Formulations of DDT have been applied to standard mud blocks. Toxicities to Glossina palpalis and Aëdes aegypti, and the proportions of insecticide recovered from an outer layer of approximately 0·1 mms. thickness have been compared.

Absorption of DDT in oil solutions was considerable, and amounts recovered from the outer layer were only from 8–19 per cent, of the total dosage applied. Adsorption of the insecticide from the oil on to mud occurred. There was some correlation between the capillary rise of the solvent and the extent of absorption. Toxicities of the blocks to test insects were low.

Using concentrations of 2 per cent., 5 per cent, and 10 per cent. in power kerosene, there was no increase in the proportion held on the surface. Application of excessively heavy dosages increased the amounts in the outer layers but there was a trend towards greater absorption, and therefore to greater waste, at the high dosages. Repeated applications similarly built up a larger dosage in the outer layer but did not increase the proportion there.

Emulsions were intermediate between solutions and wettable powders as regards absorption and toxicity.

Up to 77 per cent, of the insecticides applied as wettable powders was recovered from the outer layer, and toxicities were correspondingly high. When benzene hexachloride wettable powder was used there was rapid loss of benzene hexachloride from the surface by volatilisation. After fifteen days the dosage had decreased considerably and the percentage in the outer layer had fallen from over 70 per cent, to 20 per cent.

Loss of DDT by penetration of the carrier oil through the leaf cuticle may occur when an oil solution is sprayed on to vegetation. The extent of penetration varies with different plants.

There is an indication that small amounts of DDT are transferred from the inside of treated leaves to other untreated parts of young coffee and Avocado pear plants.

Deposits of DDT on leaves exposed to ordinary climatic conditions remained toxic to tsetse flies for a longer period when applied as an emulsion than as an oil solution. Deposits from a water suspension of a wettable powder were washed off readily by rain.

There is some evidence that continuous exposure to sunlight produced some chemical change in, and reduced the toxicity of, DDT deposits applied to glass plates as a solution in kerosene.

A small reclamation experiment staged in the coral rag thicket under unfavourable conditions proved successful in eradicating Glossina austeni and G. brevipalpis and in virtually eradicating G. pallidipes. Applied with adequate protective clearings, it is thought that the method may prove entirely successful in eradicating G. pallidipes as well as G. austeni and G. brevipalpis.

Under both dry and wet season conditions traps proved quite ineffective.

Green (in Stebbing, 1902) described a species collected by Stebbing at Dehra Dun in 1899 as Monophlebus stebbingi. The principal diagnostic character of this species was the presence of six fleshy tassels at the caudal extremity of the male (fig. 1, a). Green (in Stebbing, 1903) proposed the name Monophlebus stebbingi var. mangiferae for a form found on mango in the Shalimar Gardens near Lahore in which the adult male carried eight fleshy caudal tassels. Later (1908) he described material from the Shalimar Gardens on mango as Monophlebus stebbingi var. octocaudata.

The great increase, in recent years, in the number of contact insecticides has created a demand for methods whereby the content of active substance in samples of these insecticides may be estimated quantitatively in a simple manner. Such methods are important, because on the one hand the producer wishes to know if his product meets the necessary requirements and on the other hand the official services concerned with the control of insect pests must be able to test the fundamental value of commercial preparations. Moreover quantitative methods for the estimation of contact insecticides are useful for scientific research in this field.

The term “Bush Locust” is defined.

The synonymy and known distribution of Phymateus aegrotus are given and previously published records of its occurrence are reviewed.

The occurrence of hopper-bands, and of adults, in East Africa for the years 1938–47, inclusive, is outlined.

P. aegrotus and other species of the genus are normally unimportant economically as adults, but the hoppers form bands after the manner of, though on a much smaller scale than, true locusts. Outbreaks of these hopper-bands appear to be sporadic but they are sometimes destructive to crops.

P. aegrotus has usually been of only local importance as an agricultural pest but areas in which the crops have been damaged are noted. Among wild host-plants there appears to be a preference for Euphorbiaceae although the hoppers are more or less polyphagous.

Other East African species which form hopper-bands and which are known to attack crops are mentioned.

The life-history of P. aegrotus is described so far as it is known, and observations made by Dr. H. B. N. Hynes on the closely related species, P. pulcherrimus, in Ethiopia are also recorded.

Reflex actions in Phymateus species, including such phenomena as autohaemorrhage and colour display by the adults when alarmed, are noted and the literature on the subject is reviewed.

Observations are made on hopper behaviour and band-size of P. aegrotus. The latter is usually only a square yard or two in extent but bands up to 25 square yards in area have been observed by the author and there are reports of even larger ones. These bands are very dense both when marching and when stationary (60–80 finalinstar hoppers per square foot). Notes on areas of infestation are also given.

In most cases it is sufficient to beat out the bands with branches. Poison bait and dusting with 7 per cent, di-nitro-ortho-cresol are also successful.

Detailed descriptions of the coloration of final-instar hoppers of P. aegrotus and the other East African Phymateus species discussed are given. Keys for the identification of these hoppers and of the adults of the four species, P. aegrotus (Gerst.), P. pulcherrimus I. Bol., P. viridipes Stål and P. purpurascens Karsch (for all of which standardised English names are proposed), are also included.

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 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.

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.

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.

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.