Abraham Hefetz

The epicuticle of Cataglyphis niger is endowed with hydrocarbons comprising both linear and branched alkanes. For linear alkane, it is hypothesized that the primary driving force for their evolution was acquiring means for attaining cuticular impermeability that protects the ants from desiccation, and, secondarily, was co-opted as cues and signals. For example, being more abundant in foragers, they signal colony foraging intensity and, accordingly, adjust task allocation. Branched alkanes serve mostly in communication, but their evolution is less clear. Studies of the biosynthesis of both classes of hydrocarbons revealed disparate pathways, which suggests an independent evolution. The biosynthesis of branched alkanes hints at their possible evolution. They are derived from branched fatty acids, which have evolved as protective means due to their bactericidal activity. It is hypothesized that their biosynthetic pathway was secondarily co-opted for producing branched alkanes as signals and cues. Branched alkanes blend within the linear alkane layer to evenly cover the ants’ body surface and enhance the ants’ communicative capacity by conveying larger informational content due to their numerous positional and stereoisomers. The present study presents the occurrence of substantial amounts of branched fatty acids with branching position that matches that of the branched alkanes. The disparate biosynthesis pathways and the postulated differences in their evolutionary roots lend credence to the hypothesis of their independent evolution.

The epicuticle of Cataglyphis niger is endowed with hydrocarbons comprising both linear and branched alkanes. The linear alkanes create an impermeable layer that protects the ants from desiccation, whereas the branched alkanes have communicative roles. Studies of the biosynthesis of both classes of hydrocarbons revealed disparate pathways, which suggests an independent evolution. It is hypothesized that the driving force for the evolution of alkanes was acquiring means for attaining impermeability. Being more abundant in foragers linear alkanes have been secondarily coopted for signaling colony foraging intensity and accordingly adjusting task allocation. The evolution of branched alkanes is less clear and seems more complex. They are biosynthetically derived from branched fatty acid that may have been the roots of their evolution. Due to their bactericide activity branched fatty acids evolved as protective means. Secondarily, the biosynthesis of these acids was coopted for producing branched alkanes for communicative roles. Using branched alkanes as signals is adaptive due to their numerous isomers that convey large informational content. Moreover, being hydrophobic they blend within the linear alkane layer that covers the ants’ body surface. However, branched alkanes decrease the cuticular impermeability, so hypothetically their proportions are the result of a tradeoff steady state.

Many pheromone responses are hardwired into the insect’s nervous system and are essential for critical behaviors such as mating, alarm signaling, and trail following. Workers of social species are assumed to respond innately to queen pheromones, affecting their behavior and reproductive physiology. However, accumulating evidence suggests that learning and experience may also shape responses to social chemical cues. To examine if the response to queen-associated odors can be learned, we exposed Bombus terrestris workers to a novel odor by treating the queen daily with unfamiliar floral scents, either anisyl alcohol or methyl anthranilate. We allowed perfumed queens to establish colonies and examined worker attraction and egg laying following exposure to these odors in the absence of the queen either with or without brood as context. In a two-choice olfactometer, workers preferred the queen odor they learned during colony development. Exposure of workers to the queen-associated odor in the absence of the queen influenced worker egg laying only in the presence of brood, surprisingly resulting in increased egg laying. Our study demonstrates that workers can learn novel odors that are associated with their queen or nest, which in turn function as context-dependent social cues that modify their social and reproductive behavior.

The invasive Argentine ants (Linepithema humile) and the red imported fire ants (Solenopsis invicta) constitute a worldwide threat, causing severe disruption to ecological systems and harming human welfare. In view of the limited success of current pest control measures, we propose here to employ repellents as means to mitigate the effect of these species. We demonstrate that cuticular hydrocarbons (CHCs) used as nestmate-recognition pheromone in the Japanese carpenter ant (Camponotus japonicus), and particularly its (Z)-9-tricosene component, induced vigorous olfactory response and intense aversion in these invasive species. (Z)-9-Tricosene, when given to their antennae, caused indiscriminate glomerular activation of antennal lobe (AL) regions, creating neural disarray and leading to aversive behavior. Considering the putative massive central neural effect, we suggest that the appropriate use of certain CHCs of native ants can facilitate aversive withdrawal of invasive ants.

