Cuticular Hydrocarbon Profile of Parasitic Beetles, Aethina tumida (Coleoptera: Nitidulidae)

Cuticular hydrocarbons (CHCs) cover insects’ bodies and play important roles in chemical communication, including nestmate recognition, for social insects. To enter colonies of a social host species, parasites may acquire host-specific CHCs or covertly maintain their own CHC profile by lowering its quantity. However, the chemical profile of small hive beetles (SHBs), Aethina tumida, which are parasites of honey bee, Apis mellifera, colonies, and other bee nests, is currently unknown. Here, adults of SHB and honey bee host workers were collected from the same field colonies and their CHC profiles were analysed using GC-MS. The chemical profiles of field-sampled SHBs were also compared with those of host-naive beetles reared in the laboratory. Laboratory-reared SHBs differed in their CHC profiles from field-sampled ones, which showed a more similar, but ten-fold lower, generic host CHC profile compared to host workers. While the data confirm colony-specific CHCs of honey bee workers, the profile of field-collected SHBs was not colony-specific. Adult SHBs often commute between different host colonies, thereby possibly preventing the acquisition of a colony-specific CHC profiles. An ester was exclusive to both groups of SHBs and might constitute an intraspecific recognition cue. Our data suggest that SHBs do not use any finely tuned chemical strategy to conceal their presence inside host colonies and instead probably rely on their hard exoskeleton and defence behaviours.

Dietary and Plasmodium challenge effects on the cuticular hydrocarbon profile of Anopheles albimanus

The cuticular hydrocarbon (CHC) profile reflects the insects’ physiological states. These include age, sex, reproductive stage, and gravidity. Environmental factors such as diet, relative humidity or exposure to insecticides also affect the CHC composition in mosquitoes. In this work, the CHC profile was analyzed in two Anopheles albimanus phenotypes with different degrees of susceptibility to Plasmodium, the susceptible-White and resistant-Brown phenotypes, in response to the two dietary regimes of mosquitoes: a carbon-rich diet (sugar) and a protein-rich diet (blood) alone or containing Plasmodium ookinetes. The CHCs were analyzed by gas chromatography coupled to mass spectrometry or flame ionization detection, identifying 19 CHCs with chain lengths ranging from 20 to 37 carbons. Qualitative and quantitative changes in CHCs composition were dependent on diet, a parasite challenge, and, to a lesser extent, the phenotype. Blood-feeding caused up to a 40% reduction in the total CHC content compared to sugar-feeding. If blood contained ookinetes, further changes in the CHC profile were observed depending on the Plasmodium susceptibility of the phenotypes. Higher infection prevalence caused greater changes in the CHC profile. These dietary and infection-associated modifications in the CHCs could have multiple effects on mosquito fitness, impacts on disease transmission, and tolerance to insecticides.

Reversible plasticity in brain size, behaviour and physiology characterizes caste transitions in a socially flexible ant ( Harpegnathos saltator )

Phenotypic plasticity allows organisms to respond to changing environments throughout their lifetime, but these changes are rarely reversible. Exceptions occur in relatively long-lived vertebrate species that exhibit seasonal plasticity in brain size, although similar changes have not been identified in short-lived species, such as insects. Here, we investigate brain plasticity in reproductive workers of the ant Harpegnathos saltator . Unlike most ant species, workers of H. saltator are capable of sexual reproduction, and they compete in a dominance tournament to establish a group of reproductive workers, termed ‘gamergates'. We demonstrated that, compared to foragers, gamergates exhibited a 19% reduction in brain volume in addition to significant differences in behaviour, ovarian status, venom production, cuticular hydrocarbon profile, and expression profiles of related genes. In experimentally manipulated gamergates, 6–8 weeks after being reverted back to non-reproductive status their phenotypes shifted to the forager phenotype across all traits we measured, including brain volume, a trait in which changes were previously shown to be irreversible in honeybees and Drosophila . Brain plasticity in H. saltator is therefore more similar to that found in some long-lived vertebrates that display reversible changes in brain volume throughout their lifetimes.

