Effect of conditioning on discrimination of oilseed rape volatiles by the honeybee: use of a combined gas chromatography-proboscis extension behavioural assay.

The coupled gas chromatography-proboscis extension assay technique was used on restrained worker bees to study responses to components of an extract of oilseed rape floral volatiles. Bees were stimulated with the effluent from the gas chromatograph after either paired or unpaired conditioning to the extract, or after a control treatment. Proboscis extension activity was elicited in six areas of the chromatogram. However, the number of bees responding in two of these areas were too low to be considered in the present study. One significant area of activity was associated with the major component, (E,E)-alpha-farnesene, whilst the others were associated with several minor components. Although all three groups of bees, irrespective of the treatments applied, showed some responses to the components eluting from the GC column, only bees subjected to paired conditioning consistently responded when re-tested to the mixture. In addition, paired conditioning increased the responsiveness of individuals in terms of the number of bees responding at least once to the effluent from the gas chromatograph. This work confirmed the occurrence of key compounds in floral volatile mixtures. Possible synergistic/inhibitory effects between components, relating to olfactory experience, are discussed.

Antennal perception of oilseed rape,Brassica napus (Brassicaceae), volatiles by the cabbage seed weevilCeutorhynchus assimilis (Coleoptera, Curculionidae).

The response of theCeutorhynchus assimilis antenna to volatiles in air entrainment-derived extracts of oilseed rape,Brassica napus, was studied using coupled gas chromatography (GC)-electroantennography (EAG) and coupled GC-single cell recording (SCR). By means of these techniques and coupled gas chromatography-mass spectrometry (GC-MS), 25 active compounds were identified, including isoprenoids and compounds derived from fatty acids and amino acids. Some of the latter, the isothiocyanates and goitrin, and probably indole and benzyl cyanide, are catabolites of glucosinolates. The electrophysiological activity of the identified compounds was confirmed by EAG using a physiologically discriminating dose, and by SCR studies. The importance of the combined use of the EAG and SCR techniques was demonstrated, since specific olfactory cells were located for five compounds that did not elicit significant EAG responses. The majority of the olfactory cells from which single cell recordings were obtained showed very high specificity, and in numerous recordings there were consistent pairings of specific cell types.

Discrimination of oilseed rape volatiles by honey bee: Novel combined gas chromatographic-electrophysiological behavioral assay.

A novel technique for the simultaneous monitoring of electroan-tennogram (EAG) and conditioned proboscis extension (CPE) responses of honey bees to the effluent from a gas chromatograph (GC) was developed to locate biologically active components in blends of plant volatiles and to investigate odor recognition at the peripheral and behavioral levels. A six-component mixture, comprising compounds previously identified as oilseed rape floral volatiles, was used as the stimulus. Standard CPE and EAG recordings were done as a reference. EAG responses were elicited from unconditioned bees by all the components presented either in the coupled or the standard mode. Conditioned bees gave larger EAG responses than unconditioned bees, suggesting that antennal sensitivity is enhanced by conditioning. At the behavioral level, in both the standard and the coupled modes, only conditioned bees showed the proboscis extension response, with the majority of individuals responding to linalool, 2-phenylethanol, and benzyl alcohol.

Oilseed rape--a new allergen?

Oilseed rape (Brassica napus) is a commonly grown crop in Europe and it has been suggested that its pollen may be a potent new allergen. The prevalence of sensitization in a normal exposed population and an objective study of those patients found to be allergic to the rape pollen is described. The results show a low prevalence of allergy to oilseed rape pollen (less than 0.2%) unless the subjects were occupationally exposed. Those affected, with one exception, were already atopic and allergic to other pollens. The role of volatile materials given off by the plant remains to be elucidated.

A comparative bronchodilator study of salbutamol and salbutamol sulphate that were administered by metered-dose inhalers.

Twenty-one patients with mild-to-moderately-severe asthma participated in a placebo-controlled, double-blind, cross-over, randomized bronchodilator study of 200 micrograms of salbutamol (Glaxo) and 200 micrograms of salbutamol in the form of salbutamol sulphate (Riker; 50-microL and 25-microL valves) that were administered by metered-dose inhalers. The mean baseline forced expired volumes in one second (FEV1) were similar for the four separate study days. The three active treatments caused a significantly-greater FEV1 response than did placebo for four hours (P less than 0.05) and no difference was found between the treatments (P greater than 0.05). The power of the study was 75% with a clinically-significant difference in the FEV1 response of 25%. The administration of 200 micrograms of salbutamol (Glaxo) caused the same FEV1 response as did that of 400 micrograms of salbutamol at the end of that study day (P greater than 0.05), but both 200-micrograms doses of salbutamol sulphate (Riker) caused a smaller FEV1 response than did the 400 micrograms of salbutamol sulphate (P less than 0.05). These observations indicate that no clinically-significant difference occurs between the bronchodilator effects of salbutamol and those of salbutamol sulphate which is administered as 200 micrograms of salbutamol equivalent, with different propellant mixtures, dispersal agents and valvular systems.

Male-produced aggregation pheromone in pea and bean weevil,Sitona lineatus (L.).

The attraction ofS. lineatus to live baits comprisingS. lineatus feeding onVicia faba (L.) was studied in a field experiment in the early spring. There was clear evidence that maleS. lineatus produced an aggregation pheromone which attracted approximately equal numbers of both sexes from overwintering sites. No evidence was obtained for the production, in the spring, of any semiochemical by female weevils.

Field response of the dutch elm disease vectors,Scolytus multistriatus (Marsham) andS. scolytus (F.) (Coleoptera: Scolytidae) to 4-methyl-3-heptanol baits containing α-, ß-,δ-, or δ-multistriatin.

The field responses of English populations of the Dutch elm disease vectors,Scolytus multistriatus andS. scolytus to baits containing 4-methyl-3-heptanol, a host synergist [(-)-α-cubebene or (-)-limonene] and (±)-α-, (+)-ß-, (-)-ß-, (±)-γ-, or (±)-δ-multistriatin were examined. (±)-α-Multistriatin, released at 5-10 µg/day, enhanced the response ofS. multistriatus to baits containing 4-methyl-3-heptanol and either of the host synergists but had no effect on the capture ofS. scolytus. The release of larger amounts (57 or 365 µg/day) of (±)-α-multistriatin interrupted the response of both species to the 4-methyl-3-heptanol baits. It appears that α-multistriatin has multiple functions as a behavior-modifying substance for the two beetles. The (+)-ß-, (-)-ß-, (±)-γ-, and (±)-δ-multistriatins were inactive when released at 5-10 µg/day. The results of these field experiments suggest that one bait can be formulated to capture both species.

Responses of the olfactory receptors ofScolytus scolytus (F.) (Coleoptera: Scolytidae) to the stereoisomers of 4-methyl-3-heptanol.

Electroantennogram (EAG) and single-cell recording techniques have been used to demonstrate the presence of separate receptors for (-)-threo- and (-)-erythro-4-methyl-3-heptanol on the antenna ofS. scolytus. The majority of single-cell recordings showed spikes of two different amplitudes. The cell giving spikes of larger amplitude responded to the (-)-threo stereoisomer while the cell with the small-amplitude spikes responded to (-)-erythro-4-methyl-3-heptanol. It is suggested that in most recordings the two cells are associated with a single sensillum basiconicum.