A detailed tsetse-fly survey of 41,000 sq. miles in the inland savannah zone of the Gold Coast (Ghana) was completed in five years using an entirely African staff and working only six months each year.

This undertaking was made possible because studies of the species of Glossina concerned, G. palpalis (R.-D.), G. tachinoides Westw. and G. morsitans sub-morsitans Newst., had provided knowledge of their habitat, food-hosts and activity rhythm, on which could be based a standard yet simple survey technique, within the compass of independent native teams.

The restricted activity rhythm of the flies, subject to both daily and seasonal variations, meant that nothing less than a ‘day’ of eight hours of observation could be accepted as a valid sampling unit.

With tsetse flies at low densities, a day's search was inadequate, giving only 40 per cent, reliability compared with 6-day observations. Four days' search gave 90 per cent, reliability and was adopted as the minimum period of search.

Each survey team was under the charge of a Kecorder or Field Assistant, with fly-boys devoting the whole of their time to catching. Comparability of survey data was ensured by keeping teams to the same size, two fly-boys being the optimum, since it was found that the size of the catch was not always proportionate to the number of boys, the relationship varying according to a variety of factors.

In surveying G. palpalis and G. tachinoides the ‘picket’ system of more or less stationary teams, measuring their catches by the ‘day ’, was found overwhelmingly superior to the ‘fly-round’ technique.

The survey procedure described for savannah woodland country was not effective in sampling G. nigrofusca Newst. in the Ashanti forest or G. longipalpis Wied. in the coastal savannah, but Morris's ‘animal’ traps were found to take both species readily in places where they had not been detected or only occasionally caught by fly-boys. Experiments showed that trap catches were superior, both numerically and in giving a more representative sample of the tsetse population present. It was also shown that trapping could be a valuable means of studying the biology of these two ‘man-shy’ species of Glossina. Traps were also effective in taking G. pallicera Big. and G. medicorum Aust.

The greater value of traps compared with fly-boys as a means of sampling various species of tsetse fly is discussed, and suggestions are put forward for developing trapping as a method of survey.

The type of trap employed is regularly catching insects of several other families, including a number of species among the Tabanidae, and of several other orders.

A detailed tsetse-fly survey of 41,000 sq. miles in the inland savannah zone of the Gold Coast (Ghana) was completed in five years using an entirely African staff and working only six months each year.

This undertaking was made possible because studies of the species of Glossina concerned, G. palpalis (R.-D.), G. tachinoides Westw. and G. morsitans sub-morsitans Newst., had provided knowledge of their habitat, food-hosts and activity rhythm, on which could be based a standard yet simple survey technique, within the compass of independent native teams.

The restricted activity rhythm of the flies, subject to both daily and seasonal variations, meant that nothing less than a ‘day’ of eight hours of observation could be accepted as a valid sampling unit.

With tsetse flies at low densities, a day's search was inadequate, giving only 40 per cent, reliability compared with 6-day observations. Four days' search gave 90 per cent, reliability and was adopted as the minimum period of search.

Each survey team was under the charge of a Kecorder or Field Assistant, with fly-boys devoting the whole of their time to catching. Comparability of survey data was ensured by keeping teams to the same size, two fly-boys being the optimum, since it was found that the size of the catch was not always proportionate to the number of boys, the relationship varying according to a variety of factors.

In surveying G. palpalis and G. tachinoides the ‘picket’ system of more or less stationary teams, measuring their catches by the ‘day ’, was found overwhelmingly superior to the ‘fly-round’ technique.

The survey procedure described for savannah woodland country was not effective in sampling G. nigrofusca Newst. in the Ashanti forest or G. longipalpis Wied. in the coastal savannah, but Morris's ‘animal’ traps were found to take both species readily in places where they had not been detected or only occasionally caught by fly-boys. Experiments showed that trap catches were superior, both numerically and in giving a more representative sample of the tsetse population present. It was also shown that trapping could be a valuable means of studying the biology of these two ‘man-shy’ species of Glossina. Traps were also effective in taking G. pallicera Big. and G. medicorum Aust.

The greater value of traps compared with fly-boys as a means of sampling various species of tsetse fly is discussed, and suggestions are put forward for developing trapping as a method of survey.

The type of trap employed is regularly catching insects of several other families, including a number of species among the Tabanidae, and of several other orders.

The observation in Kenya that Aëdes (Skusea) pembaensis (Theo.) associates with the crab, Sesarma meinerti, was duplicated in Lumbo, on the northern coast of Mozambique. Eggs were seen abundantly on crabs inhabiting certain colonies among mangroves at the edge of a tidal estuary. Females of A. pembaensis were caught in gradually decreasing abundance at collecting sites progressively further inland from the head of the estuary, while males were almost totally confined to the breeding area. Swarms of males were not seen, and it was suspected that mating took place within crab burrows.

