Following increased yields of cotton in the Sudan Gezira by DDT spraying, during the 1952/53 season 22,300 and 6,700 feddans of X1730A cotton were sprayed once and twice, respectively, in the Gash Delta of eastern Sudan, where nearly 60,000 feddans were grown under controlled flush irrigation. Each spray consisted of 1 lb. technical DDT per feddan and was applied by aircraft in 2 gals, of spray per feddan.

Systematic observations were made on the incidence of cotton pests in 30 observation stations scattered throughout the Gash Delta, such stations being selected more or less at random from cotton sprayed once and twice and unsprayed, ten amongst each of these three treatments.

A single DDT spray applied 50–70 days after sowing gave entirely satisfactory control of the Jassid, Empoasca lybica (de Berg.), and the thrips, Hercothrips fumipennis Bagn. & Cam. and H. sudanensis Bagn. & Cam., throughout the growth of the crop. There was little lasting control of the flea-beetle, Podagrica puncticollis Weise. The second spray, applied 70–90 days later, had little effect on any of these pests which were then present in low numbers.

The incidence of bollworms was observed between December and March, covering the important fruiting period. During these months, over 70 per cent, more larvae of Diparopsis watersi (Roths.) and 40 per cent, more larvae of Earias insulana (Boisd.) were observed on sprayed than on unsprayed cotton. Significantly more larvae of D. watersi were recorded on cotton sprayed twice than sprayed once; conversely, significantly fewer larvae of E. insulana were recorded on twice- than on once-sprayed cotton. Moreover the estimated total number of fruits damaged by or shed in association with bollworm attack between January and March was over 30 per cent, greater, and nearly 30 per cent, more bollworm damage to nearly mature bolls was recorded between December and March, on sprayed than on unsprayed cotton.

Yields of seed cotton were significantly less from twice-sprayed than from the other treatments. Once-sprayed cotton yielded less but not significantly so, than unsprayed cotton. Yield was negatively correlated with the number of sprays but the correlation coefficient just failed to reach significance.

Further analysis of the data from stations where yield differences were most marked indicated that D. watersi lowered the yield potential of the crop as expressed by fruit production and retention, as a result of continuous shedding of the damaged fruit. Attack, however, was concentrated on cotton with the best yield potential. The effect of spraying was to increase the numbers of D. watersi and thus to give rise to excessive shedding, increased production of fruit primordia, an increased number of damaged bolls, and finally reduced yield.

It is concluded that any benefits which the crop enjoyed, as a result of elimination of leaf-feeding insects by DDT spray, were completely lost through increased bollworm attack, which moreover reduced the yield below that of unsprayed cotton.

Six new species of stem-boring AGROTIDAE are described from Africa. The new genera, Carelis, Poecopa and Manga are erected to accommodate three of these species; the other three species are described in the genus Busseola.

A key to nine genera is given, and also one to separate five extremely similar species, Poeonoma serrata (Hampson), B. fusca (Fuller), B. quadrata, sp. n., B. phaia, sp. n., and B. segeta, sp. n.

The following description is based on material submitted for identification to the Commonwealth Institute of Entomology by the Government Entomologist, Coimbatore, S. India. The specimens were immediately recognisable as a new genus of the well-defined Mirid subfamily Bryocorinae tribe Odoniellini of which only 18 genera are known. Of these no less than 15 genera are represented in the British Museum (Nat. Hist.).

Trials are described with window-trap huts to test residual insecticides against vector mosquitos in Malaya. DDT, BHC and dieldrin were tested as wettable powders against Anopheles maculatus Theo., A. sundaicus (Ednw.) and Culex pipiens fatigans Wied. Some results were also obtained with Anopheles barbirostris Wulp, A. letifer Sandosham and A. umbrosus (Theo.), with species of Culex other than C. p. fatigans, with species of Mansonia, and with Aëdes albopictus (Skuse) and Aë. butleri Theo. All these mosquitos, except C. p. fatigans, are essentially outdoor species which enter houses only to bite, and which feed freely on animals as well as on man.

The validity of the window-trap hut method is discussed. It is concluded that although some mosquitos escape through the entrance louvres, and a treated hut is not quite the same as a treated and occupied room, the kills recorded are a good guide to the kills that may be expected in treated houses.

It is shown that there is usually some reduction, seldom sufficient to be important, in the number of mosquitos entering the huts in the first few weeks after treatment. This is probably due to air-borne particles of insecticide drifting through the louvres and acting on mosquitos waiting to enter.

