Ingrid H. Williams

Wound‐induced increases in the glucosinolate content of oilseed rape and their effect on subsequent herbivory by a crucifer specialist

Damage to the oilseed rape plant (Brassica napus L.) by the cabbage stem flea beetle, Psylliodes chrysocephala L. (Coleoptera: Chrysomelidae) induces systemic changes to the glucosinolate profile, most noticeably an increase in the concentration of indole glucosinolates. When jasmonic acid was applied to the cotyledons of the plant, a similar effect was observed. Feeding tests with artificial substrates compared a glucosinolate fraction from jasmonic acid-treated plants with a similar fraction from untreated plants. In these tests, alterations to the glucosinolate profile increased the feeding of a crucifer-specialist feeder (P. chrysocephala). However, in whole plant tests, P. chrysocephala did not feed more on the jasmonic acid treated plants than on the controls. This implies that other aspects of the damage response are being induced by the jasmonic acid treatment and having a negative effect on subsequent herbivory.

The Major Insect Pests of Oilseed Rape in Europe and Their Management: An Overview

The oilseed rape crop in Europe is attacked by six major pests that often require control by growers to protect seed yield: the cabbage stem flea beetle, pollen beetle, cabbage seed weevil, cabbage stem weevil, rape stem weevil and brassica pod midge. These attack the crop successively at various growth stages and damage different parts of the plant. They are all widespread but their relative importance varies with country and year. Their control is still mainly through the application of chemical insecticides, often applied prophylactically. The pollen beetle has developed widespread resistance to pyrethroids, the main group of insecticides now used, increasing the urgency for alternative control strategies. The past decade has seen considerable progress in our knowledge of the parasitoids, predators and pathogens that contribute to biocontrol of the pests and of how to incorporate biocontrol into integrated pest management systems. More efficient targeting of insecticides in time and space can be achieved using economic thresholds, crop monitoring and computer-based decision support systems. Push-pull strategies are being developed that use host plant preferences and behavioural responses to semiochemicals to influence pest and natural enemy distributions on the crop. There is also potential for natural enemy conservation through modification of within-field crop husbandry practices as well as, on the landscape scale, through habitat and environmental manipulation to encourage vegetational diversity of the agroecosystem incorporating hedgerows, cover crops, flowering conservation headlands and field margins to provide refuge, food, overwintering sites and alternative prey or hosts for natural enemies.

Honey-bee-mediated infection of pollen beetle (Meligethes aeneus Fab.) by the insect-pathogenic fungus, Metarhizium anisopliae.

Pollen beetles (Meligethes aeneus) are pests that feed and oviposit in the buds and flowers of oilseed rape. Honey-bees foraging from a hive fitted with an inoculum dispenser at the entrance effectively delivered dry conidia of the entomogenous fungus, Metarhizium anisopliae , to the flowers of oilseed rape in caged field plots. In both winter- and spring-sown rape experiments, a greater mortality of pollen beetles occurred in treated plots than in control plots. The mortality (61% on winter rape, 100% on spring rape) was greatest during peak flowering, when the feeding activity of both bees and beetles from the flowers was maximal, providing optimal conditions for inoculum dissemination and infection. Conidial sporulation occurred on a significant proportion of the dead pollen beetles. There was no evidence of any adverse effect on the honey-bee colonies.

The spatio-temporal distribution of adult Ceutorhynchus assimilis in a crop of winter oilseed rape in relation to the distribution of their larvae and that of the parasitoid Trichomalus perfectus.

The spatio‐temporal distribution of Ceutorhynchus assimilis Payk. (Coleoptera: Curculionidae) adults caught in a rectangular grid of flight traps in a crop of winter oilseed rape (Brassica napus L.) was mapped and was analysed using Spatial Analysis by Distance IndicEs (SADIE). Their distribution was compared to that of their larvae and that of their parasitoid Trichomalus perfectus (Walker) (Hymenoptera: Pteromalidae) in pods. The distribution of immigrating C. assimilis adults was consistent with their arrival at the crop boundaries and movement within the crop towards its centre. Adult C. assimilis were aggregated at all times, invasion being on two fronts, leading to the formation of two major clusters within the crop. Large areas of the crop remained relatively unpopulated. During the emigration phase, numbers declined simultaneously in all parts of the crop. The distributions of adult and larval C. assimilis and of larval T. perfectus were spatially associated. The distribution of the parasitoid did not show a density dependent relationship with that of its host. We discuss the movements of insects which underlie their population distributions, the value of integrating spatial information into improved management strategies for C. assimilis and the potential for the spatial targeting of insecticides to reduce the amount applied and to conserve T. perfectus.

Parasitoids of Oilseed Rape Pests in Europe: Key Species for Conservation Biocontrol

The six most important pests of oilseed rape are host to at least 80 species of parasitoid, mostly parasitic Hymenoptera, particularly braconids, chalcids and ichneumonids. Most of them attack the egg or larval stages of their hosts. Based on reviews of the literature and extensive sampling programmes during the EU project MASTER (QLK5-CT-2001-01447), 12 species have been identified as the key parasitoid species of these pests in winter oilseed rape, and, with little divergence, also in spring rape in nearly all European countries where their hosts occur. Some key species have been recorded for the first time in individual partner countries. They are sufficiently widespread and abundant across Europe to be of potential economic importance for conservation biological control of the target pests. Their incidence and abundance in European countries were associated with the occurrence of their hosts, thereby indicating close host-parasitoid-relationships.

