Scientists at Rothamsted Research Institute in Hertfordshire have identified a growing threat from the grain aphid (Sitobion avenae), a major crop pest that can reduce farmers' yields by damaging cereal crops and spreading plant diseases, most notably the Barley yellow dwarf virus (BYDV).

The researchers have warned, following a study of the pest, that the aphid could become an increasing problem from this autumn. Following new research, part funded by Defra, Rothamsted researchers said the grain aphids are becoming more resistant to the popular pyrethroid insecticides.

Pyrethroids account for a quarter of insecticide-based control agents used worldwide and the reason for this increased resistance may be due to the number of grain aphids carrying the knock-down resistance (kdr) mechanism which has increased in frequency this year.

Whilst there is a suggestion that these problems could affect UK farmers as early as this autumn, research leader Dr Steve Foster of Rothamsted Research, said “Our research does give us cause for concern but we should not panic just yet because BYDV is also transmitted by the bird cherry-oat aphid which is a more important vector and there's no sign of kdr in this aphid yet.”

Nevertheless, growing resistance to chemicals is causing widespread concern around the world, particularly in the United States, where research has shown resistance to herbicides in weeds, thought to have been accelerated by the widespread cultivation of herbicide-tolerant genetically modified crops, has led to an increase in the use of damaging agrochemicals. Last month, the country’s Environmental Protection Agency also revealed the extent of resistance in root worms to GM maize engineered to exude a toxin intended to kill off root worms.

Commenting on the situation in the UK, Rothamsted’s Dr Foster added, “When grain aphids are the main pest present then growers need to be aware that pyrethroid sprays may not be effective. If growers apply timely applications at the full dose rate and suspect that control has been poor then they should not spray again with a pyrethroid-based product but switch to an insecticide with an alternative mode of action.”

Two new publications have been released by HGCA and IRAG which will assist with management of grain aphids this autumn, including best practice measures to limit the risk of resistance and strategies that could be deployed if resistance is suspected during the autumn spraying period.

The new publications, which can be downloaded from HGCA here, are:

• A new HGCA publication (Information Sheet 16) contains the latest information on aphid management in both cereals and oilseed rape.
• A new IRAG publication provides specific advice on the control of grain aphid populations that may contain individuals with resistance to pyrethroid sprays.

Professor Lin Field, Head of the Biological Chemistry and Crop Protection Department at Rothamsted Research stressed that, given the evidence of emerging resistance, “We should not take our eye off the ball, the threat of pyrethroid resistance is very real and we need to continue researching to establish how potent this resistance is and whether pyrethroids will work in the future."

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