This paper deals with Glossina pallidipes, G. austeni and G. brevipalpis as they occur on the Kenya coast.

Temperature and saturation deficiency both exert a generally inverse effect on the activity and apparent density of both G. pallidipes and G. austeni. True density also varies inversely as the s.d.

The persistent toxicity of films of pyrethrum in P31 oil may endure on suitable surfaces under warehouse conditions for much longer periods than hitherto supposed, but unexplained fluctuations in toxicity may occur.

Within the range 0·8 per cent. to 1·3 per cent. total pyrethrins, the pyrethrum content appears to be only a minor factor in determining the persistent toxicity of such films.

The nature of the surface sprayed is of great importance in determining the persistent toxicity of pyrethrum films in P31 oil, which is negligible on concrete and increases steadily through the following list of surfaces—brick, heavy hessian, light hessian, jute, cotton, and wood; the last-mentioned two being particularly good substrates.

Residual deposits of DDT or “ Gammexane ” derived from kerosene sprays are of little use on concrete, but appear otherwise little affected by the nature of the surface treated; they give a uniform degree of persistent toxicity on the various surfaces listed.

Oryctes rhinoceros, L., the Asiatic Rhinoceros beetle, was accidentally introduced into Western Samoa, apparently with rubber plants from Ceylon, sometime prior to September 1910. The results were disastrous to the coconut industry, and caused grave anxiety to coconut planters in the adjoining groups.

The present paper is the first of two dealing with the seasonal distribution, hourly variation in biting activity, and vertical distribution of certain Southern Nigerian mosquitos. The technique employed in the studies under discussion resembled that used by Haddow (1947) in Uganda. Human bait was used in both cases and the agreement between the results obtained in the two localities is felt to be such as fully to justify the employment of such methods. Over fifty species of mosquitos were taken in all and fourteen of these proved to be sufficiently abundant to yield significant figures. Four of these are discussed and the remainder will be dealt with in the second paper.

The most remarkable feature of the seasonal distribution was the very restricted period during which Anopheles gambiae was present in any abundance. This species occurred in large numbers only during the heavy rains of June and July and, to a less extent, in association with the small rains of September–October. During the dry season it almost disappeared. Aëedes africanus showed a similar distribution to that of gambiae but Taeniorhynchus africanus and Anopheles hargreavesi were most numerous during the dry season. It is suggested that in the area under consideration the latter species may well be a more important malaria vector than gambiae owing to its greater abundance and more uniform seasonal distribution.

Experimental results indicated that the mortality rate of Anophelines depends on the time of exposure. No evidence of differential reaction between the various stages of larvae was found.

Definite and positive evidence of the action of DDT on mosquito pupae was obtained.

Laboratory trials indicated that mortality of adult Anophelines following contact with DDT is relatively slow, and the period of exposure required for a lethal dose is approximately 15 minutes.

Adult flies required a much shorter period of exposure, viz., 30 secs., and the rate of mortality was higher.

Evidence of the mechanical transference of DDT by flies is also presented.