Observations on the Life-history of the Red Locust, Nomadacris septemfasciata (Serv.) in the solitary Phase

Abstract

The populations of Nomadacris septemfasciata described in this paper were all of solitaria or neai-solitaria phase.Sexual maturation as measured by the developing ovaries took place rapidly though irregularly through the population. Its onset coincided with an increase in the daily number of hours of relative humidity at or above 75 per cent., and abundance of green food; Copulation, which started after the first wide-spread rain, took place before the ovaries of many females were completely mature.Caged locusts gave a mean fecundity of 183 eggs contained in 2·4 pods which is probably a minimum figure. Pods were laid at intervals of about two weeks and each was laid before the next batch had visibly developed.The period spent in the egg was at least 39 days, at most 46 days and probably 42 days. Adults appeared 67 days after the first hatchings. Both these periods are greater than those recorded in phase transiens or gregaria.Solitaria locusts were found to pass through seven instead of six nymphal instars as do gregaria. This difference seemed to be constant. The extra instar was probably interpolated between the second and third of gregaria but was not an exact duplicate of any other instar.The number of vertical dark eye-stripes is a convenient and fairly constant indicator of the instar. The number of antennal segments in the later instars and in the adult, and also the number of adult eye-stripes, is greater in the solitaria phase.Amongst the hoppers three main types of coloration were encountered and are briefly described but they could not be closely related to phase. The amount of dark pigment present in late stage nymphs was reflected in the young adult, the appearance of which is described in some detail. Subsequent changes during the dry season are briefly noted, in particular the pink of the hind wing, which becomes faintly visible within a month of the last moult.The changes in pigmentation which take place during sexual maturation are described in detail. In addition to pronounced darkening of the tegmina which completely changes the appearance of the solitaria locust, certain bright pigments are laid down which are later obscured by a general blackening. It is unsafe to classify Nomadacris septemfasciata as to phase on colour alone unless the date of capture and its relation to the breeding season in the locality is taken into consideration. Solitaria do not normally develop the general reddening of the body which is shown by migrating swarms, even when these are only transiens in phase.