Efficient visual learning by bumble bees in virtual-reality conditions:Size does not matter

Recent developments allowed establishing virtual-reality (VR) setups to study multiple aspects of visual learning in honey bees under controlled experimental conditions. Here, we adopted a VR environment to investigate the visual learning in the buff-tailed bumble bee Bombus terrestris. Based on responses to appetitive and aversive reinforcements used for conditioning, we show that bumble bees had the proper appetitive motivation to engage in the VR experiments and that they learned efficiently elemental color discriminations. In doing so, they reduced the latency to make a choice, increased the proportion of direct paths toward the virtual stimuli and walked faster toward them. Performance in a short-term retention test showed that bumble bees chose and fixated longer on the correct stimulus in the absence of reinforcement. Body size and weight, although variable across individuals, did not affect cognitive performances and had a mild impact on motor performances. Overall, we show that bumble bees are suitable experimental subjects for experiments on visual learning under VR conditions, which opens important perspectives for invasive studies on the neural and molecular bases of such learning given the robustness of these insects and the accessibility of their brain.

Bumblebees adjust protein and lipid collection rules to the presence of brood

Animals have evolved foraging strategies to acquire blends of nutrients that maximize fitness traits. In social insects, nu trie nt regulation is complicated by the fact that few in dividuals, the foragers, must address the diverge nt nutritional n eeds of all colony members simulta neously, includi ng other workers, the reproductives, and the brood. Here we used 3D nutritional geometry design to examine how bumblebee workers regulate their collection of 3 major macronutrients in the presence and absenee of brood. We provided small colonies artificial nectars (liquid diets) and pollens (solid diets) varying in their compositions of proteins, lipids, and carbohydrates during 2 weeks. Colo nies give n a choice betwee n nutrition ally complementary diets self-selected foods to reach a target ratio of 71% proteins, 6% carbohydrates, and 23% lipids, irrespective of the presenee of brood. Whe n con fined to a single nutrition ally imbalanced solid diet, colonies without brood regulated lipid collection and over-collected protein relative to this target ratio, whereas colonies with brood regulated both lipid and protein collection. This brood effect on the regulation of nutrient collection by workers suggests that protein levels are critical for larval development. Our results highlight the importa nee of con sidering bee nu trition as a multidimensi onal phe no men on to better assess the effects of environmental impoverishment and malnutrition on population declines.

Floral trait variation across individual plants within a population enhances defense capability to nectar robbing

Floral trait variation may help pollinators and nectar robbers identify their target plants and,thus,lead to differential selection pressure for defense capability against floral antagonists.However,the effect of floral trait variation among individuals within a population on multi-dimensional plant-animal interactions has been little explored.We investigated floral trait variation,pollination,and nectar robbing among individual plants in a population of the bumble bee-pollinated plant,Caryopteris divaricata,from which flowers are also robbed by bumble bees with varying intensity across individuals.We measured the variation in corolla tube length,nectar volume and sugar concentration among individual plants,and evaluated whether the variation were recognized by pollinators and robbers.We investigated the in-fluence of nectar robbing on legitimate visitation and seed production per fruit.We found that the primary nectar robber(Bombus nobilis)preferred to forage on plants with long-tubed flowers,which produced less nectar and had lower sugar concentration compared to those with shorter corolla tubes.Individuals with shorter corolla tubes had comparatively lower nectar robbing intensity but higher visitation by legitimate visitors(mainly B.picipes)and higher seed production.Nectar robbing signifi-cantly reduced seed production because it decreased pollinator visits.However,neither pollination nor seed production differed between plants with long and short corolla tubes when nectar robbers were excluded.This finding suggests that floral trait variation might not be driven by pollinators.Such variation among individual plants thus allows legitimate visitors and nectar robbers to segregate niches and enhances population defense against nectar robbing in unpredictable conditions.

Survey of insect visitation of ornamental flowers in Southover Grange garden, Lewes, UK

Ornamental flowers commonly grown in ttrban gardens and parks can be of value to flower-visiting insects. However, there is huge variation in the number of insects attracted among plant varieties. In this study, we quantified the insect attractiveness of 79 varieties in full bloom being grown in a public urban garden that is popular due to its beautiful flowers and other attractions. The results showed very clearly that most varieties （77%, n = 61） were either poorly attractive or completely unattractive to insect flower visitors. Several varieties （19%, n = 15） were moderately attractive, but very few （4%, n = 3） were highly attractive. Closer examination of Dahlia varieties showed that ＂open＂ flowered forms were approximately 20 times more attractive than ＂closed＂ flowered forms. These results strongly suggest that there is a great potential for making urban parks and gardens considerably more bee- and insect-friendly by selecting appropriate varieties.