Insecticide Resistance Spreads in Australia's Bluegreen Aphid Populations, Study Finds

Insecticide resistance in the bluegreen aphid, a pest that damages alfalfa, medic, clover and pulse crops and spreads plant viruses, is spreading across southern Australia, according to research conducted from 2022 to 2025. The pest can complete a generation in around 10 days under favorable conditions, following the first confirmed case of insecticide resistance in the species in 2021-22.

Researchers collected bluegreen aphid populations from pasture, pasture seed and pulse crops across South Australia, Victoria and southern New South Wales, particularly where insecticide applications had failed to control the pest, and compared them with insecticide-susceptible populations in laboratory tests. The study identified 21 more populations resistant to one or more organophosphate, carbamate or synthetic pyrethroid insecticides, found from the Eyre Peninsula to near Tamworth and across several parts of Victoria.

Resistance was particularly common in alfalfa but was also detected in lentil crops on the Yorke Peninsula and in Victoria's Wimmera and Mallee regions; resistance to organophosphates and synthetic pyrethroids was generally more common and stronger than resistance to pirimicarb. The project also tested three newer active ingredients — flupyradifurone, sulfoxaflor and flonicamid — against resistant and susceptible populations and found no field-evolved resistance or cross-resistance, suggesting they may offer alternative control options.

A separate survey collected 132 parasitoid wasps from 25 locations across South Australia, New South Wales and Victoria, and every one of them was the species Aphidius ervi, which lays its eggs inside aphids that are eventually killed as the wasp develops. The finding suggests natural control of the bluegreen aphid may depend heavily on this single wasp species.

The research recommends a resistance-aware integrated pest management approach: correctly identifying aphids, monitoring pest pressure and beneficial insects, applying insecticides only when justified, and avoiding repeated use of the same insecticide mode of action.