1. A series of exploratory experiments on the relationship between temperature and toxicity of DDT films to adults of Tribolium castaneum, and larvae of Plutella maculipennis, are described. The main conclusions with T. castaneum are:—

(a) When the insects are continuously kept on the film at different temperatures there is a higher kill at higher temperatures.

(b) When the insects are exposed to the film for about 24 hours at the same temperature and then kept away from it at different temperatures there is a higher kill at the lower temperature.

(c) When the insects are kept on the film at different temperatures for about 24 hours and then kept away from the film for reaction at the same temperature, there is a higher kill in those kept on the film at the higher temperature.

(a) and (b) above apply equally to larvae of P. maculipennis but (c) is reversed. The probable cause of this reversal appears to be the observed fact that at higher temperatures these larvae cover the film with much more silk thread and thus avoid contact to a greater extent than at lower temperatures.

2. A review of literature, in the light of the conclusions arrived at, indicate that many of the observations made upon the temperature-toxicity relationship can be accounted for by the following generalisations:—

(a) Insect resistance to poisons changes with temperature as do its other vital activities, increasing up to a critical degree and afterwards declining.

(b) The amount of poison reaching the site of action in unit time also varies with the temperature, generally but not always, increasing with its rise. Insect activity, especially locomotor and respiratory, may play an important part in these effects.

(c) The apparent effects of temperature on insecticidal action is the combination of these two factors, namely, resistance and pick-up.

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”.

Railway trains running through tsetse-infested country between Mombasa and Nairobi in Kenya Colony carry G. longipennis, G. pcdlidipes and G. brevipalpis on to stock-farming areas beyond the natural limit of the fly belt, thus being largely responsible for outbreaks of animal trypanosomiasis and a reluctance on the part of European, Asian and African settlers to develop the land, affected by this form of fly dispersal, to its full capacity.

The country through which the trains travel is described together with an account of a survey of the fly distribution.

Tabulated figures are given of the monthly totals of tsetses collected from passenger and goods trains by teams of fly boys posted at Emali and Sultan Hamud railway stations about 17 and 25 miles respectively outside the fly belt towards Nairobi More than 24,000 flies were collected over a period of one year and many, not collected by the de-flying teams, were carried up-country even as far as Nairobi, 101 miles from the fly belt.

Tsetses were collected from inside passenger trains, but very much larger numberswere taken from the outer surfaces and undercarriages of goods trucks.

Reference is also made to the rôle of motor traffic, especially when in convoy in the dispersal of tsetses.

The incidence of animal trypanosomiasis along the line of the railway is dealt with and the association of the disease with tsetses carried by trains is supported by results of laboratory experiments on the transmissibility of Trypanosoma congolense, T. vivax and T. brucei by the three species of flies concerned.

Bush-clearing on stock farms outside the fly belt will not protect the cattle from infection carried by flies brought by trains but bush-clearing in specified localities of fly concentration in the infested country is recommended as a measure to reduce the numbers now attracted to trains. It is considered that the spraying of trains will bring considerable relief to farmers ; but, so far, no suitable spraying apparatus has been devised nor has a reasonably cheap insecticide been found for this purpose.

A new method of determining the duration of the aquatic stages of Anophelines in nature is described. Repeated daily dippings of a stretch of stream were made, and the numbers of pupae and of larvae of each instar were recorded. The duration of the aquatic stages was then determined by analysis of the sequences of peaks in these numbers.

The duration of larval life of A. minimus, when living in a stream at an average daily range of water temperature between 26·5°C. and 30·6°C, was seven days.

The full life cycle of A. minimus, under monsoon conditions in Assam, probably occupied 14 days—egg 2 days, larva 7 days, pupa 2 days, adult to first egg-laying 3 days.

The effect of aerially sprayed 5 per cent. DDT solution against Anopheline larvae and adults has been investigated.

An account is given of a rapid field method for estimating the concentration in milligrammes per square metre.

