Laboratory of  Experimental Entomology and BioControl Theory Russia, 199034, St.-Petersburg, Zoological Institute. Phone: +7 (812) 114 0442; Fax: +7 (812) 114 0444; E-mail: sreznik@zin.ru

Host search, host selection and host-parasitoid interrelations
in Alysia manducator (Hymenoptera: Braconidae)

Project conducted by Drs. S.Ya. Reznik, D.G. Chernoguz and K.B. Zinovjeva in 1985-1990.

Host habitat selection

Alysia manducator females are olfactorily attracted to meat. Meat infested with host larvae arrests parasitoids with the same high efficiency throughout the stages of larval development. Meat without hosts arrests parasitoids only for that short period when it is suitable for oviposition by the flies.

Host species selection

Endoparasitoid Alysia manducator Panz (Hymenoptera: Braconidae) parasitize larvae of Calliphora vicina R.D. (Diptera: Calliphoridae) and several other species of flesh flies. Host acceptance by A. manducator females is divided into four steps: (1) contact with the fly larva, (2) probing by the ovipositor, (3) attack, i.e., an attempt to stick the ovipositor and (4) oviposition. Rejection of the host possible at every stage. Probing is stimulated by the smell of carrion and by movements of the larvae. The probability of probing after the antennal contact increases with increasing size of the host larvae, but does not depend on the species in all studied carrion-feeding Diptera. The probability of passage from the probing to the attack, on the contrary, is host species - specific but does not depend on the size of the larvae. The probability of the successful oviposition is also host-specific. Significant positive correlation between host acceptance and host suitability suggests the adaptive behavior, in spite of 'mistaken' oviposition, which sometimes happen.

Host stage selection

Probability of successful completion of larval development depends on the parasitoid ability to control host's ontogeny. This regulation ability is realized in the limited range of blowflies. In Calliphora vicina (one of preferred natural hosts), when the host develops without the diapause, the mortality sharply increases if parasitization took place (1) during the feeding of host larvae of the 3rd instar and (2) before pupariation. When the host develops with the diapause, only the first peak of mortality takes place.

Host preference is maximal at the middle of the 3d instar, when in natural conditions the host larvae normally leave their food substrate. Host suitability is maximal at 1st-2nd instar and at the end of the 3d instar, therefore in A. manducator more suitable host instar are parasitized with lower probability. One possible reason of this "maladaptive" behavior is the limitation for the host food, and the high probability of host starvation. Taking this fact into account, the most suitable and as it turns out also most preferable hosts appear to be those larvae that have already finished their feeding but have not yet left their food substrate. Such coincidence of host suitability and parasitoid preferences can be demonstrated only after considering both experimental results and natural observations concerning habitat selection by host, host suitability, habitat and host selection by parasitoid.

Host-parasitoid relations in Calliphora vicina (Diptera, Callophoridae) and Alysia manducator (Hymenoptera, Braconidae)

It was known that effect of injury caused by the parasitoid A. manducator during oviposition resulted in interruption of larval diapause and the puparium formation in C. vicina. Through ligation of blow-fly larvae infected with braconid, it was found that pupation triggering factor comes from parasitic larva at the end of instar I before molt to instar II. It was important to distinguish an indirect stress effect caused by parasitization and true parasitoid regulation of the host's physiology. Using some manipulations (burning or pricking the host's cuticle by the pin, interrupted oviposition, isolation of parasite in the host's body, ligation experiments) it was shown that effect of interruption of host's diapause and the puparium formation have been induced by the developing parasite larvae, but not by stress of parasitization. Haematological data confirmed this conclusion. The experiments with ligations shown that induction of the host's pupariation did not require the participation of its endocrine centers. Histological investigation of some host's tissues indicated that parasitization provoked only the puparium formation and blocked the pupation (metamorphosis). Interaction of both the effects, i.e. the pupation blocking and the induction of the puparium formation, constitute the mechanism of host regulation, which provides for the parasitoid's active role in developmental synchrony.

References
(those published in English are indicated by blue color)

Vaghina N.P. & Chernoguz D.G. 1995. Stress or regulation? Interruption of larval diapause in Diptera by parasitization with Braconidae. Zool. Zhurn. 74(3): 88-101 (in Russian).

Reznik S.Ya., Chernoguz D.G. & Zinovjeva K.B. 1992. Host searching, oviposition preferences and optimal synchronization in Alysia manducator (Hymenoptera: Braconidae), a parasitoid of the blowfly, Calliphora vicina. Oikos 65: 81-88.

Reznik S.Ya. & Chernoguz D.G. 1988. Temporal alterations of host's substrate limits host detection behavior in Alysia manducator Panz parasitic hymenopteran. Zhurn. Obsch. Biol. 49: 519-526. (in Russian).

Chernoguz D.G. & Reznik S.Ya. 1987. Ethological and physiological components of host specificity of Alysia manducator Panz. (Hymenoptera: Braconidae). Entomol. Obozr. 66: 499-510. (in Russian).

Chernoguz D.G., Reznik S.Ya. & Zinov'eva K.B. 1987. The role of age and physiological conditions of Calliphora vicina for parasitization by Alysia manducator. Zool. Zhurn. 66: 533-542. (in Russian).

Chernoguz D.G. & Vaghina N.P. 1987. An experimental detection of the developmental stage of parasitoid, Alysia manducator, causing pupation of its host. Zool.Zhurn. 66(8): 1209-1213 (in Russian).