Chiasma-induction and tyrosine metabolism in locusts

The production of a gregarization pheromone has been postulated in locusts, with effects on melanization of the hopper cuticle and increased chiasma frequency during meiosis in the adult on crowding or gregarization. Lack of chiasma-inducing effect of the pheromone on albino strains is correlated with the absence or deficiency of some of the products of the metabolic pathways of tyrosine. Some of these products, commercially obtainable, are the amino acids phenylalanine and tyrosine leading to both the melanization and sclerotization pathways; dopamine formed from dopa in the lastnamed pathway; three products of dopamine i.e. protocatechuic acid, noradrenaline and adrenaline. The injection of solutions of these metabolites into the haemolymph of solitary hoppers has shown that only dopa to some extent but noradrenaline to a large extent are effective in raising chiasma frequency in solitarised individuals of normal-coloured strains of Locusta, while in two albino strains, which differ genetically, the injection of dopa, dopamine, protocatechuic acid and noradrenaline proved effective; phenylalanine was effective in only one of these albino strains, while adrenaline was effective in neither. The chiasma-inducing effect of noradrenaline, common to the three strains, is accompanied in the normal-coloured strain by a greater retention of dark coloration during solitarization and by some attainment of the crowded type of morphometric ratios which is a third physical criterion of gregarization. The genetic blocks to the physical criteria of gregaria in the albino strains lie at the immediate level of dopa production or previous to this reaction; it may be construed that such a block in the solitaria of normal-coloured strains also lies at this early level, in this case being induced by too low a pheromone concentration.