The apparatus previously used to demonstrate the repellent properties of DDT, fuel oil and methylated naphthalene auxiliary solvents towards certain Diptera was used in further studies of olfactory repellency in an attempt to narrow down the ingredients responsible for this effect, and consideration was given to the possibility of finding substitutes for them with less repellent or even attractive properties.

Light, medium and heavy fractions were obtained by fractional distillation of fuel oil and each of two methylated naphthalene auxiliary solvents. In all these spray components the repellent properties are inversely related to the boiling point, and appear to be non-specific both chemically and by insects. Tests with materials of low volatility, however, showed that the effect is not a simple broad relationship between volatility and repellency.

Butoxy-polypropylene glycol, widely used as a ‘repellent’ ingredient of livestock sprays, shows olfactory attractiveness to Musca domestica L. and Aëdes aegypti (L.). The odour of Drosophila melanogaster Mg. was shown to be attractive to the insect, regardless of sex.

It is concluded that there seems little hope of an economic non-repellent material.

It is suggested that the repellency of spray components might be counteracted by the addition of specific attractants, sex or other, to spray formulae. Alternatively, a useful space repellent spray, containing no toxicant, might be formulated from the lighter fractions of the solvent materials.

Experiments were conducted with Trinidad strains of Oryzaephilus surinamensis (L.) and O. mercator (Fauv.), the average sizes of which were smaller than those given in the literature. Limited observations on their biology on cereal products showed that whereas the egg-production of O. mercator was comparable with that recorded by other workers under similar conditions, that of O. surinamensis was much lower.

Larvae of both species were able to complete their development on raw and yellow-crystal sugar, but there was a high mortality among those of O. surinamensis. Both species showed very low oviposition rates on sugar and this, together with a high larval mortality, would indicate that infestations of O. surinamensis on these products would die out. O. mercator, on the other hand, could multiply very slowly. Oviposition rates rise rapidly when females return from sugar to cereal products.

Unrefined sugars should accordingly not be disregarded as sources of Oryzaephilus infestation, especially in the humid tropics.

A dieldrin emulsion spray containing 3 per cent, dieldrin (w/v) was applied once to the putative resting places of Glossina morsitans Westw. throughout a comparatively isolated 17-sq.-mile fly-belt in the Kabiganda Valley in southwestern Uganda between October 1957 and September 1958. Concentration areas of the fly consisted of one or more tall trees with associated understorey and thicket. The lower sides of the branches of an average of 6·75 such trees per acre were treated at a rate of about one-fifth of a pound of dieldrin per acre and at a cost of about £250 per sq. mile.

Chemical analysis showed a deposit of approximately 0·8g. dieldrin per sq. metre on the surface sprayed, and although 90 per cent, of this had disappeared from the surface after about four months, it is thought that the application remains effective for this period.

A very great reduction in the tsetse population was achieved. Small numbers of flies continued to be caught, but it was thought possible that these were being brought in from neighbouring valleys by buffalo, and, hence, that insecticidal application of this sort, if carried out over a wide enough area, might eradicate a tsetse population.

The rearing of a complete generation of Mansonia (Coquillettidia) aurites (Theo.) is described with notes on the methods used.

Variation in the leg ornamentation of the adults forming the progeny of a single egg-raft was found to cover the range usually observed in this species.

A plea is made for conformity in the use of terms describing the various kinds of aggregations of eggs.

Egg-rafts are discussed, and a tentative key is given to the eggs of six of the Ethiopian species of Coquillettidia, based on egg-raft shape.

A modification of the ‘natural’ arrangement is suggested for the Ethiopian species of Coquillettidia, based not only on adult and larval characters, but on oviposition behaviour as judged by egg-raft shape.

The possibility of natural interspecific hybridisation is mentioned.

The general slowness in many of the life processes found in the genus is put forward as an adaptation to its peculiar mode of life.

