Cuticular lipids of insects—IV. hydrocarbons of the cockroaches Periplaneta japonica and Periplaneta americana compared to other cockroach hydrocarbons

Antenna Cleaning Is Essential for Precise Behavioral Response to Alarm Pheromone and Nestmate-Non-Nestmate Discrimination in Japanese Carpenter Ants (Camponotus japonicus)

Simple Summary

Grooming is a common behavior in animals. It serves the function of removing foreign materials and excessive amounts of self-secreted materials from the body’s surface. Social insects, such as honeybees or ants, use various types of pheromones, some of which propagate information about the environment to conspecific individuals, for chemical communication. The individuals that receive such information can respond with suitable behaviors to protect themselves and their society. Hence, grooming is important for the maintenance of the correct performance of their sensory organs on antennae for pheromone perception. Here, we experimentally limited self-grooming of the antennae in workers of the Japanese carpenter ant (Camponotus japonicus) by removing a pair of antennal cleaning apparatuses from the forelegs and investigated their behavioral change in response to exposure to the alarm pheromone or to encounters with nestmates or non-nestmates. Comparisons between self-grooming-nonlimited and self-grooming-limited ants showed that the self-grooming-limited ants gradually exhibited decreased locomotion activity in their fight-or-flight response to the alarm pheromone and experienced increased failure in nestmate and non-nestmate discrimination. Thus, the results of the present study suggest that antennal sensory system maintenance supports social communication, which is indispensable not only to the individual workers but also to the survival of their society.

Abstract

Self-grooming of the antennae is frequently observed in ants. This antennal maintenance behavior is presumed to be essential for effective chemical communication but, to our knowledge, this has not yet been well studied. When we removed the antenna-cleaning apparatuses of the Japanese carpenter ant (C. japonicus) to limit the self-grooming of the antennae, the worker ants demonstrated the self-grooming gesture as usual, but the antennal surface could not be sufficiently cleaned. By using scanning electron microscopy with NanoSuit, we observed the ants’ antennae for up to 48 h and found that the antennal surfaces gradually became covered with self-secreted surface material. Concurrently, the self-grooming-limited workers gradually lost their behavioral responsiveness to undecane—the alarm pheromone. Indeed, their locomotive response to the alarm pheromone diminished for up to 24 h after the antenna cleaner removal operation. In addition, the self-grooming-limited workers exhibited less frequent aggressive behavior toward non-nestmate workers, and 36 h after the operation, approximately half of the encountered non-nestmate workers were accepted as nestmates. These results suggest that the antennal sensing system is affected by excess surface material; hence, their proper function is prevented until they are cleaned.

Chemical Ecology, Biochemistry, and Molecular Biology of Insect Hydrocarbons

Insect cuticular hydrocarbons (CHCs) consist of complex mixtures of straight-chain alkanes and alkenes, and methyl-branched hydrocarbons. In addition to restricting water loss through the cuticle and preventing desiccation, they have secondarily evolved to serve a variety of functions in chemical communication and play critical roles as signals mediating the life histories of insects. In this review, we describe the physical properties of CHCs that allow for both waterproofing and signaling functions, summarize their roles as inter- and intraspecific chemical signals, and discuss the influences of diet and environment on CHC profiles. We also present advances in our understanding of hydrocarbon biosynthesis. Hydrocarbons are biosynthesized in oenocytes and transported to the cuticle by lipophorin proteins. Recent work on the synthesis of fatty acids and their ultimate reductive decarbonylation to hydrocarbons has taken advantage of powerful new tools of molecular biology, including genomics and RNA interference knockdown of specific genes, to provide new insights into the biosynthesis of hydrocarbons.

Environmental decomposition of olefinic cuticular hydrocarbons of Periplaneta americana generates a volatile pheromone that guides social behaviour

