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Abstract. Direct behavioural assays were used to investigate the influences of host size and parasitoid egg load on the decision to host feed versus oviposit made by the parasitoid Aphytis lingnanensis Compere. Egg load was manipulated without concurrent influences on the history of host contact by exploiting size‐related variation in fecundity and by holding parasitoids at different temperatures to vary the rate of oocyte maturation. Host feeding comprised a series of feeding bouts, separated by renewed probing of the scale insect body. Successive feeding bouts were progressively shorter, suggesting that hosts represent ‘patches’ yielding resources at a decelerating rate. Parasitoids were significantly more likely to host feed on smaller hosts and oviposit on larger hosts. Neither egg load nor the treatment variables (parasitoid size and holding temperature) exerted significant influences on the decision to host feed versus oviposit on second instar (low quality) hosts. The failure to observe an effect of egg load on host‐feeding decisions was not simply a reflection of the parasitoids being entirely insensitive to egg load; significant effects of egg load on parasitoid search intensity and clutch size decisions were observed. Parasitoids developing on second instar (low quality) hosts experienced high levels of mortality late during development and yielded very small adults. The discord between these experimental results and predictions regarding the importance of egg load underscores the need for additional work on the proximate basis for host‐feeding decisions and the nutritional ecology of insect parasitoids.

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Production of males in uniparental lines of two species in the parasitic wasp genus Aphytis was induced by rifampicin, and male sexual functioning was determined. Wolbachia-specific 16S rDNA primers were used in a PCR in order to: (1) assess correlation between thelytokous reproduction and the presence of Wolbachia; (2) detect the loss of Wolbachia DNA in uniparental A. lingnanensis following antibiotic treatments, with or without the presence of a host; and (3) clone and sequence part of the Wolbachia 16S rDNA from the uniparental Aphytis species for phylogenetic studies. Males produced viable sperm that was transferred to the female spermatheca following mating. However, sperm failure to effect egg fertilization resulted in all-male progeny. Wolbachia were found in the two uniparental (A. lingnanensis and A. diaspidis) but not in the two biparental (A. lingnanensis and A. melinus) Aphytis lines tested. They can be detected in wasps up to 7 days following antibiotic treatments, regardless of the presence of host. The 16S rDNA for the symbionts in the two Aphytis species is virtually identical, and is most closely related to the Wolbachia found in Muscidifurax uniraptor (Pteromalidae).

AdultMaladera matrida Argaman (Coleoptera: Scarabaeidae: Melolonthinae) males emerge from soil for an active period at dusk, a few minutes before the females. Adults are found during most of the active hours on the foliage in aggregations composed of an equal sex ratio. The mechanism of aggregation behavior ofM. matrida beetles was studied in a Y-shaped olfactometer. No evidence was found for the existence of an aggregation pheromone released either by males or by females, but behavior tests indicate that adultM. matrida beetles, males as well as females, are attracted to volatiles of an injured host plant. The following scenario is suggested: Males emerge daily from soil at dusk, a few minutes before the females, and immediately start feeding. Additional males are attracted to the injured host's volatiles and form aggregations. When females emerge from soil, the attractant volatiles are concentrated in spots, and the females join the aggregations, forming an equal sex ratio.

In parasitic Hymenoptera, severe sex ratio distortions are sometimes associated with the presence of symbiotic microorganisms. Symbiont-induced uniparental reproduction is found in several species of the genus Aphytis and is suspected in others. These intracellular bacteria (called Wolbachia) reside within the egg cytoplasm. In order to follow their vertical transmission, the distribution pattern of the symbionts in ovaries and eggs of two uniparental lines (A. lingnanensis and A. yanonensis) was studied by electron, confocal, and two-photon microscopy. The results obtained suggest that Wolbachia move from nurse cells to developing oocytes. In freshly laid eggs, the symbionts are concentrated in the posterior pole, away from the micropyle, and in later stages of embryogenesis they are found surrounding nuclei throughout the embryo.