Populations of A. pembaensis in 1959 and 1960 were approximately equivalent at Lumbo, whereas some other mosquito species with fresh-water larval stages were reduced in 1960 owing to failure of the rains. The estuarine environment, regulated by the tides, is apparently more stable than are terrestrial habitats. Cycles of A. pembaensis may therefore be less variable than among dry-land forms.

Females of A. pembaensis disturbed at a crab colony were found to bite spontaneously in the day-time. Captured specimens showed a marked discrimination in biting preference for one human out of three tested. The preferred individual experienced a severe reaction to the bites, while the other two had none whatsoever.

Precipitin tests indicated human beings as the only source of blood in A. pembaensis, although the method of collection probably lends bias to this observation. Eight strains of an apparently new virus were isolated from females of A. pembaensis in 1959 and four in 1960. In addition, two strains of a virus of the Bunyamwera group were isolated in 1960. The source of these viruses and their significance in A. pembaensis require further investigation.

As part of a general study of the conditions required for satisfactory maintainance of Pieris brassicae (L.) in laboratory culture, an investigation was made of the factors affecting mating behaviour. Notes are given on certain characteristics of the culture from which the experimental material was drawn.

It was established that P. brassicae, over one day old, mated readily at temperatures between 20 and 32°C. provided the daylight illumination was above about 200 lumens/sq. ft. Mating occurred more readily at the higher temperatures and illumination levels than at the lower. It was depressed at very high atmospheric humidities. The size of the cage in which the insects were held was not critical, and pairs formed readily in cages as small as one cubic foot. The population density in the cage was also varied over wide limits without significantly influencing the rate at which pairs formed.

Mating took place much less readily in the artificial lights which were tested than in daylight. The most satisfactory light was found to be bilaterally arranged ‘daylight ’-type fluorescent lamps. The level of mating in this light would probably have been sufficient to maintain a culture but it was far lower than in daylight of the same intensity.

After mating, the females do not usually pair again for five or more days. The males, however, mate more frequently and will often pair several times in the same day.

Observations in eastern England during 1957, 1958 and 1959 showed natural mortality of pupae of wheat bulb fly, Leptohylemyia coarctata (Fall.), to be high. The part of this due to parasitisation is considered in some detail.

At Rothamsted, the main parasite was Trybliographa spaniandra Kerrich & Quinlan, and this affected about 10 per cent, of the population in 1957 and about 5 per cent, in 1958. At Whittlesey and Peterborough, in 1959, parasitisation affected 5·5 and 13·7 per cent, of the populations, respectively. The two main parasites found were Aleochara bipustulata (L.) and A. inconspicua Aubé (Coleoptera, Staphylinidae). Phygadeuon trichops Thoms. (Hymenoptera, Ichneumonidae) also occurred but was much less frequent. Notes and original observations on the biology of these parasites are given.

Several insects and other small arthropods were observed to prey on various stages of wheat bulb fly. Details of these and notes on the biology of some of them are given.

Following successful small-scale trials, an attempt was made, by aircraft application of insecticide, to eradicate Glossina morsitans Westw. and G. pallidipes Aust. from an isolated block of savannah woodland, approximately 11 sq. miles in extent, at Chungai in the Central Province of Tanganyika between July 1958 and January 1959. A single-engined aircraft, fitted with two belt-driven rotary-cage atomisers, was used to apply a 5 per cent, solution of γ BHC in power kerosene at a nominal dosage of 0·08 gal. per acre (0.04 lb. γ BHC per acre). Seven applications were made at approximately 28-day intervals, the time taken to complete an application varying from five to eight days. The operation failed to control the flies. Although each of the first two applications reduced the apparent density of G. morsitans by about 90 per cent, and that of G. pallidipes by a lesser, although still considerable, factor, later applications gave varying and often low mortalities, and the populations increased slowly for some time, the insecticide applications causing only temporary depressions in numbers. Numbers fell towards the end of the operation, but final reductions were only about 50 per cent, or less. Kills of female flies were low, and this undoubtedly led to the eventual failure.

The low volume-dosage, a drop spectrum that possibly contained too few droplets of the required size, meteorological conditions, and biological factors that apparently favoured the survival of female flies are suggested as contributory elements to the low mortalities.

Operational costs were considerably lower than in previous work.

In the North Block at Chungai, comprising about 11 sq. miles of thorn savannah and thicket in Central Province, Tanganyika, an Auster J5G aircraft was used between July 1959 and March 1960 to apply a 2·5 per cent. solution of dieldrin in oil at the rate of 0·125 gal. per acre in an attempt to eradicate Glossina morsitans Westw. and G. pallidipes Aust. Eight applications were made at approximately four-weekly intervals. Swath width was 55 yd., and the aircraft emitted the insecticide as a coarse aerosol of volume median diameter 50–60μ as it flew in both directions over the block.

