Published online by Cambridge University Press: 10 July 2009
My breeding experiments on Locusta migratoria, L., in 1913−14 enabled me to establish that the progeny of this species sometimes belongs to the form which was previously regarded as a distinct species, L. danica, L., and in the same way, the latter insect may give rise to progeny that is typical of L. migratoria. These results have been used by B. P. Uvarov in developing his theory that the periodicity of locusts is due to a kind of irregular alternation of two phases, swarming (ph. migratoria) and solitary (ph. danica), respectively. I shall not dwell here on that theory or on the differences between the two phases, referring those interested in the subject to Uvarov's paper, but will describe further breeding experiments conducted during the year 1923 with a view to obtaining an idea as to what may be the factors that cause the variation in the species.
page 241 note † Translated from the Russian manuscript by B. P. Uvarov.
page 241 note ‡ Bull. Entom. Res., xii, 1921, pp. 135–163.
page 243 note † [The experiments described in this paper are extremely interesting, as they show that the problem of transformation of the swarming phase of locusts into the solitary one is very complicated, and the actual factors of transformation not easy to discover. The results of the experiments are in most remarkable agreement with those obtained by Professor Faure with the South African Locustana pardalina (Journ. Dept. Agric. S. Africa vii, 1923, no. 3, pp. 205–224), in which crowding of larvae of the solitary phase also invariably led to transformation into the swarming phase, while larvae of the swarming phase bred singly transformed into solitary ones. It is difficult even to suggest what the factors of transformation are, but one point seems to be fairly clear—that the transformation is due to some unknown influences on the larvae, not on the eggs or the adults, and that those influences are in some way connected with the density of larvae in a given space. Only further extensive and more precise experiments, in which all possible factors would be carefully registered and measured, can throw better light on this highly interesting and mysterious phenomenon.—B. P. Uvarov.]