ABSTRACT
Wing formation in presumptive alate morphs (virginoparae and males) was observed for the pea aphid, Acyrthosiphon pisum, exposed to attack by the parasitoid, Aphidius ervi, at different stages of host development. Morphological abnormalities in parasitized aphids such as complete apterization (development of a wingless form), formation of rudimentary wing buds, and deformed wings indicate a possible disruption of the endocrine system. Changes in the body shape and the number of olfactory secondary rhinaria on the antennae could indicate an influence of juvenile hormone in parasitized A. pisum but the development of fifth-stadium supernumerary larvae (indicated by an extra moult and which can be induced by exogenous juvenile hormone treatments) was not found in parasitized aphids. In addition, while apterization of virginoparae can also be induced by the pro-allatocidal compound Precocene III, this was not possible in the male. Males which survived parasitoid attack without forming aphid mummies (indicating that oviposition had not occurred) developed as wingless individuals suggesting that the reproductive-tract-fluids from the female parasitoid were important in the wing inhibition process. Teratocytes from the parasitoid appeared to promote developmental arrest in parasitized aphids.
ABSTRACT
In the aphid parasitoid Aphidius ervi Haliday, the incidence of diapause around the critical photoperiod was dependent on temperature. At a photoperiod of 12 h light:12 h dark, a significantly higher proportion of diapausing individuals was found at 12 degrees C than at 15 degrees C. The second larval stage of the parasitoid was most sensitive to photoperiod and localised-illumination experiments showed that the parasitoid responded independently of the aphid host. The sex ratio of the population which emerged after rearing in short-days and/or after diapause was male biased. Topical application of the juvenile hormone-mimic, pyriproxyfen, before or during diapause delayed emergence of Aphidius ervi but did not induce diapause or influence its termination. The ecdysteroid mimic RH 5849 induced diapause in a few treated individuals but did not affect diapause termination.
