Reproduction of Varroa destructor in worker brood of Africanized honey bees (Apis mellifera)

Reproduction and population growth of Varroa destructor was studied in ten naturally infested, Africanized honeybee (AHB) (Apis mellifera) colonies in Yucatan, Mexico. Between February 1997 and January 1998 monthly records of the amount of pollen, honey, sealed worker and drone brood were recorded. In addition, mite infestation levels of adult bees and worker brood and the fecundity of the mites reproducing in worker cells were determined. The mean number of sealed worker brood cells (10,070 ± 1,790) remained fairly constant over the experimental period in each colony. However, the presence and amount of sealed drone brood was very variable. One colony had drone brood for 10 months and another for only 1 month. Both the mean infestation level of worker brood (18.1 ± 8.4%) and adult bees (3.5 ± 1.3%) remained fairly constant over the study period and did not increase rapidly as is normally observed in European honey bees. In fact, the estimated mean number of mites fell from 3,500 in February 1997 to 2,380 in January 1998. In May 2000 the mean mite population in the study colonies was still only 1,821 mites. The fertility level of mites in this study was much higher (83–96%) than in AHB in Brazil(25–57%), and similar to that found in EHB (76–94%). Mite fertility remained high throughout the entire study and was not influenced by the amount of pollen, honey or worker brood in the colonies. This revised version was published online in July 2006 with corrections to the Cover Date.     

A comparison of the reproductive ability of <Emphasis Type="Italic">Varroa destructor</Emphasis> (Mesostigmata:Varroidae) in worker and drone brood of Africanized honey bees (<Emphasis Type="Italic">Apis mellifera</Emphasis>)

Colony infestation by the parasitic mite, Varroa destructor is one of the most serious problems for beekeeping worldwide. In order to reproduce varroa females, enter worker or drone brood shortly before the cell is sealed. To test the hypothesis that, due to the preference of mites to invade drone brood to reproduce, a high proportion of the mite reproduction should occur in drone cells, a comparative study of mite reproductive rate in worker and drone brood of Africanized honey bees (AHB) was done for 370 mites. After determining the number, developmental stage and sex of the offspring in worker cells, the foundress female mite was immediately transferred into an uninfested drone cell. Mite fertility in single infested worker and drone brood cells was 76.5 and 79.3%, respectively. There was no difference between the groups (X ² = 0.78, P = 0.37). However, one of the most significant differences in mite reproduction was the higher percentage of mites producing viable offspring (cells that contain one live adult male and at least one adult female mite) in drone cells (38.1%) compared to worker cells (13.8%) (X ² = 55.4, P < 0.01). Furthermore, a high level of immature offspring occurred in worker cells and not in drone cells (X ² = 69, P < 0.01). Although no differences were found in the percentage of non-reproducing mites, more than 74% (n = 85) of the mites that did not reproduce in worker brood, produced offspring when they were transferred to drone brood.     

Reproductive biology of <Emphasis Type="Italic">Varroa destructor</Emphasis> in Africanized honey bees (<Emphasis Type="Italic">Apis mellifera</Emphasis>)

Since its first contact with Apis mellifera, the population dynamics of the parasitic mite Varroa destructor varies from one region to another. In many regions of the world, apiculture has come to depend on the use of acaricides, because of the extensive damage caused by varroa to bee colonies. At present, the mite is considered to contribute to the recent decline of honey bee colonies in North America and Europe. Because in tropical climates worker brood rearing and varroa reproduction occurs all year round, it could be expected that here the impact of the parasite will be even more devastating. Yet, this has not been the case in tropical areas of South America. In Brazil, varroa was introduced more than 30 years ago and got established at low levels of infestation, without causing apparent damage to apiculture with Africanized honey bees (AHB). The tolerance of AHB to varroa is apparently attributable, at least in part, to resistance in the bees. The low fertility of this parasite in Africanized worker brood and the grooming and hygienic behavior of the bees are referred as important factors in keeping mite infestation low in the colonies. It has also been suggested that the type of mite influences the level of tolerance in a honey bee population. The Korea haplotype is predominant in unbalanced host-parasite systems, as exist in Europe, whereas in stable systems, as in Brazil, the Japan haplotype used to predominate. However, the patterns of varroa genetic variation have changed in Brazil. All recently sampled mites were of the Korea haplotype, regardless whether the mites had reproduced or not. The fertile mites on AHB in Brazil significantly increased from 56% in the 1980s to 86% in recent years. Nevertheless, despite the increased fertility, no increase in mite infestation rates in the colonies has been detected so far. A comprehensive literature review of varroa reproduction data, focusing on fertility and production of viable female mites, was conducted to provide insight into the Africanized bee host-parasite relationship.     

