Alison R. Mercer

Exposing honey bees to isopentylacetate (IPA) can cause stress-related changes in learning performance. In bees of foraging age, IPA’s effects on learning are mimicked by C-type allatostatins (AstCC, AstCCC) injected into the brain. Here we ask whether allatostatins induce a similar response in young (6-day-old) bees and if so, whether their effects on learning performance are modulated by queen mandibular pheromone (QMP). We found that young bees exposed to IPA responded less to the conditioned stimulus during training than controls (Type 1-like stress response). AstCC treatment induced a similar response, but only in bees maintained without QMP. Bees exposed to QMP responded to AstCC with increased odour responsiveness and odour generalisation in the 1-h memory test (Type 2-like response). Type 2-like responses could be induced also by the A-type allatostatin, AstA. However, in bees exposed to QMP, AstA-induced odour generalisation was absent. Effects of AstCCC treatment in young bees were weak, indicating that responsiveness to this peptide changes with age. Our findings are consistent with the hypothesis that honey bee allatostatins play a role in stress reactivity, but suggest in addition that allatostatin signalling is age dependent and susceptible to modulation by pheromone released by the queen bee.

InDrosophila melanogaster, aversive (electric shock) stimuli have been shown to activate subpopulations of dopaminergic neurons with terminals in the mushroom bodies (MBs) of the brain. While there is compelling evidence that dopamine (DA)-induced synaptic plasticity underpins the formation of aversive memories in insects, the mechanisms involved have yet to be fully resolved. Here we take advantage of the accessibility of MBs in the brain of the honey bee to examine, using fast scan cyclic voltammetry, the kinetics of DA release and reuptakein vivoin response to electric shock, and to investigate factors that modulate the release of this amine. DA increased transiently in the MBs in response to electric shock stimuli. The magnitude of release varied depending on stimulus duration and intensity, and a strong correlation was identified between DA release and the intensity of behavioural responses to shock. With repeated stimulation, peak DA levels increased. However, the amount of DA released on the first stimulation pulse typically exceeded that evoked by subsequent pulses. No signal was detected in response to odour alone. Interestingly, however, if odour presentation was paired with electric shock, DA release was enhanced. These results set the stage for analysing the mechanisms that modulate DA release in the MBs of the bee.

Worldwide, studies of interactions between introduced and native bees have produced contradictory evidence regarding the potential for competition. Different resource requirements and the impact of tongue length on resource use are often overlooked aspects of these studies. Here, we examine floral resource use and niche overlap between introduced social bees and native solitary bees over two flowering seasons on The Remarkables mountain range, South Island, New Zealand. The native bee fauna of New Zealand is composed of short‐tongued solitary bees in the families Colletidae and Halictidae. Long‐tongued social bees were introduced 150 years ago, and Apis mellifera and Bombus species are now widespread. We analysed floral resource utilization by introduced bees (mainly Bombus terrestris) and native bees in relation to resource abundance across elevations in montane to alpine grassland communities. We modelled resource utilization and overlap between bee taxa using a novel index of floral resource availability, developed to more accurately describe floral density. Additionally, we sought to quantify the impact of honey bees by introducing hives, however, low densities in study plots prevented direct conclusions from being drawn. Native and introduced bees did, however, have distinctly different floral preferences over the flowering season with more niche overlap within, rather than between, native and introduced groups. Introduced bees showed a preference for introduced species in the family Fabaceae which native bees could not access. Native bees heavily utilized introduced Asteraceae as well as native floral resources that introduced bees did not prefer. The limited resource overlap between bee taxa indicated that bee communities in New Zealand may have reduced potential for competition, owing to the different resource requirements of solitary versus social bees and their differing abilities to access floral resources. These findings provide some potential explanations for contradictory evidence worldwide regarding the perceived detrimental impacts of introduced social bees.

As honey bee populations worldwide are declining there is an urgent need for a deeper understanding of stress reactivity in these important insects. Our data indicate that stress responses in bees (Apis mellifera L.) may be mediated by neuropeptides identified, on the basis of sequence similarities, as allatostatins (ASTA, ASTC and ASTCC). Effects of allatostatin injection are compared with stress-related changes in learning performance induced by the honeybee alarm pheromone, isopentylacetate (IPA). We find that bees can exhibit two markedly different responses to IPA, with opposing effects on learning behaviour and memory generalisation, and that strikingly similar responses can be elicited by allatostatins, in particular ASTCC. These findings lend support to the hypothesis that allatostatins mediate stress reactivity in honey bees and suggest responses to stress in these insects are state dependent.

