John R. Harbo

Suppressed mite reproduction explained by the behaviour of adult bees

SUMMARY Suppressed mite reproduction (SMR) is a heritable trait of the honey bee (Apis mellifera) that can control the parasitic mite, Varroa destructor. The purpose of this study was to determine whether adult bees with the SMR trait affect mites in brood after cells are capped. Colonies with or without the SMR trait were each given a comb of newly-capped worker brood that was naturally infested with varroa. Each of 7 source colonies provided a comb of brood to at least one SMR (n = 9) and one control colony (n = 8). These combs were removed from their host colonies 8 days later and mite populations evaluated in cells with bee pupae that were >8 days post-capping. Colonies with SMR bees averaged 2.2% of their cells infested with mites; controls averaged 9.0%. Therefore, bees with the SMR trait apparently removed mites from capped cells. Of the mites that remained, the SMR colonies had a much lower rate of reproductive mites, 20% vs. 71%. This suggests that bees with the SMR trait removed reproductive mites more often than they removed non-reproductive mites. When comparing only the number of mites that produced no progeny, the groups were almost identical averaging 1.2 and 1.3 mites per 100 cells of brood. This suggests that the SMR bees did not remove mites from brood cells if the mites did not lay eggs. By targeting the reproductive mites, bees with the SMR trait give the illusion that nearly all of the mites are non-reproductive. Therefore, our selection for a low frequency of reproductive mites may have produced bees that remove reproductive mites from capped brood.

Effect of Population Size on Brood Production, Worker Survival and Honey Gain in Colonies of Honeybees

SummaryThe effect of population size on brood production, worker survival and gain or loss of honey was studied in colonies of honeybees (Apis mellifera) in Louisiana, USA. About 11 kg of bees were caged, stored for two days and subdivided into five populations numbering 2300, 4500, 9000, 17 000 and 35 000 bees. Each colony was started with a laying queen, no brood, and 230 bees per 1000 cm3 of hive space. The test ended 19 days after queen release, just before adult bees began to emerge. The test was conducted 10 times (two replicates being used in each of February, April, June, August and October). The two largest populations produced more honey per bee and in dearth times and winter consumed less honey per bee. Colonies of 4500 bees produced the most brood per bee; as population increased above that number brood production per bee decreased. However, during summer dearth, the colonies of 9000 bees produced the most brood per bee. Overall, the optimal colony size was 9000 bees; the rate of weight gain i...

Responses to Varroa by honey bees with different levels of Varroa Sensitive Hygiene

Summary Mite resistance that we had earlier called suppression of mite reproduction (SMR) is a form of hygienic behaviour that we have named Varroa Sensitive Hygiene (VSH). With VSH, adult worker bees (Apis meiiifera) disrupt the reproduction of parasitic mites (Varroa destructor) by removing mite infested bee pupae from their cells. This study determines which brood cells are targeted by bees with VSH and which are not, and describes the relationship between brood removal and the sudden prevalence of sterile mites. We produced 26 colonies with different levels of VSH by backcrossing 14 queens from a high line, H (100% expression of VSH), and 12 queens from a low line, L (no VSH), to drones produced by an HL (high × low) queen. Because each of the 26 queens was mated to one drone, the resulting colonies were expected to represent the complete range of variability (0 to 100% of the alleles for VSH). To estimate brood removal, we measured mite populations in capped worker brood that was 0–3 days postcapping and again 7 days later when the cohort was aged 7–10 days postcapping. We correlated removal of mite-infested brood with the relative presence (at 7–10 days postcapping) of three classes of foundress mites: (1) viable: those with at least one daughter that could mature before emergence of the host bee; (2) nonviable: those with progeny but with no daughters that could reach maturity; and (3) no eggs: those with dead or nonovipositing foundress mites. As the rate of removal increased, both classes 1 and 2 showed significant declines, whereas class 3 was unchanged. Therefore, oviposition of the mite or something associated with mite oviposition provides the stimulus for bees with the VSH trait to remove mite infested pupae.

Resistance to Varroa destructor (Mesostigmata: Varroidae) When Mite-Resistant Queen Honey Bees (Hymenoptera: Apidae) Were Free-Mated with Unselected Drones

Abstract 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 × 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 ≈0.9 kg of bees that were naturally infested with ≈650 mites. Colonies with resistant × 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.

Alarm pheromone production by two honeybee (Apis mellifera) types

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.

