Mason: Identification of Pest Population of Lygus Species and Their Parasites in Canola

Date: May 2001
Term: 3 years
Status: Completed
Researcher(s): Peter Mason and R.G. Footit, Agriculture and Agri-Food Canada, Eastern Cereal and Oilseed Research Centre, Ottawa and M.A. Erlandson, L. Braun, D. Hegedus, J. J. Soroka, Agriculture and Agri-Food Canada, Saskatoon Research Centre
SaskCanola Investment: n/a
Total Project Cost: n/a
Funding Partners: AAFC Matching Investment Initiative

Project Summary

In the mid 1990s, Lygus bugs were becoming an increasingly important pest in canola. Researchers from Agriculture and Agriculture Canada in Ottawa and Saskatoon launched a three-year project in 1998 to develop a routine assay and diagnostic key to identify populations of Lygus in western Canada and immature stages of Peristenus species, a potential biological control. They also wanted to develop unique molecular markers for Peristenus species. The information generated and the techniques developed from the research provided the basis for developing integrated management for specific populations of Lygus infesting canola and the introduction of biological control agents to provide cost saving natural control.

In the mid 1990s, Lygus bugs were becoming an increasingly important pest in canola, potentially reducing seed yields by as much as 20%. In 1996, approximately 25,000 acres of canola were sprayed in the Vulcan area of Alberta. In 1997, very high numbers of Lygus nymphs were reported from a larger area in southern Alberta but also in the Meadow Lake and Spiritwood areas of Saskatchewan. Although damage was extensive, chemical spraying was not recommended because of the significant negative impact of insecticides on beneficial species, particularly insect pollinators essential for facilitating maximum canola yields. Alternative control strategies, such as the potential for biological control agents like wasps in the Peristenus genus, were being studied.

Researchers from Agriculture and Agriculture Canada in Ottawa and Saskatoon launched a three-year project in 1998 to develop a routine assay and diagnostic key to identify populations of Lygus in western Canada and immature stages of Peristenus species. They also wanted to develop unique molecular markers for species of Peristenus parasites attacking Lygus species.

In 1998 and 1999, season-long sampling of Lygus spp. in canola, mustard and alfalfa fields was conducted at two Saskatchewan locations, Vonda and Saskatoon, to determine the nature of the recent Lygus spp. infestation in canola. The dominant species present in canola were L. lineolaris followed by L. borealis. Overwintered adult Lygus spp. migrated to budding canola where females laid eggs and produced a single generation.

Parasitism of Lygus spp. nymphs was negligible (<1%) in canola and mustard fields because the parasitoid species (Peristenus pallipes) that attacks young Lygus nymphs has a single yearly generation and occurs early in the season, before eggs are laid in canola. However, in alfalfa, young L. borealis nymphs were present early in the season and parasitism ranged up to 70%. Introduction of a parasitoid species that has two yearly generations or that occurs when Lygus nymphs are present in canola could reduce pest populations.

Figure 1. Fifth instar nymph (left) and adult (right). Photo courtesy of Agriculture and Agri-Food Canada.In 1999 and 2000, researchers worked on developing a one-step PCR diagnostic technique based on species-specific primers to distinguish nymphs of L. borealis and L. lineolaris. Lygus spp. collections from western and eastern Canada were used in the research. The technology developed can be used by any diagnostic laboratory versed in simple PCR techniques and provides an unambiguous test to distinguish the two species. The flexibility of the technique and the DNA sequence analysis of additional Lygus spp. indicated that the technique could be used to developed primers for other Lygus spp. commonly found in western Canada.

Using a similar approach, researchers also developed a technique to distinguish three species of Peristenus parasitoids associated with Lygus populations in North America. The success of the PCR technique made it possible to efficiently determine the species make up of field populations of Lygus and the parasitism rates by Peristenus.

Overall, the research results showed that L. lineolaris was the major pest species in canola. It also showed that there were important seasonal and genetic differences between Lygus species and populations of a species, and there was a lack of natural enemy pressure to control Lygus in canola.

From the research, molecular techniques were developed to: differentiate species and populations within a species of Lygus, determine whether Lygus nymphs were parasitized, and differentiate species of the parasitoid. The information generated and the techniques developed provided the basis for developing integrated management that targets specific populations of Lygus infesting canola and the introduction of biological control agents to provide cost saving natural control.

Scientific Publications

Braun, L., D. Baldwin, M.A. Erlandson, R.G. Foottit, P.G. Mason, J.J. Soroka, and D. Hegedus. 2001. Seasonal occurrence, species composition, and parasitism of Lygus spp. (Heteroptera: Miridae) in canola and alfalfa in Saskatchewan. The Canadian Entomologist 133: 565-577.

Erlandson, M., L. Braun, D. Baldwin, J. Soroka, M. Ashfaq, and D. Hegedus. 2003. Molecular markers for Peristenus spp. (Hymenoptera: Braconidae) parasitoids associated with Lygus spp. (Hemiptera: Miridae).8The Canadian Entomologist 135: 71 – 83.

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