A ‘super pest’ moth resistant to a class of common plant protection is now also capable of surviving through the UK’s cold winter conditions, according to new research.

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Diamondback moth (DBM) caterpillars feed on crops including cabbage, broccoli, swedes and Brussels sprouts, causing cosmetic damage, which could result in the loss of up to 100 per cent of the crop. Brassicas were worth more than £200m to UK agriculture last year.

The pests, which have developed resistance to the pyrethroid class of plant protection products often have reduced fitness levels so don’t survive through winter. However, experts from Rothamsted Research and AHDB are concerned because this is not the case with this new strain of moth.

Growers are being asked to submit samples of the DBM either when seen through winter, or in spring when numbers start to rise, to aid the continued monitoring and development of control strategies to manage the pest.

Dr Dawn Teverson, Knowledge Exchange Manager at AHDB, said: “This new research reconfirms what we found last year. It’s important that Brassica growers are aware of this pyrethroid resistance and plan their crop protection programmes to treat against diamondback moths, accordingly.

“If pyrethroids are used, not only does this now fail to control DBM but it could also kill beneficial insect predators which would naturally help control the pest, further exacerbating the problem.”

Pyrethroid resistant DBM have been found overwintering on swede crops grown under insect netting.

Dr Steve Foster, research entomologist at Rothamsted Research, said: “We have seen in aphids that those which have developed resistance may not survive the winter, however this doesn’t seem to be the case with this new strain of DMB.

“The identification of pyrethroid resistance in this season’s population of moths suggests that they are descendants of 2016’s migrating diamondbacks and therefore that the resistance hasn’t stopped them from surviving over winter.”

Andrew Rutherford, farm and agronomy manager at K. S. Coles, said: “This study has been extremely helpful to growers, allowing them to increase their understanding of the pests they are trying to control and which actives will be effective.”

The diamondback moth is often described as a 'super-pest' because it has a rapid lifecycle, providing more opportunities for resistance to develop through gene mutation.  In 2016, Steve Foster at Rothamsted Research tested three diamondback moth samples for resistance from Lincolnshire, Suffolk and Scotland. All three samples were resistant to pyrethroids.

AHDB’s co-funded project ‘FV 344a Monitoring and Managing Insecticide Resistance in UK Pests’ is currently due to end in March 2018. For further information about diamondback moth and control options, visit horticulture.ahdb.org.uk/diamondback-moth or contact dawn.teverson@ahdb.org.uk for more details.