The history of the use of pyrethrum formulations to control Antestiopsis spp. on arabica coffee in Kenya is reviewed.

The material with which the present work was done comprised three distinct forms of Antestiopsis of doubtful taxonomic status; these were not observed to differ in their response to the insecticidal treatments used.

Laboratory experiments showed that Antestiopsis was highly susceptible to pyrethrum and that the addition of piperonyl butoxide, a pyrethrum synergist, did not affect this response.

Preliminary field experiments showed that concentrations of pyrethrins higher than those found effective in the laboratory were required. A hypothesis is advanced and established that this was due to a variable proportion of insects becoming paralysed and falling off the tree before acquiring a lethal dose.

These observations and experiments suggested a two-phase method of control, using pyrethrum as a non-persistent foliage spray at an economical but effective concentration of 0·005–0·006 per cent, pyrethrins, coupled with a 5 per cent. DDT or 0·5 per cent, dieldrin dust applied to the bole of the tree to form a persistent toxic barrier. The spray removed the bugs from the tree whilst the dust prevented the return of or killed those that had only received a sub-lethal dose of pyrethrum. It seemed unlikely that such a localised application of the persistent insecticide would have any appreciable effect on beneficial insects.

This two-phase treatment has been used successfully both in trials and in commercial practice for the control of Antestiopsis. When the initial population is in excess of 20 per tree, two spray applications and one dusting are necessary to effect control.

Experiments were made at three different sites in Malaya between 1952 and 1957 to compare the numbers of mosquitos attracted to man, calf or goat under the same conditions. The baits being compared (either two men and one calf or two men and two goats) were exposed simultaneously in two net traps placed about 50 yd. apart. This procedure is referred to as comparative trapping.

The total number of mosquitos caught with each bait showed calf to be much the most attractive, followed by goats and then men. However, there were three species, the dark-winged form of Anopheles barbirostris Wulp, Aëdes albo-pictus (Skuse) and Culex pipiens fatigans Wied. that were attracted in larger numbers to man than to calf, and six species attracted in larger numbers to man than to goat.

To compare the host preferences of the different species as between man and calf, the numbers of each caught with man and with calf have been expressed as a ratio (the man: calf attraction ratio). For most species the ratios from the different sites were much the same, showing that the method produced repeatable results. The data from the three sites were therefore combined.

On the combined data the ratios range from 3·4:1 in favour of man for the dark-winged form of Anopheles barbirostris to 1:82 in favour of calf for A. vagus Dön.

As might be expected, the ratios show that the vectors of malaria, filariasis and virus diseases are among the more anthropophilous species.

Attraction ratios have been calculated from suitable data published by various authors for ten different species in five countries. The ratios obtained place the Anophelines in an order that agrees well with their status as vectors of malaria.

It appears that if the results of comparative trapping are expressed as attraction ratios, this offers a method of comparing the host preferences of mosquitos of the same or different species, at different times and places in a country, or even in different countries.

A method of obtaining locust eggs which could be expected to be deficient in carotene is described. It involved rearing a parental generation on an artificial diet which, because of certain pigmentation abnormalities it induced, was probably itself deficient in carotene.

Using crowded hatchlings of Locusta migratoria (L.) from eggs thus modified, it was shown that they were sensitive to dietary carotene, whereas hatchlings from normal eggs were indifferent. The absence of carotene was marked by inferior growth, lessened activity and most notably by an extremely different coloration in both hoppers and adults. Without carotene, melanisation was absent or greatly reduced and in many cases the integument developed a greenish-blue colour. With carotene, heavy melanisation occurred in the hoppers, and the colour of the adults was characteristically gregarious.

It was concluded that in normal eggs the amount of carotene present is usually sufficient to mask the expression of a dietary deficiency during nymphal growth, but that with normal eggs having low amounts of carotene, a dietary deficiency might become apparent as it did with modified eggs.

