Possible function of substances excreted by Trichogramma and darkening their hosts

When Trichogramma (Hym.: Trichogrammatidae) reach the prenymph stage, they secrete a substance which darkens the hosts (insect eggs). Several hypothes es were expressed about the role of this dark substance. Two were tested, o ne assuming a protection against the predators, and one assuming a reductio n of the developmental duration after temperature increase. Ephestia kuehni ella (Lep.: Pyraiidae) eggs wheither non parasitized (clear) or parasitized (dark, i.e. black or brown) by Trichogramma fuentesi were consumed equally by Chrysoperia carnea (Pla.: Chrysopidae) larvae. Thus, the dark substance has no interest for the protection against this predator. Trichogramma giv ing black hosts have a faster development than Trichogramma giving brown ho sts. Thus, the dark substance allows the acceleration of the parasitoid dev elopment and probably, in an indirect way, the reduction of predation risks .