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Diflubenzuron (DFB), a benzoylphenylurea derivative, when fed to adult females ofTenebrio molitorduring sexual maturation (i.e., from adult ?? to day 9), was found to accumulate in the fat body and to quantitatively and qualitatively affect lipid synthesis. DFB treatment decreased the overall lipid level in the fat body and caused perturbations in both the rate of incorporation and distribution of radiolabeled oleic acid in the different classes of lipids. Compared to untreated controls, a significant increase in the level of saturated fatty acids and a significant decrease in the level of unsaturated fatty acids were observed in the fat body. In the ovaries, the fatty acid composition of total lipids was not affected by the DFB. However, a drop in the rate of incorporation of a radiolabeled precursor in the ovarian lipids, especially in the triacylglycerol, was observed.

Flucycloxuron, a novel benzoylphenylurea (BPU) derivative, exhibited insecticidal activity when injected into newly ecdysed pupae ofTenebrio molitor. Mortality occurs because of defective adult ecdysis. Treatment caused a reduction in both cuticle thickness and incorporation of14C-labelled precursor into chitin, although it had no significant effect on the protein synthesis. The potencies of other BPU compounds as inhibitors of chitin biosynthesis have been examined and results showed that diflubenzuron was less effective than either flucycloxuron or triflumuron.

The PAS-positive reaction of chitin requires periodic oxidation of hydroxyacetyl-amino groups of N-acetyl-glucosamine units. Periodic oxidation of N-acyl-hydroxyamino acids and of different sugars shows that hydroxy-acetyl-amino groups are not clived under PAS conditions. Thus, chitin, considered as poly-N-acetylglucosamine, is PAS-negative.

The formation of the ecdysial membrane during the pupal life of Tenebrio molitor is studied by histochemical and electron microscopical techniques.

The cytological modifications of the epidermal cells secreting sternal and pleural cuticle of adultTenebrio are studied, specially during the formation and evolution of the outer and inner epicuticle.

Bursicon active hemolymph ofTenebrio, injected into host pupae deprived in bursicon, induces a 2-fold increase of cyclic AMP in the epidermis of the hosts 5 min after the injection. No increase is observed by injecting bursicon inactive hemolymph or insect Ringer. From these experiments it can be concluded that cyclic AMP is a second messenger of bursicon.