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

Author
item Byers, John
item ZADA, ANAT - Plant Protection Institute - Israel

Submitted to: Chemoecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/10/2010
Publication Date: 11/25/2010
Citation: Byers,J.A., Zada,A. 2010. Individual variation of (S)-4-methyl-3-heptanone in heads of braconid wasp, Leiophron uniformis, and Pogonomyrmex ants indicates costs of semiochemical production. Chemoecology. 21:35-44.

Interpretive Summary: Red harvester ants (Pogonomyrmex species) are well known to release an alarm pheromone, from mandibular glands in their heads. The alarm pheromone is released when the nest is attacked by rodents and birds and causes the ants to swarm and look for enemies to sting. Using gas chromatograph coupled with mass spectrometry, we found that both sexes of the unrelated braconid wasp Leiophron uniformis (Hymenoptera: Brachonidae), which is a parasitoid of plant bug pests such as Lygus hesperus of agricultural crops, contain 2-6 ng of the same volatile in their heads. To study the ecological function of this ketone, a wasp’s leg or antenna was grasped with fine forceps and the small 0.4-mg wasp immediately tried to escape by beating its wings, biting the forceps, and released the volatile into the air. Since the adult wasps do not live communally and feed only on nectar, their sharp piercing mandibles in combination with this escape and biting behavior indicate the ketone is used for defense rather than for an alarm function. The large red harvester ant, Pogonomyrmex rugosus (about 20 mg body weight), and California harvester, P. californicus (about 8 mg), were analyzed for amounts of their alarm pheromone, (S)-4-methyl-3-heptanone; they contained about 2000 and 1000 ng per head, respectively. We found that P. rugosus ants frequently released alarm pheromone when attacking prey (moth caterpillars) or ants of other nests or species, which suggests the compound may serve an additional defensive/aggressive function in harvester ants in conjunction with their formidable stinger. The amount of (S)-4-methyl-3-heptanone in heads increased with weight of the wasps or of the two ant species, suggesting a cost of defensive/pheromone production. T

Technical Abstract: (S)-4-methyl-3-heptanone is known as an alarm pheromone released from the mandibular glands in heads of red harvester ants (Pogonomyrmex spp.). Using GC-MS, we found that both sexes of the braconid wasp Leiophron uniformis, which is a parasitoid of plant bug pests of agricultural crops, contain 2-6 ng of the same volatile in their heads. To study the ecological function of this ketone, a wasp’s leg or antenna was grasped with fine forceps and the small 0.4-mg wasp immediately tried to escape by beating its wings, biting the forceps, and released the volatile into the air. Since the adult wasps do not live communally and feed only on nectar, their sharp piercing mandibles in combination with this escape and biting behavior indicate the ketone is used for defense rather than for an alarm function. The large red harvester ant, Pogonomyrmex rugosus (about 20 mg body weight), and California harvester, P. californicus (about 8 mg), were analyzed for amounts of their alarm pheromone, (S)-4-methyl-3-heptanone; they contained about 2000 and 1000 ng per head, respectively. We found that P. rugosus ants frequently released alarm pheromone when attacking prey (moth caterpillars) or ants of other nests or species, which suggests the compound may serve an additional defensive/aggressive function in harvester ants in conjunction with their formidable stinger. The amount of (S)-4-methyl-3-heptanone in heads increased with weight of the wasps or of the two ant species, suggesting a cost of defensive/pheromone production.