Social immunity forms an essential part of the defence repertoire of social insects. In response to infestation by the parasitic mite Varroa destructor and its associated viruses, honey bees (Apis mellifera L.) have developed a specific behaviour (varroa-sensitive hygiene, or VSH) that helps protect the colony from this parasite. Brood cells heavily infested with mites are uncapped, the brood killed and the cell contents removed. For this extreme sacrifice to be beneficial to the colony, the targeting of parasitized brood for removal must be accurate and selective. Here we show that varroa-infested brood produce uniquely identifiable cues that could be used by VSH-performing bees to identify with high specificity which brood cells to sacrifice. This selective elimination of mite-infested brood is a disease resistance strategy analogous to programmed cell death, where young bees likely to be highly dysfunctional as adults are sacrificed for the greater good of the colony.

Chlorpyrifos is an organophosphate pesticide used around the world to protect food crops against insects and mites. Despite guidelines for chlorpyrifos usage, including precautions to protect beneficial insects, such as honeybees from spray drift, this pesticide has been detected in bees in various countries, indicating that exposure still occurs. Here, we examined chlorpyrifos levels in bees collected from 17 locations in Otago, New Zealand, and compared doses of this pesticide that cause sub-lethal effects on learning performance under laboratory conditions with amounts of chlorpyrifos detected in the bees in the field. The pesticide was detected at 17 % of the sites sampled and in 12 % of the colonies examined. Amounts detected ranged from 35 to 286 pg.bee⁻¹, far below the LD₅₀ of ~100 ng.bee⁻¹. We detected no adverse effect of chlorpyrifos on aversive learning, but the formation and retrieval of appetitive olfactory memories was severely affected. Chlorpyrifos fed to bees in amounts several orders of magnitude lower than the LD₅₀, and also lower than levels detected in bees, was found to slow appetitive learning and reduce the specificity of memory recall. As learning and memory play a central role in the behavioral ecology and communication of foraging bees, chlorpyrifos, even in sublethal doses, may threaten the success and survival of this important insect pollinator.

Sequencing of the honeybee genome revealed many neuropeptides and putative neuropeptide receptors, yet functional characterization of these peptidic systems is scarce. In this study, we focus on allatostatins, which were first identified as inhibitors of juvenile hormone synthesis, but whose role in the adult honey bee (Apis mellifera) brain remains to be determined. We characterize the bee allatostatin system, represented by two families: allatostatin A (Apime-ASTA) and its receptor (Apime-ASTA-R); and C-type allatostatins (Apime-ASTC and Apime-ASTCC) and their common receptor (Apime-ASTC-R). Apime-ASTA-R and Apime-ASTC-R are the receptors in bees most closely related to vertebrate galanin and somatostatin receptors, respectively. We examine the functional properties of the two honeybee receptors and show that they are transcriptionally expressed in the adult brain, including in brain centers known to be important for learning and memory processes. Thus we investigated the effects of exogenously applied allatostatins on appetitive olfactory learning in the bee. Our results show that allatostatins modulate learning in this insect, and provide important insights into the evolution of somatostatin/allatostatin signaling.

Octopamine- and dopamine-based neuromodulatory systems play a critical role in learning and learning-related behaviour in insects. To further our understanding of these systems and resulting phenotypes, we quantified DNA sequence variations at six loci coding octopamine—and dopamine-receptors and their association with aversive and appetitive learning traits in a population of honeybees. We identified 79 polymorphic sequence markers (mostly SNPs and a few insertions/deletions) located within or close to six candidate genes. Intriguingly, we found that levels of sequence variation in the protein-coding regions studied were low, indicating that sequence variation in the coding regions of receptor genes critical to learning and memory is strongly selected against. Non-coding and upstream regions of the same genes, however, were less conserved and sequence variations in these regions were weakly associated with between-individual differences in learning-related traits. While these associations do not directly imply a specific molecular mechanism, they suggest that the cross-talk between dopamine and octopamine signalling pathways may influence olfactory learning and memory in the honeybee.

The Varroa mite (Varroa destructor) is implicated as a major disease factor in honey bee (Apis mellifera) populations worldwide. Honey bees are extensively relied upon for pollination services, and in countries such as New Zealand and Australia where honey bees have been introduced specifically for commercial pollinator services, the economic effects of any decline in honey bee numbers are predicted to be profound. V. destructor established in New Zealand in 2000 but as yet, Australia remains Varroa-free. Here we analyze the history of V. destructor invasion and spread in New Zealand and discuss the likely long-term impacts. When the mite was discovered in New Zealand, it was considered too well established for eradication to be feasible. Despite control efforts, V. destructor has since spread throughout the country. Today, assessing the impacts of the arrival of V. destructor in this country is compromised by a paucity of data on pollinator communities as they existed prior to invasion. Australia’s Varroa-free status provides a rare and likely brief window of opportunity for the global bee research community to gain understanding of honey bee-native pollinator community dynamics prior to Varroa invasion.