It is suggested that the blue colour of modified Locusta hoppers reared without carotene is due to mesobiliverdin, a prochromogen of insectoverdin, the green pigment of the solitaria phase of locusts. Insectoverdin itself could not be formed because it contains carotenoids, and these were absent from the diet. The effect of extreme deprivation of carotene is therefore to induce solitaroid tendencies, notably in regard to colour (suppression of melanin and production of mesobiliverdin) but also in regard to activity.

Crowded hoppers of Schistocerca gregaria (Forsk.) reared on synthetic diets lacking carotene usually had turquoise-blue blood by the fifth instar. It was shown, by the electrophoresis of yellow, green and blue bloods in parallel, that the blue chromoprotein of blue blood is the same as the blue chromoprotein of green blood. Its prosthetic pigment must therefore be mesobiliverdin.

The abnormalities of coloration which arise in crowded Locusta and Schistocerca when deprived of carotene are normal in the solitary phase. Moreover, they resemble those abnormalities of coloration consequent upon the implantation of additional corpora allata into gregarious hoppers. The implications of this are discussed in relation to the validity of phase criteria, and an attempt is made to relate these findings to hypotheses on the humoral regulation of phase.

Field and laboratory experiments were carried out in Ghana on the tsetse fly, Glossina medicorum Aust., to discover the senses used by the fly in finding its host. In laboratory experiments on vision a model locomotive with a black screen attached to it was used as a ‘host’. The flies were stimulated to move by the movement of the screen. When the screen was stopped and started for short periods the increase in activity became less each time the screen was put in motion but the fall off was less rapid than in experiments with continuous movement. The possible significance of this is discussed in the light of the normal habitat of the species in the field.

In the field, G. medicorum did not respond to a moving object more than 25 ft. away but G. morsitans Westw. showed a good response at distances up to 150 ft.

Tethered flies were attracted to the model screen and showed a preference for landing on the lower edge near the centre.

Laboratory experiments using a guineapig and a goat as sources of smell produced no response from the flies but a strong reaction was obtained with the vapour of dilute acetic acid. In field experiments, using cows which were not visible to the fly, a very marked response to the smell of the cows was obtained. Orientation to a source of smell probably involves orientation to air movement and G. medicorum showed a strong upwind orientation in a wind tunnel even when blinded.

It is concluded that G. medicorum, which lives in thicket or forest where visibility is poor, probably responds initially to the smell of a potential host. An upwind orientation would then bring it to the general vicinity of the animal and the final approach might be visual.

An account is given of marking and release experiments with Anopheles gambiae Giles in a coastal area of Tanganyika. Laboratory-reared mosquitos were used, labelled either by the topical application of paint or by the introduction of radioisotopes into the larval breeding pans. Two different isotopes were used, 32P and 35S, and recaptures were recognised by autoradiography.

Routine catching stations were established within a circle of radius of 1¼ miles. Releases were made either in the centre or near the periphery of the experimental area, so that recaptures were possible up to a maximum of 2¼ miles.

The following results were obtained:

1. Of 132,000 mosquitos released, 1,019 were recaptured.

2. The mean flight range of females released in the centre was estimated to be 0·64 mile, and of males 0·52 mile. Of females released on the periphery, the mean range of dispersion was estimated to be 0·98 mile. Individuals of both sexes were caught at the maximum range of 2¼ miles.

3. The dispersion of recaptured mosquitos was shown to be non-random and to be related primarily to the distribution of human settlements.

4. In certain series of releases the direction of the prevailing wind had a definite effect on the dispersal of mosquitos. But in general this was a minor factor.

5. Dispersion during the first day or, in many instances, during the first two days after release was more restricted, compared with that of older mosquitos. But no difference in the distribution of catches was detected between those aged three-nine days and those more than nine days old.

