Host Selection and Number of Eggs per Oviposition in the Egg-Parasite Trichogramma embryophagum Htg.

Abstract

IT has been shown by Salt^1,2 and Laing³ that the behaviour of Trichogramma in parasitizing host eggs can be divided in the following elements: (a) The parasite makes random movements on the substrate and is visually attracted by small objects which rise above the surface. (b) The parasite climbs up the object and spends some time in walking over its surface in a characteristic way, making intensive movements with the antennæ (here called drumming). If the object has already just been parasitized by Trichogramma, it will be rejected if the odour of the first female is still present on the chorion. (c) After drumming, the parasite starts drilling on the surface of the object, not only on eggs, but also on small seeds and grains of sand. Odour, colour and texture of the surface of the object seem not to play a predominant part in stimulating the drilling act. The object can be rejected, however, if its measurements are such that the development of the parasite in the inside is an impossibility¹. (d) If the object is a host egg the chorion is eventually perforated and the parasite's eggs are deposited. The host is rejected after perforation, however, if it has been parasitized before² or the embryo has reached an advanced stage in development^4,5.