The enemy release hypothesis (ERH) states that decreased regulation by natural enemies allows plants to increase in distribution, abundance and vigour following their introduction into an exotic range. Invasive plants rarely escape herbivory entirely, and for hoary cress [Lepidium draba L. (Brassicaceae)] it has been demonstrated that generalist insect abundance is greater in its introduced North American range than in the native European range. We assessed the role of increased generalist herbivory on hoary cress using representatives of four important herbivore niches commonly found in the introduced range. We experimentally examined the density dependent impact of these herbivores individually and in combination on hoary cress in a series of greenhouse experiments. We found that defoliation of the oligophagous diamondback moth Plutella xylostella (L.) (Lep., Plutellidae) had the strongest and most consistent impact, while damage by the stem-mining weevil Ceutorhynchus americanus Buchanan (Col., Curculionidae) tended to have the highest per capita effect. Plant response to feeding by the oligophagous crucifer flea beetle Phyllotreta cruciferae (Goeze) (Col., Chrysomelidae) was minor despite obvious feeding damage, and the impact of the polyphagous tarnished plant bug Lygus hesperus Knight (Het., Miridae) was negligible. In multiple-species experiments, herbivore impacts were usually additive. In general, we found that hoary cress can tolerate high densities of oligophagous insect herbivory and effectively resisted attack by the polyphagous L. hesperus, but also the oligophagous C. americanus. Our results indicate that a combination of plant resistance and tolerance allows hoary cress to withstand increased generalist herbivore load in its introduced range, consistent with the predictions of the ERH.

Classical biological control of weeds is based on the assumptions that: (1) plant species are in part invasive in their introduced range because of the absence of coevolved specialist herbivore arthropods and plant pathogens; and (2) that these specialist herbivores can regulate host-plant populations. Although the need for quantitative post-release monitoring studies testing these assumptions has been acknowledged repeatedly, the number of assessments is still remarkably small and usually restricted to systems with notable impact of an agent species. However, studying systems where biological control agents cause no observable target weed reductions may be important to identifying factors that limit the population size or impact of biological control agents. Three biological agents were released for the control of the herbaceous perennial rush skeletonweed, Chondrilla juncea in North America between 1975 and 1977. Although all three species are widely established, weed densities are increasing and there is little quantitative information on factors limiting biological control efficacy. We examined the winter biology and survivorship of the rush skeletonweed gall mite Aceria chondrillae at two rush skeletonweed field sites in south-western Idaho over 2 years. Gall mite winter mortality was high (> 90%) in both years and for both sites. Gall mites were more abundant on plants that produced rosettes in fall and rush skeletonweed plants growing on southern aspect were 3.4 times more likely to produce rosettes than those growing on northern aspects. Our data suggest that A. chondrillae population densities are limited by its high winter mortality. The gall mites may require fall rosettes to successfully survive the winter, which are commonly absent on north-facing aspects, impairing the efficacy of A. chondrillae to control rush skeletonweed in the intermountain western United States.

Oilseed Bassica is susceptible to attack by the cabbage seedpod weevil while commercial yellow mustard, Sinapis alba L., is resistant. The objective of this study was to determine if canola-quality S. alba would maintain its resistance traits. In laboratory choice and nochoice tests we found the number of eggs laid by the weevil to be low or non-existent in all S. alba genotypes. Key words: Ceutorhynchus obstrictus, Ceutorhynchus assimilis, Sinapis alba, plant resistance

Phyllotreta cruciferae is an important insect pest of spring-planted Brassica crops, especially during the seedling stage. To determine the effect of early season P. cruciferae infestation on seed yield, 10 genotypes from each of two canola species (Brassica napus L. and Brassica rapa L.) and two mustard species (Brassica juncea L. and Sinapis alba L.) were grown in 2 yr under three different P. cruciferae treatments: (1) no insecticide control; (2) foliar applications of endosulfan; and (3) carbofuran with seed at planting plus foliar application of carbaryl. Averaged over 10 genotypes, B. rapa showed most visible P. cruciferae injury and showed greatest yield reduction without insecticide application. Mustard species (S. alba and B. juncea) showed least visible injury and higher yield without insecticide compared with canola species (B. napus and B. rapa). Indeed, average seed yield of S. alba without insecticide was higher than either B. napus or B. rapa with most effective P. cruciferae control. Significant variation occurred within each species. A number of lines from B. napus, B. juncea, anid S. alba showed less feeding injury and yield reduction as a result of P. cruciferae infestation compared with other lines from the same species examined, thus having potential genetic background for developing resistant cultivars.

