Andrew W. Ferguson

Spatial distribution of pest insects in oilseed rape: implications for integrated pest management

Abstract Insect pests, plant growth and plant yield in a crop of winter oilseed rape ( Brassica napus L.) were studied to assess the potential value of spatial information in integrated pest management for this crop. Ceutorhynchus assimilis Payk., Ceutorhynchus pallidactylus (Marsh.), Meligethes aeneus (Fab.) and Dasineura brassicae Winn. were sampled from the nodes of a rectangular grid across the crop. Their spatial distributions were mapped, analysed and compared using Spatial Analysis by Distance IndicEs (SADIE). The relationships between the distributions of insects, plant growth and yield were assessed using regression techniques. The distributions of C. assimilis , C. pallidactylus and M. aeneus were complex with differing irregular patterns of aggregation, whereas D. brassicae was edge-distributed. Stem injury, chiefly caused by larval Psylliodes chrysocephala L., was associated with significant yield loss and the spatial distribution of stem injury was reflected in the distribution of oil yield. The distribution of larval M. aeneus was dissociated from that of pods which shed their seed before harvest. Spatial heterogeneity in plant maturation as a result of infestation could delay the choice of harvest date beyond the optimum to prevent seed loss from less injured plants. Some of the variability (21–31%) in insect numbers within the crop was explained by variation in plant density and in growth stage at mid-flowering. The spatial ecology of these pests is discussed in terms of the roles of environmental factors, behavioural responses and the implications of spatial patterns for yield loss and for developing sustainable integrated crop protection. The data indicate that decision support systems should use sampling strategies which incorporate spatial information to model crop loss more accurately and that there may be potential for spatially targeted applications of insecticide to optimise the influence of biocontrol agents in oilseed rape.

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.

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.

Distributions and interactions of the stem miners Psylliodes chrysocephala and Ceutorhynchus pallidactylus and their parasitoids in a crop of winter oilseed rape (Brassica napus)

The within‐field spatio‐temporal distributions and relationships of two pest insects with stem‐mining larvae, Psylliodes chrysocephala (L.) (Coleoptera: Chrysomelidae) and Ceutorhynchus pallidactylus (Marsham) (Coleoptera: Curculionidae), and their larval endoparasitoids, Tersilochus microgaster (Szépligeti) and Tersilochus obscurator Aubert (Hymenoptera: Ichneumonidae), respectively, were studied in a crop of winter oilseed rape [Brassica napus L. (Brassicaceae)]. The insects were sampled, at different life stages, at 40 spatially referenced points within the oilseed rape in 1998–99 and in the following crop of winter wheat. Distributions were analysed and compared using SADIE (Spatial Analysis by Distance IndicEs) and by tests of edge distribution. Tersilochus microgaster emerged from overwintering by the end of March and T. obscurator from mid April to mid May 2000. Tersilochus microgaster parasitized 10.8% of P. chrysocephala larvae, peak parasitism occurring in May. The distribution of each species was patchy and irregular. Psylliodes chrysocephala and its parasitoid were closely associated, but new generation C. pallidactylus and T. obscurator were less so, probably because of host mortality caused by the parasitoid. The two host–parasitoid pairs showed distributions that were polarized with respect to each other. The genesis of these spatial patterns is discussed in relation to the influence of wind direction, plant size, and interspecific interactions. The potential of these parasitoids as biocontrol agents in integrated pest management is discussed. Opportunities for conservation biocontrol in oilseed rape offered by spatio‐temporal targeting of insecticides to avoid parasitoids and by reduced soil tillage are examined.

The spatial dynamics of pollen beetles in relation to inflorescence growth stage of oilseed rape: implications for trap crop strategies.

