The attractiveness of oestriol and of a sample L-lysine to females of Aedes aegypti (L.) was tested (a) in an olfactometer of the Wieting-Hoskins type, and (b) in a free-flight cage enclosed in glass. Similar results were given by both methods, L-lysine being the more attractive at higher concentrations, but oestriol retaining its attractiveness down to much lower concentrations. When 27 L-amino acids were tested in the free-flight cage, 16 showed significantly positive stimulation. Of these lysine was the most attractive, representing a group of 11 which carried CO2 in carbaminoyl or adsorbed form or in both; the other five, of which tyrosine was the most attractive, carried no CO2.

Cattle kept at the Latoli kraal of the Indian Veterinary Research Institute at Mukteswar in the Kumaon foothills of the Himalayas were heavily infested with the tick Boophilus microplus (Can.). In order to reduce the infestation, the animals were treated with BHC dusts every season for a number of years. In 1960, it was noticed that the treatment was not as effective as in the previous years. A series of concentration/response tests was therefore carried out in 1961–62 to see whether or not the tick had developed any resistance to BHC. Ticks collected from cattle in a village about five miles distant, where no acaricide had ever been applied, were used as the standard for comparison. BHC as a wettable powder was used to provide six different concentrations of γ BHC for engorged females and unfed larvae, respectively. Treatment was by appropriate dipping techniques. Analysis of the results showed that the population of B. microplus infesting cattle at the Latoli kraal had developed resistance to BHC. The LC50's of γ BHC for engorged females and unfed larvae, respectively, of the Latoli population were 0.5164 and 0.0182 per cent., and of the village population 0.0834 and 0.00069 per cent. This seems to be the first record of any species of tick developing resistance to an acaricide in India.

It was found that the mean number of eggs laid per tick in the control batches was higher in the village population than in the Latoli population and that the difference was highly significant.

In an experiment carried out in 1963 on the control of Glossina swynnertoni Aust. infesting open bushland in northern Tanganyika, 3 per cent, dieldrin or endosulfan was applied to certain of the resting sites of the flies. These had been determined by previous observations and consisted of the undersides of tree branches between 4 and 9 ft. from the ground, with diameters of 1 to 4 in. and inclined less than 35° from the horizontal. Eradication was achieved in an area of 35 sq. miles at a cost of £42 per sq. mile. In a subsidiary experiment, G. pallidipes Aust. infesting the narrow forest bordering a seasonal river was attacked by spraying the vegetation on the river bank up to a height of eight feet. Complete eradication was not attained, due, it is thought, to removal of the insecticide by heavy rain, so that some newly emerged flies escaped exposure to a lethal deposit. The flies were, however, eliminated from the greater part of the river at a cost of £12.5 per mile.

An account is given of seasonal changes in the incidence and relative abundance of a number of Phlebotomine sandflies which rest in termite hills in two widely separated areas of Kenya.

The annual pattern of rainfall distribution is shown to be of greater importance than the total precipitation in influencing the gross distribution and local abundance of many sandflies.

Kenya sandflies fall readily into ‘ perennial ’ and ‘ rainy-season ’ groups: the former have a wide distribution and appear to breed throughout the year. The distribution of the ‘ rainy-season ’ sandflies is relatively restricted, since these species are found almost exclusively in areas with a bimodal pattern of annual rainfall; it is suggested that they may survive the intervening dry periods in larval diapause. The length rather than the severity of the dry seasons is thought to be the limiting factor in the distribution of ‘ rainy-season ’ species.

Examples are given of the seasonal changes in structure of populations made up of several species sharing, in the adult form, the same termite-hill habitat.

The rate of development of six species of Bruchidae (Acanthoscelides obtectus (Say), Zabrotes subfasciatus (Boh.) and four species of Callosobruchus) attacking stored pulses was studied over a wide range of constant temperature and humidity and the rate of oviposition of five of them investigated over a range of temperatures at 70 per cent. R.H. and a range of humidities at 30°C.

