Insect Pest Incidence and Injury to Herbicide-Tolerant Canola in Western Canada H. A. Ca ´ rcamo* and R. E. Blackshaw ABSTRACT Genetically modified herbicide-tolerant (HT) canola (Brassica napus L.) cultivars dominate the acreage planted to this oilseed crop in western Canada. We conducted a 3-yr (2000–2002) field study near Lethbridge, AB, Canada to compare the incidence and damage of three key insect pests in Roundup Ready, Liberty Link (both HT), and Q2 (a conventional cultivar). Flea beetle (Phyllotreta cruciferae and P. striolata [Coleoptera, Chrysomelidae]) damage in 2000 ranged from 31 to 32% of foliage consumption at the cotyledon stage, which surpassed economic thresholds but was not related to cultivar. Cab- bage seedpod weevil (Ceutorhynchus obstrictus Marsham [Coleoptera, Curculionidae]) damage to canola pods ranged from 58 to 70 holes per 100 pods in 2001, and lygus plant bugs (Lygus spp. [Heteroptera, Miridae]) at the early pod stage reached densities of .37 individuals per 10 sweeps in 2000 and 2002. For both insect pests, their damage or abundance was similar among the conventional and HT cultivars. We conclude that, in the short term, the insect pests common in southern Alberta do not exhibit a preference to invade and damage the trans- genic herbicide canola cultivars commonly planted in the prairies. C ANOLA, ALSO KNOWN AS OILSEED RAPE, is among the top cash crops in Canada with over 5 million ha planted every year and an estimated overall contribu- tion of .$6 billion (Canadian dollars) to the national economy (Canola Council of Canada, 2005). More than 100 HT cultivars have been introduced during the last decade, and by 2005 they accounted for 95% of the total canola acreage (Canola Council of Canada, 2005). Transgenic cultivars tolerant to glyphosate (55%) and glufosinate (28%) are dominant. Clearfield varieties (BASF, Mississauga, ON, Canada) (tolerant to imazamox and imazethapyr), bred using traditional methods, ac- counts for 12% of canola production. The convenience of controlling a wide spectrum of weeds with a single postemergence application and increased yields and eco- nomic returns explain the rapid adoption of this tech- nology (Harker et al., 2003). Massive adoption of new technologies in agriculture can affect agroecosystem components including existing or potential pests such as weeds, pathogens, and insects. Broadleaf, grassy, annual, and perennial weeds vary in their susceptibility to glyph- osate and glufosinate; therefore, the diversity of weeds in crops can be affected by the choice of HT canola system (Harker et al., 2000), which in turn may influence com- munities of arthropods (Norris and Kogan, 2000). The steady increase of canola acreage in the Canadian prairies has resulted in a concomitant increase in the incidence of insect pests (Lamb 1989). Plant bugs in the genus Lygus (Lygus elisus , L. keltoni, and L. borealis in southern Alberta) are native polyphagous insects that are chronic pests of seed alfalfa, but occasionally reach pest densities during the early pod stage and cause eco- nomic damage by feeding on the seeds of ripening canola pods (Butts and Lamb, 1990). A serious outbreak of lygus bugs throughout Alberta from 1996 to 1998 required spraying of about half a million hectares of ca- nola. The most serious widespread pests of canola in the prairies are introduced flea beetles that feed on seedlings and can kill them at the cotyledon stage, thus reducing stand density and delaying maturity, which increases the risk of losses to frost in the fall (Lamb, 1984). In southern Alberta and Saskatchewan, cabbage seedpod weevil, another pest of European origin, has been increasing during the past 10 yr to become a se- rious threat to production, occasionally requiring insec- ticide sprays (Ca ´ rcamo et al., 2005). Genetic variability among HT crop cultivars along with the associated chemical weed management system may affect their susceptibility to insect pests, but despite their wide adoption, they have not been assessed with respect to insect abundance and damage. Inherent vari- ability in seedling vigor may influence tolerance to flea beetle damage and/or their ability to rapidly grow past the vulnerable cotyledon stage (Elliott et al., 2005). Other agronomic traits of the cultivars can influence in- sects. For example, cultivars that flower earlier can at- tract more cabbage seedpod weevils and suffer greater damage (Ca ´ rcamo et al., 2007). Indirect effects of HT canola on insects may result from increased incidence of grassy weeds in glufosinate systems that add vege- tation diversity to the agroecosystem. In a study of transgenic and conventional soybeans, Buckelew et al. (2000) found that leaf hoppers (Empoasca fabae Harris) were more abundant in plots with fewer weeds, but the number of tarnished plant bugs (L. lineolaris) was higher in the weedier plots. Changes in weed commu- nities of canola agroecosystems may indirectly increase the abundance of insect pests by providing alternate broadleaf hosts for lygus bugs (generalists), but reduce the populations of specialists, such as flea beetles and cabbage seedpod weevils that may be deterred by the presence of grasses and other nonhosts. The objective of this study was to compare the inci- dence of three key insect pests and their injury: (i) flea beetles, (ii) cabbage seedpod weevil, and (iii) lygus bugs in conventional canola (Q2) managed with standard herbicides and two HT cultivars (Liberty Link and Roundup Ready) managed with their designated her- bicides. These cultivars were selected because they were the most commonly grown at the time and would pro- Agriculture and Agri-Food Canada, Lethbridge Research Centre, Lethbridge, AB, Canada T1J 4B1. This study was financed through the Agriculture and Agri-Food Canada A-base research program. Re- ceived 21 Aug. 2006. *Corresponding author (carcamoh@agr.gc.ca). Published in Agron. J. 99:842–846 (2007). Canola doi:10.2134/agronj2006.0236 ª American Society of Agronomy 677 S. Segoe Rd., Madison, WI 53711 USA Abbreviations: HT, herbicide tolerant. Reproduced from Agronomy Journal. Published by American Society of Agronomy. All copyrights reserved. 842 Published online May 11, 2007