Once emitted, semiochemicals are exposed to reactive environmental factors that may alter them, thus disrupting chemical communication. Some species, however, might have adapted to detect environmentally mediated breakdown products of their natural chemicals as semiochemicals. We demonstrate that air, water vapour and ultraviolet (UV) radiation break down unsaturated cuticular hydrocarbons (CHCs) of Periplaneta americana (American cockroach), resulting in the emission of volatile organic compounds (VOCs). In behavioural assays, nymphs strongly avoided aggregating in shelters exposed to the breakdown VOCs from cuticular alkenes. The three treatments (air, water vapour, UV) produced the same VOCs, but at different time-courses and ratios. Fourteen VOCs from UV-exposed CHCs elicited electrophysiological responses in nymph antennae; 10 were identified as 2-nonanone, 1-pentanol, 1-octanol, 1-nonanol, tetradecanal, acetic acid, propanoic acid, butanoic acid, pentanoic acid and hexanoic acid. When short-chain fatty acids were tested as a mix and a blend of the alcohols and aldehyde was tested as a second mix, nymphs exhibited no preference for control or treated shelters. However, nymphs avoided shelters that were exposed to VOCs from the complete 10-compound mix. Conditioned shelters (occupied by cockroaches with faeces and CHCs deposited on the shelters), which are normally highly attractive to nymphs, were also avoided after UV exposure, confirming that breakdown products from deposited metabolites, including CHCs, mediate this behaviour. Our results demonstrate that common environmental agents degrade CHCs into behaviourally active volatile compounds that potentially may serve as necromones or epideictic pheromones, mediating group dissolution.

Organic Tracers from Asphalt in Propolis Produced by Urban Honey Bees, Apis mellifera Linn

Propolis is a gummy material produced by honey bees to protect their hives and currently has drawn the attention of researchers due to its broad clinical use. It has been reported, based only on observations, that honey bees also collect other non-vegetation substances such as paint or asphalt/tar to make propolis. Therefore, propolis samples were collected from bee hives in Riyadh and Al-Bahah, a natural area, Saudi Arabia to determine their compositional characteristics and possible sources of the neutral organic compounds. The samples were extracted with hexane and analyzed by gas chromatography-mass spectrometry. The results showed that the major compounds were n-alkanes, n-alkenes, methyl n-alkanoates, long chain wax esters, triterpenoids and hopanes. The n-alkanes (ranging from C₁₇ to C₄₀) were significant with relative concentrations varying from 23.8 to 56.8% (mean = 44.9+9.4%) of the total extracts. Their odd carbon preference index (CPI) ranged from 3.6 to 7.7, with a maximum concentration at heptacosane indicating inputs from higher plant vegetation wax. The relative concentrations of the n-alkenes varied from 23.8 to 41.19% (mean = 35.6+5.1%), with CPI = 12.4-31.4, range from C₂₅ to C₃₅ and maximum at tritriacontane. Methyl n-alkanoates, ranged from C₁₂ to C₂₆ as acids, with concentrations from 3.11 to 33.2% (mean = 9.6+9.5%). Long chain wax esters and triterpenoids were minor. The main triterpenoids were α- and β-amyrins, amyrones and amyryl acetates. The presence of hopanes in some total extracts (up to 12.5%) indicated that the bees also collected petroleum derivatives from vicinal asphalt and used that as an additional ingredient to make propolis. Therefore, caution should be taken when considering the chemical compositions of propolis as potential sources of natural products for biological and pharmacological applications. Moreover, beekeepers should be aware of the proper source of propolis in the flight range of their bee colonies.

Contact solid-phase microextraction with uncoated glass and polydimethylsiloxane-coated fibers versus solvent sampling for the determination of hydrocarbons in adhesion secretions of Madagascar hissing cockroaches Gromphadorrhina portentosa (Blattodea) by gas chromatography-mass spectrometry

Molecular profiles of adhesion secretions of Gromphadorrhina portentosa (Madagascar hissing cockroach, Blattodea) were investigated by gas chromatography mass spectrometry with particular focus on a comprehensive analysis of linear and branched hydrocarbons. For this purpose, secretions from the tarsi (feet), possibly contributing to adhesion on smooth surfaces, and control samples taken from the tibiae (lower legs), which contain general cuticular hydrocarbons that are supposed to be not involved in the biological adhesion function, were analyzed and their molecular fingerprints compared. A major analytical difficulty in such a study constitutes the representative, spatially controlled, precise and reproducible sampling from a living insect as well as the minute quantities of insect secretions on both tarsi and tibiae. Thus, three different in vivo sampling methods were compared in terms of sampling reproducibility and extraction efficiency by replicate measurement of samples from tarsi and tibiae. While contact solid-phase microextraction (SPME) with a polydimethylsiloxane (PDMS) fiber showed higher peak intensities, a self-made uncoated glass fiber had the best repeatability in contact-SPME sampling. Chromatographic profiles of these two contact-SPME sampling methods were statistically not significantly different. Inter-individual variances were larger than potentially existing minor differences in molecular patterns of distinct sampling methods. Sampling by solvent extraction was time consuming, showed lower sensitivities and was less reproducible. In general, sampling by contact-SPME with a cheap glass fiber turned out to be a viable alternative to PDMS-SPME sampling. Hydrocarbon patterns of the tarsal adhesion secretions were qualitatively similar to those of epicuticular hydrocarbon profiles of the tibiae. However, hydrocarbons were in general less abundant in tarsal secretions than secretions from tibiae.

