none Galleria mellonella; ENZYMES-; JH-esterase activity; Premetamorphic behavioural relations; HAEMOLYMPH-; JH-&-ecdysteroid titres; Premetamorphic behaviour effects, hymenopteran parasite presence influence; HORMONES-; JH-&-ecdysteroids, haemolymph titres; Premetamorphic activity relations; LARVAL-DEVELOPMENT; Haemolymph JH & ecdysteroid titre effects, hymenopteran parasite relations; ECDYSIS-; Haemolymph JH & ecdysteroid titre relationships; Premetamorphic behaviour relations, effects of hymenopteran parasite; METAMORPHOSIS-; Premetamorphic behaviour; Hymenopteran parasite effects; BEHAVIOUR-; Premetamorphic; Effects of hymenopteran parasite presence; HYMENOPTERAN-PARASITES; Apanteles galleriae; Larval host premetamorphic behaviour & JH & ecdysteroid titre effects; COCOONS-; Spinning, haemolymph JH & ecdysteroid titre relations; Effects of presence of hymenopteran parasite, larvae Apanteles galleriae; LEPIDOPTERAN-HOSTS; Galleria mellonella; Host premetamorphic behaviour & JH & ecdysteroid titre effects, larvae Parasitization of Galleria mellonella (Lepidoptera: Pyralididae) larvae by a larval endoparasitoid Apanteles galleriae (Hymenoptera: Braconidae) leads to the precocious expression of premetamorphic behavior in the sixth (normally penultimate) instar host larvae prior to the parasitoid's emergence. We investigated the role of parasitization with A. galleriae on the alteration of development and/or behavior of its host. The ecdysteroid titer in the hemolymph of parasitized sixth instar larvae (the last instar of parasitized larvae) was higher than that of unparasitized ones, and the high ecdysteroid concentrations induced premetamorphic behaviors such as wandering and cocoon spinning. However, the epidermis of the parasitized larvae was not pupally committed through this stage. The activity of JH esterase in the parasitized larvae remained low, and application of a JH analogue to these larvae caused the production of a larval-type cocoon. These facts suggest that the parasitization by A. galleriae induces precocious premetamorphic behaviors of G. mellonella larvae by changing host endocrine conditions without causing the typical larval-pupal metamorphosis.