Following the recent introduction of the invasive fruit fly, Spotted wing drosophila (SWD), Drosophila suzukii, growers of several crops including caneberries, blueberries and cherries have been battling to keep this insect under control. When this pest invades fruit, the female lays eggs in ripening fruit by sawing through the soft flesh using a modified ovipositor, and then deposits her eggs. After the larvae hatch, they feed on the fruit, which rapidly softens and then decays.
It appears that SWD larvae can also survive in fruit that has fallen to the ground. This can be a particular problem for growers who often do not remove fallen fruit from the ground, and then properly dispose of it. While they continue to spray for SWD on their bushes, the berries on the ground remain unaffected, and the larvae are left to develop, and then emerge as adults. One way to reduce the likelihood of having this happen is to remove fallen fruit from the ground and then dispose of it. While this does take time and energy, it can also help to reduce the number of SWD that are present in the field.
Over the past few years we have been conducting research to determine whether or not disposing of fallen fruit is beneficial in reducing the likelihood of a SWD infestation. Fallen fruit was collected in the field, and placed underneath shelters to give the SWD time to infest the fallen fruit, or if larvae were already inside of the fruit, they could develop. Over the course of several weeks this fruit was collected in small batches and taken back to the lab and inspected for larvae. Larvae were collected from some of the fruit samples and allowed to develop to adulthood, because adults are much easier to identify. SWD were found in some of the samples, indicating that they can successfully develop in fallen fruit.
Based on our results, we highly recommend removing fruit that has fallen to the ground, and disposing of it by sealing it into plastic bags, and then throwing it in the trash. While this may seem like a trivial and time consuming task, the benefits can be very worth the effort, particularly if you’re plagued by SWD. If you own a U-pick farm, encourage your customers to help you by picking up fallen berries, you might be surprised by how receptive they are and willing to pitch in a few extra minutes of their time.
Author: Heather Andrews