Care-giver identity impacts offspring development and performance in an annually social bumble bee

Background The developmental fates of offspring have the potential to be influenced by the identity of their care-givers and by the nature of the care that they receive. In animals that exhibit both parental and alloparental care, such as the annually eusocial insects, the influence of care-giver identity can be directly assessed to yield mechanistic and evolutionary insights into the origins and elaboration of brood care. Here, we performed a comparative investigation of maternal and worker brood care in bumble bees, a pollinator group where mothers (queens) rear the first offspring in the nest, and then daughters (workers) assume this role upon their emergence. Specifically, we compared the effects of queen and worker brood care on offspring development and also offspring performance, for a set of traits related to sensory biology, learning, and stress resistance. Results We found that queen-reared workers were smaller-bodied than worker-reared offspring, suggesting that bumble bee queens influence body size determination in their offspring. We also found that queen-reared workers were more resistant to starvation, which might be beneficial for early nesting success. These maternal influences could not be explained by feeding rate, given that we detected a similar offspring feeding frequency in both queens and workers. Conclusion Bumble bee queens have a unique influence on the development of the first offspring in the nest, which they rear, relative to worker-reared workers. We propose that bumble bee brood care has been shaped by a suite of evolutionary and ecological factors, which might include a maternal influence on traits that promote survival of incipient colonies.

Correction: Floris, I., et al. How the Infestation Level of Varroa destructor Affects the Distribution Pattern of Multi-Infested Cells in Worker Brood of Apis mellifera. Veterinary Science 2020, 7, 136

We have recently been made aware by the reviewer and the Journal Editorial Offices of the following weaknesses in our recent paper [...]

Chronic High Glyphosate Exposure Delays Individual Worker Bee (Apis mellifera L.) Development under Field Conditions

The ongoing debate about glyphosate-based herbicides (GBH) and their implications for beneficial arthropods gives rise to controversy. This research was carried out to cover possible sublethal GBH effects on the brood and colony development, adult survival, and overwintering success of honey bees (Apis mellifera L.) under field conditions. Residues in bee relevant matrices, such as nectar, pollen, and plants, were additionally measured. To address these questions, we adopted four independent study approaches. For brood effects and survival, we orally exposed mini-hives housed in the “Kieler mating-nuc” system to sublethal concentrations of 4.8 mg glyphosate/kg (T1, low) and 137.6 mg glyphosate/kg (T2, high) over a period of one brood cycle (21 days). Brood development and colony conditions were assessed after a modified OECD method (No. 75). For adult survival, we weighed and labeled freshly emerged workers from control and exposed colonies and introduced them into non-contaminated mini-hives to monitor their life span for 25 consecutive days. The results from these experiments showed a trivial effect of GBH on colony conditions and the survival of individual workers, even though the hatching weight was reduced in T2. The brood termination rate (BTR) in the T2 treatment, however, was more than doubled (49.84%) when compared to the control (22.11%) or T1 (20.69%). This was surprising as T2 colonies gained similar weight and similar numbers of bees per colony compared to the control, indicating an equal performance. Obviously, the brood development in T2 was not “terminated” as expected by the OECD method terminology, but rather “slowed down” for an unknown period of time. In light of these findings, we suggest that chronic high GBH exposure is capable of significantly delaying worker brood development, while no further detrimental effects seem to appear at the colony level. Against this background, we discuss additional results and possible consequences of GBH for honey bee health.

How the Infestation Level of Varroa destructor Affects the Distribution Pattern of Multi-Infested Cells in Worker Brood of Apis mellifera

The mite Varroa destructor, the main ectoparasite of honey bees, is a threat to apiculture worldwide. Understanding the ecological interactions between Varroa and honeybees is fundamental for reducing mite impact in apiaries. This work assesses bee colonies with various Varroa infestation levels in apiaries to determine: (1) the relationship between multi-infested brood cells and brood infestation level, (2) the damage caused by Varroa to parasitized honey bee pupae, and (3) mite reproduction rate at various infestation levels. Data were collected from 19 worker brood combs, each from a different colony, ranging from 160 to 1725 (mean = 706) sealed cells per comb. Mite distribution was aggregated, ranging from about 2% to 74% infested cells per comb. The percentage of cells invaded by one, two, three, four, or more than four foundress mites, as a function of infestation level, was estimated by five highly significant (p < 0.0001) second-degree polynomial regression equations. The correction factors found could increase the precision of prediction models. Varroa fertility and adult bee longevity decreased as multi-infestation levels increased, and the implications of this relationship are discussed. Finally, these findings could improve sampling methods and the timing of mite treatments in apiaries, thus favoring sustainable management strategies.

