Nesting biology and nest structure of the exotic bee Megachile sculpturalis.

From the 1990s, the Southeast Asia native giant resin bee Megachile sculpturalis (Smith, 1853) was introduced first to North America, and then to many countries in Europe. Despite increasing studies on its invasive potential and geographical expansion, information on nesting behaviour of this species is still extremely scarce. To increase knowledge on the nesting biology of M. sculpturalis, we studied multiple aspects of nesting and pollen provisioning in three consecutive years in artificial nests in Bologna, Italy. We observed 166 bees visiting nests, and followed individual nesting behaviour and success of 41 adult females. We measured cavity diameter in 552 nests and characterised the structure in 100 of them. More than 95% of nest diameters ranged between 0.6 and 1.2 cm, overlapping with several sympatric species of cavity-nesting hymenopterans in the study area. Most nests had a first chamber from the entrance of variable length without brood, followed by an average of about two brood cells with a mean length of 2.85 ± 0.13 cm each. The pollen stored in brood cells was almost monofloral, belonging to the ornamental plant Styphnolobium japonicum (L.) Schott. We estimated that a single female should visit ≈180 flowers to collect enough pollen for a single brood cell. These results fill knowledge gaps on the nesting biology and nest structure of the exotic M. sculpturalis, and they are discussed in relation to possible competition with native bees for nesting sites and foraging resources.

Effect of amino acid enriched diets on hemolymph amino acid composition in honey bees.

Amino acids (AAs) are an abundant class of nectar solutes, and they are involved in the nectar attractiveness to flower visitors. Among the various AAs, proline is the most abundant proteogenic AA, and γ-amino butyric acid (GABA) and ß-alanine are the two most abundant non-proteogenic AAs. These three AAs are known to affect insect physiology, being involved in flight metabolism and neurotransmission. The aim of this study was to investigate the effects of artificial diets enriched with either ß-alanine, GABA, or proline on consumption, survival, and hemolymph composition in honey bees belonging to two different ages and with different metabolism (i.e., newly emerged and foragers). Differences in feed intake among diets were not observed, while a diet enriched with ß-alanine improved the survival rate of newly emerged honey bees compared to the control group. Variations in the hemolymph AA concentrations occurred only in newly emerged honey bees, according to the diet and the time of hemolymph sampling. A greater susceptibility of young honey bees to enriched diets than older honey bees was observed. The variations in the concentrations of hemolymph AAs reflect either the accumulation of dietary AAs or the existence of metabolic pathways that may lead to the conversion of dietary AAs into different ones. This investigation could be an initial contribution to studying the complex dynamics that regulate hemolymph AA composition and its effect on honey bee physiology.

Effects of Non-Protein Amino Acids in Nectar on Bee Survival and Behavior.

Nectar mediates complex interactions between plants and animals. Recent research has focused on nectar secondary compounds that may play a role in regulating some of these interactions. These compounds may affect the behavior of nectar feeders by interacting with their neurobiology. Non-protein amino acids (NPAAs) can constitute a large portion of the amino acid content of floral nectar, but their ecological function has, to date, not been investigated. In this study, we tested the effects of diets with low and high concentrations of γ-amino butyric acid (GABA) and ß-alanine on the survival and behavior of Bombus terrestris and Apis mellifera. The most apparent effect on longevity was observed for B. terrestris workers that fed on high concentration of GABA, with longevity increased. By contrast, neither of the two NPAAs (at either concentration) had an affect on A. mellifera longevity. At the low NPAA concentration, only B. terrestris workers showed a difference in consumption, consuming more ß-alanine solution than the other two solutions. By contrast, at the high NPAA concentration, only A. mellifera workers showed a difference in consumption, consuming more ß-alanine solution. The effects of the NPAAs on behavior differed between the two species, with B. terrestris appearing more sensitive to the NPAAs than A. mellifera. After consuming NPAAs, B. terrestris showed changes in three (walking, flying, stationary) of the four behaviors recorded, although the effects varied with concentration and compound. In contrast, honey bees only showed a change in feeding behavior, with consumption of both NPAAs (at low concentrations) resulting in a decrease. Thus, pollinator intake of NPAAs may have important behavioral/ecological implications.

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. © 2016 Society of Chemical Industry.