Immigrant insects

Alternatives Journal, Jan-Feb, 2009 by Samantha Magnus

IN THE DITCH next to a canola field in Switzerland, I'm squatting over a plastic tray of picked-over seed pods. My colleague Mike arrives with a sweep net brimming with angry bugs. At my nod, he empties it into the tray.

[ILLUSTRATION OMITTED]

Insect life explodes in our faces. Indignant bees escape in a flurry. Grasshoppers leap onto our shoulders and into our hair before taking off. We gently sort through the thrashing mass of ladybirds, caterpillars, aphids and other arthropods left behind. Using aspirators, Mike and I suck our target bugs into collection vials to take to the lab.

We are seeking females of two parasitoid wasp species: Mesopolohus morys and Trichomalus perfectus. Unlike their prey, these liny bronze and emerald bee-like creatures are uniquely European citizens.

The cabbage seedpod weevil (Ceulorhynchus obstrctus) is native to Europe, but invasive to North America, where it menaces canola crops. As the weevil's main parasitoids, "Mesos" or "Trichs" may meet stringent requirements for immigration into Canada.

Bringing a predator from a pest's homeland to battle it in its newly invaded habitat (this weevil appeared in Albertan canola in 1995) is called classical biological control. Agriculture and Agri-Food Canada believes that it can be a cost-effective and environmentally friendly strategy for fighting pests.

Importing "beneficial" bugs is an idea that makes many environmentalists squirm, since they know that well-intentioned introductions can turn catastrophic. The major risk is that the new species doesn't stick to the prey it was supposed to control and instead proliferates on a diet of non-target native species, or outcompetes other predators.

Infamous examples of classical biological control gone bad include mongoose that were introduced to control snakes in Hawaii and cane toads that were used to battle beetles in Australia.

Insect introductions can go afoul too. The Asian ladybird (Harmonia axyndis) does a great job controlling aphids in North American orchards, but also outcompetes native ladybirds. The introduced thistle-loving weevil (Rhinocyllus amicus) snacks away on rare, native North American prickles as well as the invasive species it was intended to control.

Because of cases like these, the Canadian Pood Inspection Agency now rigorously evaluates candidate control agents, scrutinizing mounds of research on any potential "immigrant" with a vigour that would impress a US border guard.

Today, both lab and field tests are prerequisites, and prey infidelity would stop an introduction in its tracks. As for the jewel-coloured Mesos and Trichs that we seek, it will be years before they may be judged sufficiently weevil-monogamous to allow us to release them into Canadian crops.

When she isn't aspirating Mesos and Trichs for Agriculture and Agri-Food Canada, Samantha Magnus is an undergraduate student who co-produces the University of Victoria's student radio news program.