N-3-Methylbutanoyl-O-methylpropanoyl-L-serine Methyl Ester - Pheromone Component of Western Black Widow Females

Chemical communication is common in spiders but few pheromones have been identified. Female widow spiders in the genus Latrodectus spin webs that disseminate an attractive sex pheromone, and a contact pheromone on the silk elicits courtship behavior by males. The methyl ester of N-3-methylbutanoyl-O-(S)-2-methylbutanoyl-L-serine is a contact pheromone of the Australian redback spider Latrodectus hasselti. We hypothesized that the contact pheromone of congeneric L. hesperus resembles that of L. hasselti. The silk of virgin L. hesperus females was extracted with methanol, and analyses by gas chromatography-mass spectrometry (GC/MS) provided evidence for the presence of N-3-methylbutanoyl-O-methylpropanoyl-L-serine methyl ester (MB-MP-S), a lower homologue of the L. hasselti contact pheromone. Behavioral responses of L. hesperus males to test stimuli were assayed on T-shaped rods with the end sections of the horizontal arm enveloped in filter paper. Males spent 40 % longer in contact with paper bearing female silk than with blank paper, and 39 % longer in contact with paper treated with silk extract than with solvent controls. Contact with silk and silk extract induced courtship behavior by 96 % and 80 % of males, respectively, indicating that there was a methanol-soluble courtship-eliciting contact pheromone on the silk. Males responded less strongly to synthetic MB-MP-S than to silk or silk extract. Paper impregnated with synthetic MB-MP-S (10 or 100 mu g) induced courtship behavior in 3-16 % of males, and prompted males to stay 10-16 % longer than on control paper. Our data support the conclusion that MB-MP-S is part of a multi-component contact pheromone of L. hesperus.