José D. Villa

Evidence of autogrooming as a mechanism of honey bee resistance to tracheal mite infestation

SUMMARYInfestations of tracheal mites (Acarapis woodi) were measured in honey bees (Apis mellifera) whose autogrooming ability was compromised by having legs or segments of legs amputated. Bees of two stocks, one more resistant (Buck-fast) and one more susceptible to tracheal mite infestation, were tested by performing amputations on uninfested, young (0–24 h) adult bees, exposing the treated bees to mites in infested colonies, then retrieving and dissecting the bees to measure parasitism. In both stocks, bees that had mesothoracic legs amputated had greatly increased mite abundances. However, the relative increase in infestation was greater in resistant bees. Mite infestation increased as more (0 vs. 1 vs. 2) mesothoracic legs were removed. In bees with only one leg removed, mite infestations were greater on the treated side. In subsequent tests with resistant stock bees only, removing the mesotarsi resulted in infestations equalling those found when entire mesothoracic legs were removed, but amputating ...

Variable Population Growth of Varroa destructor (Mesostigmata: Varroidae) in Colonies of Honey Bees (Hymenoptera: Apidae) During a 10-Year Period

Abstract 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 mites in capped brood explained 6%. The joint expression of both variables accounted for another 4%. Thus, residual error reflected most of the total variation in r, which suggested possible climatic or environmental effects on mite growth. The lowest growth rates occurred in three consecutive years of drought in Louisiana. Measures of ambient temperature and relative humidity correlated to growth of mite populations among different years. Reduced growth rates were probably the result of diminished reproductive rates by varroa mites during periods of hot and dry weather.

Honey bees (Hymenoptera: Apidae) with the trait of varroa sensitive hygiene remove brood with all reproductive stages of varroa mites (Mesostigmata: Varroidae).

ABSTRACT Varroa sensitive hygiene (VSH) is a trait of honey bees, Apis mellifera L. (Hymenoptera: Apidae), which supports resistance to Varroa destructor Anderson & Trueman. VSH is the hygienic removal of mite-infested pupa. Bees selectively bred for VSH produce colonies in which the fertility of mites decreases over time. In addition, mite fertility decreases after infested brood is exposed to VSH bees for 1 wk. The purpose of this study was to decide whether the reduction in mite fertility is caused by selective removal of mites that produce offspring. Initially, we monitored changes in a small patch of capped brood during exposure to VSH bees at 2-h intervals through 60 h, which provided a reference for the subsequent experiment. The first test showed that VSH bees uncapped, recapped, and began to remove many pupae in ≈2 h. The approach in the second experiment was to compare the percentage of fertile mites from brood exposed to VSH bees for a 3-h period to the percentage of fertile mites in brood that was protected from hygiene by a screen. There were no significant differences in fertility between mites on pupae that were being removed by the bees and mites on protected pupae. These results suggest that neither egg-laying by foundress mites nor mite offspring are the stimuli that trigger hygienic removal of mite-infested pupae by VSH bees. It may be that hygienic activities such as the uncapping of brood cells inhibits or disrupts reproduction by varroa mites.

Swarming Behavior of Honey Bees (Hymenoptera: Apidae) in Southeastern Louisiana

Abstract Reproductive swarming phenology, swarm sizes, and cavity selection were studied in a European-derived population of Apis mellifera L. in southeastern Louisiana before and immediately after the initial detection in 1992 of Varroa destructor Anderson & Trueman (Acari: Varroidae). Frequency of swarms was highest between early April and early May in each of 6 yr. Swarm weight averaged 1.42 kg (range 0.17–4.30 kg) and did not change significantly the year after detection of V. destructor. Swarms spent an average of ≈20 daylight hours scouting for a new nest-site from a temporary location and moved more frequently to cavities of 30-liter than to those of 13-liter volume. Swarms were random in direction of movement. Dance tempos at the time of swarm departure indicated movement to cavities at distances from 200 m to ≈10 km. The genetic composition of this honey bee population is likely to change after natural and artificial selection for resistance to new parasites, such as V. destructor and Aethina tumida Murray (Coleoptera: Nitidulidae), and as Africanized bees expand their range. Swarming characteristics are also likely to change both from direct effects of parasites on colony reproduction, and by changes toward bee populations with differing life histories.

