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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.

We measured significant variation in the instantaneous growth rates for varroa mites, Varroa destructor (Anderson & Trueman) from 1993 to 2002 in Baton Rouge, LA. Mite population growth was monitored in colonies of honey bees, Apis mellifera L., with queens from miscellaneous U.S. sources that had not been selectively bred for varroa resistance. Mite populations were measured at the beginning and end of short field tests that started in the late spring of each year. Analyses of multiple regression showed that only the first two of the following regressors were linear predictors of r, the instantaneous growth rate: 1) percentage of reproducing female mites, 2) proportion of total mites in capped brood, 3) mortality of mites in brood cells, 4) growth of the bee population, 5) capped brood area at the end of a test, and 6) duration of the test. Analysis of commonality indicated that the percentage of reproducing female mites explained ≈26% of the total variation in r, and the proportion of total mit...

This study demonstrated (1) that honey bees, Apis mellifera L, can express a high level of resistance to Varroa destructor Anderson & Trueman when bees were selected for only one resistant trait (suppression of mite reproduction); and (2) that a significant level of mite-resistance was retained when these queens were free-mated with unselected drones. The test compared the growth of mite populations in colonies of bees that each received one of the following queens: (1) resistant--queens selected for suppression of mite reproduction and artificially inseminated in Baton Rouge with drones from similarly selected stocks; (2) resistant x control--resistant queens, as above, produced and free-mated to unselected drones by one of four commercial queen producers; and (3) control--commercial queens chosen by the same four queen producers and free-mated as above. All colonies started the test with approximately 0.9 kg of bees that were naturally infested with approximately 650 mites. Colonies with resistant x control queens ended the 115-d test period with significantly fewer mites than did colonies with control queens. This suggests that beekeepers can derive immediate benefit from mite-resistant queens that have been free-mated to unselected drones. Moreover, the production and distribution of these free-mated queens from many commercial sources may be an effective way to insert beneficial genes into our commercial population of honey bees without losing the genetic diversity and the useful beekeeping characteristics of this population.

This study uses sibling analysis to measure the heritability in honey bees, Apis mellifera L., of characteristics that have been associated with resistance to the mite, Varroa jacobsoni Oudemans. Twenty-eight uniform colonies of bees were established on 13 May in Baton Rouge, LA, each with 1 kg of mite-infested bees and a queen. The 28 unrelated queens in these colonies were divided into 7 groups of 4 based on the insemination of 4 queens with the same mixture of semen from 1 of 7 sire colonies. After worker progeny from these queens had replaced the initial bee populations, a colony was related as a full sister to the other 3 colonies in its sire group and unrelated to the other 24 colonies. Heritability ( h 2) was 1.24 for proportion of mites in brood, 0.65 for hygienic behavior, 0.89 for the duration of the capped period, 0.46 for suppression of mite reproduction, and 0.00 for physical damage to mites (measured by the presence of physically broken or dented mites on the bottom board). These results suggest that it should be possible to enhance the expression of 4 of these 5 characteristics with selective breeding of bees, thus reinforcing confidence in our ability to breed honey bees for resistance to V. jacobsoni.

A breeding program for honey bees, Apis mellifera L., resistant to varroa mites, Varroa jacobsoni Oudemans, selected for bees that maintain low populations of mites with decreased reproduction. This study examines the causes for this suppressed mite reproduction. Nonreproductive mites were classified into 3 groups as follows: (1) mites that were alive but did not lay eggs, (2) mites that began laying eggs later than normal, and (3) mites that died before laying eggs (usually

The purposes of this study were to select honey bees, Apis Mellifera L., for resistance to varroa mites, Varroa jacobsoni Oudemans, and to find a probable cause for this resistance. As a genetic source, we assembled 8 colonies that we thought had potential for resistance to varroa. Queens and drones were propagated from this group to produce 43 instrumentally inseminated queens, each queen mated to only 1 drone. Colonies from 27 of these queens were tested in Louisiana and 16 were tested in Michigan. Each colony in the Louisiana test began with 986 ± 13 g (mean ± SD) of bees and =290 mites; Michigan colonies began with 3,212 ± 171 bees and =51 mites. The populations of mites and bees were measured 10 wk later. Three of the 43 colonies had fewer mites at the end of the test than at the beginning. During the experiment, we evaluated each colony for grooming behavior, hygienic behavior, the duration of the postcapping period, and the frequency of nonreproducing mites in brood cells. of these 4 characteristics, only nonreproduction of mites was highly related to a change in the mite population. The duration of the postcapping period was marginally related, and the other 2 characteristics were apparently unrelated to the growth of the mite population. This study showed that resistance to varroa mites is present in the honey bee population in the United States, nonreproduction of mites was highly correlated with the growth of a mite population, and nonreproduction of mites may be a valuable characteristic for selecting bees for resistance to varroa mites.

This study measured the effects of hive volume on the productivity and growth of colonies of honey bees, Apis mellifera L., in Baton Rouge, LA. In a winter experiment, populations of 5,000, 10,000, and 15,000 bees were installed in hives to produce population densities of 150 or 550 bees per liter of hive volume (3 by 2 factorial, n = 60). More crowded bees consumed less honey (6.8 ± 1.9 mg per bee/d [mean SD] versus 12.2 ± 2.6 mg per bee/d) but produced less brood (0.34 ± 0.20 versus 0.72 -±0.31 cells per bee) and had a shorter life span than less crowded colonies. In spring, summer, and autumn, experiments were conducted with initial populations of 9,600 bees per colony. At 100, 200, 300, and 500 bees per liter ( n = 32), more crowded bees produced more honey. Average honey production was -70, -17, +28, and +67 g/d for the least to most crowded bees, respectively. More crowded bees produced less brood, but the difference was less marked than in winter. A final experiment measured the effects of adding hive space that did not contain comb ( n = 27). Of three treatments, colonies with five combs in a 25-liter hive produced the most honey (105 g/d), and colonies with additional space and combs (10 combs in a 47-liter hive) produced the least (29 g/d). Colonies with combless space (five combs in a 47-liter hive) were intermediate (62 g/d). The treatment with combless space produced more brood than the more crowded treatment but less than the treatment with 10 combs.

