The earliest reference to the occurrence of Helopeltis in Ceylon was made by the French entomologist, Signoret (1858), when he described Helopeltis antonii, the so-called “Mosquito Blight”. Helopeltis attacking cacao in Ceylon was first recorded in the year 1880 or 1881 in the Matale district (Green, 1901), the damage to the young leaves and stems having attracted the attention of cacao planters. Populations of Helopeltis occurring on cacao today, however, favour the pods, damage to young leaves and stems being relatively rare and generally associated with poor shade over the cacao plant. This apparent change of feeding habits prompted a careful and critical examination of the existing species of Helopeltis in Ceylon. Extensive collections of Helopeltis from the major cacao-growing areas in the island, including the Matale district, have not provided any specimens referable to Helopeltis antonii. The new species described below was the only species of Helopeltis found on cacao at Teldeniya, Kundasale and in the Matale district, which may be regarded as representative of the major cacao-growing areas of Ceylon.

An instrument is described that will brighten and dim a light source and control its “on” and “off” timing.

The periods of brightening and dimming and the period of full illumination are both adjustable.

The instrument is being used successfully for studying the effects of changing light intensity and photoperiod on the activity and development of insects.

Sixteen varieties of Rubus, comprising four species, were tested with the Aphid, Amphorophora rubi (Kalt.), which is a vector of virus diseases of Rubus in Europe and N. America, to establish the range of resistance to the development of populations of the insect. The phenomenon of resistance was then further investigated from the aspect of fecundity, reproductive rate, length of life, growth rate and behaviour of the Aphid. In these latter investigations only four varieties of raspberry were employed. The varieties Malling Promise and Lloyd George showed no resistance. Malling Landmark proved to be highly resistant but showed a slight reduction in resistance in the autumn. Newburgh appeared to occupy an intermediate position between Malling Landmark and the other two varieties. There were indications, however, that under field conditions its degree of aphid resistance may be greater than was observed under experimental conditions. Resistance seems to involve a slowing down of the reproductive rate, a shortening of the length of life of adults and prevention of development of the nymphs. The practicability of using aphid-resistant varieties of raspberry to minimise virus spread is discussed.

Ephialtes brevicornis (Grav.) has been found to parasitise the prepupal stage of Plutella maculipennis (Curt.) under laboratory conditions.

A general description of the life-cycle of E. brevicornis on P. maculipennis is given and it is found to occupy 16 days from egg to adult at 20°C. and a R.H. of 60 per cent. Comparative descriptions are given of the five larval instars. The egg is also described.

The method of measuring relative humidity by matching the colours of tissue paper impregnated with cobalt thiocyanate has now been made more convenient by the commercial production of impregnated paper and coloured glass standards.

Although the method as used straightforwardly is not at all precise, it is especially useful for the measurement of humidity in small or relatively inaccessible spaces, e.g., cracks in floors, air spaces in stored grain, under bark, or inside small tubes, etc., and for general use when elaborate equipment cannot be employed.

A piece of the paper is exposed to the humidity to be measured, preferably for two hours, then mounted on white opal glass in oil (liquid paraffin) and matched, in a simple comparator, against the coloured glass standards. When matching is done at a temperature other than 20°C., corrections are required as tabulated.

Tables of error are given, showing the range of variation from different causes, with estimates of 95 per cent, confidence limits. To cover all the sources of variation normally affecting the measurements under various conditions, limits up to ±5 are allowed for relative humidities down to 70 per cent.; these limits increase at lower humidities to a maximum of ±15, about 30 per cent. Various ways of avoiding errors are described, and it is shown that if special precautions are taken the method can be used with considerable accuracy, particularly at relative humidities above 65 per cent.

The possibility of controlling the human body louse, Pediculus humanus humanus L., through the development of clothing which is inimical to it on physical rather than chemical grounds was investigated. Claw size in lice was shown to be related to diameter of host hair. The grip force of lice on fabrics made of fibres of various diameters and compositions, some spun and some unspun, and of various weaves largely dictated by availability, was measured with an apparatus of which the essential parts were a torsion balance and a kymograph motor. The force was found to be a maximum at fibre-diameters approximating that of human hair. The ability of lice to grab hold of a fabric when dropped on to an inclined surface of it was also measured and found to vary with fibre-diameter in a similar manner to grip, but less strongly. The number of eggs laid on fabrics when no choice was offered was also found to vary with fibre-diameter in a similar manner. While this physical method of louse control is not promising for immediate practical application, it has possibilities which may be enhanced by developments in textile technology.

Reactions of 3-day-old first- and fourth-instar hoppers of Schistocerca gregaria (Forsk.) of phase gregaria, to three physical factors, namely to relative humidity, temperature and light have been studied in an alternative chamber apparatus designed to give an enclosed space with gradients of humidity. The responses to each factor independent of the others, and to the interactions of these factors, were considered.

