Cabbage Seedpod Weevil Research Articles

Landscape Effects on the Cabbage Seedpod Weevil, Ceutorhynchus obstrictus (Coleoptera: Curculionidae), and on Its Parasitoid, Trichomalus perfectus (Hymenoptera: Pteromalidae), in Canola

The cabbage seedpod weevil (CSW), Ceutorhynchus obstrictus, an exotic pest accidentally introduced in North America in 1931, spread all over this continent and is now a major pest of canola crops. One of its main natural enemies in Europe, Trichomalus perfectus, was observed in eastern Canada in 2009. This study aimed to evaluate the landscape influence on CSW infestation and abundance and on T. perfectus parasitism in Quebec to understand the optimal conditions to potentially release this parasitoid in the Canadian Prairies. Field research was conducted in 19 to 28 canola fields per year, from 2015 to 2020, among eight Quebec regions. CSW was sampled by sweep net during canola blooming and parasitoids by collecting canola pods kept in emergence boxes until adults emerge. Infestation and parasitism calculations were based on pod emergence holes. For analysis, 20 landscape predictors were considered. Results show that CSW infestation and abundance increased if there were more roads and cereal crops in the landscapes. Meanwhile, T. perfectus parasitism decreased when hedgerows length and distance from water were longer. However, it increased when landscape diversity and average crop perimeter-to-area ratio were higher, and along with more hay/pastures and soybean crops. This study's results highlight that these four landscape predictors could provide more resources and overwintering areas, promoting greater efficiency of T. perfectus to control the CSW.

Toxicity of essential oils on cabbage seedpod weevil (Ceutorhynchus obstrictus) and a model parasitoid (Nasonia vitripennis)

Plant essential oils are being increasingly studied as a potential environmentally friendly alternative to synthetic insecticides. The insecticidal efficacy of essential oils on the cabbage seedpod weevil (Ceutorhynchus obstrictus), an important oilseed rape pest, has not been previously tested. We examined the impact of six essential oils on C. obstrictus via contact with dry residues on leaf and flower surfaces. We also examined the effect of these essential oils on a model non-target parasitoid wasp, Nasonia vitripennis. Exposure to dry residues of cumin (Cuminum cyminum) and cinnamon (Cinnamomum verum) essential oils (applied to oilseed rape leaves) resulted in significant loss of mortality and immobility in C. obstrictus adults. Treatment with C. cyminum essential oil at 1.5% resulted in 50.71% mortality and 87.3% combined mortality and immobility in C. obstrictus. Cinnamomum verum oil, at 1.5% concentration, resulted in 88.8% mortality and immobility among C. obstrictus 24 h post-treatment. All treatments studied with essential oil dry residues at 0.3% concentration caused high mortality and immobility in N. vitripennis. The greatest mortality and immobility were observed at 0.3% concentration in F. vulgare and C. verum treatments (54 and 53% loss respectively). At 0.1% concentration, F. vulgare and T. vulgaris significantly reduced parasitoids mobility and at 1.5% concentration all essential oils resulted in 100% mortality of N. vitripennis after 3 h. Our study revealed that C. cyminum and C. verum essential oils may have potential in the management of C. obstrictus. However, their impact on non-target organisms, including parasitoids, needs to be studied more thoroughly to determine the potential of essential oil main compounds in integrated pest management.

Biology and management of Ceutorhynchus obstrictus (Coleoptera: Curculionidae) in spring-planted canola on the Northern Great Plains

Abstract The cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsham) (Coleoptera: Curculionidae), is an invasive pest infesting canola (Brassica napus L. and B. rapa L. (Brassicales: Brassicaceae)) crops in North America. Larval feeding causes significant damage leading to yield losses of 5–30%. Native to the Palearctic region, the species was accidentally introduced to North America over 90 yr ago, and now occupies most temperate regions of Canada and the United States. Currently, the species has been projected to continue its range expansion to potentially infest most canola producing regions in North America. Here, we review the taxonomic nomenclature, distribution, biology, pest status, and management of the cabbage seedpod weevil in North America with an emphasis on spring-planted canola crops in the Great Plains and highlight areas for future research to develop a comprehensive integrated pest management program against this debilitating pest.

