Background
Spotted Wing Drosophila (Drosophila suzukii), 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. It was found in New England in late summer 2011 shortly after Hurricane Irene and caused significant crop damage in fall raspberries among other crops. While fruit flies (or vinegar flies) are nothing new in the US, this species is different in it's ability to infest healthy fruit. Other species typically infest over-ripe or damaged fruit. Females of this species have serrated ovipositors that can cut into healthy fruit to insert eggs. This can lead to problems with deteriorating fruit in the field or with customers who find multitudes of larvae in fruit after harvest.
Crops at Risk
This insect has a wide host range but is primarily a pest of berry crops and some stone fruits (cherry, nectarine, peaches), but may also be found in high tunnel tomatoes.
| Crop Host | Crop Host | Wild Host |
|---|---|---|
| Apple | Grapes | American Pokeweed |
| Asian Pear | Italian Plums | Autumn Olive |
| Asian Plum | Mulberries | Beach Plum |
| Blackberries | Nectarines | Climbing Nightshade |
| Blueberries | Peaches | Crabapple |
| Boysenberries | Persimmons | Fox Grape |
| Cherries | Plumcots | Japanese Yew |
| Cold Hardy Kiwis | Raspberries | Kousa Dogwood |
| Elderberries | Strawberries | Porcilainberry |
| Tomatoes | Wild Rose |
Identification/Lifecycle
The first step in dealing with this new pest is identification. Spotted Wing Drosophila is a small vinegar fly. Both males and females have red eyes. Males have two spots on their wings, which is a key identifying feature. Females lack the wing spots but have a robust and serrated ovipositor that distinguishes them from other species of fruit fly. Seeing the ovipositor requires some magnification; a hand lense will do.
- Overwinter as adults and maybe pupae in leaf litter, duff, and rotting fruit
- Adult flies live for up to 2 weeks
- Females can lay 300 eggs
- Can develop from egg to adult in as little as 8 days
- Likely to have over 10 generations per growing season
Damage:
- Females lay eggs in fruit
- Larvae eat flesh, which renders it unmarketable or causes customer discontent (infested fruit ‘melts down’ in 2 days)
- Egg laying introduces fungal pathogens, which rot fruit
Significance:
- Unlike other fruit flies, SWD attacks sound ripening fruit
- Once eggs laid in fruit, no longer able to control with pesticides
- Short lifecycle and overlapping generations make spray timing difficult
- Requires sprays near harvest time
- Requires multiple sprays which can lead to pesticide resistance
Management:
Monitoring
- Use traps to establish presence and abundance of SWD
- Set traps out prior to fruit ripening to establish onset of infestation
- Check traps frequently (at least once per week)
- Replaice bait weekly to maintain effectiveness (don't dump old bait on ground; remove from field)
Identification
- Use sticky cards inside traps or sieve contents to and check to confirm presence of SWD (males are easiest to see)
- Use hand lense and ID key to help with ID
- Record date and number of SWD caught to determine trend
Control
Sanitation - keep area free of overripe fruit to reduce habitat for build up; eliminate wild hosts as much as possible
Exclusion - small areas can be covered with fine netting or row covers prior to fruit ripening to keep SWD out
Biological Control - researchers are looking for suitable predators, parasitoids, pathogens and other beneficial organisms that might help suppress SWD populations.
Chemical Control - use of short residual pesticides (organic and conventional) are likely the most effective short term solution for this pest.