The effect of treatment on the biting and resting behaviour of the mosquitos varied widely, being due to a combination of the properties of the particular insecticide and the habits and susceptibilities of the different species. Broadly speaking, all three insecticides tended to reduce the proportion of mosquitos obtaining a blood-meal, and the proportion remaining in the hut in the morning. But these tendencies might be modified or quite obscured by particular characteristics of the mosquito species or of the insecticide. Thus, for example, the percentage of A. maculatus obtaining a blood-meal was only reduced by 11 per cent, in the first month after treatment with DDT, compared with a 60 per cent, reduction in C. p. fatigans. It is suggested that perhaps A. maculatus did not touch the treated walls before biting and C. p. fatigans did. This difference applies to other species of Anopheles and Culex, and the average reductions in biting rate for the two genera were 19 and 62 per cent.

As another example, before treatment rather more than half of the C. p. fatigans, an indoor-resting species, remained in the hut; after treatment with DDT, which does not easily kill C. p. fatigans, over 80 per cent, were found in the window trap. By contrast, in the outdoor-resting species, A. maculatus, which is easily killed by DDT, over 90 per cent, were in the window trap before treatment, and fewer after treatment. The effect of DDT (and BHC) was to kill some of the A. maculatus before they could leave the hut, thereby reducing the proportion reaching the window trap to about 70 per cent. There was no reduction in the percentage of A. maculatus reaching the window trap with the slow-acting dieldrin.

Judged chiefly by the effect upon C. p. fatigans, DDT influenced mosquito behaviour mainly by its irritant effect, which persisted after the insecticide was no longer killing. The effect of BHC upon behaviour was due to a combination of irritance and rapid lethal action, but this did not last as long as the effect of DDT. Dieldrin has no irritant effect and it influenced behaviour only by lethal action for a short time while it was fresh; it continued to kill after it was no longer doing so rapidly enough to affect behaviour.

The most important finding was the wide range of susceptibility to the insecticides among the ten species or groups of species tested, and the fact that only two (Anopheles maculatus and A. umbrosus) seemed susceptible enough to be effectively controlled in practice by the fairly heavy doses used (200 mg. DDT, 40 mg. γ BHC or 40 mg. dieldrin) per sq. ft. With A. maculatus (and probably A. umbrosus) the 24-hour kill remained above 50 per cent, for about six months or more. With A. sundaicus (and probably A. barbirostris, A. letifer, Mansonia and Aë. butleri) the 24-hour kill fell below 50 per cent, in from one to four months. With C. p. fatigans (and probably Culex spp. and Aë. albopictus) the kill never reached 50 per cent, with DDT, and was only above 50 per cent, for one to two months with BHC and dieldrin.

A. maculatus was the most susceptible species to all three insecticides and C. p. fatigans the least; the latter was particularly insusceptible to DDT.

Heavier doses of dieldrin might be effective against the less susceptible species, and a dose of 100 mg. per sq. ft. has been found to remain effective for six months against Mansonia.

Except for the trial with light doses, dieldrin gave the best results against all species. When fresh it gave kills as high as or higher than those of BHC, and it remained effective longer than DDT or BHC.

Dieldrin and BHC when fresh gave complete or nearly complete kills of all species, but the rate of decline in the kills with time varied widely, and was quickest with the least susceptible species. With DDT, on the other hand, the rate of decline in the kill seemed to be roughly the same with all species, and it was the initial kill which varied. For the least susceptible group of species this was well under 50 per cent, in the first month, and was only 5 per cent, with one strain of C. p. fatigans; with the most susceptible it was between 80 and j 90 per cent.; it never reached 100 per cent.

Few mosquitos were found dead in treated huts, the great majority escaped into the window traps, especially with the slow-acting dieldrin. With A. maculatus in the first four months after treatment with DDT, only 25 per cent, of those dying in 24 hours were found dead in the hut. With BHC and dieldrin the corresponding figures were 14 and 2 per cent. The immediate kill (total found dead in the hut and window trap in the morning) was commonly less than half of the 24-hour kill. These results clearly show the importance of using window traps and holding mosquitos, if possible for 24 hours, if a reliable estimate of the effect of the insecticides is required.

Light doses (100 mg. DDT, 10 mg. γ BHC or 10 mg. dieldrin per sq. ft.) were tried against A. maculatus; DDT and BHC remained effective for three months, but dieldrin only for one month.

