Experiments are described in which the concentration-time-mortality relationships with certain insects were investigated for the insecticides DDT and γ-BHC, the insecticides being used in film form. Adults of Tribolium castaneum, the larvae of Plutella maculipennis and adults of the Aphid, Macrosiphoniella sanborni, were used as test insects. T. castaneum proved the most suitable insect for experimental laboratory work on films, since it can be kept in continuous contact with them without difficulty.

A description is given of the techniques employed for T. castaneum and also for the other insects which are able to progress on perpendicular glass surfaces. Techniques are described for experiments in which attempts were made to eliminate as far as possible the fumigation effect of γ-BHC and to differentiate it from that of direct contact. The fumigation effect of this compound is considerable and it appears impossible to eliminate it entirely.

With T. castaneum the characteristic curves connecting log. concentration with percentage mortality varies with time of exposure, from horizontal lines showing on the one hand zero toxicity and, on the other, complete mortality at all concentrations. Sigmoid curves are represented between these limits. The average survival period of T. castaneum adults gradually decreases with the strength of poison in the film.

The surface upon which toxic films are deposited was shown in preliminary experiments to have a definite bearing upon their effectiveness. Waxed surfaces showed least toxicity, and amongst a few leaves used Geum gave the highest and water lily, at lower critical concentrations, the least effect. High concentrations on water lily were little different from others in toxic action.

The room used for housing a colony of Anopheles punctulatus punctulatus is described. Its main features were an insulation system to enable some degree of temperature control during the winter months, and eight windows to ensure that the room had good natural lighting.

The adults were kept in breeding cages, which were large enough to allow the insects to manoeuvre during mating and oviposition, and designed to ensure a high humidity and at the same time expose the adults to daily fluctuations in light intensity. Provision was made for easy access to the interior during feeding and management operations.

The essential feature of larval management was that the larvae were kept throughout their development as separate batches, representing daily age groups. During the first three days after hatching they were left in the dishes containing soil and water in which the eggs were laid. From the third day, they were reared in shallow glass dishes. They were fed with Farex at intervals throughout the day.

Glossina pallidipes does not readily attack objects moving along the edge of vegetation forming its habitat; fewer tsetse attack under humid than Under dry conditions, but those that do seem to range further.

Parties of men moving out of heavily infested thicket did not carry tsetse far into the open. Few tsetses attached themselves to the men and these became gorged within a few yards of the thicket edge. Similar results were obtained when bait cattle were used.

Experimental catches in a glade showed, even during the humid season, an extraordinary reluctance on the part of G. pallidipes to approach a party moving through the glade even at so short a distance as 8 yards from the thicket, but further experiments showed that a party staying in the glade for a short time made a much larger catch.

The following is a description of a mosquito found to occur in the hills surrounding Tambunan Plain, North Borneo, whilst working with the Malaria Research Department, in 1939–42. It appears to represent a new variety of the Anopheles aitkeni type, which it is proposed to name Anopheles aitkeni borneensis.

Tambunan is an elevated and isolated plain in the interior of North Borneo, occupied by irrigated paddy cultivation, surrounded by jungle-covered hills, and inhabited by a primitive native population subject to severe malaria.

The Malaria Research Department of North Borneo carried out surveys in this locality during 1939–42 for larval and adult Anopheles as part of an investigation into the causes and control of malaria in Borneo. The main findings of this work, and the incrimination of A. leucosphyrus, Dön., as a vector of malaria, have been described elsewhere (McArthur 1947), but brief accounts are given below of the habits and characteristics of the Anopheles in the locality.

In 1923, under the name Oscinis pallipes, C. G. Lamb described a tiny black fly from Khartoum, Sudan. In the accompanying notes by Cottam (1923), this fly was said to swarm in immense numbers on ceilings and upper parts of rooms and verandahs in September to December. The swarms were said to be larger than those frequently recorded in Europe for “Chloropisca circumdata Meigen” which is now known as Thaumatomyia notata (Meigen). While it is not primarily an eye gnat, as are the Hippelates flies in the Americas, Cottam noted that the flies “are attracted to artificial light at night, and constitute a nuisance by swarming round lamps or on dinner tables and getting into people's eyes”.

The three species of Laemophloeus commonly associated with stored products have been shown, by a survey of recorded information, to be cosmopolitan and to occur on a large variety of foodstuffs.

The egg, four larval instars and pupa of L. minutus have been described briefly and the life-history outlined.

Mated females of Laemophloeus minutus lay eggs continuously throughout their long life at the rate of about 0·5 eggs per day at 17°C. rising to 4·0 eggs per day at 30°C. Humidity changes over the range 55–90 per cent. R.H. have little effect on the rate of oviposition. Oviposition is stimulated by the constant presence of the male.

A short account of the life-cycle and symptoms of damage of the cotton Jassid, Empoasca lybica, de Berg., is given. In the initial cage experiments it is shown that DDT emulsion was superior to the copper compounds used. Experiments on the residual toxicity of DDT and “Gammexane” sprays are described. Tests with DDT emulsion showed that very young cotton is injured by emulsion containing as little as 0·025 per cent. DDT, but that emulsions containing up to 0·5 per cent. DDT can be used with safety on plants which are two months old. A coarse DDT suspension caused severe leaf distortion, but a fine suspension used later was quite safe at the concentration used.

The parasites and predators found attacking the Aphids, Myzus persicae, Macrosiphum solanifolii and Aulacorthum solani, during field survey work of potato Aphids in the Northern Agricultural Advisory Province during 1944 and 1945, are treated individually, receiving the proportionate attention which their occurrence merits.

Aphidius avenae was the most important primary parasite, and in potato seed growing areas, the only one; while Asaphes vulgaris in particular, augmented by Lygocerus testaceimanus composed the majority of hyperparasites. The effect and relative importance of both types of parasite upon the Aphid populations of the survey are discussed with their percentage figures.

Predacious Syrphids included Platychirus manicatus and P. immarginatus whose life-histories were previously unknown; feeding records are also given for these two, and the former species accompanied invariably by P. scufatus occurred regularly on potatoes. More unusually, but often more effectively, Syrphus balteatus appeared. Other species were found.

An experiment to ascertain whether extermination of Glossina pallidipes could be brought about by introducing large numbers of DDT-treated oxen into its habitat was carried out in a small isolated block of bush in Tanganyika.

The oxen were sprayed with a solution of 9 per cent, w/v pure DDT and 9 per cent, w/v resin in groundnut oil. It was estimated that when sprayed once weekly about 70 per cent, of tsetse settling on them were killed, and when sprayed twice weekly, about 95 per cent. Oxen so treated were introduced in a numerical superiority of about 6 to 1 over the larger game in the bush, but were fewer than the small game.

After 3 months in which oxen sprayed once weekly were herded in tens in the bush for ten hours each day, the population of female tsetses was reduced by about 70 per cent. After a further 2 months in which oxen sprayed twice weekly were herded in fives a reduction of 80 per cent, amongst the survivors was brought about.

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.

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.