Teagasc entomologist, Dr. Louise McNamara, has confirmed that all of the insecticides now available contain the same pyrethroid chemistries. This, in turn, raises the issue of resistance.

Dr. McNamara provided an extensive overview of the yield threat posed by Barley Yellow Dwarf Virus (BYDV) aphids to late sown barley crops, on the most recent episode of the Tillage Edge podcast.

“All the current insecticide brands, essentially, contain the same chemistries with the same mode of action.

“So, if growers keep putting out the same chemistry, the risk of creating resistance within aphid populations continues to increase.”

The Teagasc research scientist went on to confirm that resistance may already be an issue.


Previous Teagasc survey work had looked at the issue of resistance linked to neonicotinoid chemistries. However, their use was banned back in 2018.

Now Teagasc is looking at the impact of pyrethroid chemistries on grain aphids, from a resistance perspective.

“The percentage of resistance will be very variable, depending on the year,” McNamara explained.

“Previously, insecticide level resistance of 35% had been identified within aphid populations. But in other years, this figure had dropped to just 2%.

“We are pushing ahead with surveys in 2023 to try and draw conclusions from the results we are achieving. But this is not a straightforward matter.”

According to McNamara, it will take time to work through the loss of neonicotinoid chemistries and the subsequent impact on the insecticides that are available.

Aphid control

She went on to confirm that the aphid control achieved from pyrethroid chemistries remains good.

So can a farmer identify the presence of an insecticide resistance-related problem in his fields?

“Growers should go out and inspect their crops within a week of an insecticide being applied,” McNamara explained.

“If they find aphids that all look the same at that stage, then resistance may well be an issue.

“In addition, if un-winged aphids are identified in the crop, this means that the insects survived the treatment.

“The appearance of winged aphids would indicate that the insects in question might well have flown-in from another location since the application of the insecticide.”

According to Dr. McNamara, the treatment will probably last for a week. It depends on UV light breaking the chemistry down.

“But, if after spraying, the farmer sees un-winged aphids of the same colour and type, these may well be insects that have survived the treatment,” she concluded.