Pierre Giovenazzo

Differential gene expression between hygienic and non-hygienic honeybee (Apis mellifera L.) hives

BackgroundHygienic behavior is a complex, genetically-based quantitative trait that serves as a key defense mechanism against parasites and diseases in Apis mellifera. Yet, the genomic basis and functional pathways involved in the initiation of this behavior are still unclear. Deciphering the genomic basis of hygienic behavior is a prerequisite to developing an extensive repertoire of genetic markers associated to the performance level of this quantitative trait. To fill this knowledge gap, we performed an RNA-seq on brain samples of 25 honeybees per hives from five hygienic and three non-hygienic hives.ResultsThis analysis revealed that a limited number of functional genes are involved in honeybee hygienic behavior. The genes identified, and especially their location in the honeybee genome, are consistent with previous findings. Indeed, the genomic sequences of most differentially expressed genes were found on the majority of the QTL regions associated to the hygienic behavior described in previous studies. According to the Gene Ontology annotation, 15 genes are linked to the GO-terms DNA or nucleotide binding, indicating a possible role of these genes in transcription regulation. Furthermore, GO-category enrichment analysis revealed that electron carrier activity is over-represented, involving only genes belonging to the cytochrome P450. Cytochrome P450 enzymes’ overexpression can be explained by a disturbance in the regulation of expression induced by changes in transcription regulation or sensitivity to xenobiotics. Over-expressed cytochrome P450 enzymes could potentially degrade the odorant pheromones or chemicals that normally signal the presence of a diseased brood before activation of the removal process thereby inhibit hygienic behavior.ConclusionsThese findings improve our understanding on the genetics basis of the hygienic behavior. Our results show that hygienic behavior relies on a limited set of genes linked to different regulation patterns (expression level and biological processes) associated with an over-expression of cytochrome P450 genes.

Detection of Nosema apis and N. ceranae in honeybee bottom scraps and frass in naturally infected hives

Current sampling methods for identification of honeybee microsporidians (Nosema apis and Nosema ceranae) involve killing adult honeybees. The current study monitored the presence of N. apis and N. ceranae in honeybee frass and bottom scraps collected from six hives located in Deschambault, Quebec, Canada, from 2009 to 2010. Infection rates of N. ceranae and N. apis were quantified using duplex qPCR enabling the simultaneous detection of single and co-infections of the two species. Screening of all sample types revealed a greater presence of N. ceranae. qPCR infection levels for both Nosema species in bees and bottom scraps were correlated and showed a significant correlation (P < 0.001) between infection rates of N. apis, while no significant correlative relationship (P = 0.1037) was observed between those of N. ceranae. This study has demonstrated that Nosema spp. can be detected and reliably quantified in bottom scraps and frass of bee hives using qPCR diagnostic assays, and additionally, these techniques are not detrimental to the hive health, faster, and as reliable as sampling bees from within the colony when combined with qPCR diagnostic tests.

Pupal Development of Aethina tumida (Coleoptera: Nitidulidae) in Thermo-Hygrometric Soil Conditions Encountered in Temperate Climates

ABSTRACT The pupal development of Aethina tumida Murray (Coleoptera: Nitidulidae) was studied at various combinations of thermo-hygrometric soil conditions (temperatures of 16, 18, and 20°C and soil water content levels of 0.37, 0.56, and 0.73 m3 water per cubic meter of dry soil) representative of southeastern Canada. Survivorship and development duration of A. tumida pupae, as well as sex ratio and life span of emerging adults, were assessed. Assays were conducted in growth chambers on an average of 50 third-instar larvae per thermo-hygrometric combination. Results show that survivorship of pupae decreased with lower temperature and higher soil water content. Pupal development time shortened as temperature increased (69–78 d at 16°C, 47–54 d at 18°C, and 36–39 d at 20°C), but was longer in dryer soil. Optimal soil water content for pupal development was 0.56 m3 water per cubic meter of soil. We estimated that the minimum development temperature for pupae is between 10.2 and 13.2°C, depending on soil water content. The sex ratio of emerging adults was influenced by soil water content. We measured one female to one male for dry and intermediately wet soils and three females to one male for wet soils. Higher soil water content reduced the life span of emerging adults by half. This study contributes to a better understanding of A. tumida population dynamics in eastern Canada.

Deleterious Interaction Between Honeybees (Apis mellifera) and its Microsporidian Intracellular Parasite Nosema ceranae Was Mitigated by Administrating Either Endogenous or Allochthonous Gut Microbiota Strains

Honey bees (Apis mellifera) are facing multiple stressors affecting their lifespan, health and productivity. Among them, Nosema ceranae is an intracellular microsporidian parasite, which plays a major impact on honey bees colonies. However, both efficiency and innocuity of current treatment against N. ceranae are observed, thus raising the urgent need to develop alternative prophylactic and curative strategies. Endogenous microbial communities (i.e. host microbiota) are known to play a major role in disease prevention, and more recently both bacterial and yeast strains issued from gut microbiota were observed to improve hosts resistance against intracellular parasites both in mammals and insect models. The use of probiotics in honey bee nutrition is therefore promising to treat or prevent diseases. Therefore, further investigations are needed to properly select microorganisms with probiotic properties. In an in vivo experimental infection by Nosema ceranae, the probiotic effect of two honeybee gut bacterial strains (Parasaccharibacter apium (PC1 sp.) and (Bacillus sp. (PC2 sp.)), and two broad spectra probiotics (Bactocell® and Levucell SB®) has been measured. Both curative and prophylactic administrations were tested: honey bees infected with N. ceranae and non-infected. For the four probiotic candidates, significant increases of survival probabilities (20-30%) were measured after two weeks of treatment with the administration of 103 CFU/mL in sugar syrup, both in curative and prophylactic treatments. The present study shows that endogenous bacterial strains were at least as much efficient and safe than broad spectra probiotics in increasing survival in the context of experimental infection with N. ceranae. Therefore, taking advantage of beneficial host microbiota properties is a promising avenue to develop efficient and sustainable curative strategies against opportunistic diseases in honey bee colonies.

Preservation of Domesticated Honey Bee (Hymenoptera: Apidae) Drone Semen

Abstract Preservation of honey bee (Apis mellifera L., Hymenoptera: Apidae) sperm, coupled with instrumental insemination, is an effective strategy to protect the species and their genetic diversity. Our overall objective is to develop a method of drone semen preservation; therefore, two experiments were conducted. Hypothesis 1 was that cryopreservation (–196 °C) of drone semen is more effective for long-term storage than at 16 °C. Our results show that after 1 yr of storage, frozen sperm viability was higher than at 16 °C, showing that cryopreservation is necessary to conserve semen. However, the cryoprotectant used for drone sperm freezing, dimethyl sulfoxide (DMSO), can harm the queen and reduce fertility after instrumental insemination. Hypothesis 2 was that centrifugation of cryopreserved semen to reduce DMSO prior to insemination optimize sperm quality. Our results indicate that centrifuging cryopreserved sperm to remove cryoprotectant does not affect queen survival, spermathecal sperm count, or sperm viability. Although these data do not indicate that centrifugation of frozen-thawed sperm improves queen health and fertility after instrumental insemination, we demonstrate that cryopreservation is achievable, and it is better for long-term sperm storage than above-freezing temperatures for duration of close to a year.