Perception of cuticular hydrocarbons by the olfactory organs in Periplaneta americana (L.) (Insecta: Dictyoptera)

Despite the importance of cuticular hydrocarbons (CHs) in insect chemical communication, direct proof that they are detected and recognized by insects by contact or by olfactory receptors are rare. In Periplaneta americana, CHs induce aggregation. The aim of our study was to investigate how CHs are detected by P. americana antennae. Using solid phase microextraction and gas chromatography, the three main CHs of the species profile were identified in the volatiles emitted by these insects. Gas chromatography coupled to electroantennography recordings demonstrated that the antennae responded to these three CHs. Furthermore, CHs had an attraction effect in Y-olfactometer bioassays when presented at high concentrations. As CHs can be perceived by P. americana, at least from a short distance, they could play a role in attracting conspecifics during aggregation processes, in addition to inducing aggregation when direct contact is possible.

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.

Tissue and chain length specificity of the fatty acyl-CoA elongation system in the American cockroach

The elongation of fatty acyl-CoAs, reactions involved in hydrocarbon biosynthesis, was examined in the cockroach, Periplaneta americana. Products were analyzed by radio-HPLC and radio-GLC. The majority of the elongation activity was observed in microsomes prepared from abdominal epidermal tissue. Linoleoyl-CoA (18:2-CoA) was elongated most efficiently followed by stearoyl-CoA (18:0-CoA), linolenoyl-CoA (18:3-CoA; n-3) and oleoyl-CoA (18:1-CoA). The products of 18:2-CoA elongation included all even numbered acyl groups up to 28 carbons, and the products of 18:0-CoA included all even numbered acyl groups to 26 carbons. The 18:3-CoA was elongated only to 20 and 22 carbons. Radioactivity from both 18:2-CoA (5.4%) and 18:0-CoA (1.2%) was recovered in the hydrocarbon fraction. Analysis of this hydrocarbon fraction showed that the radio-activity from 18:2-CoA was present in (Z,Z)-6,9-heptacosadiene and that the radioactivity from 18:0-CoA was present in n-pentacosane. These data demonstrate for the first time in an in vitro insect system that the fatty acid elongation reactions are coupled with the conversion of the elongated product to hydrocarbon. Thus, each of the expected intermediates in the conversion of 18:0 and 18:2 to 25 and 27 carbon hydrocarbons, respectively, was observed, and the results demonstrate high tissue, substrate, and product specificity.

De novo biosynthesis of polyunsaturated fatty acids in the cockroach Periplaneta americana

The de novo biosynthesis of 6,9,12-linolenic acid, 11,14-eicosadienoic acid, 5,11,14-eicosatrienoic acid, and arachidonic acid was demonstrated in adult female cockroaches, Periplaneta americana. These four polyunsaturated fatty acids (PUFA) were present primarily in the phospholipid (PL) fraction of both males and females. They were purified by AgNO3 thin-layer chromatography and high pressure liquid chromatography. The double bond positions of the major isomer of eicosatrienoic acid were shown to be at the delta 5,11,14 positions by gas chromatography-mass spectrometry (GC-MS) of both methoxy and epoxide derivatives and gas-liquid chromatography (GLC) and GC-MS of ozonolysis products. The other PUFAs cochromatographed with standards on both packed and capillary GLC columns. The in vivo incorporation of [1-14C]acetate into 5,11,14-eicosatrienoic acid, 11,14-eicosadienoic acid, 6,9,12-linolenic acid, and arachidonic acid was demonstrated by radio-GLC and radio-HPLC and for 5,11,14-eicosatrienoic acid by radio-GLC of ozonolysis products. The latter technique clearly demonstrated that the entire eicosatrienoic acid molecule was labeled. Thoracic tissue contained the highest amount of radiolabeled 5,11,14-eicosatrienoic acid (1.6% of total radioactivity incorporated into PL) while radiolabeled 11,14-eicosadienoic acid was found primarily in abdominal epidermal tissue (2% of total radioactivity incorporated into PL). Radiolabeled arachidonic and 6,9,12-linolenic acids comprised 0.1 and 0.02%, respectively, of the total radioactivity in the PL fraction. These data document the de novo biosynthesis of di-, tri-, and tetraunsaturated fatty acids in the American cockroach, and indicate that this animal can desaturate on both sides of the delta 9 double bond of oleic acid.