Saskatchewan researchers find that at low dosages, sulfoxaflor is less toxic than the currently used neonic imidacloprid
A locust sits front row and centre inside a huge dome in its very own 3D IMAX-like theatre.
The frosted “curtain” rises, lights dim and the finger-sized insect watches as computer generated images are projected on the private viewing screen — minus the sound and popcorn.
Expanding black discs flash across the screen, which from the locust’s perspective look like a black curve ball coming right at it.
Just like a baseball batter waiting to swing, it stimulates a reaction to move away from the black object being thrown at its head.
The production is all part of a novel technique being used by researchers at the University of Saskatchewan to measure the locust’s escape behaviour while under the influence of a new sulfoxamine pesticide being tested called sulfoxaflor.
The goal is to compare the effects of sub-lethal doses of two families of pesticides (neonicotinoids and sulfoxamines) used in agriculture to observe the effects of insect behaviour and insect neurobiology.
For several years Jack Gray, a biology professor and expert in neural control of animal behaviour, as well as Rachel Parkinson, a former U of S PhD student, have been studying how neonicotinoids alter the vision and motion detection of migratory locusts.
It’s the same species of locust that is wreaking havoc in East Africa, potentially endangering economies in a region heavily dependent on agriculture for food security.
Neonics are widely used in crop production as a seed treatment, but they are also controversial, particularly when it comes to their possible effect on birds and insects.
The controversy has motivated researchers to look for alternatives.
In their most recent study, Gray and Parkinson have found that at low dosages, sulfoxaflor is less toxic than the currently used neonic imidacloprid, which at non-lethal doses on insects and other species needed to be investigated further.
The results of their latest study were recently published in the Proceedings of the National Academy of Science.
“What we’ve found suggests that this sulfoxamine is less toxic, which could have less of an impact on a non-target insect potentially — meaning one that’s not an economic pest,” said Gray.
In an effort to compare nervous system activities, researchers embed electrodes into the thorax of the locust and then feed it a small amount of pesticide.
They found that the two pesticides are equally fatal at the same dose.
The pesticides have similar lethal dose (LD) 50 values, which is the amount that kills 50 percent of animals.
“It’s a measure that you can compare different chemicals and it gives you an idea of one might be more toxic than another,” Gray said.
“So if you have a lower LD 50, it means it’s more toxic because it takes less of it to kill 50 percent of the test subjects that you have.”
However, it appears that sulfoximine at lower doses is considerably less toxic than the neonicotinoid pesticide.
“As you increase the concentration, you get more and more animals dying until you kill off 50 percent of your population,” he said.
“With the sulfoxamine at the low doses, they’re all surviving, then suddenly half of them die. So it’s like at the low dose, there’s much less toxicity. It’s not having an effect on them.”
The scientists also compared the two chemicals to observe the locust’s escape behaviour inside the dome theatre, which in this case is a jumping action.
“What we’ve found is that with the neonicotinoid, consistent with our previous work, is that at low doses, even though it was not killing the animals, it was severely impairing their ability to jump away from something,” he said.
“With the sulfoxamine at those same low doses, the animal was responding, the locust was jumping away. At low doses neonicotinoids prevent it from jumping. Sulfoxamines do not. So sulfoxaflor seems to be less toxic, it kills fewer of them and has less of an effect on their behavior through their ability to jump away from an object.”
Gray said parts of the nervous system are similar across many species of insects when it comes to self-preservation.
“In fact, it’s even similar in amphibians, reptiles, mammals and probably us because it seems in an evolutionary sense to be one of the best ways to detect something coming at you,” he said.
And because locusts are a well-studied species, inferences can be made about what could happen in other kinds of species exposed to a non-lethal dose, such as bees.
Gray plans to study bees this summer using similar techniques that he has learned with locusts.
However, previous research indicates bees respond differently to moving objects compared to locusts.
They tend to embrace or match a particular movement as a way of reducing that motion on their eyes, which helps them steer their way to find nectar or fly home to their hive.
“That’s a strategy they use when they’re out foraging. They want to keep their flight track straight when they’re navigating and trying to find things,” he said.
“So that’s a behavioral assay that we’re going to use to say, if you are treating the bees with some pesticide … does it impair their ability to track that rotation? If it does, that suggests that it’s severely impairing their ability to navigate.”
