Benzoquinones in the defensive secretion of a bug (Pamillia behrensii): a common chemical trait retrieved in the Heteroptera

Abstract

Benzoquinones are a phylogenetically widespread compound class within arthropods, appearing in harvestman, millipedes and insects. Whereas the function of benzoquinones as defensive compounds against potential predators and microbes has been well established, the full extent of benzoquinone usage across arthropods, and especially within Insecta, has yet to be established. Adding to the growing list of unique evolutionary origins of benzoquinone employment, we describe in this paper the metathoracic scent gland secretion of the mirid bug Pamillia behrensii, which is composed of heptan-2-one, 2-heptyl acetate, 2,3-dimethyl-1-4-benzoquinone, 2,3-dimethyl-1-4-hydroquinone as well as one unknown compound. Similarly, to many other arthropods that use benzoquinones, Pamillia releases the contents of its gland as a defensive mechanism in response to harassment by other arthropod predators. Morphological investigation of the gland showed that the benzoquinone-producing gland complex of P. behrensii follows a similar blueprint to metathoracic scent glands described in other Heteropterans. Overall, our data further underpins the widespread convergent evolution and use of benzoquinones for defense across the Arthropoda, now including the order Hemiptera.

Evolutionary assembly of cooperating cell types in an animal chemical defense system

“…We next focused on BQ synthesis. Although defensive BQs have arisen in myriapods, arachnids, earwigs, termites, cockroaches, grasshoppers, capsid bugs, and at least seven times in beetles (Wagner et al, 2020), their mechanistic origins were hitherto unknown in any species. Aromatic compounds in animals are often acquired from dietary aromatic amino acids or symbiotic microbes, or sometimes synthesized de novo (Bru ¨ckner et al, 2020;Torres et al, 2020).…”

The genomic and cellular basis of biosynthetic innovation in rove beetles

“…Upstream of Dmd, the mechanisms of intracellular trafficking of hydroquinone precursors were previously unknown. Despite the widespread use of benzoquinones in arthropod chemical defenses (75), it has been unclear how these highly cytotoxic compounds are safely produced and transported inside cells prior to secretion (32,76). In plants, small molecule toxins are often conjugated to sugars, creating glycosides that render many such compounds relatively harmless (77,78).…”