Gherardo Bogo

Synergistic mortality between a neonicotinoid insecticide and an ergosterol‐biosynthesis‐inhibiting fungicide in three bee species

BACKGROUND Neonicotinoid insecticides have been identified as an important factor contributing to bee diversity declines. Nonetheless, uncertainties remain about their impact under field conditions. Most studies have been conducted on Apis mellifera and tested single compounds. However, in agricultural environments, bees are often exposed to multiple pesticides. We explore the synergistic mortality between a neonicotinoid (clothianidin) and an ergosterol-biosynthesis-inhibiting fungicide (propiconazole) in three bee species (A. mellifera, Bombus terrestris, Osmia bicornis) following oral exposure in the laboratory. RESULTS We developed a new approach based on the binomial proportion test to analyse synergistic interactions. We estimated uptake of clothianidin per foraging bout in honey bees foraging on seed-coated rapeseed fields. We found significant synergistic mortality in all three bee species exposed to non-lethal doses of propiconazole and their respective LD10 of clothianidin. Significant synergism was only found at the first assessment times in A. mellifera (4 and 24 h) and B. terrestris (4 h), but persisted throughout the experiment (96 h) in O. bicornis. O. bicornis was also the most sensitive species to clothianidin. CONCLUSION Our results underscore the importance to test pesticide combinations likely to occur in agricultural environments, and to include several bee species in environmental risk assessment schemes.

Effects of queen mating status, pre-diapause weight and pupae’s sex on colony initiation in small-scale rearing of Bombus terrestris

Diapause control and colony initiation are among the major problems encountered in the rearing of bumble bee colonies in small-scale rearing. In this study, we used Bombus terrestris queens obtained from commercial colonies to investigate (1) the diapause survival in virgin and mated queens, (2) the diapause and colony initiation performance of mated bumble bee queens in relation to the pre-diapause weight and (3) the effect of pupae’s sex on colony initiation. We found that diapause survival is negatively affected by mating and by the low pre-diapause weight, but first egg deposition and development of the first adult worker were delayed in heavy queens. We found no significant differences in the egg-laying success in relation to pupae’s sex; however, queens stimulated with queen pupae laid more eggs per cell and developed a first brood larger than those stimulated with male pupae. Our results can be useful in small-scale rearing, including the rearing of wild queens for conservation purposes.

Effects of nonprotein amino acids on survival and locomotion of Osmia bicornis : β-alanine and GABA effects on Osmia bicornis

To investigate the effects of two nectar nonprotein amino acids, β‐alanine and γ‐aminobutyric acid (GABA), on Osmia bicornis survival and locomotion, two groups of caged bees were fed with sugar syrup enriched with β‐alanine and GABA, respectively. A further control group was fed with sugar syrup. Five behavioural categories were chosen according to the principle of parsimony and intrinsic unitary consistency from start to end, and recorded by scan sampling: two states (remaining under paper or in tubes) and three events (walking on net, feeding from flower and flying). We also analysed the amino acid content of haemolymph sampled from an additional 45 bees fed the same diets (15 per diet type). Bees fed with β‐alanine had a significantly shorter survival time than those fed with the control and GABA diets. The GABA diet induced higher levels of locomotion than β‐alanine. The former nonprotein amino acid was only detected in the haemolymph of bees fed GABA. The results suggest that insects consuming nonprotein amino‐acid‐rich diets absorb and transfer these substances to the haemolymph and that nonprotein amino acids affect survival and locomotion. Ecological consequences are discussed in the framework of plant reproductive biology.

Different reproductive strategies and their possible relation to inbreeding risk in the bumble bee Bombus terrestris

In many species, inbreeding avoidance mechanisms prevent mating between close relatives, but these mechanisms are poorly studied in bumble bees. The probability of inbred matings within a colony in eusocial insects may depend on the timing of gyne and male emergence and on their sex ratio. In this study, we compared the development of 35 colonies of the bumble bee Bombus terrestris from founding to the emergence of the last gyne, and we investigated the probability of inbred mating in colonies with fertile newborn gynes and males. We calculated a novel colony inbreeding risk index (IRI), which considers the overlap period between fertile gynes and males, their numbers, and the colony sex ratio. We found that the IRI values were strictly correlated with the time elapsed between the gyne point and the switch point (i.e., from the moment of deposition of the first diploid egg that produces a gyne to the first haploid egg). We separated the colonies into two groups based on the mean value of the IRI: colonies with low IRI produced more gynes (93.8 ± 9.4), for a longer period (32.1 ± 1.8 days) and with a lower percentage of overlapped gynes (69 ± 5%) than colonies with high IRI (57.1 ± 21 gynes, 23.3 ± 2.9 days, and 100% overlapped gynes, respectively). A low IRI is connected to a reduced risk of inbred mating, while colonies with a high IRI may be advantaged in conditions of isolation, in case of the absence of non-related reproducers. Inbreeding risk index proved to be a good indicator of the colony reproductive strategy.

Pollen load diversity and foraging niche overlap in a pollinator community of the rare Dictamnus albus L.

Bees collect pollen as an important resource for offspring development while acting as pollen vectors for the plants visited. Foraging preferences of pollinators together with plant species availability shape the web of interactions at the local scale. In this study, we focused on the bee pollinator community of a population of the rare protected perennial herb Dictamnus albus, with the aim to characterise the pollen preferences and the foraging niche overlap among species through time. Bees were sampled during four consecutive years in a natural population of D. albus, throughout the blooming period of the plant species. We performed an analysis of insect pollen loads to investigate the interactions with the study species and the co-flowering plants in the area, and to evaluate the degree of foraging overlap among pollinators. Over the study years, all bee species showed a high fidelity to D. albus (60–80%), even if some taxa preferentially collected pollen from other flowering species. The foraging niche overlap in the pollinator community decreased together with an increased diversity of co-flowering plant species. The results obtained indicate that bees preferentially forage on D. albus in the studied area, but that co-flowering species contribute to complement their diet and likely reduce competition for foraging resources. It appears therefore important to maintain a high diversity of co-flowering plants to preserve the diversity in the studied pollinator community of D. albus.