Influence of Baikal EM1 preparation on the productive parameters of bee colonies (Apis mellifera L.) during spring and autumn feeding

The aim of the present study is to investigate the effect of Baikal EM1 on the productive parameters of the bee colonies (Apis mellifera L.) during spring and autumn feeding and the chemical composition of the worker bee bodies. Two groups of bee colonies were formed (1 experimental group and 1 control group). During the spring feeding the experimental group was fed with Baikal ЕМ1 at a dose of 5 ml/0.500 L added in the sugar syrup (sugar:water 1:1) for 4 consecutive days at the start of the experiment. Each bee colony received 5 L sugar syrup. During the autumn feeding the experimental group received Baikal ЕМ1 at a dose of 20 ml/10 L sugar syrup. Each bee colony received 10 L sugar syrup. The control group received only sugar syrup. The spring and autumn feeding of the group fed with Baikal EM1 significantly increases the strength of the bee colonies and the amount of the sealed worker brood compared to the control group. According to the results obtained for the strength of the bee colonies and the bee brood supplementary feeding with Baikal EM1 is very effective in the autumn feeding. For these two parameters there are significant differences between the experimental and control on 29.08. (p<0.01), 10.09. (p<0.05) and 22.09.2018 (p<0.01). Statistically significant differences were reported for the strength of the bee colonies (p<0.01) and the amount of sealed worker brood (p<0.001) in the experimental group receiving Baikal EM1 before wintering compared to the control group. It can be expected to reveal a tendency for better spring development in the next year. Feeding with Baikal EM1 does not affect the chemical composition of worker bee bodies.

Chronic high glyphosate exposure delays individual worker bee (Apis mellifera L.) development under field conditions

ABSTRACTThe ongoing debate about glyphosate-based herbicides (GBH) and their implications for beneficial arthropods give rise to controversy. This research was carried out to cover possible sublethal GBH effects on brood and colony development, adult survival, and overwintering success of honey bees (Apis mellifera L.) under field conditions. Residues in bee relevant matrices such as nectar, pollen and plants were measured in addition. To address these questions, we adopted four independent study approaches. For brood effects and survival, we orally exposed mini-hives housed in the “Kieler mating-nuc” system to sublethal concentrations of 4.8 mg glyphosate/kg (T1, low) and 137.6 mg glyphosate/kg (T2, high) over the period of one brood cycle (21 days). Brood development and colony conditions were assessed after a modified OECD method (No. 75). For adult survival, we weighed and labeled freshly emerged workers from exposed colonies and introduced them into non-contaminated mini-hives to monitor life span for 25 consecutive days. Results from these experiments showed a trivial effect of GBH on colony conditions and survival of individual workers, even though hatching weight was reduced in T2. The brood termination rate (BTR) in the T2 treatment, however, was more than doubled (49.84%) when compared to the control (22.11%) or T1 (20.69%). This was surprising as T2 colonies gained similar weight and similar numbers of bees per colony compared to the control, indicating equal performance. Obviously, the brood development in T2 was not “terminated” as expected by the OECD method terminology but rather “slowed down” for an unknown period of time. In light of these findings, we suggest that chronic high GBH exposure is capable of delaying worker brood development to a significant extent while no further detrimental effects seem to appear at the colony level. Against this background, we discuss additional results and possible consequences of GBH for honey bee health.