A hatch of the order of 80 per cent, of the eggs of A. obtectus, which are scattered among stored seeds, was recorded over the temperature range 17·5–30°C. at both 30 and 90 per cent. R.H. and over the range 15–35°C. at 70 per cent. R.H. None hatched at 40°C. The optimum conditions for rapid development of the egg are close to 30°C. and 70 per cent. R.H., where the egg hatched in just under five days. The period to hatching is increased at both lower and higher humidities as well as at lower and higher temperatures. The optimum for the rapid development of the post-oval stages is also 30°C. and between 70 and 80 per cent. R.H., in which conditions the first beetle emerged 20 days after the larvae were placed on haricot beans (Phaseolus vulgaris), the mean developmental period to adult emergence being 22·5 days, or 27·5 days including the egg stage. No beetles emerged at 35°C. and few at 15°C. Low humidity and very high humidity retarded development.

The eggs of Z. subfasciatus and the species of Callosobruchus are stuck to the seeds, and data for the egg stage were not obtained separately. The optimum for the rapid development of Z. subfasciatus on haricot beans is close to 32·5°C. and 70 per cent. R.H., where the first beetle emerged in 23 days and the mean developmental period was 24·5 days. No adults emerged at 37·5 or 17·5°C. and few emerged at 20°C. or at low humidity at 35°C.

The optimum conditions for rapid development of the species of Callosobruchus are 32·5°C. and 90 per cent. R.H. for C. chinensis (L.), about 30°C. and 70 per cent. R.H. for C. rhodesianus (Pic), 32·5°C. and about 70 per cent. R.H. for C. analis (F.), and 32·5°C. and 90 per cent. R.H. for C. maculatus (F.). None of the species could complete development at 37·5°C. and all four fared poorly at 35°C. Two species, C. chinensis and C. rhodesianus, were able to develop at 17·5°C. and the other two at 20°C. The performances of all the four species on dried garden peas (Pisum sativum) were poor; all did much better on cowpeas (Vigna unguiculata). The rate of development was slower on garden peas, the percentage mortality was higher and the developmental limits more constricted. In addition, the developmental period in all conditions on garden peas was so variable that the mean gave an unreliable estimate of performance and the time to the first emergence was used instead. The shortest mean developmental periods in days recorded were 22·5 for C. chinensis, 23 for C. maculatus, 25 for C. rhodesianus and 27 for C. analis. The shortest developmental period for an individual bred in garden peas was 18 days for C chinensis, 21 for C. maculatus and 26 for C. analis.

The sex ratio was close to unity throughout. The developmental period of the female was slightly longer than that of the male in A. obtectus and C. chinensis, and also in C. maculatus when bred in garden peas but not when bred in cowpeas. At 30°C. on cowpeas, breeding in mass culture at a low density gave rates of development similar to those observed with isolated insects in the cases of A. obtectus, Z. subfasciatus and C. chinensis, but with C. analis and C. maculatus a large proportion of those bred in mass cultures grew much more slowly than did isolated insects.

On garden peas, more than 50 per cent, of the eggs of the species of Callosobruchus grew to the free-living adult stage only in the most favourable conditions. For these species on cowpeas, and for A. obtectus and Z. subfasciatus on haricots, over 80 per cent, completed development over a wide range of conditions. Normally most of the mortality was of eggs or very young larvae, but at high humidity (80–100 per cent.) and at low (22·5°C. and below) and high temperatures (32·5°C. and above) a considerable number of individuals died after completing larval feeding, some after pupating.

In all the species studied except C. analis, at emergence the female was on average heavier than the male by 0·75–1·25 mg. In Z. subfasciatus, the weight range of the two sexes at any condition rarely overlapped. Callosobruchus spp. bred from cowpeas were heavier than those reared in garden peas. The heaviest beetles were bred towards the bottom of the temperature range, at 50 and 70 per cent. R.H. The weight decreased slightly at 90 per cent. R.H., more markedly at low humidity, slightly up to 30°C. and more abruptly at higher temperatures.

The rate of development of C. maculatus at 30°C. was shown to be. relatively consistent on several varieties of cowpea, the mean developmental periods on the best seven covering a range of less than 2 days (22·1 to 23·8). This mean was a further two days longer (25·7) on the two remaining varieties. Only one seed (Phaseolus aureus) from a series of ten other legumes had a mean developmental period within this range, and only from this seed and from P. mungo, brown peas and the nine varieties of cowpea were 30 or more beetles bred from 50 eggs.

