Laboratory and Þeld studies were undertaken to determine the effects of increased numbers of trichomes on seedling stems, petioles, and Þrst true leaves of Brassica napus L., canola, on the feeding and behavior of the crucifer ßea beetle Phyllotreta cruciferae (Goeze) (Coleoptera: Chrysomelidae). Seedlings of ÔWestarÕ canola with genes inserted from Arabidopsis thaliana L. for increased trichome production, called Hairy1, 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 Þeld trials at Saskatoon and Lethbridge, Canada. Analyses of prefeeding and feeding behavior in no-choice tests of Þrst true leaves found that ßea beetles interacted with their host while off Hairy1 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, ßea beetles fed more on cotyledons and second true leaves of Westar than on comparable tissues of the transgenic line. In Þeld trials, variations in feeding patterns were seen over time on cotyledons of the line with elevated trichomes. However, all four young true leaves of Hairy1 seedlings were fed upon less than were the parental lines. Feeding on Hairy1 plants frequently occurred at levels equal to or less than on cultivars grown from insecticide-treated seed. This study highlights the Þrst host plant resistance trait developed in canola, dense pubescence, with a strong potential to deter feeding by crucifer ßea beetles.

A suite of commercially available volatile compounds was tested in an olfactometer bioassay for responses by the crucifer flea beetle (Phyllotreta cruciferae). Flea beetles were inhibited by exposure to hexane, pentane, and ethanol. Allyl-isothiocyanate, a crucifer-specific volatile, was moderately attractive to spring and early fall flea beetles, but inhibitory to late fall flea beetles. Spring flea beetles were most attracted to (+)-sabinene and E-beta-ocimene, and 1-hexanol, 1-pentanol, and Z-3-hexen-1-ol were stronger attractants than allyl-isothiocyanate. Spring beetles were strongly inhibited by (-)-E-caryophyllene, beta-ionone, indole, (+/-)-linalool, (+)-limonene, E-geraniol, and (-)-beta-pinene and moderately inhibited by (-)-verbenene and hexenal. Our study showed that older leaves and flowers of Brassica napus variety AC Excel contained small amounts of beta-ionone, but seedlings did not. beta-Ionone has not been documented previously in B. napus.

Plant growth and insect resistance characteristics were determined for two Brassica napus Linnaeus (Brassicaceae) lines, AtGL3+ and K-5-8, developed for enhanced trichome densities relative to their parental cultivar Westar. In the field, both transgenic lines had glabrous cotyledons that curled upwards at emergence but flattened with time, and young leaves with elevated trichome density. Flea beetle (Phyllotreta cruciferae (Goeze) and Phyllotreta striolata (Fabricius); Coleoptera: Chrysomelidae) feeding was reduced on true leaves of both lines by 30–50% compared with insecticide-free Westar. Flea beetle feeding levels on cotyledons of the two hairy-leaved lines were lower than on unprotected Westar and similar to those seen on insecticide-treated Westar. Antixenosis and antibiosis resistance was observed when diamondback moths (Plutella xylostella (Linnaeus); Lepidoptera: Plutellidae) interacted with the hairy AtGL3+ and K-5-8 lines in the laboratory. Although the numbers of eggs laid by female diamondback moths on the transformed lines were similar to or higher than on Westar, in feeding bioassays larvae moved off AtGL3+ plants and larval feeding injury decreased on the transformed lines compared with Westar leaves. No agronomic or seed yield penalties were found for plants of K-5-8. These data highlight the utility of manipulating trichome regulatory genes to increase plant resistance against brassicaceous insect pests.

The currently accepted lower threshold temperature for the development of diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae), the world's most destructive insect pest of cruciferous crops, is around 6.0°C, and there is no known upper threshold temperature. Neither are there established threshold temperatures for diamondback moth's major natural enemy, Diadegma insulare (Hymenoptera: Ichneumonidae). Laboratory studies were undertaken to determine the survival and development of a North American diamondback moth population and its parasitoid D. insulare at 20 constant temperatures ranging from 2.0 to 38.0°C. Diamondback moth completed development from second instar to adult within a temperature range of 4.0-37°C, and D. insulare completed its life cycle from egg to adult within a temperature range of 4.0-33°C. The developmental data were fitted into one linear and four nonlinear models. Using goodness-of-fit and the ability to estimate parameters of biological significance as selection criteria, the Wang model was the most acceptable among the nonlinear models to describe the relationship between temperature and development of both species. According to this model, the lower and upper threshold temperatures for diamondback moth were 2.1 and 38.0°C, respectively, and for D. insulare they were 2.1 and 34.0°C, respectively. Based on the Degree Day model, diamondback moth required 143 d above the lower threshold of 4.23°C to complete the life cycle, while D. insulare required 286 d above the lower threshold of 2.57°C. This study suggests that temperatures during the crop-growing seasons in North America are not limiting factors for development of either diamondback moth or D. insulare.

Crucifer-feeding flea beetles, Phyllotreta spp., are chronic insect pests in Canadian prairie canola production. Multiple laboratory and field feeding bioassays were conducted to determine the susceptibility of a wide range of crucifer species, cultivars, and accessions to feeding by flea beetles with the goal of discovering sources of resistant germplasm. In 62 bioassays of 218 entries, no consistent decreased feeding by flea beetles was seen on any entries of Brassica carinata A. Braun, Brassica juncea (L.) Czern., Brassica napus L., or Brassica rapa L. There was reduced feeding on condiment mustard Sinapis alba L. lines but not on canola-quality lines with reduced amounts of glucosinolates, which were fed on at levels equal to B. napus. Analyses of glucosinolate content found decreased quantities of hydroxybenzyl and butyl glucosinolates in preferred canola-quality S. alba lines and increased levels of hydroxybutenyl glucosinolates compared with levels in condiment S. alba lines. Eruca sativa Mill. was an excellent flea beetle host; Camelina sativa (L.) Crantz lines experienced little feeding. Lines of Crambe abyssinica Hochst. ex R. E. Fries and Crambe hispanica L. had reduced feeding levels compared with Brassica entries, but Crambe glabrata DC did not. The results indicate possible sources of resistance to Phyllotreta flea beetles, while highlighting the complicated roles that glucosinolates may play in Phyllotreta host preference.