Search

Honeybees have evolved a social immunity consisting of the cooperation of individuals to decrease disease in the hive. We identified a set of genes involved in this social immunity by analysing the brain transcriptome of highly varroa-hygienic bees, who efficiently detect and remove brood infected with the Varroa destructor mite. The function of these candidate genes does not seem to support a higher olfactory sensitivity in hygienic bees, as previously hypothesized. However, comparing their genomic profile with those from other behaviours suggests a link with brood care and the highly varroa-hygienic Africanized honeybees. These results represent a first step toward the identification of genes involved in social immunity and thus provide first insights into the evolution of social immunity.

Cet article examine les methodes de selection d'abeilles melliferes resistantes a l'acarien V. jacobsoni. Un plar. de selection est decrit ci-apres, qui devrait etre mis en œuvre dans tout programme de selection prenant en compte les caracteres des abeilles mesures au niveau de la colonie. 1) Developper des methodes pour mesurer les populations d'abeilles et d'acariens et pour mesurer les caracteres associes a la resistance. 2) Identifier les caracteres specifiques en relation avec la croissance des populations d'acariens. 3) Determiner si ces caracteres sont hereditaires. 4) Renforcer ces caracteres par un elevage selectif. 5) Regrouper les composantes de la resistance dans des abeilles productives et resistantes aux acariens. Dans cet article on entend par resistance a V. jacobsoni la selection chez les abeilles de caracteres qui vont retarder la croissance de la population d'acariens etablie dans la colonie. Lors du criblage initial des caracteres, nous avons utilise des reines fecondees par un seul mâle. Nous pensons que cela a permis de detecter aussi des caracteres peu frequents. Les caracteres au niveau de la colonie auraient pu etre caches si les reines avaient ete fecondees par plusieurs mâles. Notre approche decrit la croissance de la population d'acariens au sein d'une colonie d'abeilles par l'equation: P (ab)II = P 2 , ou P 1 et P 2 sont les populations initiale et finale d'acariens, a la variation de la population tant que les acariens sont dans les cellules de couvain, b la variation quand ils sont hors des cellules de couvain et n le nombre de cycles reproducteurs de l'acarien. L'equation est valable pour une colonie qui a un apport regulier en couvain d'ouvrieres de facon a permettre la reproduction de l'acarien. Seules les femelles adultes d'acariens sont comptees et toutes les mesures sont des moyennes pour la colonie. En comparant les taux de croisssance des populations d'acariens de chaque colonie (P 2 / P 1 ), on peut determiner la croissance reelle dans chaque colonie. Les valeurs a, b et n peuvent alors expliquer comment la population d'acariens est passee de P 1 , a P 2 en termes de composantes mesurables du cycle reproducteur de l'acarien. Les variations de la population d'acariens doivent se refleter dans une ou plusieurs de ces composantes. Les caracteres specifiques des abeilles (qui sont la base de la selection) peuvent alors etre associes a l'une de ces trois composantes. Quand plusieurs caracteres specifiques agissent sur une meme composante (par exemple, la suppresssion de la reproduction de l'acarien et le comportement hygienique), leur effet combine n'est pas necessairement additif ni benefique. Si en revanche un meme caractere specifique agit en meme temps sur differentes composantes, ceux-ci se combineraient probablement pour donner une colonie ayant une resistance accrue a V. jacobsoni. Jusqu'ici notre selection s'est concentree sur un caractere, la suppression de la reproduction de l'acarien, qui provoque la non reproduction des acariens qui penetrent dans les cellules de couvain. Sur la base de ce seul caractere hereditaire, nous avons produit des colonies dans lesquelles la population d'acariens decline durant une periode test de 70 j. Deux autres caracteres hereditaires, le comportement hygienique et la proportion d'acariens sur le couvain, peuvent avoir aussi une importance pour la selection d'abeilles resistantes.

This study examines changes in reproduction and mortality of Varroa destructorwhen queens from stocks of honey bees (Apis mellifera L.) that differ in susceptibility to the mites were exchanged between colonies. Queens were selected for suppression of mite reproduction (SMRD). In two experiments uniform colonies of bees were established; half the colonies were given queens selected for SMRD, and half were given unselected queens. Queens were exchanged after 7 (exper- iment 1) and 13 weeks (experiment 2). The percentage of mites that had no progeny was determined for each colony at 5 times (2 before and 3 after exchanging queens). Mites that had no progeny included live and dead mites. Results showed (1) that reproduction of mites is suppressed by adding a queen selected for SMRD, and (2) that a mite population recovers its reproduction when a SMRD queen is replaced by an unselected queen. Selection of the SMRD trait can be reduced to counting only live mites that laid no eggs and dead mites. Apis mellifera / Varroa destructor / resistance to pests / suppression of mite reproduction (SMRD)

Drone production between 2 groups of worker honeybees (Apis mellifera L.) was compared in Baton Rouge, Louisiana : an older heterogeneous population of bees (> 54 days old at beginning of egg laying period), and a smaller group of young bees (11-15 days old). Six of 9 broodless, queenless colonies (providing the «old » bees) were each given 150 young bees that were heterozygous for visible mutations. The remaining 3 colonies were controls. Young workers produced a much higher proportion of drones in 3 of 6 the test colonies than did the old workers (Tabl. 1). Old workers produced at least as many drones per bee as did the young workers in the other 3 test colonies. Workers 2* 54 days old produced eggs in all colonies.

Egg-laying rates of queen honey bees, Apis mellifera L., were measured in colonies containing no brood and ca. 3,000 or 12,000 worker bees. Naturally mated queens were heavier and laid more eggs per day than instrumentally inseminated queens. CO2 narcosis caused weight loss in queens and may account for at least some of the difference. When nitrogen narcosis replaced carbon dioxide during instrumental insemination, queen weights increased, but still did not equal those of naturally mated queens that received no narcosis. The correlation between egg-laying rate and queen weight was r = 0.73 ( n = 112).

Africanized and European honey bee (Apis mellifera) populations showed quantitative differences in colony defensive behavior. Africanized bees responded faster and in much larger numbers than European honey bees and produced 8.2 and 5.9 times as many stings during two different experiments. Times to react to alarming stimuli were negatively correlated with the number of bees responding and to the total number of stings. The number of bees responding was significantly correlated to the total number of stings only for the Africanized population.

Of 12 alarm pheromones assayed in European and Africanized honeybees, nine were found in larger quantities in the Africanized population. Isopentyl and 2-heptanone levels were similar in both; 2-methylbutanol-1 was greater in European workers. These differences were not due to age or geographical location. Significant positive correlations between alarm pheromone levels and defensive behavior, especially numbers of stings, were observed.