In Vitro Effects of Pesticides on European Foulbrood in Honeybee Larvae

Neonicotinoid and fungicide exposure has been linked to immunosuppression and increased susceptibility to disease in honeybees (Apis mellifera). European foulbrood, caused by the bacterium Melissococcus plutonius, is a disease of honeybee larvae which causes economic hardship for commercial beekeepers, in particular those whose colonies pollinate blueberries. We report for the first time in Canada, an atypical variant of M. plutonius isolated from a blueberry-pollinating colony. With this isolate, we used an in vitro larval infection system to study the effects of pesticide exposure on the development of European foulbrood disease. Pesticide doses tested were excessive (thiamethoxam and pyrimethanil) or maximal field-relevant (propiconazole and boscalid). We found that chronic exposure to the combination of thiamethoxam and propiconazole significantly decreased the survival of larvae infected with M. plutonius, while larvae chronically exposed to thiamethoxam and/or boscalid or pyrimethanil did not experience significant increases in mortality from M. plutonius infection in vitro. Based on these results, individual, calculated field-realistic residues of thiamethoxam and/or boscalid or pyrimethanil are unlikely to increase mortality from European foulbrood disease in honeybee worker brood, while the effects of field-relevant exposure to thiamethoxam and propiconazole on larval mortality from European foulbrood warrant further study.

Reproduction of Distinct Varroa destructor Genotypes on Honey Bee Worker Brood

Honey bees play important roles in pollination for many crops and wild plants, but have been facing great threats posed by various pathogens and parasites. Among them, Varroa destructor, an obligate ectoparasite of honey bees, is considered the most damaging. Within the last century, V. destructor shifted from the original host, the Asian honey bee Apis cerana to the new host, the European honey bee A. mellifera. However, the reproduction of Varroa mites, especially of different haplotypes in the two hosts, is still largely unknown. In this study, we first investigated the existing Varroa haplotypes in local colonies in southern China, and then compared the reproduction of different haplotypes on the worker brood of both the original and new hosts by artificial inoculation. We confirmed that there are two haplotypes of V. destructor in southern China, one is the Korea haplotype and the other is the China haplotype, and the two types parasitized different honey bee species. Although Varroa females from A. mellifera (Korea haplotype) are able to reproduce on the worker brood of both honey bee species, they showed better reproductive performance in the new host A. mellifera with significantly higher fecundity (number of offspring per mother mite) and reproductive rate (number of adult daughters per mother mite), suggesting that this parasite gains higher fitness after host shift. The data further showed that a short stay of Varroa females inside the A. cerana worker cells decreased their fecundity and especially the reproductive rate in a time-dependent manner, suggesting that the A. cerana worker cells may inhibit Varroa reproduction. In contrast, Varroa mites derived from A. cerana colonies (China haplotype) were entirely sterile in A. mellifera worker cells during two sequential inoculations, while the control mites from A. mellifera colonies (Korea haplotype) reproduced normally. In addition, all the infertile mites were found to defecate on the abdomen of bee pupae. We have revealed that two haplotypes of V. destructor exhibit differential reproduction on the worker brood of the original and new host honey bees, providing novel insights into the diversity and complexity of the reproduction of V. destructor.

Drone and Worker Brood Was Unexpectedly Well Heated Both in Standard-Cell and Small-Cell Comb Colonies

Temperatures of worker- and drone-brood rearing in various hive locations were compared in both colonies kept on small-cell combs (4.90 mm) (SMC) and standard-cell combs (5.50 mm) (STC) in two seasons. Temperatures close to the worker-brood comb placed near the rightmost storage-comb were lower than those near the worker brood in the nest centre but equal to those near the outskirt drone-brood comb (34.37-35.24°C) regardless of the month and the comb-cell size. Temperatures of the brood rearing in the SMC did not differ from those in the STC, independently on the location (center-periphery) and the brood type (drone-worker). Occasionally, they were even higher in the STC near the peripheral drone-brood comb and in the nest centre. We concluded that the drones which are involved in colony reproduction could affect its thermoregulation. The peripheral drone brood can be heated just as well as the worker brood, if the colony is strong enough and has the proper drone-worker ratio. Therefore, it is doubtful whether a higher temperature near the worker brood in the SMC limit the development of the V. destructor population. A lower temperature may not be a factor in encouraging V. destructor females to prefer trap-drone-combs for reproduction in the SMC. Strong field colonies may be especially prone to such behaviour. Therefore, temperature cannot be considered a mechanism of effective Varroa control in SMC.