Claudine Masson

Comparative study of the antennal lobes and their afferent pathway in the worker bee and the drone (Apis mellifera)

SummaryThe topography of the antennal afferent path-ways was studied comparatively in the worker bee and the drone of Apis mellifera L. by cellular marking, following localized application of cobalt chloride to the cut end of one antenna. This study dealt principally with the first relay of the afferent pathway in the glomeruli of the antennal lobe. The counting and measurement of all the glomeruli were performed on 5 worker bees and 5 drones. An important sexual dimorphism, represented by 4 large and easily identifiable glomerular complexes, was demonstrated in the drone. In both worker bee and drone, four main regions of the glomerular neuropil were distinguished according to corresponding afferent bundles. The worker possessed 166 glomeruli and the drone 103. The number, position and dimensions of the glomeruli indicated that the glomerular organization was unvarying in worker bees and in drones. Concerning the internal structure of the glomeruli, two types were distinguished: the great majority (95%) exhibited a cortical layer, whereas in the 7 posterior glomeruli the synaptic fields of association seemed to be scattered throughout the whole volume. The main results of this work (glomerular invariance, sexual dimorphism) support the hypothesis of the functional unit of the glomeruli.

Attraction of the Parasitic Mite Varroa to the Drone Larvae of Honey Bees by Simple Aliphatic Esters

An important parasitic threat to honey bees, the mite Varroa jacobsoni, is attracted to its major prey, drone larvae, by methyl and ethyl esters of straight-chain fatty acids, in particular methyl palmitate. These esters were extracted from drone larvae with n-hexane and were identified by gas chromatography-mass spectrometry. Their behavioral effect was evaluated with the use of a four-arm airflow olfactometer.

Identification of a Brood Pheromone in Honeybees

1. Reddy, G. R.: Can. J. Soil Sci. 44, 254 (1964) 2. Zacherl, B., Amberger, A.: VDLUFASchriftenr. 11, 55 (1984) 3. Amberger, A., Vilsmeier, K.: Z. P flanzenernaehr. Bodenkd. 142, 778 (1979) 4. Vilsmeier, K.: ibid. 143, 113 (1980) 5. Vilsmeier, K.: Z. Wasser-AbwasserForsch. 21, 140 (1988) 6. Rathsack, K. : Landw. Forsch. 6, SH, 116 (1955) 7. Hauser, M., Haselwandter, K.: Soil Biol. Biochem. 22, 113 (1990)

Ontogeny maturation and plasticity of the olfactory system in the Workerbee

Abstract The ontogeny and maturation of the olfactory system in the workerbee have been studied using a combination of neurophysiological (first order neurones) and neuroanatomical techniques (second order neurones). EAG recordings show that normal maturation of the olfactory response takes place during the first 4 days following emergence, and is closely related to the sensory environment during the same period. The synaptic organization of first order and second order neurones of the antennal afferent pathway (analyzed at the level of the glomeruli in the deutocerebrum) is essentially complete three days before emergence. These results are discussed in relation to a possible role of the sensory environment during the period from 3 days before until 8 days after emergence.

Temporal pheromonal and kairomonal secretion in the brood of honeybees

In a honeybee colony, brood care is ensured by adult bee behavior adapted to the different ages and castes of larvae. The brood is incubated, the larvae are fed, and their cells are capped [ 1 3]. In order to adopt the appropriate behavior, adult workers must be able to recognize the age and the caste of a larva. Like most social Hymenoptera, chemical signals play an essential role in brood recognition for the honeybee [4]. When the worker larvae are 9 days old (from the time of egg-laying), adult bees close the top of the brood cell with a wax cap [5]. This behavior can be artificially triggered by four of the ten methyl and ethyl fatty acid esters present on the surface of larvae: methyl palmitate, methyl oleate, methyl linoleate, and methyl linolenate (MP, MO, ML, MLN) [6]. The six other fatty acid esters identified in the larval cuticle are: ethyl palmitate (EP), methyl stearate (MS), ethyl stearate (ES), ethyl oleate (EO), ethyl linoleate (EL), and ethyl linolenate (ELN). The parasitic mite, Varroa jacobsoni, reproduces on the brood of honeybees. It is attracted by worker and drone larvae just before their cells are capped, and reproduces in the sealed cell until the adult bee emerges at 21 days of age. Among the compounds present in cuticular larval extract, only three esters methyl and ethyl palmitates, and methyl linolenate (MP, EP, MLN) are attractive to Varroa [7]. Thus, two of these esters act both as pheromones and as kairomones. It seems likely that the presence of these esters in the larval cuticle on the 9th day is responsible for both the entry of Varroa females into the cells and for the capping behavior of workers. This hypothesis is now supported by evidence

Sunflower volatiles involved in honeybee discrimination among genotypes and flowering stages