Effects of carbon dioxide on levels of biogenic amines in the brains of queenless worker and virgin queen honey bees (Apis mellifera)

SUMMARYSeveral experiments were conducted to examine the effects of exposure to CO2 or CO2 containing 20% O2 on the amounts of biogenic amines in the brain, and on development of ovaries in worker and queen honey bees. When workers were fed pollen and exposed to CO2, their ovaries were less developed and brain dopamine (DA), tryptophan (TRP) and tyrosine (TYR) levels were significantly reduced versus untreated controls that were also fed pollen. If workers were not fed pollen and exposed to CO2, the differences in brain amine content between untreated controls and CO2-treated workers were not significant; however, a significant reduction in brain TRP and TYR levels through time was found for both groups of workers. Treatment with CO2 stimulated free-running queens to lay eggs sooner than untreated free-running queens, but CO2 narcosis had no significant affect on queen brain chemistry. However, the brain chemistry of caged queens (many queens caged within a single colony) responded differently from free-r...

Artificial Mixing of Spermatozoa from Honeybees and Evidence for Sperm Competition

SummaryIn each of 6 experiments, about 300 μl of honeybee (Apis mellifera L.) semen was diluted, mixed, and used to inseminate about 20 queens. The mixture for each experiment contained a portion of genetically marked sperm. Since the queens were also genetically marked, one could estimate the ratio of marked and unmarked sperm in each queen by counting her marked and unmarked progeny. The objective was to determine if each queen received equal proportions of marked sperm. In two experiments having semen mixtures with about 50% marked sperm, the 95% confidence interval for percent marked progeny was ±9·7% among the 22 queens in group 1 (semen was diluted 1:1 and stirred for 3·5 min) and ±9·0% among the 16 queens in group 6 (semen diluted 1:40 and centrifuged). The confidence intervals were similar and both were significantly greater than ±4·5% (expected 95% confidence interval when sampling a perfect mix with 500 workers from each queen) (P<0·0l). In experiments having a very low frequency of marked sperm...

Effect of brood rearing on honey consumption and the survival of worker honey bees

SUMMARYThe cost of rearing a worker honey bee (Apis mellifera) was measured in terms of honey lost by the colony and the lifespan of the adult worker bees. Test colonies for each experiment were created by collecting bees from many different sources into a large cage and then subdividing those bees to make a group of uniform colonies. Colonies were evaluated outdoors in Baton Rouge, Louisiana, USA, during February when there was pollen but no nectar for bees to collect. Brood production did not have a significant effect on adult survival during the first cycle of brood rearing, but colonies that reared more brood during the first brood cycle had greater adult mortality during the next brood cycle. Bees used 121 g of honey to produce 1 000 cells of mixed-aged brood (eggs, larvae and pupae in a normal brood nest) and about 163 mg of honey to rear one worker bee to the pupal stage. In colonies containing brood of all stages, the weight of brood was nearly equal to (about 25% less than) the weight of honey th...

Effect of Queenlessness on Worker Survival, Honey Gain and Defence Behaviour in Honeybees

SummaryThe effects of queenlessness on worker honeybees (Apis mellifera?) were tested with 50 colonies in groups of 10 (five treatments and two replicates) in August, October and December, 1984 and February and April, 1985 in Baton Rouge, Louisiana. The 10 colonies in each group were all from a single heterogeneous mixture of bees, and each colony began with about 6000 workers and no brood. The five treatments each lasted for 28 days and consisted of (1) caged queen for 28 days, queenless for 0 days; (2) caged queen for 21 days, queenless for 7 days; (3) caged queen for 14 days, queenless for 14 days; (4) caged queen for 7 days, queenless for 21 days and (5) caged queen for 9 days, laying queen for 19 days (control). With prolonged queenlessness worker survival, colony weight gain and defence behaviour (number of stings) decreased. Queenlessness did not induce drifting.

Effect of screen floors on populations of honey bees and parasitic mites (Varroa destructor).

SUMMARY This study compared brood production, honey consumption (in winter only), population growth of honey bees (Apis mellifera), and population growth of parasitic mites (Varroa destructor) in hives with open screen or wood as floor material. Two experiments were conducted in Baton Rouge, Louisiana, USA, one in winter (19 colonies) and one in summer (22 colonies). In both experiments, we established uniform colonies of honey bees by subdividing 30 kg of mite-infested bees. Each colony began with about 11 000 bees, no brood, and uniform populations of mites (127 and 480 mites per colony in winter and summer, respectively). The summer test included a third treatment (8 colonies) where a wooden tray (5 cm deep) closed the space beneath a screen floor. After the first 20 days of the experiments, when no adult bees or mites had yet been produced in any of the colonies, the treatments showed no differences in brood production, honey consumption, or survival of adult bees. At nine weeks, colonies with screen floors had fewer mites, a lower percentage of their mite population residing in brood cells (open screen only), and more cells of capped brood. These results suggest that colonies with open-screen floors may hold back the growth of mite populations by decreasing the rate at which mites invade brood cells.