The operation suffered delays, and three applications were incomplete to varying degrees. Kills of G. morsitans per application appeared to be 85 per cent. or higher, but the final reduction of 99·5 per cent. could theoretically have been attained with consecutive mortalities of only 65 per cent. It is suggested that this discrepancy may be due to the higher lethal dose required by pregnant females. G. pallidipes was also reduced by 99·5 per cent. Numbers of fly were reduced sufficiently for large-scale settlement with cattle, which should complete the work of exterminating the fly.

The experiment is compared with that of the previous year in the same block, using γBHC, which reduced fly catches by less than 50 per cent. It is concluded that a combination of reduced swath width, greater volume dosage, more lethal insecticide and smaller lethal drop, together with improved flying technique and the more reliable performance of the disseminating equipment, was responsible for the improved result. It is thought that without delays, interruptions, incomplete applications and reinfestation, even better results would be obtained.

This was the cheapest and one of the most successful aerial operations carried out against savannah tsetse. Costs actually over the ground were £301 per sq. mile; incidental costs due to the locality of operations were £66 per sq. mile. There is little chance of reducing the costs of flying directly, but economies are possible by the use of other insecticides or, more probably, by more efficient dispensing equipment.

The cyclic biting activities of East African mosquitos of the genus Aëdes, belonging to the subgenera Mucidus, Diceromyia, Finlaya and Stegomyia are discussed. The total number of 24-hour catches involved was 448, all in East Africa, of which 401 were made in forest in Uganda.

It is pointed out that many species in the subgenera of Aëdes dealt with show arboreal tendencies of varying degree and, while a species may show a preference for some particular level, many of them appear to make daily vertical migrations. Consequently, biting may reach its maximum intensity at different times at different levels. It is also pointed out that the habits of a species may vary from one area to another, and therefore it is often best to discuss a representative series of catches from a productive area, noting such differences as may have been observed elsewhere. It has been found further that, under certain circumstances, a species may fail to show a clear pattern of biting behaviour and the possible reasons for this are discussed.

All members of the subgenus Mucidus so far adequately studied are arboreal and nocturnal. In the subgenus Finlaya, A. ingrami Edw. is a mosquito of the forest understorey which bites most freely in the hour before sunset. It makes vertical migrations, however, and the biting cycle at ground-level differs from that in the trees. A. longipalpis (Grünb.) is a diurnal species of the forest canopy. A view formerly put forward by the writer, that the form of the biting cycle in this species could be attributed to different physiological groups biting at different times, can no longer be supported.

In the subgenus Stegomyia, A. dendrophilus Edw. and A. apicoargenteus (Theo.) are diurnal species with rather irregular biting cycles, A. dendrophilus

A study has been made of the development of Cryptolestes pusillus (Schönh.) at various combinations of high temperatures and humidities. Larval development is much quicker at 90 than at 70 per cent. R.H., and the optimal temperature is probably about 37°C. Under optimal conditions the developmental period is less than has so far been recorded for other species of Cryptolestes, the mean duration of the larval stage being as little as 8½ days at 33°C. and 90 per cent. R.H. The oviposition rate is similarly much increased at both high temperatures and high humidities. There is evidence that middle-aged females lay more rapidly than either younger or older individuals. Under optimal conditions the average oviposition rate can exceed 7 eggs/ ♀ /day, about 17 per cent. of the weight of the adult.

In cultures of adults on flour, there was no clear indication of a reduction of the oviposition rate or of a juvenile mortality at densities ranging from 1·5 g. per adult down to 0·03 per adult, but there were signs that the latter density was near a critical value.

Eggs of C. pusillus were cultured on whole English grain with the germs in poor condition, at humidities ranging from 50 to 90 per cent. The endosperm rather than the germ was attacked in almost all cases. At 50 per cent. R.H., only one individual out of 21 completed its development whereas at 90 per cent. R.H. few failed to do so. Humidity had a considerable effect on the rate of development in the larval stage. At 90 per cent. R.H. it was only slightly slower on grain than on flour.

If adults of Cryptolestes ferrugineus (Steph.), of which the females have already been fertilised, are cultured on flour at low densities, the rate of oviposition is independent of the density of adults and juvenile mortality is negligible. At high densities there is a heavy mortality amongst eggs and young larvae, and there is evidence that, providing no great degree of conditioning of the medium has occurred, an equilibrium is reached with the number of eggs plus larvae present at any time being independent of the density of adults. Cannibalism is undoubtedly a major cause of the juvenile mortality under these conditions. Where crowding of adults is so great that conditioning of the medium becomes important, the number of eggs plus larvae present at a given time after the cultures have been set up decreases with increasing density of adults, there being some indication of an inverse linear relation.

