Cabbage stem flea beetle close-up
Photo: Martin Cooper: https://www.flickr.com/photos/m-a-r-t-i-n/
By Gary Hartley

Biopesticides show promise as weapon against beetle which has hit UK oilseed rape farming

Fatty acids and an insect-killing fungus could be suitable as biopesticides against the cabbage stem flea beetle (Psylliodes chrysocephala), a prolific pest of oilseed rape crops.

In the UK, the area covered with oilseed rape crops has decreased by more than half in the last decade, coinciding with the 2013 moratorium on neonicotinoid insecticides used to control the beetle, which ultimately led to full ban in 2018. Since then, pyrethroid insecticides have been used, but this has led to P. chrysocephala developing resistance to these products, driving an ever-more urgent demand for alternatives.

Lab tests show strong effects

In laboratory tests by Claire Price at Harper Adams University, two fatty acid products, FLiPPER and Neudosan, killed all the beetles used in experiments within 24 hours. The fungus Beauvaria bassiana killed 56% of the beetles within 14 days.

In contrast, formulations of insect-killing bacteria and azadirachtin, a biopesticide derived from the fruit of the neem tree, were less successful, killing less than 50% and 40% of the beetles, respectively.

It is likely the first time fatty acids, which penetrate insect bodies and affect the cell membranes, have been tested against a hard-bodied insect. Previously they have only been applied against soft-bodied pests such as whitefly, aphids and mealybug.

The fatty acid and fungal products could be suitable for use as part of integrated pest management programmes by oilseed rape growers, suggested Price. Such programmes tend to include tactics such as early or late drilling of seeds and using attractive ‘companion crops’ to pull beetles away from the primary crop. Research also suggests that using oilseed rape varieties which are more tolerant of flea beetle damage could be a useful tool, she said.

Field performance remains elusive

Despite the promise of the fatty acids and fungi, initial tests under field conditions by Price have showed that further adjustments are required.

“What I’ve learned is that even if some products worked quite well in the laboratory to kill cabbage stem flea beetle, it’s not always the case under field conditions. At the moment, methods used in the fields need to be improved if we are going to have a chance to actually see these biopesticides used on farms,” she said.

Such improvements are likely to involve using adjuvants to protect living biological agents such as fungi and nematodes, against environmental conditions, as well as changing formulations to improve the spread of biopesticides in the field.

With more studies needed, wide use of biopesticides against the pest is still likely to be a few years away, Price predicted. Then, it is likely to be that they perform a targeted role in control efforts.

“If everything has been tried in terms of cultural control [changing sowing timings and companion planting] and there are still too many beetles, I think the idea would be to then use biopesticides to try to avoid using any synthetic chemical insecticides such as pyrethroids,” she added.

“[Successful control] is going to depend on a lot of factors, and it’s very specific to each farm. So it’s all about trying what’s best for you, and seeing what works.”

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