Foottit: Assessing Genetic Diversity of Lygus Pest Species in Crop and Non-Crop Habitats

Date: September 2004
Term: n/a
Status: Completed
Researcher(s): Dr. Robert Foottit and Dr. P. Mason, Agriculture and Agri-Food Canada (AAFC), Ottawa; Dr. L. Braun, AAFC, Saskatoon and Dr. H. Carcamo, AAFC, Lethbridge
SaskCanola Investment: n/a
Total Project Cost: n/a
Funding Partners: n/a

Project Summary

Several Lygus species are an important pest of many crops in Canada, particularly of canola and seed alfalfa, including the principal species Lygus lineolaris or Tarnished Plant Bug. The overall objective of this project was to determine the genetic structure of Lygus species populations in western Canada using an array of molecular markers, and to determine the overall geographic differences and any crop and non-crop differences in genetic diversity of each species. Analysis of genotypic patterns within L. lineolaris based on extensive geographic and host plant based sampling, uncovered the presence of 2 major genotypes. The presence of major genotypic differences among populations of Lygus lineolaris has implications for the future management of this pest.

Lygus species are an important pest of many crops in North America, particularly of canola and seed alfalfa. The principal pest species across Canada is Lygus lineolaris or Tarnished Plant Bug. In addition, in western Canada, another species L. borealis is important on canola and L. keltoni is becoming more significant in Alberta and Saskatchewan.

Recently, this genus has been the subject of biological control work using species of braconid (Peristenus) parasites. However, for biological control to be most effective, it requires detailed knowledge of demography and genetic composition of populations and species. The population structure of L. lineolaris across its range is presently unknown. Therefore, successful implementation of biological control programs for L. lineolaris needed estimates of the extent of genetic divergence within and between populations.

The overall project objective was to determine the genetic structure of Lygus spp. (L. elisus, L. keltoni, and L. lineolaris) populations in western Canada using an array of molecular markers (microsatellite flanking regions). The specific objectives were to determine the overall genetic diversity of each species, and to determine geographic (regional) differences, and any crop and non-crop differences in genetic diversity of each species. This project incorporated the results into a set of recommendations for integrated pest management of targeted Lygus populations.

Samples of Lygus lineolaris were collected throughout southern Ontario and in the Gatineau and Pontiac regions of Quebec in 1999, 2000, 2001 and 2003. Collections of L. lineolaris and other Lygus species (primarily L. keltoni and L. borealis) were taken at 142 localities in Alberta, Saskatchewan and Manitoba in 2002 and 2003. A total of 50 collections were made in 1999 from continental transects (Pennsylvania to Colorado and northern Ontario to British Columbia) of L. lineolaris, and 80 samples of L. lineolaris and several samples of L. keltoni and L. borealis were taken in 1995 throughout the agricultural areas of the Prairie Provinces.

Analysis of genotypic patterns within L. lineolaris based on extensive geographic and host plant based sampling, uncovered the presence of 2 major genotypes. These genotypes often occupied the same or overlapping geographic areas without interbreeding. L. borealis was found to be more genetically similar to the L. lineolaris group than the remaining species.

Overall, the number of samples of species other than Lygus lineolaris was limited, and therefore the analysis of geographic and host-related patterns were restricted to this species. In general, prairie populations were more uniform than those in Ontario and western Quebec. Collections from non-crop areas in close proximity to cultivated fields in parts of Ontario and Quebec showed a greater degree of variation within and between samples than is typical for this species. Therefore future collection in other non- agricultural areas is required to determine if genetic diversity in these areas is greater than in agricultural areas in general. Populations in agriculture areas may represent a subset of the total genetic diversity found in this species.

The presence of major genotypic differences among populations of Lygus lineolaris has implications for the future management of this pest. The current situation as revealed by the DNA sequence analysis may reflect a dynamic on-going process of selection and adaptation to changing agricultural practices and environmental modification.

Full Report PDF: Assessing Genetic Diversity of Lygus Pest Species in Crop and Non-Crop Habitats