Individual variation of (S)-4-methyl-3-heptanone in heads of braconid wasp, Leiophron uniformis, and Pogonomyrmex ants indicates costs of semiochemical production

Abstract

S)-4-Methyl-3-heptanone is an alarm pheromone released from the mandibular glands in heads of harvester ants (Pogonomyrmex spp.). We used gas chromatography-mass spectrometry (GC-MS) to study the variation in amounts of this ketone among individual ants of a colony. P. barbatus contained about 2,000 ng per head, while only about half of this amount was found in heads of P. rugosus and P. californicus. Individuals of P. barbatus from three different nests contained rather uniform amounts of the alarm pheromone within each colony (16-30% coefficient of variation CV; normal distributions skewed left), but one nest under food stress had a significantly lower mean amount. In contrast, both sexes of a small braconid wasp Leiophron uniformis, a parasitoid of Lygus plant bugs, contained up to 10 ng of the same volatile enantiomer in their heads; and groups of either sex of the wasp exhibited normal distributions of quantities (64% CV, skewed right). The differences in the distributions between parasitoids and ants suggest that related members within a social ant colony may attempt to maintain a uniform level of ketone compared to independent variation in unrelated, solitary wasp individuals. When the wasp's leg was grasped with forceps, it tried to escape and bite the forceps as it ejected (S)-4-methyl-3-heptanone (detected by solid phase microextraction, SPME, and GC-MS). Since adult wasps are nonsocial and feed only on nectar, their sharp piercing mandibles in combination with this escape/ biting behavior indicate the ketone is used for defense rather than for an alarm function as in harvester ants. Costs of producing the semiochemical in wasp L. uniformis and ants P. barbatus and P. californicus are suggested since populations exhibited a significant linear increase in the amount of (S)-4-methyl-3-heptanone with an increase in body weight of individuals.

Stereoselective Chemical Defense in the Drosophila Parasitoid Leptopilina heterotoma is Mediated by (−)-Iridomyrmecin and (+)-Isoiridomyrmecin

“…Both sexes produce (S)-4-methyl-3-heptanone in their head. A defensive function of the compounds has been suggested, but has not been experimentally tested (Byers and Levi-Zada, 2011).…”

‘Social glands’ in parasitoids? – convergent evolution of metapleural glands in Hymenoptera

“…While the structure of the gland and its relative position within the head may indicate homology within Hymenoptera, its function and underlying biosynthetic pathways differ greatly between taxa. The mandibular gland in various clades has been shown to produce defensive allomones (Byers and Levi-Zada 2011), sex pheromones, intraspecific defensive pheromones (Stökl and Herzner 2016), and territory marking (Goettler and Strohm, 2008).…”

Earwigs (Labidura riparia) mimic rotting-flesh odor to deceive vertebrate predators

“…A positive relationship between body weight and semiochemical amounts was found in females of cotton aphid Aphis gossypii, plant bug Lygus hesperus, moth Neoleucinodes elegantalis, and wasp parasitoid Leiophron uniformis, suggesting metabolic costs that were difficult to achieve by smaller individuals (Byers 2005(Byers , 2006Jaffe et al 2007;Byers and Levi-Zada 2011). Conditiondependent costs of pheromone signaling also were suggested because larger individuals have more pheromone than smaller individuals, or release more pheromone when reared on high- quality diet (Ming and Lewis 2010;Harari et al 2011;Blaul and Ruther 2012).…”