The phenological synchrony of Eustenopus villosus (Boheman) with its host, yellow starthistle, Centaurea solstitialis L. (Asteraceae: Cardueae), was studied in Idaho in 1995 and 1996. Field plots were observed for adult weevil activity periodically throughout the growing season, and yellow starthistle capitula were examined for adult feeding damage, oviposition damage, and larval development. At the study site, weevil phenology was well synchronized with C. solstitialis. Im mature capitula, fed upon by adults, were abundant when E. villosus began to emerge in late May. During both years, the number of weevils and capitula increased throughout June. Adult females fed on capitula for about 2 wk. Weevil ovary dissections revealed that ovaries were mature after a 2-wk period of feeding. The development of mature capitula during late July corresponded to the initiation of oviposition. Eustenopus villosus, unique among the phytophages introduced for C. solstitialis biological control, attacks four plant stages resulting in observable impact to buds. Damaged buds either died or became distorted. Weevil feeding damage on young and mature capitula may make this insect a highly effective control agent.

A population of yellow starthistle (Centaurea solstitialis L.) near Dayton, Washington developed herbicide resistance in response to repeated applications of picloram and other auxin-type herbicides. Laboratory and field experiments were conducted in 1998 to determine host acceptability and suitability of this herbicide-resistant yellow starthistle population to the biological control weevil Eustenopus villosus (Boheman) (Coleoptera: Curculionidae). In choice and no-choice feeding and oviposition experiments using excised buds, the weevil did not demonstrate a consistent preference for either herbicide-resistant (R) or -susceptible (S) yellow starthistle. When caged on buds of intact plants, the E. villosus feeding rate of 97% did not differ between R and S types. Host plant suitability, measured as larval damage and development to adult weevils, was equivalent in R and S types, with weevils maturing in 46% of the R and in 32% of the S capitula bearing oviposition scars. The number of viable achenes per capitulum was reduced by 87% due to larval feeding, with no difference between R and S types. Observations at the field site where resistance was found revealed oviposition scars on 78% of the late-bud-stage capitula on 23 June 1998 and 73% of the flowering and postflowering capitula on 15 August 1998. Selection for herbicide resistance has not created host incompatibility for E. villosus nor reduced the effectiveness of E. villosus as a biological control agent.

Canola (Brassica napus L.), yellow mustard (Sinapis alba L.) and intergeneric crosses of S. alba×B. napus were assessed for resistance (antixenosis) to the cabbage seedpod weevil (Ceutorhynchus assimilis Paykull). Pod trichomes did not appear to be a major factor in the resistance of S. alba to weevils. The number of feeding punctures and eggs per pod in S. alba was not significantly different in pods with trichomes than in those where the trichomes had been removed. Choice and no-choice laboratory tests examining feeding punctures and eggs laid per pod suggested that resistance in S. alba is not conferred in the intergeneric cross, S. alba×B. napus. Similar data on feeding and weevil oviposition were found in field test plots. However, despite many eggs being laid in S. alba×B. napus hybrid plants, fewer cabbage seedpod weevil larvae developed to exit the intergeneric hybrid pods. Glucosinolate analyses of leaves, pods and seeds showed that S. alba plants have a high concentration of p-hydroxybenzyl glucosinolate in all three plant parts, but B. napus has no p-hydroxybenzyl. Interestingly the intergeneric hybrid examined in this study had 62% and 60% of p-hydroxybenzyl concentration in the leaves and seeds, respectively, than was found in the S. alba parent. However, pod tissues contained very little (3%) compared with the S. alba parent. It is possible, therefore, that the adult cabbage seedpod weevil feeds on the pods of the intergeneric hybrid and lays eggs in the pod, because of the low concentration of p-hydroxybenzyl glucosinolate, but the larvae then fail to develop as they feed on the seeds containing high concentrations of p-hydroxybenzyl glucosinolate. It should be noted also that this hybrid produced pods that were more similar in physical shape to canola pods and that this may also be a factor determining cabbage seedpod weevil feeding and subsequent egg laying. In addition, both B. napus and the intergeneric hybrid produced 3-butenyl and 4-pentenyl glucosinolates in their pods, and degradation products (3-butenyl, and 4-pentenyl isothiocyanates) from these glucosinolate types, are known to be stimulatory kairomones that attract cabbage seedpod weevil. Further studies are being conducted to examine these factors in more detail.

