Development of a system for sterilizing tsetse flies, Glossina spp., in the field

Various autosterilizing systems were evaluated on natural populations of Glossina pallidipes Austen and G.morsitans morsitans Westwood in Zimbabwe. These involved a clear plastic tower of two or three chambers mounted at the cage position on a trap. Inside one chamber flies could be exposed to the vapour phase of the chemosterilant bisazir, P,P-bis (1-aziridinyl)-N-methylphosphinothioic amide. The system was designed to encourage flies to enter the sterilizing chamber, delaying their exit for sufficient time to expose them to a sterilizing dose. This was accomplished in the most effective system by restriction of the exit to one small hole (6 mm diameter) at the roof-side junction. The number of flies remaining in the chamber declined exponentially. The rate of exit was directly proportional to the density of flies in the sterilizing chamber and to the number of exit holes. The probability of a fly being in this chamber for at least 1 or 7 min (the times taken for female and male G.m.morsitans respectively to receive an ED50) was 0.84 and 0.67 respectively with one fly present. With sixteen flies, these probabilities were 0.76 and 0.18 respectively. Results suggest that it may be possible to develop a cheap, safe and efficient autosterilizer for use on tsetse traps.