蜜蜂巢房大小影响狄斯瓦螨的繁殖行为

在具有相同类型幼虫的雄蜂和工蜂巢房中,人工接入狄斯瓦螨Varroa destructorAnderson&Trueman,比较巢房大小不同,对于螨繁殖的影响。结果显示:狄斯瓦螨在具有工蜂幼虫的工蜂房(WW)中的繁殖率为94.4%,而在具有工蜂幼虫的雄蜂房(WD)中繁殖率只有27.7%,差异极显著。在具有工蜂幼虫的工蜂房中,每只雌螨产出后代的平均数为3.35±1.56只;在具有工蜂幼虫的雄蜂房中每只雌螨产出后代的平均数为0.49±0.93只,差异极显著。表明:在具有相同类型幼虫存在的情况下,狄斯瓦螨喜欢较小的巢房,狄斯瓦螨在较小巢房中的繁殖能力明显高于较大的巢房。     

Host brood traits,independent of adult behaviours,reduce Varroa destructor mite reproduction in resistant honeybee populations

The ectoparasitic mite Varroa destructor is an invasive species of Western honey bees (Apis mellifera) and the largest pathogenic threat to their health world-wide. Its successful invasion and expansion is related to its ability to exploit the worker brood for reproduction, which results in an exponential population growth rate in the new host. With invasion of the mite, wild honeybee populations have been nearly eradicated from Europe and North America, and the survival of managed honeybee populations relies on mite population control treatments. However, there are a few documented honeybee populations surviving extended periods without control treatments due to adapted host traits that directly impact Varroa mite fitness. The aim of this study was to investigate if Varroa mite reproductive success was affected by traits of adult bee behaviours or by traits of the worker brood, in three mite-resistant honey bee populations from Sweden, France and Norway. The mite’s reproductive success was measured and compared in broods that were either exposed to, or excluded from, adult bee access. Mite-resistant bee populations were also compared with a local mite-susceptible population, as a control group. Our results show that mite reproductive success rates and mite fecundity in the three mite-resistant populations were significantly different from the control population, with the French and Swedish populations having significantly lower reproductive rates than the Norwegian population. When comparing mite reproduction in exposed or excluded brood treatments, no differences were observed, regardless of population. This result clearly demonstrates that Varroa mite reproductive success can be suppressed by traits of the brood, independent of adult worker bees.     

Varroa-tolerant Italian honey bees introduced from Brazil were not more efficient in defending themselves against the mite Varroa destructor than Carniolan bees in Germany

In Europe and North America honey bees cannot be kept without chemical treatments against Varroa destructor. Nevertheless, in Brazil an isolated population of Italian honey bees has been kept on an island since 1984 without treatment against this mite. The infestation rates in these colonies have decreased over the years. We looked for possible varroa-tolerance factors in six Italian honey bee colonies prepared with queens from this Brazilian island population, compared to six Carniolan colonies, both tested at the same site in Germany. One such factor was the percentage of damaged mites in the colony debris, which has been reported as an indicator of colony tolerance to varroa. A mean of 35.8% of the varroa mites collected from the bottoms of the Italian bee colonies were found damaged, among which 19.1% were still alive. A significantly greater proportion of damaged mites were found in the Carniolan bees (42.3%) and 22.5% were collected alive. The most frequent kind of damage found was damaged legs alone, affecting 47.4% of the mites collected from debris in Italian bees, which was similar to the amount found in Carniolan colonies (46%). The mean infestation rate by the varroa mite in the worker brood cells in the Italian bee colonies was 3.9% in June and 3.5% in July, and in drone brood cells it was 19.3% in June. In the Carniolan honey bee colonies the mean infestation rates in worker brood cells were 3.0 and 6.7%, respectively in the months of June and July and 19.7% in drone brood cells in June. In conclusion, the 'Varroa-tolerant' Italian honey bees introduced from Brazil produced lower percentages of damaged mites (Varroa destructor) in hive debris and had similar brood infestation rates when compared to 'susceptible' Carniolan bees in Germany. In spite of the apparent adaptation of this population of Italian bees in Brazil, we found no indication of superiority of these bees when we examined the proportions of damaged mites and the varroa-infestation rates, compared to Carniloan bees kept in the same apiary in Germany.     

