Written in wax: cuticular messages

Waxy cuticle of the Woodland dor beetle (Anoplotrupes stercorosus)

Insect cuticles are protected from drying out and abrasion by a thin layer of waxes and cuticular hydrocarbons (CHCs). These epicuticular waxes are produced by secretory cells which lie beneath the epidermis (see below)

Cross-section through the integument of an insect highlighting CHC transport pathways and their deposition on the epicuticle, left: examples of the three most commonly occurring CHC compound classes n-alkanes, n-alkenes, and methyl-branched alkanes. From Holze et al. (2020)

The importance of this epicuticular layer in preventing the insect from drying out has been known for a long time, but more recently, there has been an explosion of studies investigating the role of the cuticular waxes in terms of communication.

Cuticular waxes are present on all insects, like this flatid bug, Lawana imitata (Fulgoridae)

Insects can tell a lot about each other simply by touching with their antennae!

Large Passalid beetle with waxy cuticle

Without going into too much detail, the diversity of cuticular hydrocarbon compounds in the outer layer of the insect provide it with a sort of chemical language. The different chain lengths of the hydrocarbons, their degree of saturation (the number of double bonds), and the number and positions of methyl groups provide a sort of Rosetta stone which can communicate all sorts of things about the insect.

The Rosetta Stone. Image treated, from file https://commons.wikimedia.org/wiki/File:Rosetta_Stone.JPG]

Simply by touching the cuticle of another insect with their sensitive antennae – covered in different types of sensors – an insect can ‘read’ all sorts of things about the other insect, written in wax, as it were!

Ectemnius sp. Crabronidae

The chemical language of cuticular hydrocarbons enables insects to communicate information about their identity (genus, species) their gender (is this a male or a female I am touching?), caste, age, physiological state and even mating status (have you mated before you met me?!).

Dung beetle (Trypocopris pyrenaeus var. coruscans).

The chemistry of CHCs provides a near endless series of possible combinations, with over a hundred different epicuticular components present in some insects.

Cuticular hydrocarbons (CHCs) play two critical roles in insects. They form a waxy layer on the cuticles of insects to prevent desiccation due to cuticular water loss (Chung & Carroll, 2015).
Bumpy cuticle of a large longhorned beetle (Batocera lineolata) from Thailand

Cuticular hydrocarbons are particularly important among social insects, like ants, bees and termites, because of the need to identify nest-mates, including different castes (workers, foragers, queens and so on), and invaders (parasites).

Buff-tailed bumblebee worker

Ants analyse the hydrocarbons on the cuticle of another individual to determine if it is an intruder.

Ants tending their aphids

Cuticular hydrocarbons are also used as contact sex pheromones in several beetle families.

Stag beetle cuticle.

These chemicals on the surface of an insect convey a lot of information about its identity, sex and health for example, but they will also be ‘read’ – tasted – by another insect in combination with other signals, what it can see and smell for example.

References

Chung, H., & Carroll, S. B. (2015). Wax, sex and the origin of species: dual roles of insect cuticular hydrocarbons in adaptation and mating. BioEssays37(7), 822-830.

Holze, H., Schrader, L., & Buellesbach, J. (2021). Advances in deciphering the genetic basis of insect cuticular hydrocarbon biosynthesis and variation. Heredity126(2), 219-234.

Mitov, M., Soldan, V., & Balor, S. (2018). Observation of an anisotropic texture inside the wax layer of insect cuticle. Arthropod structure & development47(6), 622-626.

2 thoughts on “Written in wax: cuticular messages

    • Three questions😊 1) I think most prey detection is probably visual. 2) Identities can be disguised. For example, parasites of social insects must either mimic the chemical profiles of their hosts, or markedly reduce the quantity of their CHC cues, so that they become ‘chemically insignificant’ and thus, unrecognisable. 3) There is probably a whole book to write about how chemical profiles change as insects develop, holo- or hemimetabolous. But yes, they do change, and profiles change as insects become sexually mature and age. Best wishes, Ray

Leave a Reply to Paul Moore Cancel reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s