|Dr. David Gillespie with some of the parasitoid cages.
Entomologist David Gillespie of the Pacific Agriculture Research Centre in Agassiz, British Columbia, has spent the past three years looking for and evaluating new parasitoids to attack green peach aphids and foxglove aphids. He updated greenhouse growers on his findings during a research day at PARC.
“There is a lot of stuff which looks interesting,” he said. After collecting and initially analyzing over a dozen different parasitoids, he has focused his attention on praon gallicum and praon humulaphidis, aphidus ervi and aphelinus asychis.
While the brown lacewing Micromerus variegatus also looks extremely promising, he has not worked on it. Instead, that research is being done by Applied Bionomics, British Columbia’s primary supplier of biocontrols for the greenhouse industry.
To test the effectiveness of each parasitoid, a number of them are placed in a cage with one or more plants and a select number of aphids. “We then watch what happens,” Gillespie stated.
DETERMINING OPTIMAL RATIO OF PARASITOIDS TO APHIDS
The number of aphids and parasitoids are regularly counted so he can determine which parasitoids perform best, and what would be the optimum ratio of parasitoids to aphids.
Recent trials showed similar results from all four parasitoids at a ratio of one adult parasitoid to five aphids. While the number of aphids in a control cage (with no parasitoids) reached 1,400 within three weeks, all four parasitoids managed to keep aphid numbers to less than 200 over the same period. The best result came from the praon humulaphidis, which kept its aphid population down to 100. “It performs best over the long term,” Gillespie said.
When confronted by parasitoids, the aphids’ survival instincts kick in. They become very active and attempt to run away from the predators or jump off the plant leaves to escape. Given that behaviour, Gillespie has tried adding sticky tape to capture the aphids dropping off the plants. The attempt appears to have worked.
POSSIBLE COMMERCIALIZATION OF PRAON HUMULAPHIDIS
“Aphid numbers plummeted by the end of the first week,” he said, but noted there were lots of variation between cages and the number of parasitoids also dropped dramatically.
“We’re not at the stage of recommending sticky tape,” he told growers. While it might help over the short term, the long-term impact is yet unknown and Gillespie does not intend to pursue it.
He is, however, pursuing commercialization of praon humulaphidis as an aphid predator. “Our next stage is to get an insectory involved.”
David Schmidt is a freelance writer and photographer in British Columbia.