Mite Fertility Research Articles

RNA interference as a next-generation control method for suppressing Varroa destructor reproduction in honey bee (Apis mellifera) hives.

The Varroa mite (Varroa destructor) is considered to be the greatest threat to apiculture worldwide. RNA interference (RNAi) using double-stranded RNA (dsRNA) as a gene silencing mechanism has emerged as a next-generation strategy for mite control. We explored the impact of a dsRNA biopesticide, named vadescana, designed to silence the calmodulin gene in Varroa, on mite fitness in mini-hives housed in a laboratory. Two dosages were tested: 2 g/L dsRNA and 8 g/L dsRNA. Vadescana appeared to have no effect on mite survival, however, mite fertility was substantially reduced. The majority of foundress mites exposed to vadescana failed to produce any offspring. No dose-dependent effect of vadescana was observed, as both the low and high doses inhibited mite reproduction equally well in the mini-hives and neither dose impacted pupal survival of the honey bee. Approximately 95% of bee pupae were alive at uncapping across all treatment groups. These findings suggest that vadescana has significant potential as an effective alternative to conventional methods for Varroa control, with broader implications for the utilization of RNAi as a next-generation tool in the management of pest species. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Recapping and mite removal behaviour in Cuba: home to the world’s largest population of Varroa-resistant European honeybees

The Varroa destructor ectoparasitic mite has spread globally and in conjunction with Deformed Wing Virus has killed millions of honeybee (Apis mellifera) colonies. This has forced Northern hemisphere beekeepers into using miticides to avoid mass colony losses. However, in many Southern hemisphere countries widespread treatment did not occur since miticides were prohibitively expensive, or a centralised choice was made not to treat, both allowing natural selection to act. The Varroa mite initially caused high losses before mite-resistance appeared in the honeybee populations. Initially, mite-resistance was only associated with African and Africanised honeybees. Although recently, several isolated mite-resistant European honeybee populations have appeared. Here we studied the mite-resistance in Cuba and found high rates of recapping of infested worker cells (77%), high removal of mites (80%) and corresponding low mite fertility (r = 0.77). These are all traits found in all naturally evolved Varroa-resistant populations. We can confirm Cuba has the world’s largest European mite-resistant population with 220,000 colonies that have been treatment-free for over two decades and illustrating the power of natural selection. Cuban honeybees are also highly productive, 40–70 kg of honey produced annually, and are mild mannered. Cuba is an excellent example of what is possible when honeybees are allowed to adapt naturally to Varroa with minimal human interference.

Decreased Mite Reproduction to Select Varroa destructor (Acari: Varroidae) Resistant Honey Bees (Hymenoptera: Apidae): Limitations and Potential Methodological Improvements.

The invasive parasitic mite, Varroa destructor (Anderson and Trueman), is the major biotic threat to the survival of European honey bees, Apis mellifera L. To improve colony survival against V. destructor, the selection of resistant lineages against this parasite is considered a sustainable solution. Among selected traits, mite fertility and fecundity, often referred to as suppressed mite reproduction are increasingly used in breeding programmes. However, the current literature leaves some gaps in the assessment of the effectiveness of selecting these traits toward achieving resistance. In the population studied here, we show a low repeatability and reproducibility of mite fertility and fecundity phenotypes, as well as a low correlation of these traits with infestation rates of colonies. Phenotyping reliability could neither be improved by increasing the number of worker brood cells screened, nor by screening drone brood, which is highly attractive for the parasite and available early in the season, theoretically allowing a reduction of generation time and thus an acceleration of genetic progress in selected lineages. Our results provide an evaluation of the potential and limitations of selecting on decreased mite reproduction traits to obtain V. destructor-resistant honeybee colonies. To allow for a more precise implementation of such selection and output reporting, we propose a refined nomenclature by introducing the terms of decreased mite reproduction and reduced mite reproduction, depending on the extent of mite reproduction targeted. We also highlight the importance of ensuring accurate phenotyping ahead of initiating long-lasting selection programmes.

Fertility and reproductive rate of Varroa mite, Varroa destructor, in native and exotic honeybee, Apis mellifera L., colonies under Saudi Arabia conditions.

Varroa mite is the most destructive pest to bee colonies worldwide. In Saudi Arabia, preliminary data indicated high infestation levels in the exotic honeybee colonies; such as Apis mellifera carnica and Apis mellifera ligustica, compared to native honeybee subspecies Apis mellifera jemenitica, which may imply higher tolerance to Varroasis. In this study, fertility and reproductive rate of Varroa mite, Varroa destructor, in capped brood cells of the native honeybee subspecies were investigated and compared with an exotic honeybee subspecies, A. m. carnica. Mite fertility was almost alike (87.5% and 89.4%) in the native and craniolan colonies respectively. Similarly, results did not show significant differences in reproduction rate between both subspecies (F = 0.66, Pr > F = 0.42). Number of adult Varroa daughters per fertile mother mite was 2.0 and 2.1 for native and craniolan honeybee subspecies respectively. This may indicate that mechanisms of keeping low infestation rates in the native honeybee colonies are not associated with Varroa reproduction. Therefore, potential factors of keeping lower Varroa infestation rates in native honey bee subspecies should be further investigated.

Reproduction of Varroa destructor 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 (X(2)=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%) (X(2)=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 (X(2)=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.