We recently reported that artificial light at night (ALAN), at ecologically relevant intensities (1.5, 5 lux), increases cell proliferation in the ventricular zone and recruitment of new neurons in several forebrain regions of female zebra finches (Taeniopygia guttata), along with a decrease of total neuronal densities in some of these regions (indicating possible neuronal death). In the present study, we exposed male zebra finches to the same ALAN intensities, treated them with 5′-bromo-2′-deoxyuridine, quantified cell proliferation and neuronal recruitment in several forebrain regions, and compared them to controls that were kept under dark nights. ALAN increased cell proliferation in the ventricular zone, similar to our previous findings in females. We also found, for the first time, that ALAN increased new neuronal recruitment in HVC and Area X, which are part of the song system in the brain and are male-specific. In other brain regions, such as the medial striatum, nidopallium caudale, and hippocampus, we recorded an increased neuronal recruitment only in the medial striatum (unlike our previous findings in females), and relative to the controls this increase was less prominent than in females. Moreover, the effect of ALAN duration on total neuronal densities in the studied regions varied between the sexes, supporting the suggestion that males are more resilient to ALAN than females. Suppression of nocturnal melatonin levels after ALAN exhibited a light intensity-dependent decrease in males in contrast to females, another indication that males might be less affected by ALAN. Taken together, our study emphasizes the importance of studying both sexes when considering ALAN effects on brain plasticity.

The main challenge facing a parasite of social insects lies in deceiving its host’s detection and defense systems in order to enter and survive within the host colony. Sphecophaga orientalis is an ichneumonid wasp that parasitizes the pupae of the Oriental hornet Vespa orientalis. In Israel’s Mediterranean region, this parasitoid infects on average 23.48% (8–56%) of the host pupal cells. Observation of colonies brought to the laboratory revealed that the parasite moves around within the colony without being aggressed by the host workers. To assess how the parasite evades host detection and defense, we compared the cuticular hydrocarbon (CHC) profiles of both species. There was little similarity between the parasite and the host workers’ CHC, refuting the hypothesis of chemical mimicry. The parasite’s CHCs were dominated by linear alkanes and alkenes with negligible amounts of branched alkanes, while the host workers’ CHCs were rich in branched alkanes and with little or no alkenes. Moreover, the parasite cuticular wash was markedly rich in oleic acid, previously reported as a cue eliciting necrophoric behavior. Since nests of Oriental hornets are typified by large amounts of prey residues, we suggest that, due to its unfamiliar CHCs and the abundance of oleic acid, the parasite is considered as refuse by the host. We also detected rose oxide in the parasitoid head extracts. Rose oxide is a known insect repellent, and can be used to repel and mitigate aggression in workers. These two factors, in concert, are believed to aid the parasite to evade host aggression.

Primer pheromones play a pivotal role in the biology and social organization of insect societies. Despite their importance, they have been less studied because of the complexity of the required bioassays and, consequently, only a few of them have been chemically identified to date. The major primer pheromones are that of the queen pheromones that regulate reproductive skew and maintain colony cohesion and function. From a theoretical viewpoint, several features regarding the chemistry of queen pheromones can be predicted. They should be generally nonvolatile in order to avoid saturation of the colony space, which might otherwise hamper their perception because of sensory habituation. Accordingly, they should be actively dispersed throughout the colony by workers. The queen pheromone should also be caste-specific, qualitatively different from any worker pheromone, and preferably multicomponent, to allow unequivocal identification of the queen. The bi-potency of the female larvae in social Hymenoptera to become queen or worker necessitates strict regulation over pheromone production. Indeed, in the honeybee, the biosynthetic pathways as well as the genomic expressions are completely disparate between queens and workers. Future advances in chemical analyses, transcriptomics, proteomics, and metabolomics will enrich our understanding of the chemistry, mechanisms, and crucial role that primer pheromones play in social evolution.

Large social insect colonies exhibit a remarkable ability for recognizing group members via colony-specific cuticular pheromonal signatures. Previous work suggested that in some ant species, colony-specific pheromonal profiles are generated through a mechanism involving the transfer and homogenization of cuticular hydrocarbons (CHCs) across members of the colony. However, how colony-specific chemical profiles are generated in other social insect clades remains mostly unknown. Here we show that in the honey bee (Apis mellifera), the colony-specific CHC profile completes its maturation in foragers via a sequence of stereotypic age-dependent quantitative and qualitative chemical transitions, which are driven by environmentally-sensitive intrinsic biosynthetic pathways. Therefore, the CHC profiles of individual honey bees are not likely produced through homogenization and transfer mechanisms, but instead mature in association with age-dependent division of labor. Furthermore, non-nestmate rejection behaviors seem to be contextually restricted to behavioral interactions between entering foragers and guards at the hive entrance.