The Effect of Giving Pollen and Pollen Supplement to Honeybee Colonies on the Amount of Pollen Collected

SummaryFeeding pollen in the hive in summer reduced the amount of pollen collected by the colony. But when a pollen supplement was provided instead, little was consumed and there was no apparent effect on pollen collection.

Deposition and longevity of oviposition-deterring pheromone in the cabbage seed weevil

Abstract The cabbage seed weevil (Ceutorhynchus assimilis Payk.) lays eggs singly into pods of oilseed rape (Brassica napus L.) through punctures bored with the mouthparts, preferring pods not recently used for oviposition. A simple new choice test has been used to test individual components of egg‐laying behaviour for their effect on oviposition site selection. It is confirmed that an oviposition‐deterring pheromone (ODP) is deposited during abdomen brushing of the pod which follows egg‐laying. Neither pin punctures, weevil feeding punctures, oviposition punctures nor eggs had any deterrent effect. Pods walked on by female weevils were not avoided by those laying eggs. Observations suggest that the ODP is sensed by contact chemoreceptors on the antennae. The deterrent effect lasted only 1–2 h. The implications of these findings on the adaptive significance of the pheromone and its possible use in pest control are discussed.

Crop Location by Oilseed Rape Pests and Host Location by Their Parasitoids

The behavioural ecology associated with location of the oilseed rape crop by its major coleopteran and dipteran pests and by their key hymenopterous parasitoids is reviewed. Results of studies investigating their responses to odour and colour cues from the crop, using olfactometers, wind tunnels, baited and/or coloured traps, and different plant lines, are presented. Host plant volatiles, particularly the isothiocyanates, carried downwind from the crop, and the colours yellow and green are important cues for orientation; odour cues can induce responses to colour cues. Species differ in the subset of cues they use and responses can vary with sex, age, generation, nutritional status, previous experience and time since last oviposition. Evidence suggests that odour-mediated upwind anemotaxis is used by the pests to locate the crop and their host plant, as well as by their parasitoids to locate the crop, the habitat of their host larvae, from a distance, while visual cues are important for orientation at closer range. Once the crop is located, pests use taste and tactile cues from the oilseed rape plant to accept or reject it while parasitoids use host-derived cues to locate their hosts. The implications for integrated pest management and conservation biocontrol are discussed.

Mapping, characterisation, and comparison of the spatio-temporal distributions of cabbage stem flea beetle (Psylliodes chrysocephala), carabids, and Collembola in a crop of winter oilseed rape (Brassica napus)

The spatio‐temporal distribution of Psylliodes chrysocephala (L.) (Coleoptera: Chrysomelidae), a pest of oilseed rape (Brassica napus) (L.) (Cruciferae) and its potential predators, carabid beetles, within a crop of winter oilseed rape is described. The distribution of Collembola, a potential alternative food source for the predators, is also investigated. Insects were collected from spatially referenced sampling points across the crop and the counts mapped, analysed, and the degree of spatial association between the distributions determined using Spatial Analysis by Distance IndicEs (SADIE). Immigration into the crop by adult P. chrysocephala occurred from two edges and resulted in a non‐uniform distribution of the pest within the crop. Infestation of rape plants by P. chrysocephala larvae was greatest within the central area of the crop. Significant spatial association between adult female P. chrysocephala and the larval infestation of plants occurred throughout October. Three carabid species were active and abundant during peak pest immigration into the crop, viz., Trechus quadristriatus (Schrank) (Coleoptera: Carabidae), Pterostichus madidus (Fabricius) (Coleoptera: Carabidae), and Nebria brevicollis (Fabricius) (Coleoptera: Carabidae). Two of these species, T. quadristriatus and P. madidus, showed significant spatial association with the larvae of P. chrysocephala during October. All three carabid species showed a significant spatial association with Collembola during mid‐September, indicating that the latter may be an important food source for carabids during this period. In laboratory feeding experiments, only T. quadristriatus consumed the eggs of P. chrysocephala suggesting that, in the adult stage, this species may be the most important of the naturally occurring carabids as a predator of P. chrysocephala in the field. Adult T. quadristriatus may be a valuable component of an Integrated Pest Management strategy for winter oilseed rape, and the conservation of this species could be beneficial.

Insect pests and their natural enemies on spring oilseed rape in Estonia : impact of cropping systems

To investigate the impact of different cropping systems, the pests, their hymenopteran parasitoids and predatory ground beetles present in two spring rape crops in Estonia, in 2003, were compared. One crop was grown under a standard (STN) cropping system and the other under a minimised (MIN) system. The STN system plants had more flowers than those in the MIN system, and these attracted significantly more Meligethes aeneus, the only abundant and real pest in Estonia. Meligethes aeneus had two population peaks: the first during opening of the first flowers and the second, the new generation, during ripening of the pods. The number of new generation M. aeneus was almost four times greater in the STN than in the MIN crop. More carabids were caught in the MIN than in STN crop. The maximum abundance of carabids occurred two weeks before that of the new generation of M. aeneus, at the time when M. aeneus larvae were dropping to the soil for pupation and hence were vulnerable to predation by carabids.