Biocontrol Could Help Manage Tarnished Plant Bug

The culprit is Lygus lineolaris, which has one of the broadest documented feeding range of any known insect. It feeds on more than 300 plants, almost a third of which are economically important crops in North America. Among this bug's favourite foods are vegetables, tender fruit, forage and some greenhouse crops.

Agriculture and Agri-Food Canada (AAFC) researchers Bruce Broadbent and Jay Whistlecraft (London), and Peter Mason, Bob Foottit and Henri Goulet (Ottawa), and University of Guelph PhD student Simon Lachance hope a classical biological control approach brings Lygus populations under control. Through the Ontario Research Enhancement Program (OREP), they're investigating the introduction of a natural parasite of Lygus called Peristenus as a sustainable way of managing the Tarnished plant bug problem in Ontario crops.

"Tarnished plant bug is one of the top 10 economic pests in North American agriculture," says Broadbent, of AAFC's Southern Crop Protection and Food Research Centre in London. "These bugs suck on the flowers, seeds and fruit of their host plants, causing blemishes and adversely affecting crop yields. Currently, crops with high populations of Lygus are sprayed with chemical insecticides."

Lygus lineolaris is a native species of Canada, but in many European countries other Lygus species have their populations kept in check by a more complex gamut of other insect species, including Peristenus. These Peristenus -- very small parasitic wasps about 2 to 3 mm long -- kill Tarnished plant bugs during their reproductive cycle. A mature female Peristenus wasp deposits her eggs in a young, immature Lygus bug, where her offspring will develop. When the offspring emerge, the Lygus host is wounded and soon dies.

The researchers hope that by bringing Peristenus to Ontario, the Lyguspopulations can be brought under control and maintained at non-damaging levels. They're using a species of Peristenus native to Europe, where it lives in climatic conditions similar to those in Canada. The Commonwealth Agricultural Bureau Bioscience Centre in Switzerland supplied Broadbent's research team with two different species of the Peristenus for their research. These wasps are being bred in quarantine in London, where they are undergoing non-target testing to determine their effects on other insect species native to Ontario. At Guelph, Lachance is studying the synchrony of the spring emergence of Lygus and Peristenus, as well as competition with native parasite species.

For this biological control system to be successful, it's essential the two species emerge at about the same time as the Tarnished plant bug. So far, the researchers have found no evidence of Peristenus displacing any other Ontario insects.

The first populations of Peristenus wasps could be released in the London area as early as this summer with the approval of the Canadian Food Inspection Agency. If the biological control agent is successful, the researchers' sustainable Lygus control system will benefit many Ontario growers and the greenhouse industry.

"This really is a ‘public good' project," says Broadbent. "We don't intend to eradicate Tarnished plant bug, but we plan to bring it under control in a sustainable way that will decrease the use of insecticides in Ontario crops."

OREP is a $4-million federally funded research initiative administered by the Research Branch of AAFC, with input from the agriculture and agri-food sector, universities and the province. OREP supports 25 research projects in universities and research centres across the province, with the University of Guelph as a major participant. Projects focus on two key areas identified by the agriculture and agri-food community: consumer demand for higher quality safe products and ensuring crop production management systems that are environmentally sustainable.