Samantha M. Cook

Are honey bees' foraging preferences affected by pollen amino acid composition?

Abstract.  1. Although pollen is a vital nutritional resource for honey bees, Apis mellifera, the influence of pollen quality on their foraging behaviour is little understood.

Behavioural and chemical ecology underlying the success of turnip rape (Brassica rapa) trap crops in protecting oilseed rape (Brassica napus) from the pollen beetle (Meligethes aeneus)

There is increasing interest in the use of trap crops as components of integrated pest management (IPM) strategies. Understanding the mechanisms underlying host plant preferences of herbivorous pests can lead to improved effectiveness and reliability of the trap crop. We investigated the behavioural and chemical ecology underlying the success of turnip rape, Brassica rapa, trap crops in protecting oilseed rape, Brassica napus, from the pollen beetle, Meligethes aeneus, which feeds in the flowers and lays its eggs in the buds causing yield loss. Using a semi-field arena bioassay, plant growth stage was found to be a major factor in the preference of this pest for B. rapa over B. napus. Plants at early-flowering growth stages were preferred over plants in the bud stage, irrespective of species. No preference was found when both species were flowering. As B. rapa develops faster than B. napus in the field, this could explain part of the mechanism of its success as a trap crop. However, B. rapa was preferred over B. napus when both species were in the bud stage, indicating some inherent preferences for B. rapa. Responses of M. aeneus in olfactometer tests to the odours of B. napus and B. rapa at the bud and flowering growth stages, reflected those of the semi-field arena bioassay. These behavioural responses can be explained by volatile compounds associated with the flowering stage. Phenylacetaldehyde, indole and (E,E)-α-farnesene were found to be present in air entrainment samples of both plant species at the flowering growth stage, but only in those of B. rapa at the bud stage. The former two compounds were behaviourally-active in olfactometer tests. These compounds are likely to be involved in host location by M. aeneus, and, at least partially, responsible for the attractiveness of B. rapa and its success as a trap crop to protect B. napus from this pest.

Do pollen beetles need pollen? The effect of pollen on oviposition, survival, and development of a flower‐feeding herbivore

Abstract.  1. Pollen is considered to be an important dietary component for many species of flower‐feeding herbivores. Its influence on oviposition site selection by the pollen beetle Meligethes aeneus, and on the development of its larvae was investigated.

Effect of a turnip rape (Brassica rapa) trap crop on stem-mining pests and their parasitoids in winter oilseed rape (Brassica napus)

AbstractConcerns about the negative effects of chemical control of oilseed rape (Brassica napus L.) pests on non-target species, human safety, and development of insecticide resistance, require alternative control strategies such as the use of trap crops and biocontrol to be developed. Psylliodes chrysocephala(L.) (Coleoptera: Chrysomelidae) (cabbage stem flea beetle) and Ceutorhynchus pallidactylus (Marsh.) (Coleoptera: Curculionidae) (cabbage stem weevil) are two major stem-mining pests of oilseed rape. This study investigated the phenology of these pests and their main parasitoids in the UK, the potential use of turnip rape (Brassica rapa L.) as a trap crop to reduce oilseed rape infestation, and the effects of insecticide treatment on pest incidence and larval parasitism. Water trap samples, plant dissections and pest larval dissections were done to determine: the incidence of adult pests and their parasitoids, the level of plant infestation by the pests and percentage larval parasitism, respectively. The turnip rape trap crop borders reduced P. chrysocephalabut not C. pallidactylus infestation of oilseed rape plots. Treatment of the trap crop with insecticide had little effect on either pest or parasitoid incidence in the oilseed rape. TersilochusmicrogasterSzép. andT. obscurator Aub. (Hymenoptera: Ichneumonidae) were the main larval parasitoids of P. chrysocephalaand C. pallidactylus, respectively. Tersilochus microgasteris reported for the first time in the UK. The implications for integrated pest management are discussed.