The lengths of the various instars of C. chinensis were determined by the dissection of samples daily, and some information on the pupae of C. rhodesianus was obtained by the use of soft X-rays.

All the five species used in oviposition experiments were short-lived and had very short preoviposition periods after emergence. All laid at a maximum rate after 2 or 3 days, the rate falling quickly at high temperatures and more slowly at low ones. The highest mean number of eggs laid was 100 by C. maculatus, 75 by C. analis, 70 by A. obtectus, 50 by C. chinensis and 40 by Z. subfasciatus. C. analis and C. maculatus laid best above 30°C., and A. obtectus and Z. subfasciatus at 25°C. C. chinensis laid most eggs at 22·5°C., but the performance up to 37·5°C. was only a little inferior and varied irregularly from temperature to temperature; it was poorest at 20 and 17·5°C. The higher humidities (70–100 per cent. R.H.) were most favourable for all species at 30°C.

Eggs of Z. subfasciatus laid at 15°C. did not hatch at that temperature, and likewise eggs laid at 37·5°C. did not hatch at 37·5°C. Very few eggs laid at 25°C. hatched at 15°C., but about half of a batch laid at 30°C. hatched at 37·5°C. Otherwise about 60 per cent, hatched at 20°C., nearly 80 per cent, at 35°C. and 80 per cent, or more at all intermediate temperatures. At 30°C. hatching was good at all humidities including 2 and 100 per cent. R.H.

The results given in published work are compared with those obtained in this work. The value of the results in determining the pest potential of these species is discussed, and suggestions for the most profitable future lines of work are made.

Records of termites attacking growing crops in Saudi Arabia have so far referred to Microcerotermes diversus Silv., one of the subfamily Amitermitinae of the Termitidae (Ayoub, 1959). This termite is also known from the Yemen, the South Arabia Federation and Iraq.

Two experiments on factors affecting the size and composition of catches of tsetse flies, principally Glossina pallidipes Aust., were carried out in 1963 in South Busoga, Uganda. Eight attractants were distributed between eight sites on eight successive days in a Latin square design for each experiment. The attractants comprised two black Zebu oxen and Morris traps covered with ordinary hessian (brown traps) or with hessian dyed black (black traps). Three of the sites were on the edge of a large thicket, two were close to isolated clumps of thicket in the midst of grassland and three were in the open grassland itself. Catching took place for 12 hours each day. The total numbers and sex ratio were recorded for each catch, and also, from dissections, the age composition and pregnancy states of the female portion of the catch. Examples of G. brevipalpis Newst., G. palpalis fuscipes Newst. and of 13 species of Tabanidae were also caught, but in smaller numbers, and were recorded in less detail.

Catches of G. pallidipes at sites close to the thicket edge were considerably greater than at sites away from the thicket, but, apart from an increased proportion of nulliparous females at the clump and grass sites, the composition of the female sample was unaffected by the type of site. The bait-oxen caught larger samples than the traps, but a smaller proportion of females, and these contained a higher proportion of young flies and of flies carrying an egg in the uterus. In comparison with brown traps, black traps caught smaller numbers of G. pallidipes, and a smaller portion of females, but a larger proportion of these were nulliparous. Although the two oxen had been selected for similarity of size and colour, they differed in the samples they attracted: one of them consistently attracted a larger sample of all the common species and, in the second experiment, a larger proportion of females in the samples of G. pallidipes. Most examples of G. palpalis fuscipes were caught at the three edge sites, and all but one example of G. brevipalpis were caught on the bait-oxen.

All examples of the 13 species of Tabanidae caught on the oxen or in the traps were females. Apart from Tabanus par Wlk. they were poorly represented in the trap-catches, and there was no obvious effect of site upon the size of the samples.

The mode of inheritance of dieldrin-resistance in house-flies, Musca domestica L., was investigated by crossing experiments, using a selected, inbred resistant colony (R) and a normally susceptible one (N). Levels of susceptibility in both colonies and in various hybrids derived from them were determined by treating batches of flies with different concentrations of dieldrin by topical application.