It was found that both the first- and the fourth-instar hoppers respond strongly to humidity. They are agitated by low, and even more by very high, humidities, but become more quiescent within a zone of 60–70 per cent. R.H., where they spend more time. Within this zone they hop and turn less and this decrease in activity appears to be a response which is independent of both temperature and of light intensity. This zone of decreased agitation has been called “the zone of minimum activity”. However, the speed of walking in contrast to the other types of activity, increased progressively with humidity.

Increase in light intensity raises the level of activity at all humidities, i.e., it increases the duration of activity within the limits of experimental time and the speed of walking. With rise in temperature there is an increase in hopping, in klinokinesis and orthokinesis.

The range of Thyridanthrax abruptus (Lw.), a widespread puparial parasite of Glossina morsitans Westw. in East Africa, is now extended to British West Africa where this species has been found parasitising a Calliphorid fly, Rhyncomyìa pìctìfacìes Big. Puparia of R. pictifacies were collected in the stream-bed sand of dry-season breeding sites of Glossina palpalis (R.-D.) and G. morsitans submorsitans Newst. at the following localities in Northern Nigeria: Gamagira, Zaria Province; Mando Road (25 miles NNW. of Kaduna), Zaria Province; Rahama, Bauchi Province. All were collected during January and February 1957. During February, eight adults of Thyridanthrax emerged from a total of 33 puparia of R. pictifacies found at Rahama.

Females of Simulium ornatum Mg. were found to contain abundant fat-body on emergence from the pupa. Unengorged individuals fed on sucrose solution in the laboratory at 16–18°C. and 22–23°C. showed depletion of the fat-body until little remained after 14 days. Females engorged on cattle in the field and kept in the laboratory at 16–18°C. became gravid in 4–5 days, when virtually no fat-body remained.

A technique for dividing populations of Anopheles gambiae Giles into three age-groups, on the basis of the degree of ovarian development and on the presence of sporozoites in the salivary glands, has previously been described. Using this method, the proportions of the three age-groups amongst females feeding during the three periods into which the night was divided were established for this mosquito in the coastal region of Tanganyika. The feeding activity of newly emerged females followed fairly closely that of older mosquitos, in which entry into experimental huts reached a peak in the period between 2200 and 0200 hr. but remained high from 0200–0530 hr. The younger females were, however, slightly more active in the period before 2200 hr. No difference in fertilisation rate was observed amongst newly emerged females caught in different periods of the night. Infective females were caught in all three periods of the night.

It is not considered that the main features of the biting cycle in A. gambiae can be explained in terms of the differential activity of the age-groups recognised in this paper.

An apparatus for exposing insects to known concentrations of vapours from odorous liquids is described; it was used in a laboratory in England to test adult tsetse flies, Glossina palpalis (R.-D.) and G. morsitans Westw., obtained from Africa as pupae, and the blowfly, Phormia terraenovae R.-D. There is a definite pattern of behaviour of the flies in olfactory stimulants, in the final phase of which they are excited to fly. The number of seconds for which a fly is in flight gives a measure of its activation by the vapour. The method gives results comparable with those obtained with a standard choice-chamber technique and has considerable practical advantages for work with tsetse flies. The effects of concentrations of vapour, period of exposure, condition of the flies and external conditions on the response of tsetse flies to vapours were studied.

The response of G. morsitans and P. terraenovae to a selection of aliphatic acids, alcohols, esters and amines was determined, using a standardised procedure. There is a marked similarity between the two species in the concentrations of vapours required to activate them. The standard molar concentration, defined as the concentration of vapour required to raise the activity of the flies to a standard level of ten times that in pure air, was calculated for each compound tested from the regression of activity on concentration. Threshold concentrations (the highest concentrations that failed to raise fly-activity) were also calculated from the regression equations.

The effects of exhaust gases and distillates of sump oil from old motor cars on the activity of Glossina palpalis (R.-D.) were briefly investigated, using a method described in the preceding paper. The exhaust gases had no effect on the tsetse flies and the threshold and standard concentrations of vapour of distillates from sump oil required to stimulate the tsetse flies decreased as the boiling point of the fractions increased. This result is consistent with the results of experiments by previous workers using series of homologous pure compounds, and suggests that any very stimulating compound could only be present in very small quantities in sump oil.

Four different methods of marking insects are described in detail. Although they have been applied by the present authors only to the British Calliphorinae, they should be of value in ecological studies of mobile arthropods in general. These methods are: individual marking with paints, mass powdering with dyes, radioactive labelling with 32P, and a combination of the last two. A fifth method, in which the emerging fly labels itself with fluorescent dust, is briefly described. The circumstances affecting the choice of method are outlined.

Earlier investigations of the effects of extreme temperatures on different stages of Aëdes aegypti (L.) were supplemented by studies of eggs, larvae and pupae in water, and of eggs and adult females in air at various relative humidities.