Assemblage of Ceutorhynchinae Weevils Associated With Brassicaceae in Quebec (Canada) Agroecosystems.

Ceutorhynchinae Gistel (Coleoptera: Curculionidae) are a highly diverse phytophagous group of weevils in which the most species rich genus, Ceutorhynchus Germar (Coleoptera: Curculionidae), is mainly associated with Brassicaceae. Some Ceutorhynchinae, such as the invasive cabbage seedpod weevil (CSW), Ceutorhynchus obstrictus (Marsham), are important pests of cultivated Brassicaceae, and others are natural enemies of weeds and potential biological control agents. This study aims to characterize Ceutorhynchinae assemblages in canola growing regions of Quebec. Ceutorhynchinae were sampled in areas adjacent to canola fields or other crops in six administrative regions of Quebec during the summers of 2019 and 2020. A total of 25 Ceutorhynchinae species were collected and identified. Canonical analysis and multivariate regression tree analysis revealed that the assemblage of Ceutorhynchinae varied regionally and was either dominated by the invasive canola pest CSW or by the native weevil Ceutorhynchus neglectus Blatchley. Our results also highlighted new biological associations between weevils and Brassicaceae like the CSW with the yellow rocket, Barbarea vulgaris R. Br., native Ceutorhynchus pauxillus Dietz with common pepper grass, Lepidium densiflorum, and native Ceutorhynchus semirufus LeConte with Pennsylvania bittercress, Cardamine pensylvanica Muhl. This study also provides a useful tool to find new biological control agents against Brassicaceae weeds and to monitor the abundance and diversity of this taxon and provide baseline data to assess future impacts of exotic parasitoids of CSW on native weevils.

The potential for reducing non-target effects on parasitoids of Ceutorhynchus obstrictus Marsham (Coleoptera: Curculionidae) through spatially targeted insecticide applications

Insecticide applications against the cabbage seedpod weevil, Ceutorhynchus obstrictus Marsham (Coleoptera: Curculionidae), in oilseed rape are conducted during the flowering of the crop. During the flowering period, many parasitoids of pest species are abundant in the crop, and therefore, the preservation of natural pest regulation mechanism is especially important. Parasitism often has a substantial mortality factor in pest populations and as far as possible, parasitoids need to be protected from harmful non-target effects of insecticides. In the present study, the effects of three different insecticidal products on the parasitism of cabbage seedpod weevil larvae were investigated. Additionally, the effects of a spatial targeting of insecticides, using conventional and dropleg application technique, were compared. This was done in field trials within a completely randomized block design and four replications at one trial site in 2019 and two sites in 2020. The parasitoid species Trichomalus perfectus Walker and Mesopolobus morys Walker (both Hymenoptera: Pteromalidae) were abundant in almost equal shares in 2019, whereas M. morys was the most important species in 2020. Only in 2019 were harmful effects of the insecticide Biscaya (a.i. thiacloprid) on parasitism rates of C. obstrictus larvae observed. Clear benefits, due to spatial targeting of insecticides using the dropleg technique on parasitoids, were not found. The harmfulness of insecticides is probably affected by properties of different insecticidal products and the temporal coincidence of parasitoid occurrence and insecticide application.