Acaricidal activities of some essential and fixed oils on the two-spotted spider mite, Tetranychus urticae

A comparison was made for studying the effect of some Essential oils: Rosemary, Garlic, Jojoba and Fixed/Vegetable oils on the important mite pest, Tetranychus urticae. The sublethal concentrations of Rosemary oil (0.125%), Garlic oil (0.5%), Jojoba oil (0.25%) and Vegetable oil (0.125%) were used. Biological tests were carried out for a susceptible laboratory two-spotted spider mites strain reared under controlled conditions of 27±2°C; 60% R.H. and 16L/8D photoperiod on Sweet Potato leaves. Results showed that Garlic oil caused the highest significant decrease in the number of deposited eggs as compared to the other tested oils. All the oils used have no effects on females mite fertility. Vegetable oil greatly affected the percentage of nymphs that reached adult stages followed by Jojoba oil then Garlic oil while Rosemary had no effects on nymph's developments. Results were tabulated, analyzed, discussed and prepared to be fit in any IPM program for combating these pest animals.

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 &amp; 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.

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

SummaryVarroa 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.

Comparative toxicity of botanical and reduced-risk insecticides to Mediterranean populations of Tetranychus urticae and Phytoseiulus persimilis (Acari Tetranychidae, Phytoseiidae)

The two-spotted spider mite Tetranychus urticae and its predator Phytoseiulus persimilis are widely spread throughout the Mediterranean area. Predator–prey interactions in crops may be affected by pesticides used to control other pests, and thus knowledge of pesticide side-effects is essential when managing spider mite populations following integrated pest management (IPM). Toxicological studies evaluating the effects of pesticides on both predator and prey can better predict their impact on mite communities. The botanical and reduced-risk insecticides recommended for the control of aphids, whiteflies and thrips, Biopiren ® plus (pyrethrins), Confidor ® (imidacloprid), Naturalis ® ( Beauveria bassiana), Oikos ® (azadirachtin), Plenum ® (pymetrozine) and Rotena ® (rotenone) were evaluated on T. urticae and P. persimilis females in the laboratory. Mite populations were collected on unsprayed vegetables in the Mediterranean area (island of Sardinia). Mite females were treated by micro-immersion and then reared on treated leaves in holding cells. The survival, fecundity and fertility of mites were assessed. All the products affected mite survival and/or fecundity. Pyrethrins and rotenone were more toxic to P. persimilis than to T. urticae; azadirachtin, B. bassiana and pymetrozine showed an opposite tendency. Imidacloprid had a similar impact on predator and prey. Additional toxicological trials were conducted with T. urticae and P. persimilis eggs. Beauveria bassiana was the most effective pesticide in reducing the hatching of T. urticae treated eggs and rotenone significantly affected P. persimilis egg hatching.

A comparison of the reproductive ability of Varroa destructor (Mesostigmata:Varroidae) in worker and drone brood of Africanized honey bees (Apis mellifera)

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.

Temporal changes inVarroa destructorfertility and haplotype in Brazil

The relationship between fertility and haplotype was studied in Varroa destructor mites sampled from colonies of A. mellifera carnica and Africanized Honeybees (Apis mellifera) in Germany and Brazil respectively. Both in Germany and in Brazil, only the V. destructor Korea haplotype was found, though the Japan-Thailand haplotype was formerly thought to have been more abundant in Brazil. The fertility of Varroa mites in Brazil has increased since 1998 and is currently (2001) at European levels. Temporal changes in mite fertility and haplotype are not fully congruent.

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 honey bee (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.

Removal ofVarroa jacobsoniinfested brood in honey bee colonies with differing pollen stores

The effects of high or low pollen storage on Apis mellifera L. brood removal behavior and Varroa jacobsoni reproduction were examined. High pollen storage colonies removed 49% of the infested larvae compared to 33% removal by the low pollen storage colonies. No difference was found in the proportion of fertile mites between those reared in high or low pollen storage colonies, although mite fertility appeared to decrease from mid to late summer in British Columbia, Canada. These findings indicate that the presence of pollen stores increases the rate of cell removal, and warrants fur- ther investigation into colony management as a potential means of V. jacobsoni infestation control.

Effects on Varroa jacobsoni from acaricides in beeswax

SUMMARYThe effect from acaricide residues in beeswax on mortality and fertility of Varroa jacobsoni was investigated. Amitraz, coumaphos and fluvalinate were added to acaricide-free wax at 0, 1, 10, 100 ppm each and the wax subsequently was used to produce comb foundation. Amitraz could not be recovered from the foundation, but foundation where coumaphos and fluvalinate had been added to the wax contained approximately the added residue levels. When mites were allowed to enter brood in combs made from this foundation, the effect from coumaphos residues was dramatic. Almost all mother mites died in combs where 100 ppm coumaphos had been added to the foundation and increased mother mite mortality occurred at the 10-ppm level. An effect from fluvalinate was only seen in combs drawn from foundation with 100 ppm fluvalinate. If one brood generation had been present prior to the brood attacked by the mites, no harmful effects to mites from wax contaminants were found, even at the highest contamination levels. This result is probably due to the honey bee cocoon acting as a barrier for acaricide transfer from the wax to the mites in the cells. It is concluded that studies of mite fertility probably do not need to consider if the wax is contaminated with up to 10 ppm of fluvalinate. At 100 ppm in the wax the effect from this acaricide on mite performance is detectable but not dramatic. However, comb drawn from foundation having 10 ppm or more coumaphos, and in which no brood was reared, dramatically reduced mother mite survival. Since frozen combs are often used when mite fertility is investigated, coumaphos in the wax may distort results at contamination levels found in European wax.