Feeding by Flea Beetles (Coleoptera: Chrysomelidae; Phyllotreta spp.) Is Decreased on Canola (Brassica napus) Seedlings With Increased Trichome Density

Abstract

Laboratory and field studies were undertaken to determine the effects of increased numbers of trichomes on seedling stems, petioles, and first true leaves of Brassica napus L., canola, on the feeding and behavior of the crucifer flea beetle Phyllotreta cruciferae (Goeze) (Coleoptera: Chrysomelidae). Seedlings of 'Westar' canola with genes inserted from Arabidopsis thaliana L. for increased trichome production, called Hairyl, were tested against Westar seedlings in no-choice and choice laboratory tests, and against parental plants and other cultivars grown from seed with and without insecticide in field trials at Saskatoon and Lethbridge, Canada. Analyses ofprefeeding and feeding behavior in no-choice tests of first true leaves found that flea beetles interacted with their host while off Hairyl leaves more so than beetles presented with leaves of Westar. Beetles required twice as much time to reach satiation when feeding on leaves with increased pubescence than on Westar leaves. In laboratory choice tests, flea beetles fed more on cotyledons and second true leaves of Westar than on comparable tissues of the transgenic line. In field trials, variations in feeding patterns were seen over time on cotyledons of the line with elevated trichomes. However, all four young true leaves of Hairyl seedlings were fed upon less than were the parental lines. Feeding on Hairyl plants frequently occurred at levels equal to or less than on cultivars grown from insecticide-treated seed. This study highlights the first host plant resistance trait developed in canola, dense pubescence, with a strong potential to deter feeding by crucifer flea beetles.