Taxonomical and biological information of the ectoparasitoid, Chlorocytus spicatus (Walker) (Hymenoptera: Pteromalidae), introduced to Korea with the cabbage seedpod weevil on rapeseed

Chlorocytus spicatus (Walker) (Hymenoptera: Pteromalidae) is first confirmed as a larval ectoparasitoid of the cabbage seedpod weevil (CSPW), Ceutorhynchus obstrictus (Marsham) (Coleoptera: Curculionidae), on rapeseed ( Brassica napus L., Brassicaceae) in Korea. The parasitism of this ectoparasitoid for the larvae of CSPW maximally was shown to be 12.5% on May 24 in Suncheon, Jeonnam Province, and 12.82% on June 12 in Andong, Gyeongbuk Province, when the damage rates of pods by the CSPW exceeded 30%, respectively. The pupal period of this ectoparasitoid was about 7 days and 6 days in females and males, respectively; the females had a life span of about 11 days; and the sex ratio was more than 4 females to 1 male. To aid their identification, we provide a detailed description supplemented by the scanning electron microphotographs of external structures and also present several biological data of its ectoparasitoid. • A pteromalid wasp, Chlorocytus spicatus (Walker), is confirmed as a larval ectoparasitoid of the CSPW in Korea. • The morphological characteristics of a pteromalid wasp, C. spicatus (Walker), are provided. • The parasitism of this parasitoid for the larvae of the CSPW was shown to be 12.5% in Suncheon and 12.82% in Andong. • The pupal period of the parasitoid was about 7 days and 6 days in females and males respectively. • The sex ratio of the parasitoid was more than 4 females to 1 male.

Effect of nitrogen fertilization on flea beetle (Phyllotreta cruciferae) and cabbage seedpod weevil (Ceutorhynchus obstrictus) injury and crop yield in dry land canola

Nitrogen (N) availability is an important factor affecting the canola (Brassica napus L.) yield. While N fertilization is commonly used to enhance the yield and quality of canola, it is also known to influence the incidence of insect pests in the crop. The flea beetle Phyllotreta cruciferae (Goeze) and the cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsh), are two economically important pests of canola in the northern Great Plains of the United States. This study investigated the effects of N fertilization (0, 56, 112 and 168 kg/ha) with or without insecticide seed treatment application on P. cruciferae and C. obstrictus injury levels, canola seed yield, and quality in replicated field trials at the two locations (Conrad and Sweet Grass) of north central Montana. The study showed that N fertilization had no influence on P. cruciferae and C. obstrictus injury levels, regardless of the study location or sampling date. However, insecticide seed treatment application significantly influenced P. cruciferae injury ratings at the both locations. In Conrad, insecticide-treated plots had significantly lower injury levels at the four leaf, pre-flower, and pod formation stages but without an effect at the cotyledon stage of canola plants when compared with untreated control plots. Similarly, in Sweet Grass, injury levels were significantly lower in insecticide-treated plots from cotyledon to pre-flowering stages but not at the pod stage of canola plants. In contrast, insecticide seed treatment had no impact on pod infestation rates by C. obstrictus at either location. Insecticide seed treatment, averaged over all the N rates, improved canola seed yield and quality parameters compared to the untreated plots.

Use of life tables to predict the impact of introducing exotic parasitoids, against the cabbage seedpod weevil in North America

ABSTRACTCabbage seedpod weevil, Ceutorhynchus obstrictus (Coleoptera: Curculionidae), is an invasive alien species that impacts seed production of canola, Brassica napus and B. rapa (Brassicaceae), one of Canada’s major agricultural crops. To determine the need for and potential impact of introduction of one or more natural enemies for biological control it is essential to understand the mortality factors associated with C. obstrictus both in the native range and in the introduced range. Life tables were constructed for Ontario and British Columbia populations to determine the mortality factors affecting C. obstrictus. These were compared with life tables generated in Switzerland, the area of origin of the weevil. Results indicated that introduction of an exotic specialist parasitoid into canola growing regions of Canada would substantially reduce C. obstrictus populations. This study is the first to compare life tables of an invasive pest in the areas of origin and introduction.

Managing cabbage seedpod weevils (Coleoptera: Curculionidae) in canola (Brassicaceae) – areLygus(Hemiptera: Miridae) affected?

