Adipokinetic hormone (AKH), energy budget and their effect on feeding and gustatory processes of foraging honey bees

The adipokinetic hormone (AKH) of insects is considered an equivalent of the mammalian hormone glucagon as it induces fast mobilization of carbohydrates and lipids from the fat body upon starvation. Yet, in foraging honey bees, which lack fat body storage for carbohydrates, it was suggested that AKH may have lost its original function. Here we manipulated the energy budget of bee foragers to determine the effect of AKH on appetitive responses. As AKH participates in a cascade leading to acceptance of unpalatable substances in starved Drosophila, we also assessed its effect on foragers presented with sucrose solution spiked with salicin. Starved and partially-fed bees were topically exposed with different doses of AKH to determine if this hormone modifies food ingestion and sucrose responsiveness. We found a significant effect of the energy budget (i.e. starved vs. partially-fed) on the decision to ingest or respond to both pure sucrose solution and sucrose solution spiked with salicin, but no effect of AKH per se. These results are consistent with a loss of function of AKH in honey bee foragers, in accordance with a social life that implies storing energy resources in the hive, in amounts that exceed individual needs.

The Role of Colony Temperature in the Entrainment of Circadian Rhythms of Honey Bee Foragers

Honey bees utilize their circadian rhythms to accurately predict the time of day. This ability allows foragers to remember the specific timing of food availability and its location for several days. Previous studies have provided strong evidence toward light/dark cycles being the primary Zeitgeber for honey bees. Recent work in our laboratory described large individual variation in the endogenous period length of honey bee foragers from the same colony and differences in the endogenous rhythms under different constant temperatures. In this study, we further this work by examining temperature inside the honey bee colony. By placing temperature and light data loggers at different locations inside the colony we uncovered that temperature oscillates with a 24-hour period at the periphery of the colony. We then simulated this temperature oscillation in the laboratory and found that using the temperature cycle as a Zeitgeber, foragers present large individual differences in the phase of locomotor rhythms with respect to temperature. Moreover, foragers successfully entrain to these simulated temperature cycles and advancing the cycle by six hours, resulted in changes in the phase of locomotor activity for the most foragers in the assay. The results shown in this study highlight the importance of temperature as a potential Zeitgeber in the field. Future studies will examine the possible functional and evolutionary role of the observed phase differences of circadian rhythms.

Evaluation of Motor Changes and Toxicity of Insecticides Fipronil and Imidacloprid in Africanized Honey Bees (Hymenoptera: Apidae)

Honey bees are important pollinators and are essential in beekeeping. Honey bees get exposed to systemic pesticides while foraging in contaminated fields, and it is important to know the toxicity (LD50) and evaluate the impacts of bees’ exposure to these molecules. Fipronil and imidacloprid are systemic pesticides widely used in Brazil and other countries. The objective of this study was to determine the LD50 (24 hours) and evaluate motor changes in Africanized honey bee foragers exposed to lethal and sublethal doses of fipronil and imidacloprid. To determine the LD50, foraging honey bees were exposed by ingestion and contact to five doses of fipronil (Regent 800WG®) and imidacloprid (Appalus 200SC®) insecticides. After 24 hours of exposure, the number of dead bees was counted, and the results were subjected to probit analysis. The motor activity of bees exposed by ingestion or contact to LD50 and sublethal doses (1/500th of the LD50) of both pesticides was assessed 4 hours after exposure using a behavioral observation box. The ingestion and contact with LD50 of fipronil were 0.0528±0.0090 and 0.0054±0.0041 μg/bee, respectively; the ingestion and contact with LD50 of imidacloprid were 0.0809±0.0135 and 0.0626±0.0080 μg/bee, respectively. Bees exposed to lethal and sublethal doses of both insecticides experienced significant motor alterations compared to the control, except for exposure to sublethal doses of fipronil by contact. Fipronil and imidacloprid are highly toxic and promote motor changes in bees. Thus, it is important to establish management methods to reduce pollinators’ exposure to these pesticides.