6. Marked females were recaptured up to 23 days after release. Apart from the first two days, the regression of density on age amounted to a daily loss of 16 per cent, of mosquitos from the experimental area. The effect of emigration could not be assessed quantitatively, but it was held to be a minor component of the total daily loss. The relatively high level of mortality suggested by these figures is attributed to the use of laboratory-reared mosquitos.

7. The corrected sporozoite rate in marked females at the time of recapture was 0·8 per cent.

8. The survival of males was only slightly lower than that of females.

9. It is concluded from the survivorship curve that the mortality rate remained constant throughout the period in which marked females were recovered.

Sorghum midge, Contarinia sorghicola (Coq.), was discovered in Nigeria in 1953, and a survey which indicated the widespread occurrence of the midge in the country was followed by the investigations reported in this paper.

Food-plants of the midge in Nigeria are guineacorn (Sorghum vulgare, sensu lato), which annually provides about two million tons of grain for human consumption, and the wild grasses, Andropogon gayanus and Sorghum arundinaceum.

At Samaru, Zaria, Northern Nigeria, midges emerge from infested guineacorn heads in the early morning with maximum emergence between 7.45 and 8.15 a.m. After mating, females fly to recently flowered heads where they lay eggs within the spikelets, laying twice as many eggs on the glumes as on the pales. Each female may lay about 50 eggs and both males and females usually die within ten hours of emergence. The egg hatches within four days and, after ten days' feeding, during which the ovary shrivels up, the larvae pupate within the spikelet. The cycle from egg to adult is completed in 19 to 22 days during the growing season but towards the end of the rains larvae spin cocoons and enter diapause.

Large numbers of diapause larvae are carried through the dry season in late-flowering heads which, because they are severely attacked by midge, are not harvested and remain on the stems which are kept in stacks and used for building and fencing or as fuel. Smaller numbers of larvae are present in threshing trash. The emergence of adults from the diapause population was observed from 1955 to 1959. In cages, the first adults were observed to emerge half way through the rains, about 5 to 7 weeks after the weekly mean R.H. had exceeded 60 per cent, and emergence continued for 9 to 12 weeks. Field observations confirmed experimental observations and showed that the build-up of the midge population before the main crop comes into flower is largely dependent on the presence of early-flowering varieties. So long as sufficient guineacorn is in flower and the weather is favourable the midge population builds up steadily to a peak in October and early November.

A. gayanus appears to be of little importance as an alternative food-plant, and preliminary evidence of the existence of a distinct biological race of C. sorghicola on A. gayanus is presented. Wild sorghum (S. arundinaceum) may be an important alternative food-plant in the south, where it is most abundant, but is of little importance in the main guineacorn-growing areas of the north where it is uncommon. Eupelmus popa Gir., Eupelmus sp., Aprostocetus sp. and two species of Tetrastichus parasitise C. sorghicola, and examples of the three genera are generally present at Samaru in the ratio 3 of Eupelmus: 1 of Aprostocetus: 1 of Tetrastichus. They are only of importance late in the season. Two spiders, a species of Thomisus and a species tentatively referred to as Diaea, prey on ovipositing midges but are apparently of little importance.

Experiments show a significant negative linear regression of yield on the proportion of spikelets attacked. There is no evidence of compensation and estimation of the proportion of spikelets attacked by midge gives a direct measure of the loss of yield. In 1957 and in 1958, random samples of guineacorn spikelets were taken from farmers' crops throughout Northern Nigeria. The proportion of spikelets containing midge larvae and pupae was estimated by dissecting 50-spikelet sub-samples taken at random from each sample, and the maturity of the sample was measured in each sub-sample by counting the number of spikelets which had not flowered. Samples should have been taken between 7 and 21 days after 50 per cent, of the crop had flowered, but many of the samples were immature and were discarded. In 52 mature sub-samples obtained in 1957, 10·5 per cent, of all spikelets contained midge and, in 167 obtained in 1958, 4·1 per cent, contained midge. In 1957, the results did not permit estimation of over-all crop losses but in 1958 it was estimated that at least 91,100 tons of grain, valued at £1,822,000 and representing the produce of 218,200 acres, were lost to sorghum midge.

