Julie Soroka

Enhanced β-ionone emission in Arabidopsis over-expressing AtCCD1 reduces feeding damage in vivo by the crucifer flea beetle.

ABSTRACT Plant carotenoid derived &bgr;-ionone has been shown to have diverse biological effects on some insect herbivores and herbivore parasitoids. In this study, Arabidopsis transgenic plants over-expressing a carotenoid cleavage dioxygenasel gene (AtCCD1) were generated to test whether &bgr;-ionone emissions could be enhanced and used to control feeding by the crucifer flea beetle (Phyllotreta cruciferae Goeze). The transgenic plants exhibited a morphological phenotype indistinguishable from the wild type (WT) control over their complete life cycle. Gas chromatography and mass spectrometry analyses of headspace volatiles collected from 6-wk-old intact flowering plants revealed substantially enhanced &bgr;-ionone emission from transgenic plants compared with WT, but no &bgr;-ionone enhancement occurred at a young vegetative stage (4-wk-old seedlings). Bioassays in an enclosed environment showed that ATCCD1 over-expression resulted in ≈50% less leaf area damage by flea beetles on transgenic plants compared with WT plants. The mean number of damaged transgenic leaves per plant also was significantly lower in transgenic plants (P < 0.05). Our results indicate that AtCCD1 over-expression and induced &bgr;-ionone emission might find application in the control of pests for Brassica crops grown in greenhouse operations. Potentially, &bgr;-ionone also could be used on crops grown in open-air ecosystems if this allomone is released in sufficient quantities to discourage herbivore foragers.

Responses of the Crucifer Flea Beetle to Brassica Volatiles in an Olfactometer

ABSTRACT 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-&bgr;-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, &bgr;-ionone, indole, ( ± )-linalool, ( + )-limonene, E-geraniol, and ( - ) -&bgr;-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 &bgr;-ionone, but seedlings did not. &bgr;-Ionone has not been documented previously in B. napus.

Resistance to cabbage seedpod weevil among selected Brassicaceae germplasm

Brassicaceae germplasm (Brassica napus L., Brassica rapa L., Brassica juncea (L.) Czern., Brassica carinata A. Braun, Sinapis alba L., Camelina sativa (L.) Crantz, Crambe species) with cultivar development potential for the prairies was evaluated for resistance to cabbage seedpod weevil (Ceutorhynchus obstrictus (Marsham) (Coleoptera: Curculionidae)) infestation under field conditions in southern Alberta from 2001 to 2005. Relative susceptibilities were as follows: B. rapa and B. napus > B. juncea = B. carinata > S. alba. Although some of the germplasm evaluated varied within species in terms of glucosinolate profile, erucic acid level, oil content, and plant height, none of these factors appeared to influence the degree of C. obstrictus damage. A subset of this germplasm was also evaluated in the greenhouse. Although the canola species B. rapa sustained the highest level of damage in the field tests, it was similar to other Brassica genotypes in the greenhouse. All lines of S. alba were virtually immune ...

Effect of Condensed Tannins in the Diets of Major Crop Insect

The role of leaf hydrolyzable and condensed tannins in plant defenses against herbivorous insects has been the subject of substantial investigation.1–8 Most of these early studies focused on the role of hydrolyzable tannins rather than condensed tannins in insect/plant interactions. Of the insects considered in these studies, acridids, particularly ambivorous species, appear to be distinguished by their relative tolerance to tannic acid.9,10 In contrast, the graminivorous locust, Locusta migratoria, suffered damage to the tissues of the digestive system when tannin was included in its diet.9

New threshold temperatures for the development of a North American diamondback moth (Lepidoptera: Plutellidae) population and its larval parasitoid, Diadegma insulare (Hymenoptera: Ichneumonidae).

ABSTRACT The currently accepted lower threshold temperature for the development of diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae), the worlds 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.

Spring Emergence of Canadian Delia radicum and Synchronization with Its Natural Enemy, Aleochara bilineata

Abstract To characterize time of spring emergence following post-diapause development, Delia radicum (L.) (Diptera: Anthomyiidae) from Saskatchewan, Manitoba, and southwestern Ontario were collected in fall, maintained over winter at 1 °C, then transferred to higher constant temperatures until adult emergence. At each location there were “early” and “late” phenotypes. Truncated normal models of temperature dependency of development rate were fitted for each phenotype from each location. We provide the first evidence of geographic variation in the criteria separating these phenotypes. Separation criteria and models for early and late phenotypes at the two prairie locations, approximately 700 km apart, were indistinguishable, but differed from those for Ontario. Prairie phenotypes developed more slowly than Ontario phenotypes, and more prairie individuals were of the late phenotype. Poor synchronization of spring emergence could impair predation of D. radicum eggs by adult Aleochara bilineata Gyllenhal (Coleoptera: Staphylinidae). Aleochara bilineata from Manitoba were reared and development rates modelled as for D. radicum. Models of development rates for the two species, when combined with simulated soil temperatures for two prairie locations, suggest that emergence of adult A. bilineata is well synchronized with availability of D. radicum eggs in prairie canola.

Occurrence of diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae), and its larval parasitoids across Saskatchewan, Canada

Abstract The prevalence of the diamondback moth and its larval parasitoids, was explored across Saskatchewan, Canada. Higher numbers of diamondback moths were recorded early in the season than later and in the Mixed Grassland compared to three other ecoregions. The highest proportion of parasitism was observed in the Boreal Transition ecoregion in early season.