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Antennal sensilla were compared in females of two encyrtid Hymenoptera, Epidinocarsis lopezi and Leptomastix dactylopii, parasitoids of adults and larvae of Pseudococcidae. The external morphology of these sensilla was studied using scanning electron microscopy and their ultrastructure observed under transmission electron microscopy using ultrathin sections. Female antennae have seven different types of sensilla, morphologically very similar in the two species: trichoid sensilla, which are putative mechanosensilla, sensilla chaetica types 1 and 2, which are presumably contact chemosensilla, and sensilla chaetica types 3 and 4, basiconic sensilla, and placoid sensilla, which are all presumed to be olfactory sensilla. Sensilla chaetica types 2 and 4 are thought to be directly involved in host discrimination. The only differences between the two species are in the number and distribution of some types of sensilla. These differences might be related to the varied tritrophic ecological context of the two species rather than to their similar biology.

Although hyperparasitism frequently occur in parasitic insects, many aspects of this strategy remain unknown. We investigated possible fitness costs of hyperparasitism as influenced by host size. Our study was conducted with the facultative hyperparasitoid Pachycrepoideus dubius Ashmead (Hymenoptera: Pteromalidae), which parasitizes host species differing greatly in size. We compared some fitness traits (level of successful parasitism, development time, sex ratio and offspring size) of P. dubius developing on large secondary/primary (Delia radicum L. (Diptera: Anthomyiidae)/Trybliographa rapae Westwood (Hymenoptera: Figitidae)) or small secondary/primary host species (Drosophila melanogaster L./Asobara tabida Nees (Hymenoptera: Braconidae)). In no‐choice and choice experiments, P. dubius was able to develop on different stages of T. rapae (L2 (endophagous), L4 (ectophagous), and pupae) but that it preferred to parasitize unparasitized D. radicum pupae over pupae parasitized by T. rapae. Furthermore, in P. dubius, hyperparasitism was associated with fitness costs (lower level of successful parasitism, smaller adult size) and these costs were greater on the smallest host complex. We hypothesize that the size of D. melanogaster pupae parasitized by A. tabida may be close to the suboptimal host size for P. dubius beneath which the costs of hyperparasitism make this strategy nonadaptive. Hyperparasitism in terms of trade‐offs between host quality and abundance of competitors is discussed.

Intraspecific host discrimination is frequently found in solitary parasitoids, but interspecific host discrimination, where female parasitoids recognize hosts already parasitized by females of other species, is rare. This particular behaviour appears to be adaptive only under specific circumstances. In this paper, we quantified intraspecific host discrimination in Anaphes n. sp. (Hymenoptera: Mymaridae), an endoparasitoid of the eggs of Listronotus oregonensis (LeConte) (Coleoptera: Curculionidae) and interspecific host discrimination toward eggs parasitized by Anaphes sordidatus (Girault), a sympatric species competing for the same resource in similar habitats. To examine host discrimination, choice experiments were used where the females had to choose between different categories of eggs (unparasitized, parasitized by Anaphes n. sp. or A. sordidatus). Superparasitism and multiparasitism were avoided in experiments where the female had a choice between unparasitized hosts and hosts parasitized by the same female, by a conspecific or by a female A. sordidatus. When all hosts available were parasitized, conspecific superparasitism occurred more often than self-superparasitism or multiparasitism. These results indicated that females Anaphes n. sp. were capable of self-, conspecific and interspecific discrimination. Self-discrimination followed recognition of an external marking while interspecific discrimination occurred mostly after insertion of the ovipositor. Interspecific discrimination could result from the recent speciation of these species and could be associated with a genotypic discrimination. This behavior appears to be adaptive because of the competition for common hosts between the two parasitoid species.

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