Changes in the reproductive ability of the mite Varroa destructor (Anderson e Trueman) in africanized honey bees (Apis mellifera L.) (Hymenoptera: Apidae) colonies in southern Brazil

Varroa destructor has been in Brazil for more than 30 years, but no mortality of honeybee colonies due to this mite has been recorded. Africanized bee infestation rates attained by varroa have been low, without causing measurable damage to Brazilian apiculture. The low reproductive ability of this parasite in Africanized bee worker brood cells has been considered an important factor for maintaining the host-parasite equilibrium. Nevertheless, the possible substitution of the haplotype of the mite Varroa destructor that has occurred recently in Brazil could affected the reproductive ability of the population of this parasite in Brazil. The reproductive ability of worker of the mite females was evaluated in over one thousand 17-18 day-old Africanized worker brood cells each of the two periods. The percentage of fertile mites increased from 56% in the 1980s to 86% in 2005-2006. The difference in the percentage of females that produced deutonymphs, female progeny that can reach the adult stage at bee emergence, was even greater. In 2005-2006, 72% of the females that invaded worker brood had left at the least one viable descendant, compared to 35% in 1986-1987.     

Uncapping activity of Apis mellifera L. (Hymenoptera: Apidae) towards worker brood cells infested with the mite Varroa destructor Anderson & Treuman (Mesostigmata: Varroidae)

Varroosis, a disease caused by the mite Varroa destructor Anderson and Treuman has killed hundreds of thousands of Apis mellifera L. colonies in various parts of the world. Nevertheless, the damage caused by this mite varies with the type of bee and climate conditions. Varroa causes little damage to Africanized bee colonies in Brazil, as the infestation rates are relatively stable and low. We evaluated the hygienic behavior (uncapping and removal of brood) of highly hygienic Africanized bees using combs with worker brood cells infested (naturally) and no infested with V. destructor. The daily uncapping rate, measured in eight colonies during six days, was 3.5 fold higher in the combs infested with varroa compared to no infested combs. The results show that the Africanized bees are able to recognise and remove brood cells naturally infested with V. destructor what is an important mechanism for tolerance against varroa.     

The influence of brood comb cell size on the reproductive behavior of the ectoparasitic mite Varroa destructor in Africanized honey bee colonies

Africanized honey bees (Apis mellifera, Hymenoptera: Apidae) in Brazil are tolerant of infestations with the exotic ectoparasitic mite, Varroa destructor (Mesostigmata: Varroidae), while the European honey bees used in apiculture throughout most of the world are severely affected. Africanized honey bees are normally kept in hives with both naturally built small width brood cells and with brood cells made from European-sized foundation, yet we know that comb cell size has an effect on varroa reproductive behavior. Three types (sizes) of brood combs were placed in each of six Africanized honey bee colonies: new (self-built) Africanized comb, new Italian comb (that the bees made from Italian-sized commercial foundation), and new Carniolan comb (built naturally by Carniolan bees). About 100 cells of each type were analyzed in each colony. The Africanized comb cells were significantly smaller in (inner) width (4.84 mm) than the European-sized comb cells (5.16 and 5.27 mm for Italian and Carniolan cells, respectively). The brood cell infestation rates (percentage cells infested) were significantly higher in the Carniolan-sized comb cells (19.3%) than in the Italian and Africanized cells (13.9 and 10.3%, respectively). The Carniolan-sized cells also had a significantly larger number of invading adult female mites per 100 brood cells (24.4) than did the Italian-sized cells (17.7) and the natural-sized Africanized worker brood cells (15.6). European-sized worker brood cells were always more infested than the Africanized worker brood cells in the same colony. There was a highly significant correlation (P<0.01) between cell width and the rate of infestation with varroa in four of the six colonies. The small width comb cells produced by Africanized honey bees may have a role in the ability of these bees to tolerate infestations by Varroa destructor, furthermore it appears that natural-sized comb cells are superior to over-sized comb cells for disease resistance.     