Larvae of the same stage, young pupae (defined as those less than half-an-hour old) and old pupae (at least 36 hours old), in groups of 100, 25 and 25, respectively, were kept for various periods at low temperatures in incubators, or, at high temperatures in glass cylinders closed at their lower ends by cloth filters and inserted into water baths, and then transferred to water at 28°C. and the mortality determined from the numbers surviving 24 hr. later (in the case of larvae) or becoming adult (in the case of pupae). Eggs in batches of 1,000 were similarly treated, except that periods of 24 hr. in water at 28°C. with yeast as food added were alternated with 24-hr. periods of drying, and mortality determined on the number that hatched and survived to the third or fourth stage. Adult females (four days old) were exposed in groups of 50 for various periods in jars over appropriate solutions giving a complete range of relative humidities and kept at low, medium and high temperatures. Eggs in batches of 1,000 were subjected to the same treatments. The adults were kept at 28°C. and 60 per cent. R.H. before treatment and for 24 hr. afterwards and mortality then determined. Mortality of eggs was determined after alternate 24-hr. periods of wetting and drying at 28°C., as in the case of eggs treated in water. The results of all the experiments were expressed as the exposure-times required to give 50 per cent. mortality (T50), calculated from the observed data.

The biased nature of the catches of Glossina swynnertoni Aust. made on fly-rounds at Shinyanga, Tanganyika Territory, which show an unduly low proportion of females, nearly all of which are hungry, and lack of knowledge of the fly's habits when inactive, has led to a search for resting flies.

Previous recorded observations on resting tsetse flies are briefly reviewed. These show that the resting sites chosen differ according to species and even within a species. Differences of the second kind probably reflect seasonal changes.

Simuliid larvae and pupae found in phoretic association with the fresh-water crab, Potamonautes niloticus (M.-Edw.) in Kenya rivers far from the haunts of Simulium neavei Roub. gave rise to adults which proved to be S. nyasalandicum De Meillon, a member of the neavei group. Very similar larvae, and pupae that exhibited minor differences from those of S. nyasalandicum, were found in the exhalant passages from the gill chamber of the crab. These yielded adults of S. woodi De Meillon, and no other species was found in this particular situation; nor were examples of S. woodi found on the external surface of the crab. As many as three larvae were found in one passage and, in another crab, a fully grown larva and pupa caused complete obstruction of the passage on one side. Apart from the security enjoyed by the larva in the sheltered position, it is thought probable that the association is essentially a commensal one.

During 1953 and 1954, experimental plots were set up on two sites in eastern England and regular fortnightly samples were taken in an attempt to evaluate the degree of control of the Cabbage Aphid, Brevicoryne brassicae (L.), exerted by its parasites and predators.

The plot at each site consisted of a block of 5 rows of 40 plants and each main sample consisted of a sample of three leaves (one upper, one middle and one lower leaf) from 25 per cent. of the plants. Two such samples (A & B) were taken at each visit and were so arranged that the plants were sampled in strict rotation. The leaves were taken back to the laboratory and sample A was used to assess the number of Aphids, the other for an assessment of parasitism. The Aphids were removed from sample A and put into 95 per cent. alcohol and counted. The mummies were removed from sample B and put into labelled tubes. The leaves from sample B were then kept in insect-proof containers and examined daily for the next fortnight. All mummies which formed were removed and sorted. The insects which emerged from the mummies were killed, sexed and recorded. Predators taken from this sample were identified and recorded and used for further experiments. The validity of counting Aphids from one sample and parasites and predators from another was investigated by a series of “check-samples” taken from arbitrary plots in the fields. A shorter method for assessing parasitism was tried, using a sub-sample of the main sample, and an explanation is given for the disparity between the two sets of results.

Since November 1951, trials of residual insecticides have been carried out at Taveta, Kenya, against Anopheles gambiae Giles and A. funestus Giles in native-type huts fitted with exit traps.

DDT wettable powder at over 2·5 g. DDT per sq. metre in a hut with plaster of absorbent mud gave, for eight months, kills of over 50 per cent. of the female Anophelines that entered.

BHC wettable powder in huts with absorbent walls at 0·24 g. γ isomer per sq. metre gave kills of over 50 per cent. for nine months or more. On non-absorbent walls the kill fell rapidly during the third month and was negligible by the fifth. Insecticide persisted in walls of active material after the roof of inactive materials had become relatively innocuous.

Wettable powders combining DDT and BHC were not effective unless the deposit of DDT was at least 2·1 g./m.2. For an equivalent cost, BHC alone was more effective on active walls and dieldrin on inactive ones.

BHC in urea-formaldehyde resin at 2·5 g. γ BHC per sq. metre was persistent but the persistence was not commensurate with the cost of the material and difficulty of application. The insecticide persists longest on mud surfaces, presumably because it is absorbed from the skin of resin and later released as vapour. Absorption would render permanently innocuous a nonvolatile insecticide.

Aldrin wettable powder was found considerably less persistent than BHC on absorbent walls.