Cuticular Hydrocarbon Profile Analyses Help Clarify the Species Identity of Dry-Mounted Cuckoo Wasps (Hymenoptera: Chrysididae), Including Type Material, and Reveal Evidence for a Cryptic Species

Cuckoo wasps of the Chrysis ignita species group are difficult to identify at the species level, and the taxonomic status of various taxa has consequently been controversial. COI barcoding has helped clarify some of the taxonomic problems in this group, but also revealed cryptic diversity at the genetic level that remained difficult to interpret taxonomically. Here we show that analysis of cuticular hydrocarbons (CHCs) clarifies the taxonomic status of cuckoo wasp samples with distinct COI haplotypes. The advantages of studying CHCs in insects for taxonomic purposes reside on the fact that CHC profiles evolve quickly and that all proteins required for CHC biosynthesis are encoded by nuclear genes. Using Chrysis pseudobrevitarsis as an example, we show that COI barcoding in combination with analysis of CHCs extracted from freshly collected and from dry-mounted museum specimens (including the lectotype of C. pseudobrevitarsis) provides clear evidence for a separate taxon among samples which were previously considered to be conspecific with C. pseudobrevitarsis. We describe this taxon as Chrysis parabrevitarsis n. sp. and present characters for distinguishing it chemically, genetically, and morphologically (females only) from C. pseudobrevitarsis. CHC profile comparison suggests females of C. pseudobrevitarsis may chemically mimic females of the vespid wasp Euodynerus notatus. Our study demonstrates the value of CHC analyses for supporting taxonomic inferences based on COI barcodes. It additionally underlines the value of dry-mounted collection specimens for chemical analyses and the potential of CHCs for inferring the identity of museum specimens, including type material, in a morphologically noninvasive manner.

A synopsis of the Brazilian Eucharitidae (Hymenoptera: Chalcidoidea) fauna: an annotated checklist of the family in the country, with a revised key for the New World genera

The current work provides a revised and updated key to the genera of Eucharitidae occurring in the New World, with the major traits of genera illustrated through high-resolution photomicrography. We provide an annotated list of genera and species currently known from Brazil, with a new record for a genus previously unknown for the country. Additionally, we provide a literature revision of the biology and cuticular hydrocarbon profile for the Eucharitidae. The lack of knowledge on the eucharitid Brazilian fauna is briefly discussed.

Cuticular hydrocarbon divergence in Drosophila melanogaster populations evolving under differential operational sex ratios

The ability of interlocus sexual conflict to facilitate reproductive isolation is widely anticipated. However, very few experimental evolutionary studies have convincingly demonstrated the evolution of reproductive isolation due to sexual conflict. Recently a study on replicate populations of Drosophila melanogaster under differential sexual conflict found that divergent mate preference evolved among replicate populations under high sexual conflict regime. The precopulatory isolating mechanism underlying such divergent mate preference could be sexual signals such as cuticular hydrocarbons since they evolve rapidly and are involved in D. melanogaster mate recognition. Using D. melanogaster replicates used in the previous study, we investigate whether cuticular hydrocarbon divergence bears signatures of sexually antagonistic coevolution that led to reproductive isolation among replicates of high sexual conflict regime. We found that D. melanogaster cuticular hydrocarbon profiles are sexually dimorphic. Although replicate populations under high sexual conflict displayed assortative mating, we found no significant differences in the cuticular hydrocarbon profile between the high and low sexual conflict regimes. Instead we find cuticular hydrocarbon divergence patterns to be suggestive of the Buridan’s Ass regime which is one of the six possible mechanisms to resolve sexual conflict. Sexual selection that co-vary between populations under high and low sexual conflict regimes may also have contributed to the evolution of cuticular hydrocarbons. This study indicates that population differentiation as a result of cuticular hydrocarbon divergence cannot be credited to sexual conflict despite high sexual conflict regime evolving divergent cuticular hydrocarbon profiles.