Submitted to: Naturwissenschaften
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/4/2004
Publication Date: 2/8/2005
Citation: Byers, J.A. 2005. A cost of alarm pheromone production in cotton aphids, aphis gossypii. Naturwissenschaften 92:69-72. Interpretive Summary: The aphid alarm pheromone is used by most aphid species of agricultural importance to warn related individuals in order for them to escape a predator in the vicinity. SPME (solid phase microextraction) and gas chromatography coupled to mass spectrometry (GCMS) were used to detect minute quantities released by cotton aphids, Aphis gossypii Glover, into the air. Aphids were also extracted in solvents (pentane and ether) and the amounts of alarm pheromone ranged from 0.1 to 2.5 billionths of a gram (ng) per aphid. The quantities per aphid increased with fresh weight, and variation in individual weights explained about 66% of the variation in alarm pheromone. However, the concentrations (ng/mg fresh weight) declined slightly with weight. These findings suggest that smaller aphids try to compensate by producing relatively more pheromone per weight than adults but still cannot approach an evolutionary optimal load, as assumed in adults, possibly due to the need to balance costs of growth with costs of producing the alarm pheromone.
Technical Abstract: The sesquiterpene, (E)-B-farnesene, is used by many aphid species as an alarm pheromone to warn related individuals of predation. Disturbed cotton aphids, Aphis gossypii Glover, released (E)-B-farnesene into the air as detected by solid phase microextraction and gas chromatography mass spectrometry (GC-MS). Solvent extracts of cotton aphids of various life stages and weights also were analyzed by GC-MS for sums of ions 69 and 93, which discriminated (E)-B-farnesene from coeluting compounds. Aphids of all life stages and sizes reared on cotton plants in both an environmental chamber and glasshouse contained (E)-B-farnesene in amounts ranging from 0.1 to 1.5 ng per individual. The quantities of (E)-B-farnesene in aphids increased in relation to increasing body weight, and variation in individual weights explained about 82% of the variation in alarm pheromone. However, the concentrations (ng/mg fresh weight) declined exponentially with increasing body weight. These findings indicate that aphid nymphs try to compensate for their smaller size by producing relatively more pheromone per weight than adults but still cannot approach an evolutionary optimal load, as assumed in adults with the greatest total amounts. This suggests that young aphids need to balance costs of growth and maturation with costs of producing the alarm pheromone.