THE MAGNITUDE OF SITE AND TIME INTERACTION EFFECT IN TSETSE-FLY (DIPTERA, GLOSSINIDAE) TRAP CATCHES

Site and time effects are important factors determining tray catches o f tsetse flies. These factors may interact significantly and therefore confound interpretation of time series data used for population monit oring. We therefore investigated the magnitude and importance of site x time interactions in trap catches of Glossina pallidipes Austen and G. longipennis Corti using a 2200 trap-days (400 trap-months) data set . The interaction was found to be significant (P < 0.05) in 46-100% of the combinations of different numbers of months and sites between 2 a nd 12. The mean percent variance due to the interaction ranged between 4% and 28% for G. pallidipes and 12% and 36% for G. longipennis. The interaction was usually less important than the effect of site alone b ut more important than the effect of time alone. These results suggest that tsetse researchers should examine critically the adequacy of exi sting approaches to population monitoring with traps and to testing ne w traps and odour baits.