Honey bee thermal/chemical sensor, AmHsTRPA, reveals neofunctionalization and loss of transient receptor potential channel genes

Molecular identification of chronic bee paralysis virus infection in Apis mellifera colonies in Japan

Chronic bee paralysis virus (CBPV) infection causes chronic paralysis and loss of workers in honey bee colonies around the world. Although CBPV shows a worldwide distribution, it had not been molecularly detected in Japan. Our investigation of Apis mellifera and Apis cerana japonica colonies with RT-PCR has revealed CBPV infection in A. mellifera but not A. c. japonica colonies in Japan. The prevalence of CBPV is low compared with that of other viruses: deformed wing virus (DWV), black queen cell virus (BQCV), Israel acute paralysis virus (IAPV), and sac brood virus (SBV), previously reported in Japan. Because of its low prevalence (5.6%) in A. mellifera colonies, the incidence of colony losses by CBPV infection must be sporadic in Japan. The presence of the (-) strand RNA in dying workers suggests that CBPV infection and replication may contribute to their symptoms. Phylogenetic analysis demonstrates a geographic separation of Japanese isolates from European, Uruguayan, and mainland US isolates. The lack of major exchange of honey bees between Europe/mainland US and Japan for the recent 26 years (1985-2010) may have resulted in the geographic separation of Japanese CBPV isolates.

Warmth suppresses and desensitizes damage-sensing ion channel TRPA1

Background

Acute or chronic tissue damage induces an inflammatory response accompanied by pain and alterations in local tissue temperature. Recent studies revealed that the transient receptor potential A1 (TRPA1) channel is activated by a wide variety of substances that are released following tissue damage to evoke nociception and neurogenic inflammation. Although the effects of a noxious range of cold temperatures on TRPA1 have been rigorously studied, it is not known how agonist-induced activation of TRPA1 is regulated by temperature over an innocuous range centred on the normal skin surface temperature. This study investigated the effect of temperature on agonist-induced currents in human embryonic kidney (HEK) 293 cells transfected with rat or human TRPA1 and in rat sensory neurons.

Results

Agonist-induced TRPA1 currents in HEK293 cells were strongly suppressed by warm temperatures, and almost abolished at 39°C. Such inhibition occurred when TRPA1 was activated by either electrophilic or non-electrophilic agonists. Warming not only decreased the apparent affinity of TRPA1 for mustard oil (MO), but also greatly enhanced the desensitization and tachyphylaxis of TRPA1. Warming also attenuated MO-induced ionic currents in sensory neurons. These results suggest that the extent of agonist-induced activity of TRPA1 may depend on surrounding tissue temperature, and local hyperthermia during acute inflammation could be an endogenous negative regulatory mechanism to attenuate persistent pain at the site of injury.

Conclusion

These results indicate that warmth suppresses and desensitizes damage-sensing ion channel TRPA1. Such warmth-induced suppression of TRPA1 may also explain, at least in part, the mechanistic basis of heat therapy that has been widely used as a supplemental anti-nociceptive approach.

Detection of neural activity in the brains of Japanese honeybee workers during the formation of a "hot defensive bee ball"

Anti-predator behaviors are essential to survival for most animals. The neural bases of such behaviors, however, remain largely unknown. Although honeybees commonly use their stingers to counterattack predators, the Japanese honeybee (Apis cerana japonica) uses a different strategy to fight against the giant hornet (Vespa mandarinia japonica). Instead of stinging the hornet, Japanese honeybees form a “hot defensive bee ball” by surrounding the hornet en masse, killing it with heat. The European honeybee (A. mellifera ligustica), on the other hand, does not exhibit this behavior, and their colonies are often destroyed by a hornet attack. In the present study, we attempted to analyze the neural basis of this behavior by mapping the active brain regions of Japanese honeybee workers during the formation of a hot defensive bee ball. First, we identified an A. cerana homolog (Acks = Apis cerana kakusei) of kakusei, an immediate early gene that we previously identified from A. mellifera, and showed that Acks has characteristics similar to kakusei and can be used to visualize active brain regions in A. cerana. Using Acks as a neural activity marker, we demonstrated that neural activity in the mushroom bodies, especially in Class II Kenyon cells, one subtype of mushroom body intrinsic neurons, and a restricted area between the dorsal lobes and the optic lobes was increased in the brains of Japanese honeybee workers involved in the formation of a hot defensive bee ball. In addition, workers exposed to 46°C heat also exhibited Acks expression patterns similar to those observed in the brains of workers involved in the formation of a hot defensive bee ball, suggesting that the neural activity observed in the brains of workers involved in the hot defensive bee ball mainly reflects thermal stimuli processing.