The pattern of intensity of midge attack in the survey samples suggests that in the main guineacorn-growing areas, which lie above 9°N. at an altitude exceeding 1,000 ft., midge damage is less severe than in lower latitudes and at lower altitudes where heavier attacks probably result from the longer growing seasons, higher humidities and more abundant wild sorghum.

Nigerian farmers recognise the empty heads caused by midge but are unaware of the midge itself and, until they have learned to recognise cause and effect, control measures depending on their co-operation may be unsuccessful. Cultural control by disposal of crop residues and the growing of a uniformly flowering crop would be the most natural and effective method in the main guineacorn-growing areas. There is little possibility of achieving chemical control at present and, though the field resistance of the Nunaba group of varieties (Sorghum membranaceum) from the Gold Coast has been confirmed in Nigeria, laboratory experiments suggest that when the midge is not free to choose between resistant and non-resistant varieties it is able to adapt its behaviour and will then oviposit on resistant varieties.

This paper is intended to serve as a basis for further studies of sorghum midge in Nigeria and elsewhere in West Africa.

Aphids belonging to the species Nasonovia ribis-nigri (Mosley), Aulacorthum circumflexum (Buckt.), Macrosiphum euphorbiae (Thos.), Myzus persicae (Sulz.) and A. solani (Kalt.) were exposed to attack by the parasite, Monoctonus paludum Marshall, and were sectioned and dissected at various time-intervals after attack in order to observe the developmental processes of the parasite.

The egg was always laid in the posterior mass of fused ventral nerve ganglia in the thorax of the aphid host.

The development of the parasite in N. ribis-nigri, its normal host on lettuce, is described.

In the species A. circumflexum the development of the parasite was arrested after approximately 24 hours by the secretion around it of a thin brown capsule formed by certain of the host's blood cells.

In the other three species, Macrosiphum euphorbiae, Myzus persicae and A. solani, no capsule formation occurred. The development of the parasite embryos was rather variable in these but it was common for parasites in Macrosiphum euphorbiae to reach the stage normal for 24-hour embryos and for parasites in Myzus persicae and A. solani to reach stages rather less advanced than this before degenerative changes set in.

The degenerative changes in the parasite embryos are described for each species of aphid and the nature of these changes is discussed.

Two experiments in which G. pallidipes Aust. was caught on oxen, in Morris traps and on a fly-round in south-eastern Uganda are described.

Fewer flies were caught in traps than on oxen, but the former took a higher proportion of females. The numbers in traps covered with natural-coloured hessian tended to be greater than in traps on which the hessian was painted black. A white ox attracted fewer flies than darker-coloured oxen, among which a red ox was the most attractive. Variations reflected in day and site effects indicated that the sexes were differentially affected by the factors controlling availability to the oxen and the traps. Fly-round data appeared to give an unsatisfactory estimate of the population density.

The numbers caught by the various methods were, in general, not correlated and this casts doubt on the validity of fly-round or trap data as estimates of the number of G. pallidipes likely to attack cattle.

A series of catches of G. pallidipes Aust. was made in 1½-hr. periods between 0800 and 1830 hr. each day during two experiments carried out in the early wet season (1957) and the late dry season (1958), at Lugala, Uganda, using tethered, small, shorthorned East African Zebu oxen, Morris traps and the standard flyround technique.

Flies were attracted to the oxen in greater numbers in the morning and evening than at midday, the evening increase being marked in the wet season. The daily catches of both sexes on oxen, though starting at much the same level in both seasons, fell to lower levels at the hotter times of day during the dry season and rose only slightly in the evening. Traps, on the other hand, in both seasons caught most females between 1230 and 1400 hr. and least in the mornings. Male flies were trapped in greatest numbers between 1400 and 1530 hr. in the wet season, but only in comparatively small numbers at any time in the dry season, though there was a suggestion of maximum availability between 1100 and 1230 hr. during the latter. During the dry season, catches on the fly-round and on oxen showed a similar periodicity in the case of females, but not in that of males, fly-round catches of which declined from a peak at 0930–1100 hr.