Natural selection of Varroa jacobsoni explains the different reproductive strategies in colonies of Apis cerana and Apis mellifera

In colonies of European Apis mellifera, Varroa jacobsoni reproduces both in drone and in worker cells. In colonies of its original Asian host, Apis cerana, the mites invade both drone and worker brood cells, but reproduce only in drone cells. Absence of reproduction in worker cells is probably crucial for the tolerance of A. cerana towards V. jacobsoni because it implies that the mite population can only grow during periods in which drones are reared. To test if non-reproduction of V. jacobsoni in worker brood cells of A. cerana is due to a trait of the mites or of the honey-bee species, mites from bees in A. mellifera colonies were artificially introduced into A. cerana worker brood cells and vice versa. Approximately 80% of the mites from A. mellifera colonies reproduced in naturally infested worker cells as well as when introduced into worker cells of A. mellifera and A. cerana. Conversely, only 10% of the mites from A. cerana colonies reproduced, both in naturally infested worker cells of A. cerana and when introduced into worker cells of A. mellifera. Hence, absence of reproduction in worker cells is due to a trait of the mites. Additional experiments showed that A. cerana bees removed 84% of the worker brood that was artificially infested with mites from A. mellifera colonies. Brood removal started 2 days after artificial infestation, which suggests that the bees responded to behaviour of the mites. Since removal behaviour of the bees will have a large impact on fitness of the mites, it probably plays an important role in selection for differential reproductive strategies. Our findings have large implications for selection programmes to breed less-susceptible bee strains. If differences in non-reproduction are mite specific, we should not only look for non-reproduction as such, but for colonies in which non-reproduction in worker cells is selected. Hence, in selection programmes fitness of mites that reproduce in both drone and worker cells should be compared to fitness of mites that reproduce only in drone cells. © Rapid Science Ltd. 1998     

Non-reproducing Varroa jacobsoni Oud. in honey bee worker cells—status of mites or effect of brood cells?

The parasitic mite Varroa jacobsoni Oud. reproduces in sealed honey bee brood cells. Within worker cells a considerable fraction of the mites do not produce offspring. It is investigated whether variation in the ratio of cells without reproduction is caused by properties of the worker brood, or by the state of the mites entering cells. Pieces of brood comb were taken from colonies of 12 different bee lines and were placed simultaneously into highly infested colonies. Non-reproduction was independent of the origin of the brood pieces, indicating a minor role of a variation due to different brood origin. Between colonies used for infestation, however, it differed considerably. A comparison of the proportion of cells without reproduction when infested by one Varroa mite or when infested by two or three Varroa mites showed, that non-reproduction was mainly related to the state of the mites entering cells, and only to a minor degree to an influence of the brood cells. A high ratio of worker cells without reproduction was consistently reported in bee lines which survive the disease without treatment, and a high level of non-reproduction is thus regarded to be a key factor in breeding bees for high Varroa tolerance. The current results indicate, that differences in this trait are only to a minor degree related to differences between bee lines in the ability of the bee brood to induce oviposition. These differences seem rather to depend on other, unknown colony factors influencing the reproductive state of Varroa when they enter cells for reproduction.     

Reproduction of <Emphasis Type="Italic">Varroa destructor</Emphasis> and offspring mortality in worker and drone brood cells of Africanized honey bees

Varroa destructor is known to be the most serious parasite of Apis mellifera worldwide. In order to reproduce varroa females enter worker or drone brood shortly before the cell is sealed. From March to December 2008, the reproductive rate and offspring mortality (mature and immature stages), focusing on male absence and male mortality of V. destructor, was investigated in naturally infested worker and drone brood of Africanized honey bees (AHB) in Costa Rica. Data were obtained from 388 to 403 single infested worker and drone brood cells, respectively. Mite fertility in worker and drone brood cells was 88.9 and 93.1%, respectively. There was no difference between the groups (X² = 3.6, P = 0.06). However, one of the most significant differences in mite reproduction was the higher percentage of mites producing viable offspring in drone cells (64.8%) compared to worker cells (37.6%) (X² = 57.2, P < 0.05). A greater proportion of mites in worker brood cells produced non-viable female offspring. Mite offspring mortality in both worker and drone cells was high in the protonymph stage (mobile and immobile). A significant finding was the high rate of male mortality. The worker and drone brood revealed that 23.9 and 6.9%, respectively, of the adult male offspring was found dead. If the absence (missing) of the male and adult male mortality are taken together the percentage of cells increased to 40.0 and 21.3% in worker and drone cells, respectively (X² = 28.8, P < 0.05). The absence of the male or male mortality in a considerable number of worker cells naturally infested with varroa is the major factor in our study which reduces the production of viable daughters in AHB colonies in Costa Rica.     