AbstractCabbage seedpod weevil (Ceutorhynchus obstrictusMarsham; Coleoptera: Curculionidae) andLygusHahn (Hemiptera: Miridae) species are part of the late season insect pest complex of canola (BrassicaLinnaeus; Brassicacea) in the southern prairies of Canada. From 2010 to 2013, large strips in 73 commercial fields were studied in southern Alberta to validate action thresholds for cabbage seedpod weevil and assess the impact of insecticide spraying at the early flower stage for cabbage seedpod weevils on abundance ofLygusat the pod stage. Only fields planted in April accumulated the damaging populations of cabbage seedpod weevils, such that the application of an insecticide resulted in significant yield protection. The economic injury level for the cabbage seedpod weevil was calculated at 20 cabbage seedpod weevils per 10 sweeps, but an action threshold of 25–40 is recommended because sampling mainly occurs along the edge where cabbage seedpod weevils are initially concentrated. At the pod stage,Lyguswere lower in strips sprayed with insecticides at the early flower stage than in those not sprayed, but the differences were not statistically significant. Furthermore,Lyguswere generally below economically damaging levels in early seeded fields. Therefore, there is no benefit of spraying early seeded fields to attempt to preventLygusoutbreaks when cabbage seedpod weevils are below thresholds becauseLygusmay pose a risk only in fields planted later in the season.

Cabbage Seedpod Weevil Control in Winter Canola, 2015: Table 1

Larvae of the cabbage seedpod weevil destroy canola seed within the seedpod causing direct yield loss. Insecticide control targets the adult stage during flowering to prevent eggs from being laid in developing seedpod. An insecticide efficacy trail was conducted in a grower field of winter canola in Morgan County, GA. Canola seed was planted with a grain drill in 14 inch rows on 10 Oct 2014. Plots measuring 10 rows (12 ft) by 30-ft long were established on 8 Apr when plants were at full bloom. An RCB …

Determining the host specificity of the biological control agent Trichomalus perfectus (Hymenoptera: Pteromalidae): the importance of ecological host range

We determined the host range of the parasitoid Trichomalus perfectus (Walker), a candidate for classical biological control of cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsham), an important pest of canola in Canada. Studies were conducted in Europe and in North America. In laboratory experiments, the levels of parasitism (acceptance) of Ceutorhynchus turbatus Schultze, C. cardariae Korotyaev, C. omissus Fall and C. querceti (Gyllenhal) by T. perfectus were not significantly different than of the target host C. obstrictus. Although C. typhae (Herbst), C. pallidactylus (Marsham), C. americanus Buchanan, C. neglectus Blatchely and Ceutorhynchus sp. nr. nodipennis were parasitised by T. perfectus, the levels of parasitism were significantly lower on these species than on C. obstrictus. Ceutorhynchus peyerimhoffi Hustache, C. erysimi (Fabricius), C. alliariae H. Brisout, C. roberti Gyllenhal, Mogulones borraginis (Fabricius), Mononychus vulpeculus (Fabricius) and the leaf-mining fly Scaptomyza flava (Fallén) were not attacked. Ecological host range surveys in Europe corroborated the prediction that T. perfectus would attack C. cardariae at similar rates to C. obstrictus. In North America, the recent discovery of T. perfectus in a C. omissus population suggests that laboratory findings predicting that C. omissus is a preferred host may be the case in the field. We found that T. perfectus attacks larvae of some Ceutorhynchus spp. feeding on Brassicaceae and does not attack species outside of that host range. Thus, the parasitoid can be defined as narrowly oligophagous. These results demonstrate the value of ecological host range studies in the area of origin to validate hypotheses generated through laboratory host range experiments.

Nutritional Effects on the Appearance of Canola and its Attractiveness to the Cabbage Seedpod Weevil

To investigate visual cues as a mechanism to explain phytophagous insect intraspecific host selection and to explain the effects of plant nutrition on visual cues associated with host selection we assessed the response of the cabbage seedpod weevil, Ceutorhynchus obstrictus, to plants of canola (oilseed rape), Brassica napus supplied with varied nitrogen (N) rates and sulfur to nitrogen (S:N) ratios. We assessed the effects of these treatments on B. napus appearance using photography and spectrophotometry. Plant nutrition had a significant effect on C. obstrictus; host plant attractiveness declined with increasing S:N ratios. We found strong evidence that attractiveness of host plants to C. obstrictus was mediated by several components of B. napus appearance supporting the role of visual cues in intraspecific host selection.

