Chemical detection triggers honey bee defense against a destructive parasitic threat.

Invasive species events related to globalization are increasing, resulting in parasitic outbreaks. Understanding of host defense mechanisms is needed to predict and mitigate against the consequences of parasite invasion. Using the honey bee Apis mellifera and the mite Varroa destructor, as a host-parasite model, we provide a comprehensive study of a mechanism of parasite detection that triggers a behavioral defense associated with social immunity. Six Varroa-parasitization-specific (VPS) compounds are identified that (1) trigger Varroa-sensitive hygiene (VSH, bees' key defense against Varroa sp.), (2) enable the selective recognition of a parasitized brood and (3) induce responses that mimic intrinsic VSH activity in bee colonies. We also show that individuals engaged in VSH exhibit a unique ability to discriminate VPS compounds from healthy brood signals. These findings enhance our understanding of a critical mechanism of host defense against parasites, and have the potential to apply the integration of pest management in the beekeeping sector.

Flight behavior and pheromone changes associated to Nosema ceranae infection of honey bee workers (Apis mellifera) in field conditions.

Parasites are known to cause the loss of individuals in social insects. In honey bee colonies the disappearance of foragers is a common factor of the wide extended colony losses. The emergent parasite of the European honey bee Nosema ceranae has been found to reduce homing and orientation skills and alter metabolism of forager bees. N. ceranae-infected bees also show changes in Ethyl Oleate (EO) levels, which is so far the only primer pheromone identified in workers that is involved in foraging behavior. Thus, we hypothesized that N. ceranae (i) modifies flight activity of honey bees and (ii) induces EO changes that can alter foraging behavior of nestmates. We compared flight activity of infected bees and non-infected bees in small colonies using an electronic optic bee counter during 28 days. We measured EO levels by gas chromatography-mass spectrometry and spore-counts. Bee mortality was estimated at the end of the experiment. Infected bees showed precocious and a higher flight activity than healthy bees, which agreed with the more elevated EO titers of infected bees and reduced lifespan. Our results suggest that the higher EO levels of infected bees might delay the behavioral maturation of same age healthy bees, which might explain their lower level of activity. We propose that delayed behavioral maturation of healthy bees might be a protective response to infection, as healthy bees would be performing less risky tasks inside the hive, thus extending their lifespan. We also discuss the potential of increased flight activity of infected bees to reduce pathogen transmission inside the hive. Further research is needed to understand the consequences of host behavioral changes on pathogen transmission. This knowledge may contribute to enhance natural colony defense behaviors through beekeeping practices to reduce probability of colony losses.

Detailed chemical analysis of honey bee (Apis mellifera) worker brood volatile profile from egg to emergence.

Chemical communication is a widely used mode of communication for social insects and has been demonstrated to be involved in many behaviours and physiological processes such as reproduction, nutrition or the fight against parasites and pathogens. In the honey bee, Apis mellifera, the release of chemical compounds by the brood plays a role in worker behaviour, physiology, and foraging activities and colony health as a whole. Several compounds have already been described as brood pheromones, such as components of the brood ester pheromone and (E)-ß-ocimene. Several other compounds originating from diseased or varroa-infested brood cells have been described as triggering the hygienic behaviour of workers. So far, studies of brood emissions have focused on specific stages of development and little is known about the emission of volatile organic compounds by the brood. In this study, we investigate the semiochemical profile of worker honey bee brood during its whole developmental cycle, from egg to emergence, with a specific focus on volatile organic compounds. We describe variation in emissions of thirty-two volatile organic compounds between brood stages. We highlight candidate compounds that are particularly abundant in specific stages and discuss their potential biological significance.

Non-host volatiles disturb the feeding behavior and reduce the fecundity of the green peach aphid, Myzus persicae.

BACKGROUND: The association of crops of value with companion plants could be one of the strategies to reduce the harmful effects of pests. We hypothesize that volatile organic compounds (VOCs) emitted by some aromatic plants may negatively impact M. persicae, disturbing its feeding behavior and consequently its reproduction. RESULTS: VOCs emitted from six potential companion plant species affected the reproduction of M. persicae feeding on pepper plants, Capsicum annuum. Reproduction of M. persicae was reduced when exposed to VOCs from leaves of Ocimum basilicum and flowers of Tagetes patula. Thus, species and phenology of the companion plant can influence the effect. The VOCs from O. basilicum and T. patula also reduced phloem feeding by the aphids based on electropenetrography (EPG). CONCLUSION: The reduced fecundity of M. persicae could be linked to aphid feeding disruption provoked by the VOCs emitted by O. basilicum in the vegetative stage or T. patula cv. Nana in the flowering stage. © 2020 Society of Chemical Industry.

Repellence of Myzus persicae (Sulzer): evidence of two modes of action of volatiles from selected living aromatic plants.