Varroa destructor infestation in untreated honey bee (Hymenoptera: Apidae) colonies selected for hygienic behavior

Honey bee (Apis mellifera L.) colonies bred for hygienic behavior were tested in a large field trial to determine if they were able to resist the parasitic mite Varroa destructor better than unselected colonies of"Starline" stock. Colonies bred for hygienic behavior are able to detect, uncap, and remove experimentally infested brood from the nest, although the extent to which the behavior actually reduces the overall mite-load in untreated, naturally infested colonies needed further verification. The results indicate that hygienic colonies with queens mated naturally to unselected drones had significantly fewer mites on adult bees and within worker brood cells than Starline colonies for up to 1 yr without treatment in a commercial, migratory beekeeping operation. Hygienic colonies actively defended themselves against the mites when mite levels were relatively low. At high mite infestations (>15% of worker brood and of adult bees), the majority of hygienic colonies required treatment to prevent collapse. Overall, the hygienic colonies had similar adult populations and brood areas, produced as much honey, and had less brood disease than the Starline colonies. Thus, honey bees bred for hygienic behavior performed as well if not better than other commercial lines of bees and maintained lower mite loads for up to one year without treatment.     

Effect of acaricide resistance on reproductive ability of the honey bee mite Varroa destructor

The reproduction of pyrethroid-resistant Varroa destructor mite, a brood parasite of honey bees, was observed in Weslaco, Texas, and the results compared with known susceptible mite populations from other studies. Seven Apis mellifera colonies that had mite populations resistant to the acaricide Apistan^™ were used. Pyrethroid-resistance was confirmed when only 17% rather than 90% of mites confined in dishes containing Apistan^™ died after 12 h of exposure. The average number of eggs laid by resistant mites invading worker and drone cells was 4.4 and 5.4 respectively. This is similar to the number of eggs laid by susceptible mites in worker (4.4–4.8) or drone (4.7–5.5) cells. Also the average number of fertilised V. destructor female mites produced by resistant mites in worker (1.0) and drone (2.1) cells were similar to the number produced by susceptible mites in worker (0.9) and drone (1.9–2.2) cells. In addition, no major differences between the resistant and susceptible mite populations were observed in either worker or drone cells when six different reproductive categories and offspring mortality rates were compared. Therefore, it appears that there is little or no reproductive fitness cost associated with pyrethroid resistance in V. destructor in Texas. This revised version was published online in July 2006 with corrections to the Cover Date.     

Reduction of tracheal mite parasitism of honey bees by swarming.

Based on population dynamics, tracheal mite (Acarapis woodi) parasitism of colonies of honey bees (Apis mellifera) appears to be, potentially at least, regulatory and stable. Empirical and theoretical considerations suggest, however, that intracolony population dynamics of mite-honey bee worker seem to be unstable in managed situations where honey bee worker population is allowed to grow unchecked. Experimental studies showed that tracheal mite population levels increased in a managed honey bee colony but were impaired in one in which brood rearing was interrupted by loss of the queen. Mite densities but not prevalence were lowered in experimental swarms kept from rearing brood. We propose that swarming reduces mite density within a colony, therefore implicating modern techniques of hive management in the sudden historical appearance of the mite on the Isle of Wight.     

A Comparative Study of Varroa Jacobsoni Reproduction in Worker Cells of Honey Bees (Apis Mellifera) in England and Africanized Bees in Yucatan, Mexico

The aim of this study was to investigate an underlying mechanism of the apparent tolerance of Africanized honey bees (AHB) to Varroa jacobsoni mites in Mexico. This was achieved by conducting the first detailed study into the mites' reproductive biology in AHB worker cells. The data was then compared directly with a similar study previously carried out on European honey bees (EHB) in the UK. A total of 1071 singly infested AHB worker cells were analyzed and compared with the data from 908 singly infested EHB worker cells. There was no significant difference between the number of mother mites dying in the cells (AHB = 2.0%, EHB = 1.8%); the mean number of eggs laid per mite (AHB = 4.86, EHB = 4.93); the number of mites producing no offspring (AHB = 12%, EHB = 9%); and developmental times of the offspring in worker cells of AHB and EHB. However, there was a major difference between the percentage of mother mites producing viable adult female offspring (AHB = 40%, EHB = 75%). This was caused by the increased rate of mite offspring mortality suffered by the first (male) and second (female) offspring in AHB worker cells. Therefore, only an average of 0.7 viable adult female offspring are produced per mite in AHB, compared to 1.0 in EHB.     