Infestation of Japanese native honey bees by tracheal mite and virus from non-native European honey bees in Japan

Invasion of alien species has been shown to cause detrimental effects on habitats of native species. Insect pollinators represent such examples; the introduction of commercial bumble bee species for crop pollination has resulted in competition for an ecological niche with native species, genetic disturbance caused by mating with native species, and pathogen spillover to native species. The European honey bee, Apis mellifera, was first introduced into Japan for apiculture in 1877, and queen bees have been imported from several countries for many years. However, its effects on Japanese native honey bee, Apis cerana japonica, have never been addressed. We thus conducted the survey of honey bee viruses and Acarapis mites using both A. mellifera and A. c. japonica colonies to examine their infestation in native and non-native honey bee species in Japan. Honey bee viruses, Deformed wing virus (DWV), Black queen cell virus (BQCV), Israeli acute paralysis virus (IAPV), and Sacbrood virus (SBV), were found in both A. mellifera and A. c. japonica colonies; however, the infection frequency of viruses in A. c. japonica was lower than that in A. mellifera colonies. Based on the phylogenies of DWV, BQCV, and SBV isolates from A. mellifera and A. c. japonica, DWV and BQCV may infect both honey bee species; meanwhile, SBV has a clear species barrier. For the first time in Japan, tracheal mite (Acarapis woodi) was specifically found in the dead honey bees from collapsing A. c. japonica colonies. This paper thus provides further evidence that tracheal-mite-infested honey bee colonies can die during cool winters with no other disease present. These results demonstrate the infestation of native honey bees by parasite and pathogens of non-native honey bees that are traded globally.

Cytoplasmic ankyrin repeats of transient receptor potential A1 (TRPA1) dictate sensitivity to thermal and chemical stimuli

Transient receptor potential (TRP) channels are polymodal signal detectors that respond to a wide array of physical and chemical stimuli, making them important components of sensory systems in both vertebrate and invertebrate organisms. Mammalian TRPA1 channels are activated by chemically reactive irritants, whereas snake and Drosophila TRPA1 orthologs are preferentially activated by heat. By comparing human and rattlesnake TRPA1 channels, we have identified two portable heat-sensitive modules within the ankyrin repeat-rich aminoterminal cytoplasmic domain of the snake ortholog. Chimeric channel studies further demonstrate that sensitivity to chemical stimuli and modulation by intracellular calcium also localize to the N-terminal ankyrin repeat-rich domain, identifying this region as an integrator of diverse physiological signals that regulate sensory neuron excitability. These findings provide a framework for understanding how restricted changes in TRPA1 sequence account for evolution of physiologically diverse channels, also identifying portable modules that specify thermosensitivity.

PCR-based detection of a tracheal mite of the honey bee Acarapis woodi

The effects of the tracheal mite Acarapis woodi on the health of honey bees have been neglected since the prevalence of Varroa mites to Apis mellifera colonies. However, tracheal mite infestation of honey bee colonies still occurs worldwide and could impose negative impact on apiculture. The detection of A. woodi requires the dissection of honey bees followed by microscopic observation of the tracheal sacs. We thus developed PCR methods to detect A. woodi. These methods facilitate rapid and sensitive detection of A. woodi in many honey bee samples for epidemiologic surveys.

Water loss in insects: an environmental change perspective

In the context of global environmental change much of the focus has been on changing temperatures. However, patterns of rainfall and water availability have also been changing and are expected to continue doing so. In consequence, understanding the responses of insects to water availability is important, especially because it has a pronounced influence on insect activity, distribution patterns, and species richness. Here we therefore provide a critical review of key questions that either are being or need to be addressed in this field. First, an overview of insect behavioural responses to changing humidity conditions and the mechanisms underlying sensing of humidity variation is provided. The primary sensors in insects belong to the temperature receptor protein superfamily of cation channels. Temperature-activated transient receptor potential ion channels, or thermoTRPs, respond to a diverse range of stimuli and may be a primary integrator of sensory information, such as environmental temperature and moisture. Next we touch briefly on the components of water loss, drawing attention to a new, universal model of the water costs of gas exchange and its implications for responses to a warming, and in places drying, world. We also provide an overview of new understanding of the role of the sub-elytral chamber for water conservation, and developments in understanding of the role of cuticular hydrocarbons in preventing water loss. Because of an increasing focus on the molecular basis of responses to dehydration stress we touch briefly on this area, drawing attention to the role of sugars, heat shock proteins, aquaporins, and LEA proteins. Next we consider phenotypic plasticity or acclimation responses in insect water balance after initial exposures to altered humidity, temperature or nutrition. Although beneficial acclimation has been demonstrated in several instances, this is not always the case. Laboratory studies show that responses to selection for enhanced ability to survive water stress do evolve and that genetic variation for traits underlying such responses does exist in many species. However, in others, especially tropical, typically narrowly distributed species, this appears not to be the case. Using the above information we then demonstrate that habitat alteration, climate change, biological invasions, pollution and overexploitation are likely to be having considerable effects on insect populations mediated through physiological responses (or the lack thereof) to water stress, and that these effects may often be non-intuitive.