Jerome Trouiller

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)

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.

Chemical recognition of queen cells by honey bee workersApis mellifera (Hymenoptera: Apidae)

SummaryHoney bee workers are able to nurse or to destroy and thus to recognize the capped queen cells containing a pupa. Fatty acid esters, especially methyl oleate, methyl palmitate and ethyl oleate were found in significant amounts on the queen pupal cuticle. Methyl oleate, the major component, along with smaller amounts of methyl linoleate and methyl linolenate, were involved in the recognition of queen cells by workers. In natural conditions of the colony, queen cells containing a paraffin pupal lure with methyl oleate were accepted 5.9 days by workers, releasing about 1.8 queen pupa equivalents during that period, when control cells (without ester) were kept only 2.1 days. Although these esters are non specific to honey bees, they are of great importance in social regulation of the honey bee colony.