Fungal baits offer hope for spotted-wing Drosophila biological control

An insect-devouring fungus shows promise in the control of spotted-wing Drosophila, a pest of soft fruit, according to Dutch researchers.

Wageningen Plant Research claims that a new isolate of Metarhizium robertsii "reduces reproduction of fruit flies very effectively".

After four weeks in cages with a small dish of a blueberry-fungus mix there was "virtually no reproduction" of the fruit fly Drosophila suzukii compared to a control treatment, researcher Rob van Tol said. Two parallel tested fungal products had less or no effect on reproduction.

Other biological control options for this fruit fly are in research, and while some promising parasitic wasps are found in Japan and China where the fly originates, Van Tol said, but added: "It is unlikely that these non-native natural enemies will get a registration in Europe.

Meanwhile native European parasitic "are so far not effective enough to control the pest", he said, leaving entomopathogenic (insect-lethal) fungi as a possible alternative.

But compared to existing commercial products of this type, "it needs faster working fungal strains and a different application strategy whereby young/virgin flies will be exposed to higher doses of the killing fungus," he said.

Using baits to infect the flies avoids spraying large volumes of spores on the crop, while increasing the dose that the flies are exposed to, he explained.

He added: "The bait with the entomopathogenic fungus has to be very attractive and able to compete with the fruit in the field. But the strategy could work if used in an early stage of the season before ripening of the fruit.

"What kind of bait is attractive enough in the field is still unknown and is part of the follow-up research. In 2017 we plan to move from the cages out to the field."

This research is being carried out in the EU DROPSA project.

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