Development of early infestations by the miteVarroa jacobsoni in honey-bee (Apis mellifera) colonies in cold climates

The development of an infestation by five to eight introduced adult females ofVarroa jacobsoni Oud. in 35 honey-bee (Apis mellifera L.) colonies was monitored for 16 months with no outside source of infestation. Calculations on the size of the mite populations were based on collection of debris, samples of bees and brood, and estimates of number of bees and broodcells during the summer. In the winter, only dead bees and debris were collected. Samples were taken at 3-week intervals. Data indicated that the mite population probably could increase more than 100 times within one summer, and more than ten times between years, in a climate with a brood-rearing period of less than five months. A large variation in mite population increase existed between colonies. The winter mortality of mites that die with the host or drop from the winter cluster has a large influence on the population dynamics of the mite. Data also indicated that the simple method of counting mites in hive debris is a useful parameter for monitoring the population development ofVarroa in colonies with hatching brood.     

Pathogenesis of varroosis at the level of the honey bee (Apis mellifera) colony

The parasitic mite Varroa destructor, in interaction with different viruses, is the main cause of honey bee colony mortality in most parts of the world. Here we studied how effects of individual-level parasitization are reflected by the bee colony as a whole. We measured disease progression in an apiary of 24 hives with differing degree of mite infestation, and investigated its relationship to 28 biometrical, physiological and biochemical indicators. In early summer, when the most heavily infested colonies already showed reduced growth, an elevated ratio of brood to bees, as well as a strong presence of phenoloxidase/prophenoloxidase in hive bees were found to be predictors of the time of colony collapse. One month later, the learning performance of worker bees as well as the activity of glucose oxidase measured from head extracts were significantly linked to the timing of colony collapse. Colonies at the brink of collapse were characterized by reduced weight of winter bees and a strong increase in their relative body water content. Our data confirm the importance of the immune system, known from studies of individually-infested bees, for the pathogenesis of varroosis at colony level. However, they also show that single-bee effects cannot always be extrapolated to the colony as a whole. This fact, together with the prominent role of colony-level factors like the ratio between brood and bees for disease progression, stress the importance of the superorganismal dimension of Varroa research.     

Development ofEuvarroa sinhai (Acarina: Mesostigmata), a parasitic mite ofApis florea,onA. mellifera worker brood

The development ofEuvarroa sinhai Delfinado and Baker, a parasite ofApis florea F., onA. mellifera worker brood was demonstrated for the first time. The mite fed, lived and reproduced onA. mellifera worker brood as a new host in addition toA. florea. Fertile females used once in the experiment produced 1–8 offspring (x 4.30±1.7) per cell. The actual and potential reproduction rates ofEuvarroa in honeybee worker brood cells were 3.62 and 3.95, respectively. Developmental period from egg to adult was 5 and 6–7 days for males and females, respectively. The female commences to mate soon after her deutonymph/adult moult. Copulation was observed in 18 cases.     

Sub-lethal effects of pesticide residues in brood comb on worker honey bee (Apis mellifera) development and longevity

Background

Numerous surveys reveal high levels of pesticide residue contamination in honey bee comb. We conducted studies to examine possible direct and indirect effects of pesticide exposure from contaminated brood comb on developing worker bees and adult worker lifespan.

Methodology/Principal Findings

Worker bees were reared in brood comb containing high levels of known pesticide residues (treatment) or in relatively uncontaminated brood comb (control). Delayed development was observed in bees reared in treatment combs containing high levels of pesticides particularly in the early stages (day 4 and 8) of worker bee development. Adult longevity was reduced by 4 days in bees exposed to pesticide residues in contaminated brood comb during development. Pesticide residue migration from comb containing high pesticide residues caused contamination of control comb after multiple brood cycles and provided insight on how quickly residues move through wax. Higher brood mortality and delayed adult emergence occurred after multiple brood cycles in contaminated control combs. In contrast, survivability increased in bees reared in treatment comb after multiple brood cycles when pesticide residues had been reduced in treatment combs due to residue migration into uncontaminated control combs, supporting comb replacement efforts. Chemical analysis after the experiment confirmed the migration of pesticide residues from treatment combs into previously uncontaminated control comb.

Conclusions/Significance

This study is the first to demonstrate sub-lethal effects on worker honey bees from pesticide residue exposure from contaminated brood comb. Sub-lethal effects, including delayed larval development and adult emergence or shortened adult longevity, can have indirect effects on the colony such as premature shifts in hive roles and foraging activity. In addition, longer development time for bees may provide a reproductive advantage for parasitic Varroa destructor mites. The impact of delayed development in bees on Varroa mite fecundity should be examined further.