BACKGROUND: Intercropping companion plants (CPs) with horticultural crops could be an eco-friendly strategy to optimize pest management. In this research, volatile organic compounds (VOCs) emitted by some CPs were investigated for their repellent properties towards the green peach aphid (Myzus persicae Sulzer). The aim of this study was to understand the modes of action involved: direct effects on the aphid and/or indirect effects via the host plant (pepper, Capsicum annuum L.). RESULTS: We identified two promising repellent CP species: the volatile blend from basil (Ocimum basilicum, direct repellent effect) and the mixture of (or previously intercropped) C. annuum plants with Tagetes patula cv. Nana (indirect effect). This effect was cultivar-dependent and linked to the volatile bouquet. For the 16 compounds present in the O. basilicum or T. patula bouquets tested individually, (E)-ß-farnesene, and eugenol reported good repellent properties against M. persicae. Other compounds were repellent at medium and/or highest concentrations. Thus, the presence of repellent VOCs in a mixture does not mean that it has a repellent propriety. CONCLUSION: We identified two promising repellent CP species towards M. persicae, with a likely effect of one CP's VOCs on the host plant repellency and highlighted the specific effectiveness of VOC blends. © 2018 Society of Chemical Industry.

Cuticular hydrocarbon profiles and aggregation in four Periplaneta species (Insecta: Dictyoptera).

Cuticular hydrocarbon (CH) profiles of four Periplaneta species were compared and their role in aggregation and interspecific recognition was evaluated. CH profiles are species specific and include from 19 to 25 hydrocarbons. P. brunnea, P. fuliginosa and P. australasiae have more CH components in common with one another than with P. americana. P. americana hydrocarbons include components from 24 to 43 carbon atoms but hydrocarbons for the three other species range from 21 to 41 atoms. The major compound in CH profiles in P. americana is 6,9-heptacosadiene that is absent from the three other species. The major compound in CH profiles of P. Brunnea and P. fuliginosa is 13-methyl pentacosane that is not found in the CH profile of P. americana. Major compounds in P. australasiae species are tricosene and 13-methyl pentacosane, respectively, in males and females. Binary choice tests demonstrated that specific CH extracts induced aggregation in the four species. High CH amounts were required to induce aggregation of P. americana and P. brunnea on conditioned sites, whereas low amounts were sufficient to induce aggregation of P. fuliginosa and P. australasiae. These results suggest that CHs are involved in aggregation and interspecific recognition.

HPLC assay of tomato carotenoids: validation of a rapid microextraction technique.

Carotenoids are studied for their role as pigments and as precursors of aromas, vitamin A, abscisic acid, and antioxidant compounds in different plant tissues. A novel, rapid, and inexpensive analytical protocol is proposed to enable the simultaneous analysis of four major tomato carotenoids: lutein, lycopene, beta-carotene, and phytoene. Microextraction is performed in the presence of sodium chloride, n-hexane, dichloromethane, and ethyl acetate on fresh tomato powder that has been finely ground in liquid nitrogen. The carotenoids are extracted by agitation and centrifugation and then analyzed by HPLC using a diode array detector. The principal advantage of this extraction resides in the absence of an evaporation step, often necessary to assay tomato carotenoids other than lycopene. Whatever the carotenoid, tests for accuracy, reproducibility, and linearity were satisfactory and indicative of the method's reliability. The stability of extracts over time (several days at -20 degrees C) as the satisfactory sensitivity of the assay whatever the fruit ripeness had a part in the robustness of the method. Reliable, rapid, simple, and inexpensive, this extraction technique is appropriate for the routine analysis of carotenoids in small samples.

Larval salivary glands are a source of primer and releaser pheromone in honey bee (Apis mellifera L.).

A brood pheromone identified in honeybee larvae has primer and releaser pheromone effects on adult bees. Using gas chromatography-mass spectrometry (GC-MS) to evaluate fatty acid esters--the pheromonal compounds--in different parts of the larvae, we have localized the source of the esters as the larval salivary glands. A histochemical study describes the glands and confirms the presence of lipids in the glands. Epithelial cells of the gland likely secrete the fatty acids into the lumen of the gland. These results demonstrate the salivary glands to be a reservoir of esters, components of brood pheromone, in honeybee larvae.

Regulation of behavioral maturation by a primer pheromone produced by adult worker honey bees.

Previous research showed that the presence of older workers causes a delayed onset of foraging in younger individuals in honey bee colonies, but a specific worker inhibitory factor had not yet been identified. Here, we report on the identification of a substance produced by adult forager honey bees, ethyl oleate, that acts as a chemical inhibitory factor to delay age at onset of foraging. Ethyl oleate is synthesized de novo and is present in highest concentrations in the bee's crop. These results suggest that worker behavioral maturation is modulated via trophallaxis, a form of food exchange that also serves as a prominent communication channel in insect societies. Our findings provide critical validation for a model of self-organization explaining how bees are able to respond to fragmentary information with actions that are appropriate to the state of the whole colony.