Changes in wing development and development through the stadia of Aphis fabae
are examined after parasitisation by Aphidius colemani along with the underlying
mechanisms. Parasitoid oviposition into nymphs of winged gynoparae of A. fabae
shows that wing development is inhibited and the earlier parasitism takes place, the
stronger the effect. Consideration of the timing of events indicates that the active
component(s) is most likely injected during oviposition and is not related to hatching
and growing of the parasitoid larva. When extracts of venom glands are injected into
late-second stadium aphids, many develop to fourth-stadium possessing rudimentary
wingbuds, show developmental arrest and often die while moulting to the adult stage.
Injections with extracts of female or male parasitoids into later stadia give similar
results with regard to development to the adult but aphids injected in the late-fourth
stadium develop normally. Experiments with long-day winged virginoparae reveal
similar results in development to the adult but injections into long-day wingless
aphids, which develop more rapidly, show this effect only when performed early in
the third stadium. The earlier the injection before the final moult the greater the effect
of the extract on preventing adult development. The results indicate that there is an
active factor(s) in the female parasitoid’s venom that disrupts wing development
and/or inhibits development to the adult; the loss of activity after treatment at 100 °C
or with protease makes it likely that the factor(s) is a protein. Surprisingly, injections
of extracts from male parasitoids have similar effects. The location and function of
such a factor(s) in males are unknown. Fast Protein Liquid Chromatography is used to
fractionate the parasitoid extracts and bioassays reveal activity in fractions 16-25.
Aphidius ervi venom also inhibits development of A. fabae (a non-host) whereas A.
colemani venom has no effect on the development of Megoura viciae (a non-host).
Injection with lipopolysaccharides and infection with a fungal pathogen are used to
test whether stimulation of the immune response affects wing development in the host
and the possibility that the host is in control of inhibiting its own wing development in
order to support its immune system is discussed
