Drosophila update: where next for control research?

Berry growers concerned about the persistent threat of damage from spotted-wing drosophila can take heart from new research initiatives at home and abroad aimed at controlling the pest.

Drosophila: initial project found integrated approach, novel methods and crop hygiene are key to future control - image: © EMR
Drosophila: initial project found integrated approach, novel methods and crop hygiene are key to future control - image: © EMR

AHDB Horticulture has announced a new four-year research programme to develop an integrated control strategy led by Dr Michelle Fountain, deputy head of pest and pathogen ecology at Kent research station NIAB EMR. This follows an initial AHDB research project that concluded no single method of control of drosophila (SWD, Drosophila suzukii) is adequate and that future control will depend on an integrated approach using biological and novel methods combined with high levels of crop hygiene.

"Further research is therefore essential to develop integrated control strategies and the new research programme will continue the national monitoring of pest populations in England and Scotland, with the aim of increasing the understanding of habitat preferences," according to the levy body.

This will include investigating further use of repellents and attract-and-kill strategies, along with bait sprays for control, use of exclusion netting, and studies to prolong spray intervals to reduce spray applications while maximising their effect, with findings integrated to design an effective year-round strategy.

AHDB crop production systems scientist Dr Rachel McGauley says: "Ultimately the aim is to provide growers with a wide range of control methods, which will ensure the long-term viability of soft- and stone-fruit production in spite of the continuing presence of SWD."

Success in US

Meanwhile, US researchers claim to have more than doubled the efficacy of existing lures for catching and monitoring SWD by fine-tuning relative levels of attractant chemicals within them.

By varying the levels and release rates of the four chemicals — wine and vinegar volatiles acetic acid, ethanol, acetoin and methionol — in the lure, they found that increased amounts of acetic acid, ethanol and acetoin, but not methionol, enhanced its performance. Significantly, increasing acetic acid and acetoin in tandem resulted in higher attraction than increasing either alone, suggesting a synergistic interaction between the two.

Ultimately they found that an optimised formula caught 104% more SWD males and 147% more females than the original commercial formula used in lures from US suppliers Trécé and Scentry. The paper points out that, by contrast, "food-based lures are attractive to numerous non-target insects that complicate sorting of the trap catch and can interfere with the attractiveness of the bait or lure, and effectiveness of the trap for holding captured SWD".

USDA-Agricultural Research Service entomologist Dr Peter Landolt, who co-authored the study, says:

"This is a potential significant improvement in the power of the lure, which should translate to the ability to detect a smaller population density, detect a population earlier in the season or to kill a higher percentage of a population with baits." The research was published last month in the journal Environmental Entomology.

Attract-and-kill system

In Italy, work is under way to measure the efficacy of an attract-and-kill system employing yeast-based trapping lures and compare it to a conventional insecticide-based control strategy, using field trials in a number of cherry orchards and vineyards in South Tyrol.

The three-year EU-funded DROMYTAL project will be conducted by the Laimburg Research -Centre and the Free University of Bolzano. The university’s Dr Sergio Angeli says: "The attractive component will draw the insect to the treated surface, diverting its interest away from the fruits, while the phagostimulant element will facilitate the insecticide ingestion and contact by keeping the insect on the surface."

Earlier studies at Laimburg indicated that different yeast species influence the reproductive potential and egg-laying of SWD females, while yeast volatiles also appear to have an attractive effect. "We would now like to combine these findings and develop a yeast-based lure with a suitable insecticide added, which as a formulation attracts and kills the pest on targeted surfaces without treating the fruit," explains project head Silvia Schmidt. "The advantages of this strategy lie in a reduced residue load and a greater environmental friendliness of the treatments, as less insecticide per hectare is used more effectively."

Quest for better control

Marion Regan, managing director at soft-fruit grower Hugh Lowe Farms and former AHDB soft-fruit panel chair:

"SWD remains the most serious threat to the soft- and stone-fruit industry that we have encountered in my lifetime.

"A concerted industry effort has gone into research since the pest was identified in 2012 and we have learned a great deal about the pest’s behaviour in the UK and the best control options currently available.

"It is essential, however, that AHDB continues to use grower levy money to extend our quest to develop new and improved control techniques."

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