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An experiment was carried out in 1968 in the Lossitete Forest area of northern Tanzania to compare the fly-round and the Langridge-trap as sampling techniques for assessing the effectiveness of 0·4% pyrethrum applications on Glossina pallidipes Aust. when applied from the air. From fly-rounds, population reductions of 64%, 36% and 29% after the first, second and third applications, respectively, were estimated, whereas from Langridge traps the reductions were 11%, 7% and nil, respectively. Taking into consideration the efficiency of the Langridge-trap and the limitations of the fly-round in sampling G. pallidipes populations, it is concluded that the fly-round may give a false assessment of reduction of G. pallidipes after insecticide application.

As part of a programme to test the sterile insect technique against Glossina morsitans morsitans Westw. in Tanzania, two aerial applications of endosulfan were applied to a 195-km2 test area. The applications were made with a 28-day interval to provide an initial reduction in the target species prior to the release of sterile males. A Cessna 310 aircraft equipped with a rotary atomiser and operating at night was used to apply the insecticide at a dosage of about 20 g/ha. Flyround surveys within 48 h following the spraying operations indicated that a 100% reduction of G. m. morsitans adults was achieved in both applications, while G. pallidipes Aust. was reduced by 91 5% in the first and 100% in the second.

An experiment was carried out in 1967 to assess the effects and economics of aerial applications of pyrethrum as an aerosol spray against a high density tsetse population consisting mainly of Glossina pallidipes Aust. in northern Tanzania. Complete eradication was attempted, and six applications of a 0·4% w/v solution of natural pyrethrins, synergised with 2% piperony1 butoxide in power kerosene, were applied at three-week intervals over three square miles. Application was from a Cessna 182E fitted with one Micronair rotary atomiser. Populations of G. pallidipes, assessed from fly-path catches, were reduced 95% after three applications. The final three applications had little effect and it was considered that unfavourable meteorological conditions and full leaf cover were the main factors responsible. It is suggested that, in view of the high initial kill of the fly and the possibility of using pyrethrum economically against tsetse for human settlement schemes, further work should be carried out with this insecticide.

Experiments are described on the aerial application of very low volumes (0·5 gal./acre) of oil solutions of DDT to control two pests, Heliothis armigera (Hb.) (bollworm) and Acanthomia horrida (Germ.) (brown bug), of the seed-bean crop in northern Tanzania. The method was compared with an improved variant of the standard commercial method of aerial control, in which DDT emulsion is applied at 1·85 gal./acre. This improved variant was also compared with a standard commercial treatment. Very-low-volume (solution) treatments were made with rotary atomisers, normal volume (emulsion) treatments with boom-and-nozzle equipment. The results were assessed, by measuring the amount of DDT deposited on filter papers and on the leaves of the crop and by estimating pest mortality from counts made immediately before and 48 hours after spraying.A direct comparison of very-low- and normal-volume treatments under identical conditions was not possible, but it was established that under similar conditions the proportion of DDT emitted that was deposited at crop level (percentage recovery) was much the same for the two methods, varying between 41 and 62 per cent, according to conditions. The lower leaves of a fairly young crop of an open variety received about 60 per cent, of the deposit on the upper leaves, but in a mature crop of a tall dense variety this percentage fell to 35.Standard commercial practice, with the aircraft flying very close to the crop, gave a recovery of about 55 per cent, in moderately good conditions but with a variation in deposit density across the swath of over 7:1. An identical application from 10 ft. above crop, as in our method gave in rather better conditions a recovery of 62 per cent., with the deposit-density variation reduced to 2:1. This performance was much the same as that achieved by the type of emulsion application used in the other experiments described.In similar conditions, both very-low and normal-volume treatments gave very similar mortalities of Heliothis. Acanthomia was present in only one experiment and was less readily controlled; it required deposits at crop level of about 0·4 lb./acre to give satisfactory mortality, whereas in the same experiment 0·25 lb./acre gave 96 per cent, mortality in a relatively young Heliothis population containing only 10 per cent, of sixth-instar larvae.Older Heliothis larvae required higher dosages, 0·4 lb./acre at crop level killing only 53 per cent, of a population containing 62 per cent, of sixth-instar larvae. It was shown that there is a regular decrease in the kill inflicted by a given dosage on the successively later instars (from 92 per cent, of the third to 66 per cent, of the sixth) with a recorded deposit of 0·63 lb. DDT per acre.Except in the first experiment, mortalities were much below those claimed for commercial treatments, even at lower rates of DDT per acre. The reasons for this are discussed, together with the advantages to be expected from a change to the very-low-volume technique with solutions.

An effective method of tsetse eradication has been demonstrated on a practical scale in country infested with Glossina morsitans morsitans Westw. in the Western Province of Zambia. An area of slightly over 600 miles2 (1 600 km2) was sprayed from aircraft five times, at approximately three-week intervals, with endosulfan in oil solution at an average of 8·2 gal/mile2 (14·4 litre/km2), so that the area dosage of active ingredient was 17 lb/mile2 (3 kg/km2) per application or approximately 2 oz/acre (0·15 kg/ha) for the whole operation. The insecticide was dispensed as an aerosol (most droplets of 20 μm diameter) made by injecting the spray liquid into the extended exhausts of the aeromotors. Post-spray fly-rounds showed that tsetse eradication was apparently achieved except near an unsatisfactory isolation barrier. The total cost was about K300/mile2 (£175 sterling).

An economical method of tsetse control aimed at reducing fly numbers to a low level prior to human settlement was tried in northern Tanganyika in 1964–65 in an area containing Glossina morsitans Westw., G. swynnertoni Aust. and small numbers of G. pallidipes Aust. The major central part of the infested area, about 7½ square miles, was sprayed four times at three-weekly intervals with endosulfan from an aircraft, and the remaining peripheral parts were sprayed from the ground. In the aerial applications, the volume of spray averaged 0·0121 gal./acre per application and the amount of endosulfan averaged 0·0242 Ib./acre (a total of about 1 Ib. per 10 acres for the whole operation). The results indicated that the tsetse population was probably eradicated in the part sprayed from the air. Though the ground spraying of the surrounding parts was not completely satisfactory, the tsetse population in the whole area a year later was only about ten per cent, of its original level. The cost of the air-spraying was £88 per sq. mile.