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Spotted Wing Drosophila (SWD) – a 2024 Update for PA

Berry crops are running ahead of schedule this year, and so is their nemesis, spotted wing drosophila.

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Updated:

July 17, 2024

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Spotted wing drosophila male on underside of red raspberry

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For the first time, late season June-bearing strawberries were significantly affected on several farms, as were black raspberries, which usually can ripen before SWD numbers increase. None of this bodes well for later-season berry crops like blackberries, blueberries, or day-neutral strawberries.

On the bright side, while monitoring for establishment of Ganaspis brasiliensis - an introduced parasitoid wasp of SWD being released in the mid-Atlantic region including in Centre and Adams counties in PA - it was found that a second non-native SWD parasitoid species has been establishing itself here on its own. This second species, Leptopilina japonica, can attack other fruit fly species beside SWD, so it was not a good candidate for intentional releases.

So what exactly is a parasitoid? A parasitoid is like a parasite, but instead of living along with its host, it kills it. With both Ganaspis brasiliensis and Leptopilina japonica, the adult wasp finds an SWD larvae in the fruit, and lays an egg in it. The larvae continues to grow, develop, and pupate, but instead of an adult SWD developing and hatching out (Figure 1), a wasp does (Figure 2). The wasps can then go on to attack more SWD, hopefully slowing SWD’s population growth. Each wasp is likely to parasitize around 100 SWD larvae. If the wasps can slow the rate at which the SWD population rises, the first sprays for SWD may not be needed quite as early in the season as usual, and hopefully with time, will need to be sprayed less frequently. We were happy to find parasitoid wasps this spring as we found the first SWD emerging from their overwintering sites, so it appeared that the parasitoids were ready to take on the challenge.

Figure 1. Spotted wing drosophila adult nearly ready to hatch from its pupal case. Its red eyes, wings, and legs can be seen. Photo: K. Demchak, Penn State.

Figure 2. Parasitoid wasp developing inside of an SWD pupal case (top view). Black head, wasp body shape, and wings can be seen. Photo: K. Demchak, Penn State.

Sprays for SWD will still be needed, along with every cultural control possible. These include picking fruit cleanly and frequently, removing cull fruit and bagging it (feeding it to chickens works, too!), and using landscape fabric in raspberry plantings to help with keeping cull fruit cleaned up and SWD larvae from reaching the soil to pupate. Refrigerating fruit, and keeping plantings weeded and pruned so sprays can get into the canopy where SWD prefers to hide out also help.

Below is a table with insecticide ratings provided by entomologists, growers and crop consultants with experience with spotted wing drosophila from across the country and compiled by Phillip Fanning (Univ. of Maine) and Rufus Isaacs (Michigan State Univ). Only insecticides that got a rating of “excellent” or “good” and that have a 3-day or less PHI for highbush blueberries and brambles are included. If the pre-harvest interval listed is a range, that is because it varies with the product, use rate, or another factor. If the information below does not match what is on your product label, use what is on the product label instead, as the label is the law.

Also please note that spotted wing drosophila does not appear on the labels of all products listed. In PA, a pesticide can be used for a pest not on the label if the timing, rate, site of application, and any other specifications match those on the label. If you are from outside of PA, consult the label and your state’s registrations for products legal to use in your state.

(R) following the pesticide name indicates that the material is a restricted-use pesticide.

Rating*	Product Name	Active Ingredients(s)	IRAC code (chem. class)	Pre-harvest interval: Strawberry	Pre-harvest interval: Brambles	Pre-harvest interval: Blueberries	Pre-harvest interval: Ribes	Re-entry interval (h=hours; d=days)
E	Lannate (R)	methomyl	1A	---	---	3d	---	48h
E	Mustang Maxx (R)	zeta-cypermethrin	3A	---	1d	1d	1d	12h
E	Danitol (R)	fenpropathrin	3A	2d or 3d (see label)	3d	3d (highbush); 2d or 3d (lowbush)	21d currants; 3d gooseberry	24h
E	Imidan	phosmet	1B	---	---	3d	---	24h highbush; 3d lowbush
E-G	Verdepryn	cyclaniliprole	28	1d	1d	1d	1d	4h
E-G	Bifenture EC (R)	bifenthrin	3A	---	3d	1d	1d	12h
E-G	Brigade (R)	bifenthrin	3A	0d	3d	1d	1d	12h
E-G	Exirel	cyantranili-prole	28	1d	1d	3d	3d	12h
E-G	Malathion	malathion	1B	3d	1d	1d or 2d	1d currants; 3d gooseberry	12h
E-G	Delegate	spinetoram	5	---	1d	1d or 3d	1d or 3d	4h
E-G	Radiant**	spinetoram	5	1d	---	---	---	4h
E-G	Hero (R)	zeta-cypermethrin + bifenthrin	3A + 3A	---	3d	1d	---	12h
G	Entrust	spinosad	5	1d	1d	3d	3d	4h

*E = excellent, G = good
Pre-harvest intervals: d=days; h=hours; --- =not labeled for use on this crop. See individual product labels for details.

Support of the Pennsylvania Department of Agriculture is gratefully acknowledged, as well as that provided by the USDA National Institute of Food and Agriculture and Hatch Appropriations under Project #PEN04743. Many thanks to Xingeng Wang and Kim Hoelmer (now retired) at the USDA’s Beneficial Insects Introduction Research Unit in Newark, DE; Kent Daane at the Univ. of California; Kelly Hamby and her lab at the Univ. of Maryland; Tara Gariepy at Ag Canada; and Rowan Saroka, a Penn State student, all of whom played integral roles in making releases and data collection in PA possible.