The effect of late season insect infestation on seed yield, yield components, oil content and oil quality of two canola species (Brassica napus L. and B. rapa L.) and two mustard species (B. juncea L. and Sinapis alba L.) was examined over 2 years. In each year, ten genotypes from each species were evaluated with late season insects controlled with either methyl parathion or endosulfan insecticides, and without insecticides. Major late season insect damage in 1992 was caused by cabbage seedpod weevil (Ceutorhynchus assimilis Paykull), while diamondback moth (Plutella xylostella L.) and aphids (primarily cabbage aphids, Brevicoryne brassicae L.) were major insect pests in 1993. Insecticide application was very effective in controlling diamondback moth larvae and adult cabbage seedpod weevils, but only partially effective in controlling aphids. Higher numbers of diamondback moth larvae were observed on mustard species compared to canola species. S. alba was completely resistant to cabbage seedpod weevil and there was no damage due to this pest observed. Aphid colonization was observed on plants from all species, but infestation on S. alba and B. rapa occurred too late to have a major effect on seed yield. Seed oil content of canola species was significantly reduced by insect damage although oil quality (indicated by fatty acid profile) was not affected by insect attack. Uncontrolled insect infestation reduced seed yield of canola species by 37 and 32% in B. napus and B. rapa, respectively. Least yield reduction occurred in S. alba, where average yield reduction from plants in untreated control plots was <10% of insecticide treated plants. S. alba, therefore, has good potential as an alternative crop suitable for northern Idaho because it can be grown with reduced late season insecticide application.

Abstract Plots, 3.5 X 12 ft, arranged in a split-plot design with each chem-ical treatment replicated 3 times, and each of 4 genotypes replicated twice within each treatment strip, were planted at Moscow, ID on 20 Aug, 1995 at 9.5 lb/acre using a small-plot, cone seeder. Capture 2 EC and methyl parathion 4 E were applied 5 Jun with a CO2-pressurized tractor-mounted sprayer equipped with 80° fan nozzles on an 8.3-ft boom that delivered 20 gpa at 30 psi. At the time of treatment, wind conditions were calm (<5 mph), and ambient air tem-perature was above 60°F. Plots were sampled for adult CSW 2 before treatment and 2 d after treatment by dislodging them into a 5-gal plastic bucket with a beat of a hand at each end of a plot. To determine the number of exit holes, 10 pods were removed from 10 racemes from each side of each plot on 17 and 18 Jul. Plots were harvested 15 Aug with a small-plot combine (4.6 ft header). All data were subjected to analysis of variance.

This datasheet on Microctonus melanopus covers Identity, Distribution, Further Information.

A laboratory ovipositional bioassay was developed to assess Brassica (Brassicaceae) germplasm for resistance, specifically antixenosis, to the cabbage seedpod weevil, Ceutorhynchus assimilis (Paykull). The effects of seedpod excision, cage size, seedpod length, weevil collection dates, male presence, seedpod to weevil ratios, and weevil preconditioning on C. assimilis ovipositional performance were evaluated. Standardized protocols were then used to assess the acceptability of Brassica napus L. and B. rapa L. germplasm to the weevil. Paired choice tests using B. napus as a standard ('Bridger') identified 1 resistant line, PI 176876 (B. rapa), and 2 susceptible lines, PI 469918 and PI 469849 (B. napus). These tests also confirmed that adult feeding punctures are not correlated with oviposition. In all cases, ovipositional preference was less pronounced in no-choice tests than in the paired choice tests. Results of 6 x 6 choice tests were consistent with the paired choice tests in assessing ovipositional preference.

Abstract Plots were established at the University of Idaho Plant Science Farm, Moscow, ID. ‘IMC-144’ Canola seed, supplied by Intermoutain Canola, was planted at 6 lb/acre using a 6-row (7 in spacing), small-plot, cone seeder on 19 May. Plots were 8 X 16 ft arranged in a RCBD with each treatment replicated 4 times. The plots were cultivated, harrowed and fertilized (200 lb/acre 40-0-0-6 and 150 lb/acre 16-20-0) prior to planting. Treatments were applied 31 May using a CO2-pressurized backpack sprayer equipped with 80° fan nozzles on a 6-ft boom that delivered 20 gpa at 30 psi. Flea beetle damage ratings, beetle densities, and counts of all plants in 3.3 ft of rows 3 and 10 (of 12) were made 3 and 8 d following the foliar applications. Damage to cotyledons was scored using a 0-6 rating system. Plots were harvested 22 Sep with a small-plot combine (4.6 ft header). All data were subjected to analysis of variance. To control late season aphid infestations, Capture 2EC (0.04 lb[AI]/acre) and Thiodan 3EC (1.0 lb.[AI]/acre) were applied 6 and 24 Jul, respectively.

Abstract Plots were established at the University of Idaho Plant Science, Moscow, ID. ‘IMC 144’ Canola treated by Rhone-Poulenc and untreated seed from the same lot was planted at 6 lb/acre using a 6-row (7 inch spacing), small-plot, cone seeder on 19 May. Some untreated seed plots also received granular Furadan treatments at planting. Control plots were planted with untreated seed and no Furadan. Plots were 3.5 X 16 ft arranged in a RCBD with each treatment replicated 4 times. The plots were cultivated, harrowed and fertilized (200 lb/acre 40-0-0-6 and 150 lb/acre 16-20-0) prior to planting. FB damage ratings and counts of all plants in 3.3 ft of rows 3 and 4 were made on 30 May, 2 and 7 Jun. Damage to cotyledons was scored using a 0-6 rating system. Capture 2EC (0.04 lb [AI]/acre) and Thiodan 3EC (1.0 lb [AI]/acre) were applied 6 and 24 Jul, respectively to control late season aphid infestations. Plots were havested 22 Sep with a small-plot combine (4.6 ft header). All data were subjected to analysis of variance.

