- Author: Mark Bolda
There has been significant discussion as of late as how to best trap for spotted wing drosophila, Drosophila suzukii. As a very small and mobile insect, detection and estimates of population can be challenging.
Although spotted wing drosophila lays eggs in yet unripe fruit, it is attracted to fermenting fruit to feed and thus this can be a useful medium for trapping. Additionally, there are several commercial formulations of fly trapping solutions.
This past week, the following materials were tested as a comparison for spotted wing drosophila detection and enumeration:
1. Strawberry puree, two days old.
2. Plantain + beer, two days old.
3. One part molasses mixed with 4 parts water.
4. Filth fly trap mix (AgBio Inc.)
5. Methyl eugenol plug over soapy water to trap flies
6. Apple vinegar straight
7. One part GF120 Fruit Fly Bait mixed with 4 parts water
8. Sweep netting one side of 32 feet of raspberry hedgerow, canes tapped with stick to dislodge flies. After sweeping is complete, net is inverted into a solution of soapy water and flies counted.
Most materials were tested twice in a heavily spotted wing drosophila infested raspberry field. 100 ml of the first seven treatments were placed in a 500 ml Nalgene bottle with four 7/16 inch holes drilled into the lid and hung about 3 feet from the ground, well into the hedgerow (see photo below). Food containers such as Mason jars and so on should not be used. Bottles were placed in the morning of day 1, and collected for evaluation the following morning.
In summary, the methyl eugenol and the molasses mix were useless and captured no flies in two tries.
Plantain + beer, apple vinegar and the filth fly mix, while capturing flies, caught fewer in comparison to the best treatments. On average they captured 3 flies in 24 hours in a heavily infested field. The beer and plantain mix is time consuming to make, is not worth the effort and have better use elsewhere, in my opinion. The apple vinegar and filth fly mix are easier to use.
GF120 and the strawberry puree were consistently the most effective of the baits, capturing on average 9 flies in 24 hours in a heavily infested field. The strawberry puree was more effective the second time around, since it had been around a little longer and was more fermented. Flies do not drown in the puree, thus the trap must be handled carefully prior to counting.
Finally, the sweep netting was far more effective in evaluating numbers of flies in the field. On average, 40 flies were captured over the 36 feet of hedgerow in a matter of minutes in a heavily infested field.
In conclusion, while the baits will continue to be effective as sentinels to detect initial infestations of spotted wing drosophila, it appears that they will be clearly inferior to sweep netting when making evaluations of already established populations in caneberries.