The performance of the insecticides at the higher doses can be characterised by saying that DDT is irritant and persistent, but not toxic enough except to the most susceptible of the species tested. BHC is irritant when fresh, though it kills at the same time; it is very toxic to all species, but does not remain effective long enough except against the most susceptible ones. Dieldrin is slower acting than DDT and BHC, but is non-irritant, very toxic, and remains effective longer; against less susceptible species higher doses than 40 mg. per sq. ft. will be needed. In countries where vector species rest indoors by day, dieldrin may prove particularly lasting because mosquitos will rest on treated surfaces for long periods.

The probable relation is discussed between the kills recorded in our windowtrap huts, and the degree of malaria control that may be expected when houses are sprayed. The kill necessary to control malaria depends to a large extent on how much contact the vector has with the insecticide. If its habits bring it into frequent contact with treated surfaces, a comparatively low kill on each occasion of contact may greatly reduce the population of the vector and suffice to control malaria. But if contact is infrequent, as may be expected with species of Anopheles such as those studied, which rest outdoors and feed only to a limited extent on man, then a high kill on each occasion of entry into treated houses is needed to control malaria, and there may be very little effect on the population of the vector. In these circumstances a 24-hour kill of 50 per cent., which is here considered the lower limit of effectiveness, seems a reasonable figure to adopt.

The mosquito factors which affect the degree of control achieved with residual insecticides can be thought of under three headings: (a) susceptibility to the insecticide, which largely determines the kill on each occasion of contact, and which we have shown may vary widely with different species, and is often quite low; (b) frequency of contact, which depends on habits, as these determine frequency of entry into treated shelters; (c) duration of contact on each occasion of entry, which is important when the insecticide deposit is no longer fresh, and depends mainly on whether the mosquito rests indoors by day and whether it is irritated by the insecticide.

Lucilia sericata (Mg.) has been bred successfully in small cages having a volume of about 1/60 cubic metre.

Female flies that contain ripe eggs, if given only sugar and water, will withhold their eggs for periods up to 24 days. There appears to be no decrease in the numbers of eggs laid or in the percentage of young larvae hatched, providing the delay in oviposition is not longer than ten days. If the meat is withheld for longer periods then there is a reduction in the daily egg production.

The distribution of 29 species and three varieties of Anopheles in the Sudan is shown on maps. Notes are given on each one with particular reference to distribution. Reasons are given for regarding A. rupicolus Lewis as a synonym or local form of A. rhodesiensis Theo. The former spread of A. gambiae Giles into the Palaearctic Region in Egypt is discussed, and notes are given on its distribution in the Wadi Halfa area.

The general distribution of the Sudan Anophelines is discussed.

Notes are given on malaria and on Wuchereria bancrofti.

In connection with studies on the control of tsetse flies (Glossina spp.) by insecticides, an investigation was made in Tanganyika Territory of the influence of a number of factors on the distribution of insecticide in woodland and open country. A solution of DDT in oil was disseminated as a coarse aerosol from an aircraft and its behaviour traced by the mortality suffered by caged flies. The test insects were wild-caught Musca (Eumusca) lusoria Wied., which proved more susceptible to the insecticide used than did Glossina. palpalis fuscipes Newst.

In open country, complete kills were obtained with the standard application rate (defined as one run using 10 gals, per minute of a 10 per cent, solution of DDT) for at least three hundred yds. downwind of the line of emission, in all the atmospheric conditions encountered.

Tests of the possibility of treating very thin woodland in comparatively high winds (for aerial dispersals of aerosols) and slightly unstable conditions were spoilt by variations in the emission rate of the insecticide, but it was shown that quite small numbers of twigs upwind provided a considerable degree of protection to the test insects and that the kills in cages completely exposed on the upwind side of trees were considerably less than at corresponding distances downwind in completely open country. There was evidence that in high winds and slightly unstable conditions, penetration through the trees was better than with moderate winds and small inversions, but in both conditions there was mortality behind obstacles.

Preliminary comparisons between the kill in the open and in continuous woodland composed of Acacia xanthophloea showed that in the latter mortality was greatly reduced and did not approach that frequently obtained in practical large-scale experiments in tsetse control. A search was made for factors which would increase the level of mortality.

Increased atmospheric stability caused greater average mortality at the expense of evenness of kill. This was not due solely to decreasing effective swathe width due to lighter winds.

Large natural openings in the canopy assisted the penetration of insecticide in unstable conditions, but in stable air the kill around and downwind of clearings was reduced compared with kills in unbroken woodland.

The principal factor in raising mortality to a generally high level was the summation of sublethal doses due to drifting downwind of the fringes of successive parallel swathes. The highest kill obtained in any of these trials was from summation of three swathes emitted 75 yds. apart, which produced a mean mortality of 84 per cent, for 75 yds. downwind of the third run.

