Abstract
Insect cuticular hydrocarbons (CHCs) play critical roles in reducing water loss and chemical communication. Species-specific CHC profiles have been used increasingly as an excellent character for species classification. However, considerably less is known about their potential for population delimitation within species. The aims of this study were to develop a solid-phase microextraction (SPME)-based CHC collection method and to investigate whether CHC profiles could serve as potential chemotaxonomic tools for intraspecific delimitation in Acyrthosiphon pisum. Optimization of fibers for SPME sampling revealed that 7 μm polydimethylsiloxane (PDMS) demonstrated the most efficient adsorption of CHCs among five different tested fibers. SPME sampling showed good reproducibility with repeated collections of CHCs from a single aphid. Validation of SPME was performed by comparing CHC profiles with those from conventional hexane extractions. The two methods showed no qualitative differences in CHCs, although SPME appeared to extract relatively fewer short-chained CHCs. While CHC profiles of a given population differed among developmental stages, wing dimorphism types, and host plants, wingless adult aphids showed very low variance in relative proportions of individual CHC components. Reproducibility of CHC profiles was explored further to classify wingless adult morphs of A. pisum from five different geographic regions that showed no variation in mitochondrial COI gene sequences. Our results demonstrate that CHC profiles are useful in intraspecific delimitation in the field of insect chemotaxonomy.
Highlights
Insect cuticular hydrocarbons (CHCs) are non-polar lipids that function primarily as a barrier against desiccation, serve as species, colony, and gender-specific chemical communication cues [1,2], and are involved in insecticide resistance [3]
Using the optimized solidphase microextraction (SPME) sampling coupled to gas chromatograph (GC)-MS analysis, we explored the polymorphism and plasticity of CHC profiles in A. pisum with respect to several factors, including developmental stage, wing dimorphism, and host plant
In order to confirm the identification of A. pisum species and investigate the genetic variation among different morphs, we sequenced and aligned of the mitochondrial COI (mtCOI) gene, which has been recognized as a well-known molecular marker for insect molecular taxonomy
Summary
Insect cuticular hydrocarbons (CHCs) are non-polar lipids that function primarily as a barrier against desiccation, serve as species, colony, and gender-specific chemical communication cues [1,2], and are involved in insecticide resistance [3]. CHCs in a given species can be a mixture of several to more than 100 components of 21–50+ carbon alkanes, alkenes and their branched derivatives that vary in number and position of double bond and methyl branches. SPME-based CHCs for A. pisum delimitation [1,4]. Such variation makes CHC compositions highly diverse [5], leading to an assortment of mating selection types, and informative for reproductive isolation [6]. As a result of species specificity, CHC profiles in distinct species usually display qualitative differences, such as presence or absence of CHC components. Subtypes of a given species generally vary in the levels of different components [6]. The CHC profiles can be affected by many internal and external factors, such as developmental age, geographic location, and diet [6,16]
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