Could learning of pollen odours by honey bees (Apis mellifera) play a role in their foraging behaviour

Abstract.  The role of pollen odour cues in the foraging behaviour of honey bees (Apis mellifera L.) is poorly understood. Using classical conditioning of the proboscis extension response, in which bees learn to associate an odour with a sucrose reward, the present study tests whether odours of bee‐collected pollen from the hive environment or odours of fresh pollen on the anthers of flowers could be used in pollen foraging. Honey bees efficiently learn odours from field‐bean (Vicia faba) bee‐collected pollen and oilseed‐rape (Brassica napus) bee‐collected pollen, hand‐collected pollen, anthers and whole flowers, demonstrating that honey bees can learn pollen odours associatively in biologically realistic concentrations. Honey bees learn pollen odours of oilseed rape better than field bean and, although they generalize these two odours, they easily distinguish between them in discrimination tests, suggesting that pollen odours may be used in species recognition/discrimination. There is little evidence that honey bees can recognize whole flowers based on previous experience of bee‐collected pollen odour. However, they generalize the odours of oilseed‐rape anthers and whole flowers, suggesting that anther pollen in situ may play a more prominent role than bee‐collected pollen in foraging behaviour.

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.

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.

Red oilseed rape? The potential for manipulation of petal colour in control strategies for the pollen beetle (Meligethes aeneus)

The pollen beetle (Meligethes aeneus) is a major pest of oilseed rape (Brassica napus) at the inflorescence stage and is well known to prefer colours called yellow by human observers over many other colours. While commercial cultivars of oilseed rape have yellow flowers, little is known about the potential to manipulate host plant location and reduce subsequent infestation by this pest through variation in flower colour. We investigated the responses of pollen beetles to flowers of a white-petalled oilseed rape variety that had been dyed different colours in semi-field arena and field experiments. Flowers dyed blue or red were less heavily infested than those dyed yellow or the white flowers, indicating that blue and red flowers were less attractive than yellow and white ones. This response was most likely due to differences in petal colour because olfactometer studies showed that beetle responses to the odours of the coloured treatments did not differ. The comparatively high infestation of untreated white flowers is interpreted as a consequence of their high UV reflectance; the presence of a UV receptor in M. aeneus is suggested, and its role in visually guided insect–plant interactions in this species described. The potential for manipulation of petal colour in control strategies for the pollen beetle is discussed.

Responses of Phradis parasitoids to volatiles of lavender, Lavendula angustifolia —a possible repellent for their host, Meligethes aeneus

Hymenopterous parasitoids of herbivorous insects can be useful biocontrol agents in integrated pest management strategies. However, the potential effects on these beneficials of new components in such strategies are often neglected. Essential oil of lavender, Lavendula angustifolia (Miller) (Lamiaceae), has recently been identified as a potential repellent in new control strategies being developed for the pollen beetle Meligethes aeneus (Fabricius) (Coleoptera: Nitidulidae), a major pest of oilseed rape, Brassica napus L. (Brassicaceae). We tested the electrophysiological and behavioural responses of two common parasitoids of M. aeneus: Phradis interstitialis (Thomson) and P. morionellus (Holmgren) (both Ichneumonidae) using coupled gas chromatography-electroantennodetection (GC-EAD) and olfactometry techniques. Both species elicited electrophysiological responses to lavender oil volatiles, including two compounds known to be repellent to M. aeneus. However, the parasitoids gave no significant responses to the odours of lavender oil in behavioural bioassays and there was no evidence to suggest that lavender-treated oilseed rape plants would reduce host habitat location by parasitoids of the target pest.

Manipulating field margins to increase predation intensity in fields of winter wheat (Triticum aestivum)

The effectiveness of natural enemies to control pests can be enhanced through habitat manipulation. However, due to the differences in their ecology, generalist and specialist species may respond differently to the same manipulation. Moreover, interactions among natural enemies (i.e. cannibalism, intraguild predation, hyperparasitism) may complicate the assumption that a higher density of natural enemies would increase the level of biological control. We investigated the natural enemy guild composition and the predation rate along flower vs. grass margins at the edge of winter wheat (Triticum aestivum) fields in Denmark. Natural enemies were sampled by pitfall trapping and by suction sampling; predation intensity was measured using two different sentinel prey methods: artificial caterpillars made of plasticine, and sentinel aphid colonies. Specialist and generalist species responded differently to the two margin types: specialists (mostly parasitic wasps) were attracted by the flower margins, while generalists (ground beetles, rove beetles and spiders) were more active in grass margins. The number of artificial caterpillars attacked was significantly greater in grass margins (mean = 48.9%, SD = 24.3) than in flower margins (mean = 30.7%, SD = 17.4). We found a significant positive relationship between the number of artificial caterpillars attacked by chewing insects, and activity density for large (≥15 mm) ground beetles. Predation of sentinel aphids in wheat fields did not vary significantly in relation to margin type. Our results suggest that flowering margins may be beneficial for canopy‐active specialist natural enemies, but grassy margins are more useful for ground‐active generalist predators.