Chemical Ecology, Biochemistry, and Molecular Biology of Insect Hydrocarbons

Abstract

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.

Modulation of fatty acid elongation in cockroaches sustains sexually dimorphic hydrocarbons and female attractiveness

“…The main function of insect cuticular hydrocarbons (CHCs) is to waterproof the cuticle to resist dehydration under dry conditions [18]. In many insects, CHCs have been co-opted to serve as chemical signals (pheromones) that mediate intraspecific communication [19,20]. Sexually dimorphic cuticular hydrocarbon (SDCHC) profiles are widespread in insects [21][22][23], but the regulatory networks that underlie the formation of SDCHCs largely remain unknown.…”

Genetic and genomic architecture of species-specific cuticular hydrocarbon variation in parasitoid wasps

“…The most commonly occurring compound classes are saturated straight-chain alkanes (n-alkanes), unsaturated straight-chain alkenes (n-alkenes) and alkadienes, and methyl-branched alkanes (Blomquist et al 1987;Blomquist and Bagnères 2010). Despite considerable diversity of CHC profiles across insects, to the current stage of knowledge, the pathway of CHC biosynthesis appears to be mostly conserved (Blomquist and Ginzel 2021;Holze et al 2021). Briefly, the biosynthetic pathway consists of the elongation of fatty-acyl-Coenzyme A units to produce very long-chain fatty acids (VLCFs) that are subsequently converted to hydrocarbons by subducting the carboxyl group (Nelson and Blomquist 1995;Howard and Blomquist 2005;Blomquist and Bagnères 2010, Fig.…”

“…Insects have proven to be particularly useful for QTL studies, since they combine various beneficial attributes: a multitude of quantifiable phenotypes, short generation times, large offspring numbers and, most commonly, relatively small genomes (Hoy 2005;Hunter and Kole 2008;Thomas et al 2020). Cuticular hydrocarbons (CHCs), lipids constituting a major part of the waxy layer covering the insects' epicuticle, are particular promising traits to dissect genetically via QTL mapping, as they are comparatively easily quantifiable, polygenic, and phenotypically as well as genotypically traceable (Chung and Carroll 2015;Blomquist and Ginzel 2021;Holze et al 2021).…”

Cuticular Hydrocarbon Trails Released by Host Larvae Lose their Kairomonal Activity for Parasitoids by Solidification

“…In general, CHCs have several important functions in insects, ranging from protection against desiccation to the mediation of intra-and interspecific communication (e.g., Gibbs 1998;Howard and Blomquist 2005;Lockey 1988; Menzel et al 2017;Otte et al 2018). The multifunctionality of CHCs is based on the various types of CHCs, which can be saturated or unsaturated, linear or methyl-branched (Blomquist and Bagnères 2010;Blomquist and Ginzel 2021;Gibbs 2002). According to Menzel et al (2019), the epicuticular layer of hydrocarbons forms a solid-liquid mixture over a broad range of temperatures due to the different melting temperatures of CHC types.…”