Table 1. Insecticides for Blueberries, Strawberries, Caneberries, Grapes and Stone Fruit for Spotted Wing Drosophila
| Active Ingredient | Trade name1 | IRAC code | Blueberry PHI (days) REI | Caneberry PHI (days) REI | Strawberry PHI (days) REI | Grapes PHI (days) REI | Stone Fruit PHI (days) REI | Probable Efficacy | |||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Carbaryl | Sevin | 1A | 7 | 12 hrs | 7 | 12 hrs | 7 | 12 hrs | 7 | 12 hrs | 3 | 12 hrs | Good |
| Diazinon | Diazinon | 1B | 7 | 5 days | 7 | 5 days | 5 | 3 days | Not labeled | Not labeled | 21 | 4 days | Excellent |
| Malathion | Malathion | 1B | 1 | 12 hrs | 1 | 12 hrs | 3 | 12 hrs | 3 | 24-72 hrs | 1 or 3 | 12 hrs | Excellent |
| Methomyl | Lannate | 1A | 3 | 48 hrs | Not labeled | Not labeled | Not labeled | Not labeled | Not labeled | Not labeled | Not labeled | Not labeled | Excellent |
| Phosmet | Imidan | 1B | 3 | 24 hrs | Not labeled | Not labeled | Not labeled | Not labeled | Not labeled | Not labeled | 7 | 3 day | Good |
| Bifenthrin | Brigade | 3 | 1 | 12 hrs | 3 | 12 hrs | 0 | 12 hrs | Not labeled | Not labeled | Not labeled | Not labeled | Excellent |
| Esfenvalerate | Asana | 3A | 14 | 12 hrs | 7 | 12 hrs | Not labeled | Not labeled | Not labeled | Not labeled | 14 | 12 hrs | Excellent |
| Fenpropathrin | Danitol | 3 | 3 | 24 hrs | 3 | 24 hrs | 2 | 24 hrs | 21 | 24 hrs | 3 | 24 hrs | Excellent |
| Pyrethrin | Pyganic* | 3A | 0 | 12 hrs | 0 | 12 hrs | 0 | 12 hrs | 0 | 12 hrs | 0 | 12 hrs | Good |
| Zeta-cypermethrin | Mustang Max | 3 | 1 | 12 hrs | 1 | 12 hrs | Not labeled | Not labeled | 1 | 12 hrs | 14 | 12 hrs | Excellent |
| Imidacloprid & cyfluthrin | Leverage 360 & 2.7 | 4A, 3 | Not labeled | Not labeled | Not labeled | Not labeled | Not labeled | Not labeled | 3 | 12 hrs | 7 | 12 hrs | Excellent |
| Actamiprid | Assail | 4A | 1 | 12 hrs | 1 | 12 hrs | 1 | 12 hrs | 7 | 12 hrs | 7 | 12 hrs | Fair |
| Imidacloprid | Provado†† | 4A | 3 | 12 hrs | 3 | 12 hrs | 7 | 12 hrs | 0 | 12 hrs | 0-7 | 12 hrs | Fair |
| Thiamethoxam | Actara | 4A | 3 | 12 | |||||||||
| Spinetoram | Delegate | 5 | 3 | 4 hrs | 1 | 4 hrs | Not labeled | Not labeled | 7 | 4 hrs | 7 | 4 hrs | Excellent |
| Spinetoram | Radiant | 5 | Not labeled | Not labeled | Not labeled | Not labeled | 1 | 4 hrs | Not labeled | Not labeled | Not labeled | Not labeled | Excellent |
| Spinosad | Entrust*,†† | 5 | 3 | 4 hrs | 1 | 4 hrs | 1 | 4 hrs | 7 | 4 hrs | 1 - 14 | 4 hrs | Good/Exc |
| Pyriproxyfen | Esteem | 7 | 7 | 12 hrs | Not labeled | Not labeled | 2 | 12 hrs | 21 | 12 hrs | 14 | 12 hrs | Fair/Good |
*OMRI listed
†† Stone Fruit: there are different PHI depending on specific stone fruit crop, check label before using
PHI= pre-harvest interval; time between last application and harvest
REI= re-entry interval; time between application and when workers may re-enter the field
Probable ratings based on lab and field assays in western USA and Michigan
Chart courtesy of Mary Conklin, UConn Extension
However:
- Requires a short pre-harvest interval (PHI)
- Requires > 5 day residual activity
- Requires rotation among mode of action (MoA) to avoid developing resistance