A shorter development time for the honey bee ( Apis mellifera L.) would allow the parasitic mite Varroa jacobsoni Oudemans less time to reproduce and may provide the bee colony with some resistance to the mite. 1 developed an accurate way to measure development time, measured variance and heritability of development time of honey bees in Baton Rouge, and determined if colonies with rapidly developing workers produced more rapidly developing queens. Newly hatched larvae were obtained by placing combs that contained eggs into an incubator with no adult workers present. After waiting 1–3 h, newly hatched larvae were identifiable because they had no brood food in their cells. These unfed larvae from different colonies were transferred to a single comb and reared in a nurse colony. Workers ( n = 180) from 26 different colonies averaged (mean ± SD) 114.5 ± 4.3 h for the uncapped larval period and 285.4 ± 5.1 h for the capped period. Heritability ± SEM was 0.41 ± 0.15 for the uncapped and 0.61 ± 0.19 for the capped period. Stocks with rapidly developing workers did not always produce rapidly developing queens (queen-worker regression slope not > 0), so workers must be evaluated rather than queens. These data predict that selective breeding from 10% of the population should reduce the mean capped period of workers by 5 h in a single generation.

Because a solitary worker honey bee ( Apis mellifera L.) will not lay eggs, eggs were produced from small populations of caged workers. First, worker bees from four colonies were evaluated for their rate of worker ovary development. Groups of 25 workers were kept in incubator cages at 34 ± 1°C, and each cage was given an empty section of drone comb and unlimited supplies of honey, water, and pollen. Workers from colonies A and B began laying eggs rapidly (about 9 d), workers from colony D were intermediate (about 12 d), and workers from colony C required about 25 d. Five workers from colony A were mixed with 25 workers from the same colony, from colony B, or from colony C and maintained for 10 d. The five workers developed their ovaries most rapidly with their own sisters or with workers from colony C and slowest with unrelated, fast-developing workers from colony B ( P < 0.05). When a single worker from colony A was caged with 25 workers from colony C, all eggs were laid by the worker from colony A. Overall, 50% (19/38) of the workers from colony A became egg layers when they were caged alone with workers from colony C. Although workers from colony A developed their ovaries sooner than workers from colony C, the two groups had the same number of ovarioles. Yet, among sisters, ovaries with more ovarioles were significantly more developed than ovaries with fewer ovarioles.

About 7 kg of honey bees were caged, stored for 2 days, and subdivided into 3 populations: ca. 4,400, 8,900, and 34,000 bees. The bees then were placed in hives that had no brood and a known quantity of honey. The resulting colonies had ca. 2 liters of space and one caged queen per 1,000 bees. Worker survival, honey loss per bee, colony temperature, and survival of caged queens were compared in six replicates. Each replicate covered 20 to 27 days during winter in Baton Rouge, La. Population size had no effect on survival of workers or caged queens. However, larger populations were significantly warmer than smaller populations when the ambient temperature was

Population growth was compared in 21 colonies of honey bees, Apis mellifera L., during the period of maximal population growth in Louisiana. Each colony began with 1.25 kg of bees, no brood, and 40 liters of hive space (measured empty). Colonies differed in comb size (13 by 19, 13 by 43, 20 by 43, or 26 by 43 cm), but each hive had the same comb surface area (1.1 m2). Bees were put into hives on 12 March, queens were released 15 March, and hives were expanded to 1.4 m2 of comb surface area and 48 liters on 10 April. Colonies with the largest combs produced more brood and had more adult workers on 13 May than colonies with the two smallest combs. At the end of the experiment, mean adult populations were 19,300, 22,900, 23,600, and 28,400 in colonies with the smallest to largest combs, respectively. A second experiment compared comb effects versus queen effects by measuring the amount of brood produced in 10 d by colonies with instrumentally inseminated or naturally mated queens on either the largest or smallest comb sizes. Comb effects were significant, queen effects were not. Small combs reduced brood production and diminished differences among queens; therefore, one must use large combs when evaluating queen fecundity.

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.

Mosaic male honey bees were found as the progeny of queens that had been inseminated with spermatozoa stored in liquid nitrogen. The origins of these mosaics and the genotype of their gametes were determined by using mutant markers. The mosaics probably developed from an egg pronucleus and a sperm pronucleus that did not unite after the latter had entered the egg. Instead, both pronuclei produced haploid tissue independently. The three mosaics that were mated to queens all had mosaic testes. Therefore, these were situations in which a male honey bee produced two types of spermatozoa.

Honey bee (Apis mellifera) semen was treated as follows: diluted in saline with 10 percent dimethyl sulfoxide (DMSO) and stored at -196 degrees C; same treatment but stored at 12 degrees C; diluted in saline and stored at 12 degrees C; and undiluted, unstored semen. Daughters (queens) produced from the treated spermatozoa were evaluated for total sterility. Only sterile eggs were produced from 3 percent of the queens in both groups that had DMSO (5/166 in group 1, and 6/234 in group 2). They were different (P less than 0.05) from groups 3 and 4 in which no queens were produced that laid only sterile eggs (0/151 and 0/137, respectively). These results demonstrate that, under the conditions used, a low level of sterility is induced by DMSO, and this F1 sterility raises questions about possible genetic damage by DMSO.