An attempt to cover the whole area of woodland by emitting insecticide in a series of parallel runs, as in actual control procedure, showed that in conditions of low turbulence there yet may be great unevenness in the kill obtained. Mortality varied between 21 and 100 per cent., and this irregularity was almost certainly due to the fact that during each of the runs the wind was almost directly along the aircraft track. Such contingencies are unavoidable, for unsteadiness of wind direction is a constant feature of the stable, non-turbulent conditions in the free air that are needed to permit any substantial kill within continuous woodland.

The relation between these results and those obtained in practical control experiments is discussed. It is concluded that the use of caged insects and a particular type of woodland probably accounts for the comparatively low kills obtained in this investigation, from which, nevertheless, valid conclusions can be drawn concerning the variation in mortality from place to place.

The results of a general mosquito survey of the Liberian hinterland are presented together with the findings of previous workers in this country.

Liberia is almost entirely in the Upper Guinean Forest region with an annual rainfall from over 140 in. on the coast to about 80 in. in the hinterland.

A list is given of all species recorded from Liberia.

A brief account is given of the distribution, bionomics and relation to malaria of the Anophelini, with some taxonomie notes. Thirteen species or forms of Anophelines are listed, of which ten were found in the hinterland as well as on the coast.

A summary of the distribution and bionomics of the Megarhinini and Culicini of Liberia is given, with the writer's field notes and those of earlier workers, and some taxonomic notes. Seventy one or 72 species or forms are included, of which 59 were found in the hinterland. If the first mention of some species in the two previous papers in this series be included, 41 additions to the Liberian list, three of them new species, have been made.

Field tests were conducted on Soutra Hill (1,100 ft. above M.S.L.) in the winters of 1953–4 and 1954–5 to find a suitable larvicide for controlling Culicoides impunctatus Goetgh. In one trial, four formulations (wettable powder, water-miscible concentrate, oil solution and dust) of DDT and γ BHC were applied to plots (10 × 10 yd.) at dosages of 3, 12, 50 and 200 mg. p.p′DDT or γ BHC/sq. ft., except for the γ BHC dust which was applied at 3, 6, 12 and 25 mg. γ BHC/sq. ft. In a second trial, the larvicidal properties of aldrin, dieldrin and malathion wettable powders, chlordane water-miscible concentrate and malathion emulsi-fiable liquid were investigated at three or four of the following dosages —3, 6, 12. 25 and 50 mg./sq. ft. The conclusions to be drawn from these trials were:—

1. DDT was superior to γ BHC at all dosages and in all formulations both in immediate and residual effects.

2. For immediate larval control, DDT and γ BHC wettable powders and DDT water-miscible concentrate were effective but γ BHC water-miscible concentrate was relatively ineffective.

3. Although all the DDT preparations were effective as residual larvicides, the wettable powder was the most successful.

4. For immediate larval control a dosage of 200 mg. p, p′DDT or γ BHC is required. The effect produced by 50 mg./sq. ft. is variable.

5. For residual larvicidal action a dosage of 50 mg./sq. ft. is required although 12 mg./sq. ft. may sometimes be effective.

6. Both preparations of malathion reduced the initial larval density by just over half but they had no residual effect.

7. Chlordane and aldrin achieved an immediate larval reduction of one third but whereas chlordane had a greater residual effect, aldrin was ineffective.

8. Dieldrin had very little immediate (20 per cent. control) but considerable residual effect (72 per cent. control).

9. Wettable powders are the most successful larvicidal preparations.

10. DDT and γ BHC wettable powders at 50 mg. p, p′DDT or γ BHC/sq. ft. are superior to chlordane at the same dosage and slightly better than dieldrin at 25 mg./sq. ft.

Immature nutfall, caused by the Coreid, Amblypelta cocophaga China, was prevalent in the coconut plantations of the British Solomon Islands before the late war, and was increasing in extent and intensity. Good crops were borne by palms inhabited by colonies of Oecophylla smaragdina (F.), as this ant destroyed Amblypelta; and the same was true, to a lesser extent, of another ant, Anoplolepis longipes (Jerd.). The smaller species, Pheidole megacephala (F.) and Iridomyrmex myrmecodiae Emery, did not destroy Amblypelta and consequently palms bearing these species suffered from nutfall. These non-beneficial ants were extending their areas of occupation and becoming dominant in the plantations of the Protectorate.

