Various ketones and l-octen-3-ol were used as odour attractants with biconical traps at Nguruman, south-western Kenya, to assess their effects on the catch size and composition of Glossina pallidipes Austen. Acetone, methyl ethyl ketone and l-octen-3-ol were found to be effective in increasing catch size by up to 2-4 x, but the two ketones differed in their dose-response curves. Acetone was more effective for males than females, as was l-octen-3-ol. The age composition of samples from baited and unbaited traps differed only slightly. The level of variability between traps was reduced by the use of odour. Acetone with cow urine produced increases in catch of 9-25x, and significant differences were found between samples in sex ratio and age composition. The index of increase for cow urine plus acetone, when used with a biconical trap, was correlated with temperature changes during the day. This could only be partially accounted for by variability in dose rates. Cow urine with acetone is considered to be a potentially useful combination of baits for community participation tsetse control schemes.

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Seasonal changes in the mean size of tsetse, Glossina pallidipes Austen, as indicated by wing vein length, were monitored during 1983-86 at Nguruman, southwestern Kenya. Changes in size of nulliparous females and wing fray category 1 males were shown to be correlated with the relative humidity 2 months before they were captured. Soil temperature when flies were in the pupal stage had much less effect. Size dependent mortality was demonstrated, with the mean size of flies emerging from pupae significantly less than that of field-caught flies. This mortality must occur at emergence, since there was no evidence of size-dependent mortality once the flies became available to the trap. Size was correlated with density-independent mortality acting on the parent population 2 months previously. It might therefore be possible to use size as an index of the intensity of such mortality. This could be useful when assessing the level of additional mortality required to suppress tsetse populations.

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A simple bioassay system was developed to study locomotory and ovipositional responses of screwworm, Cochliomyia hominivorax (Coquerel), flies to bovine blood inoculated with eight species of coliform bacteria that were isolated from screwworm-infested animal wounds. When exposed to odors from bacteria-inoculated blood which was incubated for 72 h at 37 degrees C, approximately 50% of 7- and 10-d-old gravid females landed on the blood by the end of 15 min test exposure. Only 17% of 7-d-old reproductively sterile females (from irradiated pupae) with previtellogenic ovaries and 2% of 4-d-old vitellogenic females responded to the same treatment. Females generally reacted in greatest numbers to bacteria-inoculated blood incubated for 72 h, followed by 48 h, then 24 and 96 h. Males of all ages tested were unresponsive. Although oviposition occurred in tests with gravid females lasting for 1 h, with both inoculated blood and an uninoculated control, the inoculated sample was significantly better than the control at 48, 72, and 96 h incubation duration. Our results are consistent with the conclusion that the inoculated blood, when incubated for 48-72 h, gives off volatile chemicals which attract gravid females and contains an oviposition stimulant that acts following contact and feeding. The volatiles, once isolated and identified, may be useful for sampling gravid females in the field as well as improving the oviposition system in the mass-production facility of the screwworm eradication program.

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