Reciprocal crosses gave closely similar results, which were pooled. Results obtained with males and females were analogous, but were treated separately. The F1 hybrids were intermediate in resistance and the F2 generation segregated into susceptible, hybrid and resistant individuals in the ratio 1:2:1. The F1 generation back-crossed to either parental strain gave 1:1 segregation, corresponding to NN + NR or NR + RR. After killing the more dieldrin-susceptible forms in each case, the remaining males were back-crossed again. The second back-cross to normal gave a further 1:1 segregation of susceptibles and hybrids. The second back-cross to resistant now gave all homozygous resistant forms.

These results strongly indicate monofactorial inheritance.

Two highly dieldrin-resistant colonies of the sheep blowfly Lucilia cuprina (Wied.) had been colonised, one from Australia and one from South Africa. These were crossed and the progeny maintained to the F2 generation. Tests with dieldrin on the F1 and F2 generations gave results resembling those obtained with the parents. Since there was no appearance of susceptible or hybrid forms in the F2, it is concluded that the genes in the two colonies occur on the same chromosome and are either allelic (possibly identical) or very closely linked.

The mode of inheritance of dieldrin-resistance in Cimex lectularius L. and Pediculus h. humanus L. was investigated. The method involved the determination of dosage/mortality regression lines by exposing batches of insects to a range of dieldrin concentrations. Reciprocal crosses were made between normal (N) and resistant (R) strains of each insect, and the F1 and F2 progeny were examined for susceptibility levels over a wide range of concentrations of dieldrin. Back-crosses were made from the F1 generation to N and R strains, and the progeny were examined in the same way. In some cases, further back-crosses were made after elimination of susceptible individuals from the progeny of the first back-cross.

All the results with C. lectularius were consistent with monofactorial inheritance of dieldrin-resistance through a gene of intermediate dominance. With P. h. humanus, the results were complicated by an apparent maternal effect which caused the F1 and F2 generations from a N ♀ × R ♂ cross to be less resistant than those from a R ♀ × N ♂ cross. In general, however, the results indicated genetic segregation consistent with the same type of monofactorial inheritance as that found in C. lectularius.

The cross-resistance characteristics of a dieldrin-resistant strain of Aedes aegypti (L.) from Puerto Rico were investigated by comparative tests on the adults of this and of a normal strain, using various insecticides. A resistance spectrum typical of that associated with resistance to BHC/dieldrin in other insects was revealed, characterised by slight or negligible cross-resistance to DDT, malathion and diazinon.

The mode of inheritance of dieldrin-resistance was studied by determining resistance levels in the progeny of direct crosses of the resistant and normal strains and of back-crosses. The F1 generation of the direct cross was of intermediate resistance, and the F1 generation showed 1:2:1 segregation into normal, intermediate and resistant individuals. Both back-crosses showed 1:1 segregation into susceptible and intermediate individuals when the back-cross was to the susceptible parent, or into intermediate and resistant individuals when it was to the resistant parent, and these results were confirmed when one genotype was eliminated and the back-cross was repeated. These results indicate monofactorial inheritance of an autosomal gene with intermediate dominance, which is typical of the BHC/dieldrin type of resistance.

Two experiments were conducted simultaneously in 1962–63 at Chungai, in central Tanganyika, to test new equipment for disseminating insecticides from aircraft and a new insecticide, isobenzan (Telodrin), in the eradication of Glossina morsitans Westw. and G. pallidipes Aust. The new equipment consisted of an aerosol generator fitted to the exhaust of a Cessna 182E high-wing monoplane, and was used in both experiments. The isobenzan was compared with dieldrin, and the two insecticides were applied at rates inversely proportional to their toxicities to G. morsitans as previously determined in the laboratory.

Two blocks of woodland, each 11 sq. miles in area, were treated, one with a 12·3 per cent, solution of dieldrin at the rate of 0·0254 gal. per acre, giving a dosage of 0·5 oz. (14 g.) toxicant per acre, and the other with a 10 per cent, solution of isobenzan at the rate of 0·0124 gal. per acre, giving a dosage of 0·2 oz. (6 g.) per acre. The former block received eight treatments with dieldrin at approximately 3-week intervals, the fourth treatment being incomplete; the latter block received six treatments with isobenzan at intervals ranging from 20 to 45 days. The effects were assessed by means of fly-catches along fixed paths which continued for one year after treatments had ceased.

