Host selection and egg allocation behaviour by Aphytis melinus and A.lingnanensis: comparison of two facultatively gregarious parasitoids

Abstract

1. The ovipositional and egg allocation behaviour of individual females of Aphytis melinus DeBach and A.lingnunensis Compere were compared.2. Both Aphytis species exhibit the same behavioural sequence during oviposition.3. Aphytis melinus laid most of its female eggs on the dorsum of a scaleinsect beneath its cover, and most of its male eggs under the scale-insect's body. Aphytis lingnanensis also oviposited both dorsally and ventrally on scale-insect hosts, but female and male progeny arose with equal frequency from eggs laid in both locations.4. Both Amelinus and A. lingnanensis are facultatively gregarious parasitoids. The degree of gregariousness depends on host size, i.e. the larger the host, the more the Iikelihood that several eggs will be deposited at each visit by the parasitoid.5. When two eggs were laid during the same host visit, both Amelinus and A.lingnanensis laid one female and one male egg more often than would be expected under an assumption of random allocation of sexes.6. Because A.melinus successfulIy utilize smaller hosts than A h p a n e n s i s to produce progeny, these parasitoids should not be considered ecological homologues, as suggested by DeBach & Sundby (1963).

Adult feeding and lifetime reproductive success in the parasitoid Aphytis melinus

“…Oviposition was identified by a series of pumping movements by the female during the encounter, and confirmed by removing the scale cover immediately after the observation and counting the number of eggs on the host (Luck et al, 1982;van Lenteren, 1994;. A. melinus typically deposit between one and four eggs on 3rd instar California red scale (Luck et al, 1982;. Host feeding was identified by observing contact of the female's mouthparts with the scale cover following a characteristic series of movements by the ovipositor (Heimpel & Rosenheim, 1995).…”

“…Each host encounter was scored as oviposition, host feeding, or rejection. Oviposition was identified by a series of pumping movements by the female during the encounter, and confirmed by removing the scale cover immediately after the observation and counting the number of eggs on the host (Luck et al, 1982;van Lenteren, 1994;. A. melinus typically deposit between one and four eggs on 3rd instar California red scale (Luck et al, 1982;.…”

Adaptive preferential selection of young coccinellid hosts by the parasitoid wasp Dinocampus coccinellae (Hymenoptera: Braconidae)

“…Natural selection should thus favour the devel opment of host recognition systems which allow recogni tion of the most suitable hosts. Evidence of the ability of parasitoids to select more suitable hosts has been obtained in several studies, whether the difference in host suit ability be dependent on host species (Kraaijeveld et al, 1995), host developmental stage (van Alphen, 1980;Luck et al, 1982), host nutritional state (Kouamé & Mackauer, 1991), host parasitisation status (Pijls et al, 1995) or host age within a developmental stage (van Alphen & Drijver, 1982;Hurst et al, 1998). In some cases, the criteria deter mining host quality centre on the suitability of the host for larval development, in others it is the ease or rate at which oviposition may be achieved that is critical (Godfray, 1994).…”

Event-driven competing risks

“…Aphytis prefers instar stages to molt stages of red scale. During the instar stage, the scale cover is free of the body and Aphytis can lay eggs on either or both the dorsal and ventral surfaces of the scale (Abdelrahman, 1974;Luck et al, 1982). During the molt and mature female stage, the cover is rigidly fused to a hardened body.…”