Source of the host marking pheromone in the egg parasitoid Trissolcus basalis (Hymenoptera : Scelionidae)

After oviposition, Trissolcus basalis females always mark the host's surfac e, depositing host marking substances for herself and to warn other oviposi ting females. The perception of these host marking substances, probably thr ough the antennae, can induce the female to leave and seek healthy hosts. P arasitoid females exposed to conspecific parasitized egg masses left the ho st egg masses significantly more often than when exposed to non-parasitized egg masses. More egg mass leaving behavior also was observed when the egg masses were treated with Dufour's gland secretion but not when treated with secretion from the common oviducts. The common oviduct has a secretory epi thelium that produces electron-dense vesicles, probably containing proteina ceous substances. The secretory cells of the accessory gland, Dufour's glan d, contain electron-lucid vesicles, whose secretion appears to be a lipid s imilarly to that found in pheromone secreting glands. Ultrastructural and b ehavioral evidence suggests that Dufour's gland is the host marking pheromo ne source. (C) 2001 Elsevier Science Ltd. All rights reserved.