In order to define the part of olfactory cues in the selective behavior of honeybees, observation on their foraging behavior was carried out on various sunflower genotypes in parallel with chemical analysis of aromatic extracts of the genotypes. Foragers show a preference for the early stages of flowering and, when they are given a choice between couples of parental lines of two commercial hybrids, Marianne and Mirasol, they are randomly distributed on Mirasol parents, but they prefer the female line of Marianne. The comparison of relative proportions of compounds among aromagrams obtained from head space trapping from the two couples of genotypes, reveals (1) a phenological stage effect for 17 compounds among 144 indexed compounds for Marianne lines and for 18 among 136 indexed compounds of Mirasol lines; most of these compounds exhibit higher relative proportions in the early flowering stages, which is related to plant attractiveness towards honeybees; (2) a sex effect for 33 compounds among 144 for Marianne lines and for 14 compounds among 136 for Mirasol lines; further semiquantitative analyses reveal a sex effect for only eight compounds of 134 for Marianne lines and 20 compounds of 250 for Mirasol lines, which represents less than 10% of the indexed compounds. These discriminatory compounds were partly identified by coupled GC-MS. Possible relations between such phenological and genotypical volatile fluctuations and forager attraction are discussed.

Foraging behaviour of honey bees (Apis mellifera L.) on transgenic oilseed rape (Brassica napus L. var. oleifera)

The impact of genetically modified oilseed rape (Brassica napus L.) on the foraging behaviour of honey bees (Apis mellifera L.) was evaluated on two different lines transformed to express constitutively heterologous chitinase in somatic tissue for enhanced disease resistance. Experiments were conducted in confinement in an indoor flight room with controlled conditions and in an outdoor flight cage with conditions more representative of the open environment. Foraging behaviour was analysed by observations of general bee behaviour (total number of visits) and of individual bee behaviour (using a video camera coupled with a special software program to process the data). The plants were analysed in terms of nectar quantity and quality (nectar volume and sugar content). The results showed no effects on bee foraging behaviour due to the modification of the genome of these plants by the introduction of a chitinase gene even though some differences between lines were found in the nectar. The methods applied in this original approach for the evaluation of the impact of genetically modified oilseed rape were shown to be sufficiently sensitive to detect changes in bee behaviour resulting from differences between plants.

Semiochemical basis of infestation of honey bee brood byVarroa jacobsoni

Capping of workerApis mellifera cells is elicited by four fatty acid methyl esters (Methyl palmitate, methyl oleate, methyl linoleate, and methyl linolenate) that are present on the surface of the worker and drone larvae only a few hours before the cell is closed. The amount of the pheromone reaches its maximum value when the cell has just been capped, at 8.5 and at 10.25 days of age, respectively, for worker and drone larvae. Thereafter, the amount of the pheromone decreases to its initial level. These data suggest that the esters also have a role in the capping of the drone cells, the temporal signal allowing the worker bees to recognize the age of the larvae and then to do the appropriate behavior. Two pheromonal components, methyl palmitate and methyl linolenate, and the inactive ethyl palmitate are kairomones attractive toVarroa females. Their secretion by the larvae follows the same pattern of development as the pheromonal signal. The longer and greater kairomonal signal in drone larvae, compared to worker secretion, could explain the preference ofVarroa towards drone brood.

Sunflower aroma detection by the honeybee : study by coupling gas chromatography and electroantennography

Combined electrophysiological recordings (EAG) and gas chromatographic separation were performed in order to investigate which volatile chemical components of a sunflower extract could be detected by honeybee workers and thus are likely to trigger the foraging behavior. A direct coupling device allowed for the stimulation of the antennal receptors with individual constituents of a polar fraction of the flower aroma shown to be attractive to bees. More than 100 compounds were separated from the extract. Twenty-four compounds elicited clear EAG responses. These compounds were identified by mass spectrometry (electronic impact and chemical ionisation). Both short- and long-chain aliphatic alcohols, one short-chain aliphatic aldehyde, one acid, two esters, and terpenic compounds were found to stimulate the antennal receptors. Six compounds identified in previous behavioral experiments were found to exhibit EAG activity. The chemicals screened by this method may be used for recognition of the plant odor and the selective behavior of honeybees.

Influence of social environment on genetically based subfamily signature in the honeybee.

In honeybees, the cuticular hydrocarbon profiles are partly genetically based and differ between subfamilies, which suggests that they might be used by the workers as labels for subfamily recognition. This ability could potentially form the basis for nepotistic conflicts between subfamilies that would be detrimental to the inclusive fitness of the colony. Here we have compared the subfamily hydrocarbon profiles of 5-day-old workers maintained in isolation with those kept in their parental colony. We demonstrate that the cuticular hydrocarbon profiles tend to be less distant between most subfamilies within the hive compared with those held in isolation. The main consequence of this partial homogenization of the majority of subfamily signatures may result in a reduction of the number of recognizable subfamilies in the colony. Nevertheless, a few subfamilies retain very distinct cuticular hydrocarbon profiles.