A New Invasive Insect in Missouri - Spotted Wing Drosophila

This information is from an email that Bruce Barrett, MU Professor of Entomology sent out to Extension as well as an email from Jaime Pinero, LU State Extension Entomologist.  Please note that this is an invasive insect which is causing lots of damage to fruits and causing economic concerns for producers on the West Coast and New England.

A couple of weeks ago the LU IPM (integrated pest management) program started the first-ever monitoring system for Spotted Wing Drosophila, (Drosophila suzukii), (SWD) using funds provided by a MO Department of Ag grant. SWD has been detected in three Missouri farms: St. Charles (June 26, 2013), Truxton (June 26, 2013), and Rogersville (near Springfield, June 27, 2013). These farms are the first ones where we deployed monitoring traps.

Also MU Professor of Entomology Dr Bruce Barrett and a colleague, after careful examination of several adult specimens identified SWD in Howard County.  The host was sweet cherry (from several trees).

The SWD is a recently introduced new species of fruit fly in the United States. It was first found on the west coast in 2008, but has rapidly colonized many fruit producing regions of the country.  SWD has a wide host range but is primarily a pest of berry crops (blackberries, blueberries, boysenberries, elderberries, strawberries), grapes and stone fruits (cherry, nectarine, peaches), as well as in high tunnel tomatoes.

How to monitor: Monitoring traps are baited with a mixture of dry active yeast, water and sugar: ½ tablespoon active dry yeast + 2 tablespoons sugar + 6 oz water. Yellow sticky cards are used to capture the responding insects. LU deployed traps mostly in fruiting Mulberry trees in the above locations. Traps need to be inspected and bait replaced weekly if possible.

 

SWD is a small vinegar-like fly, only 2-3 mm long, with yellowish brown coloration and prominent red eyes. Male SWD have dark spots on the wing tips. The adult flies are difficult to distinguish from other small vinegar flies found on overripe bananas. However, unlike these other flies, which typically feed on overripe or deteriorating fruits, SWD females lay eggs in healthy, intact, ripening fruits. In particular, SWD will feed on thin-skinned, soft fruits such as raspberries, blackberries, blueberries, strawberries, grapes, plums and cherries. Sometimes the symptoms won’t show until after the fruits are harvested and sometimes not until the fruits are in possession of the consumers. In addition to the damage caused directly by the larvae, the feeding makes the fruits susceptible to infestation by other insects and rot fungi and bacteria. The larvae will then leave the fruits to pupate and later emerge as adults. Many flies can originate from just a few individuals in just a few months. 

How to ID SWD: Look for the presence of spots on the wings and the two black bands on the forelegs of males. Females don’t have those two physical attributes, so the only way to confirm is by dissecting the fly and look for the serrated ovipositor (it is a rather small structure located at the tip of the abdomen; it needs to be pulled). More information will be made available in a LU guide sheet on SWD monitoring that will be released soon.

While other Drosophila fruit flies (or vinegar flies) are quite common in the U.S., SWD is different in its ability to infest healthy fruit.  Other fruit fly species typically infest over-ripe or damaged fruit.  But female SWD have serrated ovipositors that can cut into healthy fruit to insert eggs.  Obviously this leads to problems with deteriorating fruit in the field or with customers who find larvae in fruit after harvest.  Once eggs are laid in the fruit, you can no longer control it with a pesticide spray.  Unfortunately, sprays needed to control the fly need to be made near harvest time.  As such, the use of short residual pesticides (organic and conventional) are likely the most effective short term solution for this pest.

As more data regarding SWD in Missouri is gathered, additional information/recommendations will be forthcoming.  But in the meantime, Michigan State University has a website regarding Spotted Wing Drosophila biology and control.