Both species of tsetse fly disappeared from the two blocks before the final treatments took place, and no more were caught until 11 months after spraying ended, when one example of G. morsitans was caught in each block; both were probably immigrants. None was found in the following month, and it is concluded that the flies were exterminated in both blocks. The fact that the blocks were unusually well isolated from sources of reinfestation probably contributed to the success of the operations.

The cost per sq. mile was £224 using dieldrin and £190 using isobenzan. These were the basic costs, independent of the locality in which spraying took place. Additional costs were incurred which would vary with local conditions; for the present experiments they were £34 and £30, respectively. It is considered that there is good scope for further reductions in costs, particularly with dieldrin, and that these might make dieldrin economically competitive with isobenzan. Owing to the low fly density in the block treated with isobenzan, the efficacy of this insecticide cannot be regarded as conclusively proved until further experiments have been carried out. It may then merit serious consideration as a toxicant for aerial spraying against tsetse flies.

A dipping technique for exposing large numbers of house-flies (Musca domestica L.) to measured doses of insecticide is described. It is suitable for selecting resistant populations and, while giving consistent results, is more rapid than other techniques used for this purpose.

Up to 2,000 flies of both sexes, less than 24 hr. old, are immersed for three minutes in 100 ml. of a 70 per cent, mixture of acetone and water containing the required concentration of insecticide, using a 9-cm. sintered glass Büchner funnel as the immersion chamber. The liquid is then removed by suction, the sides of the funnel are wiped with filter paper, and the flies are allowed to drain for three minutes; they are then transferred in small batches to plastic recovery chambers containing food. Mortality is recorded next day, and the survivors are released into breeding cages.

Experiments showed that immersion for three minutes in 70 per cent, acetone was virtually harmless to the flies and that the amount of insecticide deposited on individual flies was reasonably uniform (coefficient of variation about 20%). Batches of 2,000 flies, but not more, could be treated at one time.

When the dipping technique was compared with topical application of measured drops of insecticide, using a susceptible strain of house-flies and two other strains that were resistant to DDT and diazinon, dipping gave steeper log-probit regression lines than topical application, and the LD50's and resistance factors of the resistant strains were smaller. With flies resistant to DDT, dipping gave straight regression lines whereas topical application gave compound lines.

Observations were carried out, chiefly between March and June 1962, in an area centred on Bolgatanga in northern Ghana in the hope of finding out how Simulium damnosum Theo. survives the ‘ dry season ’. The term ‘ dry season ’ is used here for the unfavourable season when running water in the rivers is evidently absent or is insufficient or perhaps unsuitable for the development of any, or more than a negligible number of, individuals of S. damnosum from egg to adult. The incidence of this season varies from year to year and does not correspond to the season without rain. It may usefully be divided into reduced-flow, main dry, pre-flow and early-flow periods.

Search was made for larvae and pupae before rivers began to flow, without result. Observations were made on the numbers of flies biting, general appearance, wing measurement, antennal colour, mid-gut, fat-body, ovaries and parasites, chiefly at the beginning of the rainy season, in an attempt to trace the history of the species during the preceding weeks. Flies appeared before the rivers began to flow but did not give evidence of having lived for months. On the days when two rivers began to flow, considerable numbers of flies were caught, and most of those dissected proved to be parous and had evidently been in the adult stage for some days. A nematode parasite of the Malpighian tubes was found only in April, with one exception up to 10th May, and was probably associated with the dry-season biology of the host.

The possibility that S. damnosum migrates from permanent foci, or exists near its breeding places in one or more stages at different times, is discussed. Migration from afar seems very unlikely. The species survives in the adult stage for at least part of the ‘ dry season ’, but more information is required to complete the picture.

Survival is apparently not dependent to a significant extent on perennial breeding locally, and there is, therefore, no easy solution to the problem of control. Operational research might show if there is a carry-over generation and if control after the rains and towards the end of the breeding season would prevent it from developing. There is some indication that the risk of infection with Onchocerca tends to be low at the end of the ‘ dry season ’, which is a time when control would be particularly difficult.

The results of observations on wing measurements, antennal colour and the peritrophic membrane are given in an Appendix.

