickly spread and out-competed other fruit flies. New records were found for Michigan, North Carolina and Connecticut in September of this year, and it appears to be spreading throughout the South as far west as Texas.

The fig fly is considered as a generalist insect feeding on various tropical fruits, but it has potential to damage small fruits (cherries, blueberries, blackberries, strawberries and raspberries). In Pennsylvania, it has been found later in the season and mostly in grapes, but has also been found in SWD monitoring traps in cherry, raspberry and blackberry plantings. Its presence and damage potential in grapes and other crops is under investigation by Biddinger’s lab and Penn State small fruit specialist Kathy Demchak. Monitoring efforts by PDA and Penn State will continue next season, and records for new hosts and new county records should be forwarded to either institution.

Since it does not have a large, sharp ovipositor like SWD females, AFF appears to only attack damaged and over-ripe fruit, and the harsher winters of Pennsylvania may prevent it from establishing as aggressively as it did in Florida. Indeed, numbers of adults collected in vinegar traps have been only a fraction of the number of SWD collected. An exception, however, has been from net collected samples in a grape vineyard, where numbers of AFF greatly outnumbered SWD. While it appears that grape is not a preferred host of SWD, it may be that grape is preferred by this new fruit fly. There is also concern in the South that it will become a pest of blueberries, according to Penn State.