Attempts to control Amblypelta by introducing parasites from Indonesia, Queensland and Fiji have all proved ineffective, and so also have past efforts to change the balance of ant populations in the plantations in favour of the beneficial species.

After the war, it was noticed that certain plantations in Guadalcanal, which had suffered severely from nutfall for several years, were recovering and bearing well. In 1948, it was found that this recovery was correlated with changes in the ant populations, Oecophylla having occupied much of the area, displacing Pheidole, which had previously been dominant. The investigators concluded that this was due to ecological changes in the. plantation undergrowth, resulting from neglect of cleaning and brushing during the war.

The present paper deals with a re-examination of the position in 1952–53. The author found a further improvement in the yield and an extension of the area of recovery on the plantation in question; Pheidole had completely disappeared, but in many parts Oecophylla had been driven back by Anoplolepis, which had now become the dominant ant. The only nutfall areas that remained here were occupied by Iridomyrmex.

A fuller examination of these and other plantations did not support the theory that nutfall recovery was due to ecological changes in the undergrowth, for these had occurred everywhere in the Protectorate during the war, yet on most other plantations yields had decreased, and Pheidole had greatly extended its pre-war area of occupation. The areas in which recovery had occurred were adjacent to wartime military installations that had been subject to regular weekly anti-malarial spraying from the air, and it is suggested that this had affected Amblypelta, both directly, and indirectly by having differentially affected the populations of Pheidole and Oecophylla. It seemed more likely that it had been caused by the long-sustained spraying programme carried out by the United States forces during and after the war.

Small-scale tests carried out with insecticidal sprays confirmed this theory: the harmful species, Pheidole and Iridomyrmex, were found to be very severely affected, while the beneficial ones, Oecophylla and Anoplolepis, suffered far less. In plots with mixed ant populations it was found possible to increase temporarily the number of palms occupied by beneficial species by spraying the palm-bases with insecticide. With the equipment available it was not possible to spray the boles and crowns: consequently, these trees were often reoccupied later by the harmful species Iridomyrmex from colonies in the crowns.

The sprays were also found to be fatal to Coreid bugs, both on contact and for a considerable residual period.

The distribution in Britain of carrion-attracted Calliphorinae was examined by simultaneous trappings, under standard conditions, at 51 stations so distributed as to be more or less representative of the country.

From published records and other sources, the known distribution of each species by vice-counties was delimited and compared with the observed results.

Lucilia sericata (Mg.), L. caesar (L.), Calliphora erythrocephala (Mg.) and C. vomitoria (L.) are generally distributed. L. illustris (Mg.) is more widely distributed than was recognised, and is probably general, though relatively uncommon in hill country. Phormia terraenovae R.-D. and Cynomyia, mortuorum (L.) are also general, though more common in the north. The decrease in frequency southwards is more pronounced with C. mortuorum. and both species occur only rarely in Wales. L. silvarum (Mg.), believed previously to be confined to England, is also possibly generally distributed; it was trapped as far north as Caithness. It is uncommon north of the Highland Line.

Lucilia ampullacea Villen., for which known records are restricted to south of the Humber-Mersey line, appears similarly to be almost general; it was taken both in hill and plains country up to the Inverness region.

Of the remaining species that show some degree of geographical limitation, Acrophaga subalpina (Ringdahl) is the most widely distributed. It occurs at least as far north as the Inverness region, and south to the Severn-Wash line.

The only Lucilia species with clearly restricted distribution is L. richardsi Collin. Its known territory was England south of the Pennines; this has now been extended into Wales and north to Cumberland and Durham, with one isolated record for the north-east of Scotland.

Calliphora loewi End., believed a northern species, was taken throughout Scotland and northern England. C. uralensis Villen. is restricted to the northwest, and the Western Isles.

Brief notes are given of the habitat preferences and seasonal distribution of the species.

Insects and mites collected within the various sections of a combined flour, oatmeal and provender mill are listed. The mill in question is one of the most northerly in Britain. Notes are given on the distribution, abundance and associations, within the mill, of the species recorded. The economic importance of those considered to be pests is assessed.

The three most important pests were found to be Ephestia kuehniella Zell., Gnathocerus cornutus (F.) and Tribolium confusum Duv. It is suggested that Endrosis sarcitrella (L.), Tipnus unicolor (Pill. & Mitt.) and Cryptophagus cellaris (Scop.) might be included in the list of “ hardy ” insects given by Solomon & Adamson (1955) in their paper on the powers of survival of storage and domestic pests under winter conditions in Britain.