Defensive Behaviour of Africanized and European Honeybees at two Elevations in Colombia

The defensive behaviour of Africanized (10) and European (8) honeybee colonies was compared at 520 and 2450 m above sea level (34° and 17°C, respectively) by measuring the time to the first sting o...

Negative evidence for effects of genetic origin of bees on Nosema ceranae, positive evidence for effects of Nosema ceranae on bees

In two tests, honey bee colonies of different origins were sampled monthly to detect possible differential infection with Nosema ceranae; colony sizes and queen status were monitored quarterly. One experiment used queens crossed with drones of the same type obtained from colonies which had previously exhibited high and low infections. A second experiment used queens from ten commercial sources. No clear genotypic (P = 0.682) or phenotypic (P = 0.623) differences in infection were evident. Colony deaths and supersedures did not relate significantly with infection except for deaths of colonies in the autumn (P = 0.02). Significant effects on colony growth were found in all seasons: average 3-month decreases in population ranged from 0.4 to 1.4 frames of bees per million N. ceranae per bee. These results confirm that N. ceranae can be involved in weakening of colonies even in warm climates and suggest that breeding for resistance may require more intense selection, larger base populations, or different screening methods.

Simplified methods of evaluating colonies for levels of Varroa Sensitive Hygiene (VSH).

Summary Varroa Sensitive Hygiene (VSH) is a trait of honey bees, Apis mellifera, that supports resistance to Varroa destructor mites. Components of VSH were evaluated to identify simple methods for selection of the trait. Mite population growth was measured in colonies with variable levels of VSH in two field trials using 24 and 16 colonies. Mite population growth was significantly lower in VSH and hybrid colonies than in control (i.e., unselected) colonies. In resident brood with mite infestations below 5%, the percentage of uncapped pupal cells did not differ significantly among VSH, hybrid and control colonies, but the percentage of recapped cells was highest in VSH colonies (P = 0.03). When brood from more highly infested colonies (9–49% of pupae infested) was introduced for forty hours, VSH colonies reduced infestation more than control colonies (P< 0.01) but final mite fertility was similar (P= 0.12). When infested brood was exposed in colonies for one week, VSH colonies reduced both mite fertility (P= 0.05) and mite infestation (P= 0.02). When highly infested brood was exposed to a subset of colonies for two hours, control colonies uncapped no or few cells while uncapping in VSH colonies was variable but on average was much higher. Mite population growth in individual colonies was negatively correlated with reduced infestation after forty hours of brood exposure and with reduced mite fertility after one week. The simpler and shorter-term measures (relative to measuring mite population growth) of uncapping, recapping, and reductions in infestation and mite fertility may facilitate selection of VSH by more bee breeders.

Functionality of Varroa-Resistant Honey Bees (Hymenoptera: Apidae) when used in Migratory Beekeeping for Crop Pollination

