The Reproduction of the Red Locust, Nomadacris septemfasciata (Serv.) (Orthoptera, Acrididae), in an Outbreak Area

Abstract

During the breeding seasons 1952 to 1955, samples of females of the Red Locust, Nomadacris septemfasciata (Serv.), were caught in the Rukwa Valley, Tanganyika Territory, and the ovaries classified according to egg length. Ovaries designated Class V were those regarded as containing eggs ready for oviposition. Population estimates and rainfall records were also taken.The data suggested that the eggs in the ovaries develop very rapidly, becoming ready to be laid about seven days after the start of development.The increase in weight of an individual female during ovary development is related to absolute size, and it was found that, during ovary development, the weight increases by approximately one-half.The most important factor initiating ovarian development seemed to be a drop in daily maximum temperature to below 36°C. The factors of high humidity and rainfall were of less importance but their influence is not fully understood. The possibility of change in length of day being an important factor in the initiation of ovarian development is discussed.The limiting factors for the number of egg-pods laid in a season are considered to be the dates of the drop in daily maximum temperature and of the drop or decline in parental population. The date of drop or decline in parental population seemed to be connected with the date of drop in daily maximum temperature.The percentage of females laying more than one egg-pod was calculated, and the resuJts were found to vary considerably from year to year, although the average of 1 pods per female agreed with past estimates. Also, the average period of 16 days between successive egg-layings agreed with past work.Drought, during the laying period, seemed to cause the females to retain their ripe eggs.The evidence tended to confirm the possibility of a Red Locust population being able to increase 100-fold in a single year.