Could the egg itself be the source of the oviposition deterrent marker in the ectoparasitoid Dinarmus basalis?

Females of Dinarmus basalis, a solitary ectoparasitoid, strongly avoid supe rparasitising hosts bearing eggs which are 20 or more hours old. Our object ive was to determine the mechanism by which the factors inducing host discr imination and such an oviposition deterring effect act, and the origin of t he deterrent. This study showed that the information is carried by the para sitised host. It is acquired by a transfer of molecules from the wasp egg o nto the host and it requires contact between egg and host for at least 4 h. The factors transferred do not, as commonly reported in other species, com e from the female's genital apparatus but from the live egg itself. Consequ ently, the D. basalis egg directly participates in the success of parasitis m by releasing factors which elicit the oviposition host deterring effect. The originality and the ecological importance of these results are discusse d. (C) 1999 Elsevier Science Ltd. All rights reserved.