Semi‐field‐scale arrays of oilseed rape (Brassica napus L.) (Brassicaceae) plants were used to observe the development of distributions of pollen beetles (Meligethes aeneus Fabricius) (Coleoptera: Nitidulidae) in a simulated trap crop system where inflorescence growth stage alone was used to manipulate the pest. Over two successive years, pairs of 1 m spaced square arrays of 100 glasshouse‐grown plants were placed 40 m apart in the field in May, and were subject to natural infestation by pollen beetles. The test plot of each pair had a simulated trap crop, with an outer row of plants at early flowering stage intended to protect more susceptible inner plants at late bud stage, and the control plot had all plants at the late‐bud stage, simulating a standard crop situation. Pollen beetles were counted daily on each plant for 10–13 days. The spatio‐temporal development of plot infestation was analysed in relation to the distribution of racemes in bud and raceme in flowers using Spatial Analysis by Distance IndicEs (SADIE), and tests of edge and centre distribution. Inflorescence growth stage characteristics were shown to be important in determining the spatial distributions of pollen beetles. In control plots, the numbers of racemes in bud and in flower were never edge or centre distributed. In test plots, racemes in flower were always edge distributed, and racemes in bud began edge distributed and became centre distributed. Pollen beetle numbers were usually spatially associated with the abundance of racemes in bud and/or in flower. In control plots, pollen beetles were neither edge nor centre distributed, but in test plots they maintained a significant edge distribution for 7–10 days. At the end of the experiments, females were more centre distributed in the test plots than males, and were more closely associated with racemes with buds, whereas males were more associated with racemes with flowers. In early flowering stage plants, the number of racemes in flowers were a good indicator of the abundance of racemes in buds, but this relationship was lost as flowering progressed. Although flowering racemes provide strong cues for immigrating pollen beetles, the abundance of buds may be a more important determinant of residence time, particularly for females, and is therefore a critical determinant of trap crop effectiveness.

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.

Factors determining the release of Nasonov pheromone by honeybees at the hive entrance

ABSTRACT. Worker bees recently denied access to their colony expose their Nasonov glands, thereby releasing pheromone, at the entrance to their hive. Odours of the following induced this response: empty comb, purified beeswax, honey, pollen, propolis, a live queen, the (E)‐9‐hydroxy‐2‐decenoic acid component of a queens mandibular glands, live drones and workers, inert material on which workers had walked inside the hive, and synthetic Nasonov pheromone. The total odour of a foreign colony also induced worker bees to expose their Nasonov glands but was less effective than the odour of their own colony. Odours of the following were not effective: the (E)‐9‐oxo‐2‐decenoic acid component of a queens mandibular glands, recently killed drones and workers, worker brood (eggs, larvae, pupae).

Evaluation of the various components of the Nasonov pheromone used by clustering honeybees

ABSTRACT. Of the various components of the Nasonov pheromone, geraniol, (E)‐citral and nerolic acid were the most important for inducing clustering. The presence of (Z)‐citral with (E)‐citral, or in a mixture of components including (E)‐citral, did not diminish clustering and sometimes increased it. Geranic acid alone encouraged clustering, but was less effective with nerolic acid or the citrals. Nerol and (E, E)‐farnesol had little obvious influence on clustering. A 1:1:1 mixture of geraniol + nerolic acid + (E)‐ and (Z)‐citrals was as effective as a mixture of all the seven components in equal proportions, which was in turn as effective as a mixture containing the components in the proportions present naturally in the Nasonov gland.

Temperature-activity relationships in Meligethes aeneus: implications for pest management

BACKGROUND Pollen beetle (Meligethes aeneus F.) management in oilseed rape (Brassica napus L.) has become an urgent issue in the light of insecticide resistance. Risk prediction advice has relied upon flight temperature thresholds, while risk assessment uses simple economic thresholds. However, there is variation in the reported temperature of migration, and economic thresholds vary widely across Europe, probably owing to climatic factors interacting with beetle activity and plant compensation for damage. The effect of temperature on flight, feeding and oviposition activity of M. aeneus was examined in controlled conditions. RESULTS Escape from a release vial was taken as evidence of flight and was supported by video observations. The propensity to fly followed a sigmoid temperature–response curve between 6 and 23 °C; the 10, 25 and 50% flight temperature thresholds were 12.0–12.5 °C, 13.6–14.2 °C and 15.5–16.2 °C, respectively. Thresholds were slightly higher in the second of two flight bioassays, suggesting an effect of beetle age. Strong positive relationships were found between temperature (6–20 °C) and the rates of feeding and oviposition on flower buds of oilseed rape. CONCLUSION These temperature relationships could be used to improve M. aeneus migration risk assessment, refine weather-based decision support systems and modulate damage thresholds according to rates of bud damage.

Techniques for studying honeybee pheromones involved in clustering, and experiments on the effect of Nasonov and queen pheromones

ABSTRACT. Techniques for investigating pheromones responsible for clustering in Apis mellifera are described. Stable queenless clusters were formed in response to synthetic Nasonov pheromone mixed with (E)‐9‐oxo‐2‐decenoic acid. This mixture plus the addition of (E)‐9‐hydroxy‐2‐decenoic acid was less potent in initiating cluster formation than it was without this addition, but the clusters once formed sometimes grew larger. Other unknown components from the queens mandibular glands encouraged cluster formation.