CHIASMA-INDUCING PHEROMONE OF LOCUSTS

To the two quantitative criteria for phase transformation of locusts, viz. nymphal colour and adult morphometric ratios, the change in chiasma frequencies during meiosis in the male can now be added: gregarization or swarming induces an increase in chiasma formation. The atmosphere around crowded locusts contains a pheromone which is absorbed and causes a reactive haemolymph in locust hoppers. This haemolymph may be injected into solitarious hoppers or nymphs to induce increased chiasma formation. Certain solvents like risella oil and dimethyl sulphoxide will extract the pheromone from such an atmosphere, and bio-assays with these extracts have been demonstrated to be chiasma-inducing. Such extracts are, however, not chiasma-inducing in the albino mutant, but the haemolymph from crowded normal-coloured hoppers is reactive in the albino hopper. In addition the albino mutant is solitaria-like in both morphometric ratios and chiasma frequencies. These data indicate a relationship between the melanization cycle and chiasma induction: the previously postulated melanin-inducing pheromone and this chiasma-inducing pheromone are probably identical. On the other hand, this pheromone of nymphs and the sex-maturation pheromone of adults are not identical, although the latter may be a modified form of the other. The effect of the nymphal pheromone on adult morphometric ratios is not clear although some correlation has been shown to exist between raised chiasma frequencies in treated solitaries and advances towards gregaria ratios. It may be that in this pheromone we have, what may be called, a gregarizing principle. © 1968 Springer-Verlag.