Abstract A large block was seeded on 7 in centers at 7 lb/acre using a plot drill on 11 May at the University of Idaho Plant Science Farm in Moscow, ID. Individual 12 × 23 ft plots were later tilled-out of the block. Insecticide treatments were arranged in a RCBD with 4 replications each. Treatments were applied on 28 Jul when about 10% of the plants were still in bloom. Temperatures at the time of spray application were 80°F. Insecticides were applied using a CO2-pressurized backpack sprayer equipped with 80° fan nozzles on a 6-ft boom that delivered 20 gal/acre at 20 psi. Pretreatment and posttreatment counts of DBM were made by dislodging larvae into a 5 gal plastic bucket with a beat of the hand at each end of the plot. The proportion of aphid-infested canola terminals was assessed by randomly selecting 50 terminals in each plot and recording the presence or absence of aphids. Plot yields were obtained by making one pass along the center of each plot with a smallplot combine (4.6 ft header). Seed was cleaned and weighed. All data were subjected to analysis of variance and protected LSD tests.

Abstract Plots were established at the University of Idaho Plant Science Farms at Moscow and Genesee. ID. Treated and untreated seed was planted at about 7 lb/acre using a 6-row (7 inch spacing), small-plot cone seeder on 11 May at Moscow and 13 May at Genesee. Plots were 3.5 × 25 ft arranged in a RCBD with each treatment replicated 4 times. The plots were cultivated and harrowed twice and fertilized (200 lb 30-0-0-6/acre) prior to planting. Seed treated with 5 rates of Gaucho (imidacloprid), a Vitavax/ Thiram (fungicide only) treatment, a Vitavax RS (Vitavax/Thiram/Lindane) standard and untreated seed were supplied by Gustafson Inc. In the case of the granular treatment of Furadan CR-10, the granules were mixed with the seed prior to planting. The foliar treatment of Sevin XLR was applied when FB damage to cotyledons was first noted (20 and 26 May for Moscow and Genesee, respectively) using a COypressurized backpack sprayer equipped with 80° fan nozzles on a 6-ft boom that delivered 10 gal/acre at 20 psi. The Moscow plots were sprayed 25 Jun and 1 Jul with endosulfan (1 lb [AI]/ acre) to control diamondback moth and cabbage aphids. The Genesee plots were sprayed 1 Jul with endosulfan (1 lb [AI]/acre) and on 29 Jul an aerial application of methyl parathion (0.5 lb [AI]/acre) was applied to also control diamondback moth and aphids. FB damage ratings and counts of all plants in 6.6 ft of rows 2 and 5 were made 3 and 8 d following the foliar application of Sevin XLR. FB damage to cotyledons was scored using a 0-6 rating system. Final stand counts were made following harvest on 24 and 23 Sep for Moscow and Genesee, respectively.

The effects of adult diet and temperature on oogenesis of the postdiapause cabbage seedpod weevil, Ceutorhynchus assimilis Paykull, were studied to examine the reproductive development of this important pest of rapeseed, Brassica napus L. Diets consisting of racemes with open flowers, racemes without open flowers, racemes with open flowers without stamens, stamens, sugar water (10% sucrose), and distilled water were evaluated with respect to C. assimilis oogenesis. Oogenesis, rated on a 1-3 scale, and measurements of follicle length, width, and volume, were significantly (P < 0.05) enhanced by diets containing racemes (flower buds, stems, and pods) over a 3-wk period. Diets without racemes did not generally result in complete ovariole development over a 3-wk period. Mortality of weevils on the diets with racemes was lower (P < 0.05) than on the diets without racemes. Rapeseed varieties containing a range of low (5 JLmoljg) to high (44 JLmoljg) levels of total glucosinolates were also evaluated. There were no significant (P > 0.05) differences in oogenesis (stage, follicle length, width, and volume) among weevils fed racemes of each variety over a 2-wk period. Ovariole development differed significantly (P < 0.05) among weevils fed rapeseed racemes and maintained at 10, 15, 20, and 25°C over four different feeding durations (1, 2, 3, and 4 wk, respectively). In general, oogenesis occurred at a faster rate in females maintained at 15 and 20°C than those maintained at 10 and 25°C. Ovariole development at 1000Cwas negligible, indicating that this temperature approached the base temperature for development. Few weevils maintained at 25°C completed their reproductive development. There were no significant (P > 0.05) differences in weevil mortality among the temperature treatments over the 4-wk period of study.