Some factors influencing oviposition in an artificial host by the pupal parasitoid Brachymeria intermedia (Nees)

Abstract

Attempts to identify factors capable of inducing Brachymeria intermedia
to oviposit in an artificial host are reported. The development of an artificial
substrate for in vitro egg laying of this hymenopterous parasitoid is also
described. When presented with a choice between pupae of the factitious host
Galleria mellonella and a blank cell in a Y tube olfactometer the females did not
show a significant olfactory preference for the pupae. The response of B. intermedia
females to G. mellonella pupae washed in hexane or untreated was also
not significantly different. The role of kairomonal cues in the cuticle of G. mellonella
pupae in attracting B. intermedia females was therefore not clear. Cylindrical
host shape, on the other hand, was apparently important in inducing parasitoid
oviposition. In fact, the females were observed to probe cylinder-shaped
artificial substrates with their ovipositors even in the absence of chemical cue.
When cylinder-shaped and purposefully flattened G. mellonella cuticles were
exposed to parasitoid females oviposition holes were recorded only in the former
and none in the latter. Cylinder-shaped artificial hosts composed of an agar-water
suspension and G. mellonella haemolymph encapsulated in Parafilm were hence
prepared and exposed to B. intermedia females. Some eggs were recorded in artificial
pupae containing 50% or 25% haemolymph. No eggs were found in 'the
pupae containing agar-water suspension alone, or 75% or 100% haemolymph.
These results suggest that G. mellonella haemolymph contains ovipositional kairomones,
an excess of which, however, prevents B. intermedia females from ovipositing.