The Cicadellid, Empoasca lybica de Berg, is an important pest of cotton in the Sudan Gezira, where over 300,000 acres of cotton are grown annually under irrigation. Cotton is sown in mid-August, and the plants are uprooted and burnt the following May. The life-cycle of E. lybica from egg to gravid adult takes 16–24 days, and the adults live for up to 40 days. There is no diapause. During the 100 days from late August to early December when breeding on cotton is of economic importance, a single male and female could give rise to some 50,000 progeny.

During May to July, when crops are confined to irrigated gardens and river banks, E. lybica is widely distributed in such places and can be found also on tree hosts, which are numerous especially in the southern Gezira and along river banks. There is circumstantial evidence of displacement over long distances, and the great majority of catches of E. lybica in sticky traps were made before the increase in population on cotton that occurs from September onwards.

Of the 53 species of host-plants that have been recorded, only Solanum dubium, Rhynchosia memnonia, Hibiscus spp. and Abutilon spp. are of importance in the ecology of E. lybica. The first two especially are common weeds in fallows, which comprise more than half the land under rotation. Populations of E. lybica in Gezira fallows at the time of cotton germination tended to be greatest where pre-sowing rains (i.e., those falling from 1st July to 15th August) were highest. Correspondingly, initial infestation of cotton was highest in seasons and places receiving the most pre-sowing rains, although density of infestation in any place was affected by sowing date and proximity to irrigated fields and gardens which supported weed host-plants.

In order to develop a system of sampling for infestations of E. lybica in the cotton crop, the distribution of nymphs on cotton plants was examined. It was found that nymphs were most numerous in the leafiest zones of the plant and a random choice of leaves seemed an appropriate means of sampling for infestation. The distribution of nymphs within and between cotton fields was also investigated and a standard sampling procedure adopted.

Peak infestations on cotton could not be predicted from the level of initial colonisation, or from surveys a month later. Peak infestations were usually inversely related to the level of initial colonisation, especially when comparisons were made between seasons, as at the Gezira Research Farm. That is to say, high levels of initial infestation, which occurred in seasons of good pre-sowing rains, tended to be followed by low rates of increase, and in years of poor pre-sowing rains, initial infestations tended to be low and rates of increase high.

The relationship of these findings to those of Cowland & Hanna (1950) and Hanna (1950) are discussed; the hypothesis that pre-sowing mud-splash is a major factor controlling numbers of E. lybica in the Sudan Gezira is discounted, although it is accepted that this factor temporarily reduces populations.

The rate of increase of infestations of E. lybica was found to be positively correlated with the concentration of nitrogen recorded 2–4 weeks previously in the cotton leaf. This concentration affected not only the rate of increase of the initial colonisers, but also the rate of recovery of populations during November and December after spray-applications of DDT. The nitrogen concentration in the leaf was increased by nitrogenous fertiliser, with a corresponding increase in infestations of E. lybica. It was also found to be negatively correlated with pre-sowing rains, which, if low, prevent the nitrate in the top 12 in. of Gezira soil being washed to lower levels, but the data presented provide no evidence that the relationship is causal.

It is concluded that localities and seasons of poor pre-sowing rains favour a high rate of increase of small populations of E. lybica because of high nitrogen concentration in cotton leaves during September and October. This tendency is augmented by application of nitrogenous fertiliser. A regression equation relating the peak infestations of E. lybica with pre-sowing rainfall and with nitrogenous fertiliser is given and the infestations computed from this are shown not to differ significantly from those recorded in the Gezira as a whole, and in the four main divisions of it separately, during the eight years 1949–1956.