At a concentration of 2–3 mg. per square metre, aerially sprayed DDT solution had little effect on Anopheline larvae breeding in water completely covered with a species of Limnanthemum. Also at this concentration tall grass gave partial protection, whereas in open water there was a complete kill.

The residual effect of DDT at a concentration of 2–3 mg. per square metre did not last longer than six days.

Under negligible wind conditions, resulting in a vertically falling spray, there was no penetration into huts even when situated in the open.

Drastic filtration of the spray resulted in a fall in the concentration from 2 to 3 mg. per square metre in the open to less than ·05 mg. per square metre under heavy shade, consequently shrubs at ground level in heavy wooded areas were greatly protected from contamination with DDT and afforded practically safe resting places for adults.

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 quantitative survey of Wheat Bulb Fly (Leptohylemyia coarctata) was made in Yorkshire in 1945, and the distribution of the fly is discussed in relation to general observations and records in the years 1935–1946. The distribution is shown in themap (fig. 2).

One hundred and thirty-six fields on 86 farms were examined and Wheat Bulb Fly was present in over half of the farms and fields; in 8 fields (6 per cent.) it was present in moderately high numbers, and in 2 fields (1·5 per cent.) it was present in numbers sufficiently high to be likely to cause a failure in a bad wheat year. It was estimated that two or three thousand acres of wheat and rye in Yorkshire are likely to have a reduced crop as a result of Wheat Bulb Fly attack in an unfavourable season. Over half the dangerous area is near Selby. The only large area where Wheat Bulb Fly was virtually absent was the Yorkshire wolds.

The depth and habits of pupation, shown by the three main species of sheep blowflies (Lucilia sericata, Chrysomyia chloropyga, and C. albiceps) are discussed in relation to parasitism by the Pteromalid, Mormoniella vitripennis.

Experimental series showed that the majority of Lucilia larvae pupate in situations which are inaccessible to the parasite, a result which agrees with field observations; whereas the two species of Chrysomyia have a large proportion of their pupal populations exposed freely to attack by the parasite. The degree of protection thus sought by the larvae appears to be directly proportional to the suitability of the puparia of the species as hosts for the parasite.

Because of this difference in pupation habits, a large proportion of the Lucilia population which survives the competition for food and the predatory attacks of C. albiceps on the carrion will produce adult flies; whereas the more exposed C. albiceps and C. chloropyga populations will be further reduced and in a proportionate manner by parasitism. This explanation is put forward as one of the main reasons for the comparative success shown by field populations of Lucilia and the unexpectedly small field populations observed in the case of C. albiceps.

It is pointed out that this phenomenon is a disadvantage where natural control of the primary flies is concerned since C. albiceps is an important controlling factor in larval populations of Lucilia.

The objects of the investigation were to describe the process of maturation of the ovaries, to clear up the question of the relation between copulation and sexual maturity, and to determine whether any relation exists between weight and sexual maturity.

The locusts used were of the transiens phase. They were kept at temperatures between 32°C. and 37°C. and relative humidities between 50 per cent, and 70 per cent.

The maturation of the ovaries was followed, and is divided into four stages distinguished chiefly by the sizes of the eggs.

It is shown that the average number of ovarioles per female does not change significantly with age.

The numbers of ovarioles in the two ovaries of an individual often shows asymmetry, which probably increases with age.

Some of the ovarioles are small. The percentage small ovarioles increases with development of the eggs. Variation between individuals in the total number of ovarioles also increases with age.

The number of egg rudiments per ovariole was calculated for different ages and stages. The differences were not significant. It is concluded that new rudiments are produced during the oviposition period.

It was found that when the food supply was relatively short, female locusts became mature and oviposited if allowed to pair, but did not mature if males were not present. With abundant food, unmated females matured, but more slowly than mated ones and fecundity was reduced. It is concluded that under unfavourable conditions pairing may be necessary for maturation of the ovaries.

