Variation in the Rates of Increase of Glossina morsitans centralis and Their Relevance to Control

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Abstract
Tsetse control operations are more likely to succeed if timed to exploit periods of natural vulnerability. One measure of a population''s condition is its rate of increase designated rs if derived from a standing age distribution or rm from a temporal distribution. The former is difficult to establish for a continuously breeding population but an attempt was made to estimate both by sampling a population of G. morsitans centralis in Botswana throughout the year. The growth rate rs varied from -0.0099-0.0022 and the mean value of -0.0053 was reflected in a declining density over the sampling period. Both rs and density were lowest during the cold, dry season and this was considered the most suitable time to undertake an insecticidal control operation. Regional variations in the growth rate were also observed and these may have been due to repeated chemical control activities. The suggestion is made that repeated low dosage applications might ultimately achieve eradication of negative growth rates can be sustained by methodical reproductive disruption.