Fecundity-reducing pheromone in Argas (Persicargas) arboreus (Ixodoidea: Argasidae)

Fed adult Argas (Persicargas) arboreus produce a fecundity-reducing pheromone which affects all or most females in crowded conditions. Unfed adults and unfed and fed nymphs do not produce this pheromone. The effect of this pheromone is probably additive, increasing with additional crowding of adults. Mechanical disturbance is excluded as the cause of fecundity reduction. Fed females separated by a perforated barrier from crowded adults also exhibit very low fecundity. Adult excretory materials used 31 days post-feeding do not contain the fecundity-reducing pheromone. Preliminary experiments suggest that this pheromone is spatially limited in action, does not affect gonadotropic hormone synthesis and/or release, and does not induce oviposition deterrence behaviour. This may be considered to be a primer pheromone, causing alteration in normal vitellogenin synthesis and/or uptake and deposition in oocytes. The source and chemical nature of this pheromone should be investigated.