Average weights of female locusts in each of the four stages were compared. Locusts in stages III and IV, i.e., those which are mature, were found to be significantly heavier than those in stages I and II. The average weight of a number of stage I locusts 13–18 days old (whose development had been retarded by unsuitable conditions) was also found to be significantly less than that of a number of stage III locusts of the same age. It is concluded that weight depends primarily on the development of the ovaries.

The relation between weight and age was investigated. Rate of increase of weight is rapid at first, is reduced for about two days, then increases again and maintains its value until the weight is about 2 gms. During the oviposition period it fluctuates irregularly.

It is shown that if conditions are unfavourable to maturation the weight rises to a certain value, after which it remains constant, or falls. The fall was best seen in stage II locusts over 14 days old.

There is little relation between weight and egg-size in stages I and II, but in stages III and IV the relation is closer. Rate of increase of weight with egg-size is at first low, but above an egg-length of about 4·5 mm. the rate of increase of weight becomes greater. It is suggested that this is because early growth of the eggs is due to transference of fat from the fat body and later stages to the laying down in the eggs of substances derived directly from the food.

Estimates were made of water and fat content of locusts of various ages. Percentage water falls rather rapidly in the first few days of adult life after which it remains approximately constant. Percentage fat rises to a maximum at about 14 days, then falls slowly. Most of the increase in weight during maturation is due to water intake.

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.

Experiments were carried out during 1945 and 1946 to determine the effect of insecticides, particularly DDT and BHC, on certain species of Syrphids and Coccinellids. In addition, some preliminary data was obtained on toxicity to parasitic Hymenoptera and a predatory Cecidomyiid species.

In some experiments other insecticides were used for comparative purposes and where possible data were obtained on the effect of the insecticide not only on the predator but also on the host and the host-predator relationship.

The present paper is the second of two dealing with field studies carried out near Lagos, Nigeria. The first paper covered four of the most abundant species encountered and the second is concerned with the remaining forty-eight. These are listed and the data relating to the thirty-eight least abundant, with the exception of two which were taken as males only, are given in tabular form. The other ten are dealt with at greater length. Males of twenty-six species were taken and in the case of three of these species they were so abundant as to create the impression that a swarming activity was involved. In the case of the ten more abundant species seasonal distribution curves are given based on average monthly catches and an attempt is made to relate these to variations in rainfall. The biting curves which are next discussed show a greater variety of types than those described in the first paper. In general, they are characterised by a fairly sharp peak associated with morning or evening twilight, but some have a more or less pronounced peak at both ends of the cycle and so correspond to the “eo-crepuscular” type of Haddow (1945). Anopheles paludis, like Taeniorhynchus africanus (described in the first paper) has an ill-defined period of maximum activity during the middle of the night. The necessity of sub-dividing the figures in order to obtain a picture of the vertical distribution of the various species led in one or two cases to anomalous results, but in general a clear and fairly convincing picture was obtained. None of the species dealt with in the present paper was sufficiently abundant to afford reliable data on hourly variations in vertical distribution. In the general discussion, which embodies such inferences as it has seemed permissible to draw from the data, attention is drawn to the fact that the so-called “biting cycle” does not, in all likelihood, depend exclusively on variations in the urge to bite, but is more probably an expression of cyclical changes taking place in the general level of activity of the mosquito. The possible relationship of such changes to changes of a similar kind in the physical environment is discussed, and it is pointed out that intrinsic rhythms in the mosquito, perhaps related to the breeding cycle, may also be involved. Some data are presented which, while partly explained by the presence of a sibling species, may also indicate an interrelationship between the breeding cycle and vertical distribution.