The parasitoid communities associated with Ceutorhynchus species (Coleoptera: Curculionidae) in Ontario and Québec, Canada

AbstractSurveys were conducted in Ontario and Québec, Canada to determine the parasitoid communities associated with Ceutorhynchus Germar (Coleoptera: Curculionidae) weevil species that are potential nontarget hosts of candidate biological control agents of the cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsham). New host plant associations are documented for Ceutorhynchus americanus Buchanan, Ceutorhynchus neglectus Blatchley, and Ceutorhynchus omissus Fall. More than 18 species of Chalcidoidea (Hymenoptera) were associated with six Ceutorhynchus species reared from siliques and stems of Brassicaceae plants. Silique-feeding Ceutorhynchus species supported a more diverse parasitoid community than stem-feeding or root crown-feeding species. The major components of the parasitoid assemblage of the native C. neglectus included Mesopolobus gemellus Baur and Muller, Mesopolobus moryoides Gibson, Trichomalus lucidus (Walker) (Hymenoptera: Pteromalidae) and a cryptic species complex previously reported as Necremnus tidius (Walker) (Hymenoptera: Eulophidae). These species, plus Trimeromicrus maculatus Gahan (Hymenoptera: Pteromalidae) were the main parasitoids attacking the native C. omissus. The major parasitoids associated with the accidently introduced Ceutorhynchus erysimi (Fabricius) and Ceutorhynchus typhae (Herbst) included T. maculatus, the N. tidius species complex, M. gemellus, and M. moryoides. Trichomalus perfectus (Walker) (Hymenoptera: Pteromalidae), a major parasitoid of C. obstrictus in Europe, is an accidental introduction first reared in Canada from that host in 2009 and first collected from C. omissus in 2011. Mesopolobus gemellus is shown to have a broad host range. These findings highlight the need for a cautious approach before introducing new biological control agents.

Identification of putative quantitative trait loci associated with a flavonoid related to resistance to cabbage seedpod weevil (Ceutorhynchus obstrictus) in canola derived from an intergeneric cross, Sinapis alba × Brassica napus.

Kaempferol 3- O -sinapoyl-sophoroside 7- O -glucoside was putatively identified as the major component of a characteristic HPLC peak previously correlated with the reduction of cabbage seedpod weevil larval infestation in a novel canola genotype. The cabbage seedpod weevil (Ceutorhynchus obstrictus [Marsham]) (CSPW) is a serious pest of brassicaceous oilseed crops such as canola in both Europe and more recently in North America. At present, the only control strategy against CSPW is the application of insecticides. As an alternative more environmentally-friendly control strategy, we developed novel canola germplasm resistant to weevil attack through introgression of Sinapis alba DNA into Brassica napus by making the wide cross followed by embryo rescue and backcrossing to the B. napus parent. We have previously characterized resistant canola lines by metabolic profiling and were able to correlate reduction of larval infestation to the presence of a characteristic HPLC peak. In this study, we have putatively identified the major component in the peak using mass spectrometry as kaempferol 3-O-sinapoyl-sophoroside 7-O-glucoside (KSSG). We have also identified quantitative trait loci (QTL) associated with this HPLC peak in a mapping population consisting of more than 200 individual doubled haploid (DH) lines derived from a cross between CSW428 (the resistant parent) and SC030686 (the susceptible parent). This QTL accounted for approximately 9.5% of the phenotypic variation in KSSG content. The observation that only one QTL was identified as surpassing the LOD threshold of 3.0 suggests that both parents may possess the positive alleles for other QTL that have not been detected in our study. This finding also indicates a complex regulatory mechanism for KSSG levels and provides an appropriate explanation for the large transgressive segregation observed in the DH lines of the QTL mapping population.

