I had not heard much about the problem in Australia, of insecticide resistance in field-collected populations of bluegreen aphids, Acyrthosiphon kondo, a pest of pulses and other legume crops, until I did my brush up, like a good dairy farmer, on science developments and cosmology at Phys.org, to keep up to step. I was surprised to be updated at this site, usually concerned with details of quantum mechanics and the likes, on this aphid problem. And according to the author of one study, these little biters are getting resistant to insecticides: "Australian growers have traditionally relied upon two types of insecticides (organophosphate and carbamates) to protect their legume crops from A. kondoi. However, in recent years, multiple growers in Southern Australia reported these insecticide sprays were no longer controlling A. kondoi, which indicated this pest may have evolved insecticide resistance for the first time."
Why is this bug a problem? First, the aphids damage crops by feeding on upper leaves, stems, and terminal buds, but second, they spread plant viruses, including cucumber mosaic virus and bean yellow mosaic virus. Combined, this can wipe out entire crops if the infestation is great, and the insecticides don't work.
The researchers thought that there was not yet resistance to the insecticide flupyradifurone, which I have never heard of, nor did Merv the dairy farmer with a legume crop next door, so far, no aphids. But, in the long term it may be time to turn to old school natural methods of aphid control (where are you lady birds?) and pest management strategies. More resistant legumes would also be a help if this can be done without genetic engineering.
"For the first time, researchers in Australia have documented insecticide resistance in field-collected populations of bluegreen aphids, Acyrthosiphon kondoi—a worldwide pest of pulses and other legume crops.
The study, published in Pest Management Science, serves as a warning to growers globally and highlights the need for new strategies to manage this pervasive pest.
Evatt Chirgwin, evolutionary biologist at Cesar Australia and corresponding author of the study, explained that the research was prompted by reports of conventional insecticides failing to control A. kondoi populations.
"Our primary motivation was to help Australian growers understand an emerging pest management challenge," said Chirgwin. "Australian growers have traditionally relied upon two types of insecticides (organophosphate and carbamates) to protect their legume crops from A. kondoi. However, in recent years, multiple growers in Southern Australia reported these insecticide sprays were no longer controlling A. kondoi, which indicated this pest may have evolved insecticide resistance for the first time."
A.kondoi is an agricultural pest in the U.S., South America, Asia, Europe, Africa and Australia. Chirgwin explained that they damage crops by feeding on upper leaves, stems, and terminal buds. "A. kondoi also causes indirect damage by spreading plant viruses, including cucumber mosaic virus and bean yellow mosaic virus," he noted.
The team collected A. kondoi populations from lentil and alfalfa paddocks where insecticide control failures have recently been reported across Victoria, South Australia, and New South Wales. The populations were exposed to different insecticides in bioassays, revealing moderate resistance to three insecticide groups: organophosphates, carbamates, and pyrethroids.
Explaining the impact of resistance at this level to Australian growers, Chirgwin said, "On a practical level, growers cannot rely on organophosphates and carbamates (at the registered rate) to confidently control these newly evolved A. kondoi populations. Still, the low-to-moderate levels (20-40 fold) of resistance shown by A. kondoi in this study is less than some other aphid species (i.e., >100 fold) have been able to evolve to these chemicals."
Chirgwin noted that the discovery of pyrethroid-resistant A. kondoi populations was unexpected—the use of pyrethroids to control A. kondoi in Australia is relatively restricted and therefore the authors did not think the insects would be under enough selection pressure to evolve resistance.
"We now suspect that A. kondoi populations are regularly exposed to pyrethroid-based insecticides because this chemical is widely used in pulse and pasture seed crops to control other pests (e.g. mirids, Helicoverpa, and other aphids) that often occur alongside A. kondoi," he explained.
The researchers found no evidence of resistance to another insecticide—flupyradifurone. This was unsurprising given the chemical was only introduced into the Australian market in 2016 and is not registered against A. kondoi in the country.
The authors conclude that flupyradifurone may, therefore, provide a new chemical option for A. kondoi control in Australia, Chirgwin provided a note of caution and stressed the importance of integrated pest management strategies to restrict the emergence of further cases of insecticide resistance."