This paper is concerned firstly with the standardisation of a technique for the estimation of the speed of action of insecticidal sprays and deposits on adult houseflies (Musca domestica), as indicated by their speed of knock down, and secondly with the application of this technique to the assessment of the biological efficiency of insecticidal solutions. The main conclusions are:—

The speeds of action of both sprays and deposits are greatly affected by the duration and intensity of illumination to which the flies have been exposed before treatment and by the ratio of the sexes in the treated population. The first factor was eliminated by conditioning the flies to an intensity of illumination of 20 foot-candles overnight, i.e. at least 17 hours, and the second was minimised by estimating the median knock down time for 50c per cent. instead of 50 per cent, where 50c=0·67x+0·y, and x and y represent the percentages of males and females respectively in the treated population. This relationship appeared to be independent of the technique as it was the same for 0·05 per cent. gammexane in petroleum distillate used as a fly spray and for deposits of pure p.p. DDT put down from petroleum distillate. The experimental evidence, on which this correction is founded, is set out in full.

It was found that there was a separate straight line relationship between the percentage knock down in terms of probits and the time after spraying (or the time of exposure) in minutes for male and female M. domestica. It follows therefore that such a relationship is not true for a population of mixed sexes. The method of calculating the corrected median knock down time (K.D.50c) is detailed.

The speed of knock down of solutions of pyrethrins, the gamma isomer of BHC and the para para isomer of DDT were proportional to the concentration of the insecticide in the solution. This conclusion has been applied to the estimation of gammexane in solutions of unknown strength and examples are given in which the calculated and actual values are compared and some conception is obtained of the accuracy of the method.

Experiments with DDT deposits on aluminium plates showed that:—

(a) The speed of action was independent of the deposit providing that this was above 2 mg. p.p. DDT/sq. ft. Although when the deposit was applied to paper-covered panels the speed of action varied with the magnitude of the deposit.

(b) A deposit of p.p. DDT from a solution of pure (100 per cent.) p.p. DDT acted more quickly than an equal p.p. DDT deposit from a solution of technical (80 per cent.) p.p. DDT.

(c) The action of a deposit was more rapid when the deposit was in a form which could act both as a stomach and contact poison and hence the ball milled technical DDT applied as a suspension acted more quickly than an equivalent deposit of technical DDT from petroleum distillate because the crystals of the latter were too tightly adherent to the panel for the flies to ingest them.

The significance of these results is discussed under the appropriate section.

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.

A review of the work carried out on mercury as a preservative against stored grain pests is given.

The influence of the duration of exposure to mercury vapour upon eggs of different stages of development is discussed.

Temperature and humidity within ordinary limits do not affect the efficiency of mercury.

Under airtight conditions this preservative is effective within a radius of three feet in receptables with or without grain.

Paper strips coated with mercury cannot be recommended for grain stored in bags and kept in piles because pressure and weight of the grain, or even shaking, will cause the mercury to be expelled from the strips.

Mercury dispersed in chalk cannot be used for grain destined for consumption. It is, however, quite suitable for preserving grain for seed.

Plastering the walls with mercury paste or afflxing slabs to the walls of godowns is not effective owing to the limited range of mercury vapour.

Application of mercury in various types of receptacles is discussed and advocated. Fumigation with mercury does not seem to be practicable.

Galuzo (1941) in his ecological studies of the tick fauna in Kazakh S.S.R. states that the nymph of Hyalomma detritum, Schulze, overwinters on the host, that he is of the opinion that H. savignyi, Gerv., hibernates in the adult stage away from the host (in animal quarters or houses) and that he found hibernating nymphs of H. marginatum, Koch, in grass meadows.

In the course of field work carried out in Palestine during the winter 1945–16 only a few adult male and female ticks (some gorged) were found in the Jordan Valley and the Negeb, and none in the more temperate parts of the country.

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.

Experiments on the effect of changes in relative humidity on the toxicity of DDT- and DNC-films to adults of Tribolium castaneum and larvae of Plutella maculipennis are described. With T. castaneum adults the toxicity of both DDT and DNC films is increased at higher relative humidities, but with larvae of P. maculipennis the toxicity of DDT films decreases while that of DNC films increases at higher humidities. Like these experiments the perusal of the literature does not help in deducing any general principle. However, it is possible to collect instances showing that besides the insect and the insecticide, there may be various factors like the range of humidity tested, the strength of the insecticide used, the stage of the insect, etc., which can affect the result of humidity changes.