What was it all about?

The green peach aphid is an endemic pest of oilseeds and vegetables, causing damage both by direct feeding and by transmitting a large number of plant viruses. The insect is known to have developed resistance to more classes of insecticides than any other insect pest.

In 2011, resistance to the carbamate insecticide Pirimicarb was detected in green peach aphid in Australia for the first time. Surveys in 2012-2013 showed this resistance to be widespread across Australia, and that the carbamate resistant aphids were also resistant to synthetic pyrethroids.

This project conducted genetic analyses on Australian and international populations of green peach aphid to determine whether these dual-resistant insects arose locally or whether they arrived in Australia via a recent incursion.

Samples from over 100 populations of green peach aphid were gathered from all states of Australia. In addition, samples were obtained from 19 populations from China as well as 30 populations from five countries in Europe.

Over 2,500 individual aphids from these collections were tested for the presence of seven resistance mechanisms. Of these, five were detected in Australia and the additional two were found only in overseas populations. The major difference between Australian and overseas populations was the absence of resistance to neonicotinoid insecticides in insects found in Australia.

Results showed that green peach aphids resistant to both carbamate and synthetic pyrethroids are now widespread in Australia. These characteristics were also displayed by samples from the UK, Greece, France, and from all but one population in China. Over 75 per cent of the aphids collected in Australia belonged to one of three genetically identical dual-resistant clones, none of which were related genetically to aphid clones previously present in Australia.

One of these clones was an exact genetic match to a sample from Wuhan province in China but not to any populations in Europe, suggesting that this clone, which dominates populations in Queensland, arrived in Australia as an incursion from China.

No exact match of the other two dominant clones was found in the European and Chinese samples, but one was genetically related to a dominant European clone.

The researchers recommended that additional work goes into investigating how these incursions of green peach aphid occurred and how Australia’s biosecurity system could be improved to prevent further incursions.

An incursion of green peach aphid with resistance to neonicotinoids including sulfoxaflor - now prevalent in China and southern Europe - would leave Australian oilseed and vegetable growers with virtually no options remaining for aphid control.

An economic analysis has estimated an increase of at least 10 per cent in production costs of canola and a potential economic impact of $542 million per year.