Gérard Arnold

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

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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

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.

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.

Patriline differences in emergency queen rearing in the honey bee, Apis mellifera

SummaryIn the polyandrous honey bee, Apis mellifera, workers can potentially increase their inclusive fitness by rearing full-sister queens. If the mother queen dies suddenly, workers feed a few larvae in worker cells with royal jelly and rear them into queens (emergency queen rearing). Using DNA microsatellite markers we determined the patriline of emergency queens reared in two colonies headed by naturally-mated queens before being made queenless. We found that some patrilines were reared more than others in one colony, but not in the other. These differences between colonies suggest that selective rearing is not always present and this might explain the mixed results of previous nepotism studies in the honey bee.

Native Prey and Invasive Predator Patterns of Foraging Activity: The Case of the Yellow-Legged Hornet Predation at European Honeybee Hives

Contrary to native predators, which have co-evolved with their prey, alien predators often benefit from native prey naïveté. Vespa velutina, a honeybee predator originating from Eastern China, was introduced into France just before 2004. The present study, based on video recordings of two beehives at an early stage of the invasion process, intends to analyse the alien hornet hunting behaviour on the native prey, Apis mellifera, and to understand the interaction between the activity of the predator and the prey during the day and the season. Chasing hornets spent most of their time hovering facing the hive, to catch flying honeybees returning to the hive. The predation pressure increased during the season confirming previous study based on predator trapping. The number of honeybee captures showed a maximum peak for an intermediate number of V. velutina, unrelated to honeybee activity, suggesting the occurrence of competition between hornets. The number of honeybees caught increased during midday hours while the number of hornets did not vary, suggesting an increase in their efficacy. These results suggest that the impact of V. velutina on honeybees is limited by its own biology and behaviour and did not match the pattern of activity of its prey. Also, it could have been advantageous during the invasion, limiting resource depletion and thus favouring colonisation. This lack of synchronization may also be beneficial for honeybee colonies by giving them an opportunity to increase their activity when the hornets are less effective.

Defensive behaviour of Apis mellifera against Vespa velutina in France: Testing whether European honeybees can develop an effective collective defence against a new predator

We investigated the prey-predator interactions between the European honeybee, Apis mellifera, and the invasive yellow-legged hornet, Vespa velutina, which first invaded France in 2004 and thereafter spread to neighbouring European countries (Spain, Portugal and Italy). Our goal was to determine how successfully honeybees are able to defend their colonies against their new predator in Europe. Experiments were conducted in the southwest of France-the point of entry of the hornet in Europe-under natural and semi-controlled field conditions. We investigated a total of eight apiaries and 95 colonies subjected to either low or high levels of predation. We analyzed hornet predatory behaviour and collective response of colonies under attack. The results showed that A. mellifera in France exhibit an inefficient and unorganized defence against V. velutina, unlike in other regions of Europe and other areas around the globe where honeybees have co-evolved with their natural Vespa predators.