Effect of Insect Herbivory on the Architecture and Seed Production of Canola, Brassica napus L.

Abstract Several native Lygus spp. (Hemiptera: Miridae) feed on buds, flowers and immature seeds of canola. These plant resources are also exploited by a recent alien pest now established in southern Alberta, Canada: the cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsham) (Coleoptera: Curculionidae). A caged study was conducted with Brassica napus L. in 2000 and 2002 to determine if various combinations and densities of lygus and seedpod weevils (0, 10 + 10, 20 of either, 20 + 20, 40 + 40, individuals per cage) affected yield and its components such as number of branches, pods and seed weight. Under severely dry conditions, cages with the intermediate (20 + 20) and high (40 + 40) insect combinations had lower grain yield as well as number of racemes and pods per raceme relative to control cages with no insects added. Under more humid conditions in 2002, similar results were observed but the damage by the cabbage seedpod weevil at 20 adults per cage was more apparent than in 2000. These results sugg...

The parasitoid communities associated with an invasive canola pest, Ceutorhynchus obstrictus (Coleoptera: Curculionidae), in Ontario and Quebec, Canada

AbstractSurveys were conducted to determine the parasitoid communities associated with the cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsham), an important invasive pest of canola in Ontario and Quebec, Canada. More than 18 species of Chalcidoidea (Hymenoptera) were associated with this pest through mass rearings from canola siliques. In southwestern Ontario, the most abundant species were a species of Chlorocytus Graham (23.6%–48.6%), Lyrcus perdubius (Girault) (0%–53%), L. maculatus (Gahan) (2.8%–14.7%), and species of Pteromalus Swederus (0.6%–23.1%) (Pteromalidae). In contrast, the most abundant species in Quebec were Trichomalus lucidus (Walker) (Pteromalidae) (33.3%–56.4%), unidentified Eulophidae (2.1%–39.1%), Mesopolobus gemellus Baur and Muller (Pteromalidae) (1.3%–21.4%), and Necremnus tidius (Walker) (Eulophidae) (11.5%–19.3%). In the Ottawa, Ontario, area, parasitoids were first recovered in 2008, and Trichomalus perfectus (Walker) (Pteromalidae), M. gemellus, and species of Pteromalus were most prevalent. Mesopolobus gemellus and T. perfectus are reported in North America for the first time. Although existing communities appear to provide substantial parasitism (e.g., 6.3%–26.3% in 2006), species composition varies among years and differs from that in other regions in North America. Thus, parasitism levels and parasitoid communities of the cabbage seedpod weevil should be monitored to assess whether these will increase or there is a need to introduce more host-specific species from Europe that could provide greater mortality.

Larval phenologies and parasitoids of two seed-feeding weevils associated with hoary cress and shepherd's purse (Brassicaceae) in Europe

AbstractIn Europe, Ceutorhynchus turbatus Schultze and Ceutorhynchus typhae (Herbst) (Coleoptera: Curculionidae) feed on seeds from hoary cress and shepherd's purse (Cardaria draba (L.) Desv. and Capsella bursa-pastoris (L.) Medik.); both plants are invasive in North America. In North America, C. turbatus is a candidate for biological control of hoary cress, C. typhae is adventive, and both are sympatric with cabbage seedpod weevil (Ceutorhynchus obstrictus (Marsham)), an invasive alien pest of canola (Brassica napus L. and Brassica rapa L., Brassicaceae). We investigated host associations among C. turbatus, C. typhae, and their parasitoids in Europe. Of particular interest was host specificity of Trichomalus perfectus (Walker) and Mesopolobus morys (Walker) (Hymenoptera: Pteromalidae), candidates for biological control of C. obstrictus in North America. We found no evidence that T. perfectus attacks C. turbatus or C. typhae; however, M. morys was the most common parasitoid associated with C. turbatus.