ABSTRACT Two types of honey bees, Apis mellifera L. (Hymenoptera: Apidae), bred for resistance to Varroa destructor Anderson & Trueman were evaluated for performance when used in migratory crop pollination. Colonies of Russian honey bees (RHB) and outcrossed bees with Varroa-sensitive hygiene (VSH) were managed without miticide treatments and compared with colonies of Italian honey bees that served as controls. Control colonies were managed as groups which either were treated twice each year against V. destructor (CT) or kept untreated (CU). Totals of 240 and 247 colonies were established initially for trials in 2008 and 2009, respectively. RHB and VSH colonies generally had adult and brood populations similar to those of the standard CT group regarding pollination requirements. For pollination of almonds [Prunus dulcis (Mill.) D.A.Webb] in February, percentages of colonies meeting the required six or more frames of adult bees were 57% (VSH), 56% (CT), 39% (RHB), and 34% (CU). RHB are known to have small colonies in early spring, but this can be overcome with appropriate feeding. For later pollination requirements in May to July, 94–100% of colonies in the four groups met pollination size requirements for apples (Malus domestica Borkh.), cranberries (Vaccinium macrocarpon Aiton), and lowbush blueberries (Vaccinium angustifolium Aiton). Infestations with V. destructor usually were lowest in CT colonies and tended to be lower in VSH colonies than in RHB and CU colonies. This study demonstrates that bees with the VSH trait and pure RHB offer alternatives for beekeepers to use for commercial crop pollination while reducing reliance on miticides. The high frequency of queen loss (only approximately one fourth of original queens survived each year) suggests that frequent requeening is necessary to maintain desired genetics.

Inheritance of resistance to Acarapis woodi (Acari: Tarsonemidae) in crosses between selected resistant Russian and selected susceptible u.s. honey bees (Hymenoptera: Apidae).

Abstract The pattern of inheritance of tracheal mite resistance in selected Russian bees was determined in bioassays and in samples from field colonies. Resistant colonies of Russian origin and colonies selected for high susceptibility in the United States were used to generate divergent parental populations. Seven groups of F1 colonies were produced by crossing queens and drones from these selected resistant Russian and selected susceptible populations. In a series of bioassays with young workers exposed in infested colonies, average mite abundance (female mites per worker) in F1 colonies was intermediate (1.04 ± 0.13 [mean ± SE]) and significantly different from that of both resistant Russian (0.74 ± 0.13) and selected susceptible (1.57 ± 0.13) colonies. Colonies representing the three populations were established in two apiaries in July 2005. Colonies surviving with original queens after 10 mo had mite prevalences supporting the findings of the bioassay. All three resistant colonies had undetectable mite levels, whereas prevalences in four F1 colonies ranged from 0 to 53%, and in 10 susceptible colonies ranged from 0 to 90%. Tracheal mite resistance in Russian bees is likely polygenic, but there may be a number of genes with major dominance interacting with minor genes. Use of selected Russian queens mated with Russian drones or with drones from unknown sources is beneficial for beekeeping in areas with persistent problems with tracheal mite infestation.

Uncapping of pupal cells by European bees in the United States as responses to Varroa destructor and Galleria mellonella

Summary We investigated the uncapping of pupal cells by honey bees in the United States as responses to infestation with V. destructor and G. mellonella. In a group of 15 colonies, we counted the number of uncapped cells with pupae, and estimated the total sealed brood area. At the same time, the infestation by V. destructor and evidence of wax moth activity were measured in uncapped pupal cells, in cells immediately adjacent (neighbours), and in cells along linear transects. The relative amount of uncapped pupal cells (uncapped pupal cells/total sealed cells) increased with infestation (linear regression R2 = 0.64, slope = 0.16). Varroa mite infestation of uncapped cells (30%) significantly exceeded that of neighbours (14%) and also that of transect cells (12%), but infestations of neighbour and transect cells were similar. The relationship between infestation of uncapped cells and that of other cells (neighbour or transect cells) had a slope significantly higher than one, suggesting that discrimination of infested cells increases with overall colony infestation. Frequencies of wax moth activity (presence of larvae, frass, tunnelling and webbing) were highest in uncapped cells (33%), lower in neighbour cells (21%) and extremely low in transect cells (4%). We followed the opening, removing and resealing of pupal cells every 24 h in a colony with one of the highest infestations with varroa mites and with one of the lowest levels of wax moths, and in a second colony with the opposite infestation levels. Many opened or partly removed cells were found in a different condition, suggesting a dynamic process under conditions of high infestation.