Five trials were conducted in Kenya in 1962–63 to investigate the effectiveness of a 0·2 per cent, w/w pyrethrum dust, synergised with 5 parts piperonyl butoxide to 1 part pyrethrins, against the stalk borer Busseola fusca (Fuller) by applying it to maize at 20 lb. per acre. In three trials, it was compared with a dust containing 5 per cent. DDT applied at the same rate. Pyrethrum showed an efficiency in controlling B. fusca equal to that of DDT. Both insecticides produced reductions of more than 50 per cent, in the incidence of infestation, and in the final trial there was a significant reduction of over 40 per cent, in the number of cobs damaged by stalk-borer larvae; at the same time, an increase in yield was apparent. Further work is required in order to determine the lowest effective concentration of pyrethrins in the dust, which is likely to be less than 0·2 per cent., and to indicate the best time of application.

The majority of sorghum in Northern Nigeria is stored unthreshed in farmers' granaries made of dried mud or plant materials such as grass matting and cereal stems. During the course of survey work and insecticide trials in 1959–61 it was possible to examine many samples of unthreshed sorghum from granaries throughout Northern Nigeria. It was found that the distribution of insect species within the Region is not uniform. Sitophilus oryzae (L.) and Sitotroga cerealella (Ol.) are the major pests. Sitophilus zeamais Motsch. was found only in the southernmost area. Heavy infestations of Rhyzopertha dominica (F.), Lasioderma serricorne (F.), Cryptolestes ugandae Steel & Howe, Oryzaephilus mercator (Fauv.), Tribolium castaneum (Hbst.) and T. confusum Duv. usually occur. Attagenus gloriosae (F.), Ahasverus advena (Waltl), Palorus ficicola (Woll.), P. ratzeburgi (Wissm.) and P. subdcpressus (Woll.) are occasionally important.

R. dominica, Bruchidius sp., G. ugandae, Planolestes cornutus (Grouv.), S. oryzae, Brachypeplus sp., T. castaneum, Sitotroga cerealella (all of which occurred on the standing crop), L. serricorne, Typhaea stercorea (L.), O. mercator, Palorus spp. and Tribolium confusum were found in sorghum sampled before storage. Insects from infested stores were found to infest sorghum growing nearby. Prestorage infestation alone can result in subsequent heavy populations of insects in the store. Cross-infestation between granaries almost certainly occurs.

Under Samaru conditions, where sorghum is harvested in November–December, insect populations remain at a low level in granary-stored unthreshed sorghum until after June, when the moisture content rises in the rainy season. In sorghum stored for nine months in provincial trials, more damage occurred during the last three months than during the previous six months of storage.

Sorghum heads stored in granaries made of plant materials such as grass matting and cereal stems are more severely damaged by insects than those stored in dried-mud granaries. This is probably due to a higher rate of immigration in the former.

In threshed grain stored in a mud granary, moisture content and damage by the most abundant insect, Sitophilus oryzae, decreased with depth. The insect population rose to a peak in November, two months after the maximum moisture content. The numbers fell rapidly during the following dry season. The annual cycle of insect damage was also assessed by taking fortnightly samples of threshed grain from a local market. S. oryzae was the most numerous insect, but even this species was uncommon from December to May, during the dry season.

The results of sixty 24-hour catches of mosquitos carried out with man as bait in the forest canopy at Zika, central Uganda, are discussed. In these catches the arrival of mosquitos was recorded to the nearest minute.

The rapid changes of light intensity in the equatorial twilight are discussed in relation to a series of readings made at Entebbe.

It is shown that among species that show a crepuscular peak of biting activity (Aedes ingrami Edw., A. africanus (Theo.), Mansonia fuscopennata (Theo.) and M. aurites (Theo.)) the peaks do not all occur at the same time, but form a succession.

Moonlight (at least in the forest canopy) has no apparent effect on the timing of these crepuscular surges of biting activity.

One species (M. fuscopennata) also shows a peak of biting activity before sunrise. This peak is closer to sunrise than the evening peak is to sunset. A brief reference to current work carried out above the canopy, where foliage, shadows, etc., do not complicate the environment, shows that this phenomenon occurs in other species also. It is concluded that in these species the morning peak must almost certainly occur in light of much greater intensity than the evening peak.

The implications of these findings are discussed with reference to the questions of endogenous rhythm and exogenous stimuli.