A Test Using Wolbachia Bacteria to Identify Eurasian Source Populations of Cabbage Seedpod Weevil,Ceutorhynchus obstrictus(Marsham), in North America

Previous research using mitochondrial haplotypes indicates that North American populations of cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsham), originated from at least two separate introductions from source populations in Eurasia. We tested this hypothesis by comparing the genetic variation of symbiotic Wolbachia bacteria in C. obstrictus among seven North American and four European populations. Because Wolbachia are maternally inherited, infections acquired by a host species at one geographic location theoretically may be present in derivative populations that have established in new regions. Use of the conserved MLST Wolbachia genes gatB, coxA, hcpA, fbpA, and ftsZ identified one strain present in all beetles. Use of the variable wsp gene identified three distinct isolates of this strain that appear to co-occur in all populations and potentially in all individuals. Use of the variable wspB gene provided independent support for the presence of these isolates and evidence of a wspB pseudogene. The lack of genetic variation for these Wolbachia genes among host populations prevents their use to clarify the origins of C. obstrictus in North America. However, the results are an interesting example illustrating disjunction in genetic variation between mitochondria and a maternally-inherited symbiont.

European ectoparasitoids of two classical weed biological control agents released in North America

AbstractThe ceutorhynchine weevilsHadroplontus litura(F.) andMicroplontus edentulus(Schultze) (Coleoptera: Curculionidae), are established in North America as biological control agents for Canada thistle,Cirsium arvense(L.) Scop., and scentless chamomile,Tripleurospermum perforatum(Mérat) M. Lainz (Asteraceae), respectively. In North America, both weeds occur sympatrically and in similar habitats as another ceutorhynchine,Ceutorhynchus obstrictus(Marsham) (cabbage seedpod weevil), an important pest of canola,Brassica napusL., andBrassica rapaL. (Brassicaceae). Ceutorhynchinae weevils released to control weeds in cultivated crops may serve as alternate hosts if agents released for biological control ofC. obstrictusare not specific to that species. Parasitoids associated withM. edentulusandH. liturainflict similar levels of mortality on their hosts, yet a single species was associated with the latter host, whereas 13 species attacked the former. The stem-miningM. edentulusappears to be at some risk but not the root-crown feedingH. litura, should the parasitoidsTrichomalus perfectus(Walker) andMesopolobus morys(Walker) (Hymenoptera: Pteromalidae) be introduced as biological control agents of the silique-feedingC. obstrictus. These findings suggest that feeding niche may be an important criterion for developing a nontarget species test list for host-range testing of potential biological control agents.

Bottom-up effects of Brassica napus nutrition on the oviposition preference and larval performance of Ceutorhynchus obstrictus (Coleoptera: Curculionidae)

The cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsham) (Coleoptera: Curculionidae), is a serious pest of canola, Brassica napus L. and Brassica rapa L., both in Europe and North America. Nitrogen and sulfur levels can be readily manipulated by growers and could potentially be exploited to improve current pest management strategies. In an effort to better understand the relationship between host plant nutrition and C. obstrictus oviposition preference and its larval developmental biology, we exposed gravid females to host plants grown under differing regimes of nitrogen and sulfur. Results indicated that plants grown with a higher supply of nitrogen were preferred as hosts. Plants with a higher sulfur supply were also preferred but only in plants grown at lower nitrogen levels. In contrast, larval development time increased with increasing nitrogen levels although larval dry weights were unaffected. The results were inconsistent with the preference-performance hypothesis. The inconsistencies between oviposition choice and larval growth and development may be due to a conflict between maternal and larval fitness. Observed changes in larval development time may not represent a significant fitness cost for larval C. obstrictus, as no corresponding change in larval weight was observed. Possible causal mechanisms for the increase in development time include differences in oil, protein and glucosinolate contents of the seed. Fertilizer management regimes currently recommended were considered to be optimal for management of C. obstrictus as the yield benefits from higher rates of nitrogen fertilization would more than compensate for increased level of infestation.