Cultures of C. ferrugineus on a mixture at 70 per cent. R.H. of sound grain and grain already slightly damaged by Crypiolestes are capable of initiating dense infestations in the laboratory, at least at moderate and high temperatures. Under optimal conditions the infestations develop within 15 days. Values deduced for the pre-adult period at various temperatures were similar to those obtained by Rilett (1949). At 17°C., development was extremely slow but the low temperature did not increase mortality. Cannibalism and competition by adults and fully developed larvae appear to play an important part in limiting the production and survival of the juvenile stages.

Sound grain at 70 per cent. R.H. is unsuitable as a medium for culturing Cryptolestes in the laboratory but it becomes suitable after relatively small additions of flour and damaged grains. At 33°C. at least, a point is suddenly reached where an infestation is initiated, the critical feature being increased survival of larvae rather than an increase in the number of eggs laid. An increase in humidity has a similar effect to adding food.

Estimates of the production of CO2 at various temperatures gave values higher than previously reported. From 21 to 33°C. the rate of increase of the respiration rate and the increase in the speed of development are proportional to rise in temperature. This is in accord with other indications that C. ferrugineus has a high optimum temperature.

A major problem in using larvicides to control Culicoides is to recognise the sites requiring treatment. The relationship between plant cover and breeding of Culicoides (mainly C. impunctatus Goetgh.) was accordingly investigated in moorland areas of Scotland. Two sites were examined on Soutra Hill, Midlothian, and one each on Bannachra Muir and at Luss, Dunbartonshire. Three vegetational zones were recognised on Soutra (site 1): bogland (I), acid grassland (III) and a zone (II) characterised by vegetation preferring a much wetter habitat than either of the foregoing. C. impunctatus was virtually the only Culicoides species found in zone I; it was relatively less abundant in zone II, where C. albicans (Winn.) reached its peak, and occurred most densely at the bogland edge of zone III, where it was associated with C. cubitalis Edw., C. heliophilus Edw. and C. obsoletus (Mg.). Further into the grassland, C. impunctatus decreased while the other three species became more numerous and other species, of the group of C. pulicaris (L.), appeared. Within each main zone there were no significant differences between the various floristic groups as regards larval densities.

Fluctuations in population density observed in late autumn were regarded as more apparent than real, and attributable to larval movement in response to an oscillating factor, possibly soil-water level. This movement was recognisable in all zones but was most strongly marked where the ground was uneven.

On Soutra (site 2), where only zones I and III were sampled, there was remarkable consistency among the larval densities of the various groups of samples examined. This applied whether the samples were classified on their angiosperm flora, moss cover or spatial arrangement. The main source of variation was within groups and it was found that two adjacent small plots (12 yd. & z.Times; 12 yd.) which were macroscopically identical showed consistent differences over a period of ten months, covering the transition from one generation to another.

On Bannachra Muir, the larvae of C. impunctatus were concentrated in an area covered by Juncus articulatus and Sphagnum where the water flowed down the hillside near the surface. C. impunctatus avoided both an area of drier leaf mould and a stagnant ditch. C. albicans, C. heliophilus and C. obsoletus preferred the ditch to the hillside flow.

Around a hillside trickle at Luss, larvae of C. impunctatus and C. truncorum Edw. were abundant in subequal numbers. In spite of the restricted size of the area (about 10 sq. yd.) they never occurred in equal numbers in any set of samples, but one or the other predominated. C. truncorum showed a preference for the very wet parts.

Laboratory studies are reported on Syntomosphyrum albiclavus Kerrich, a Eulophid of interest as a pupal parasite of tsetse flies. Material for a laboratory culture was obtained from puparia of Glossina morsitans Westw. collected in Tanganyika and sent to London by air.

‘ Natural’ and ‘unnatural’ hosts of this parasite were investigated. S. albiclavus parasitised all species of Cyclorrhaphous puparia offered in the laboratory, but has only been recorded from puparia of Glossina under natural conditions. The conditions which make a host suitable for S. albiclavus are discussed. The most important of these is the presence of the ‘sub-puparial space’ in which the eggs are laid, without which the host is unacceptable. S. albiclavus will also breed on dead pupae and in puparia containing other parasites.

The number of parasites emerging from the host puparium is shown to be directly proportional to its weight.

The fecundity of S. albiclavus is shown to be very variable and dependent upon the weight of host material consumed during larval life, which, in turn, reflects the density of parasites in the host puparium from which the females emerged.

The duration of the parasitic phase of the life-cycle and the length of life of the adults are shown to be functions of the temperature. Length of life is also affected by the relative humidity, increased mortality occurring in low humidities and in saturated air, with an optimum for survival at about 80 per cent. R.H.

It is shown that a constant temperature of 35°C. is fatal to the eggs of S. albiclavus.

The age at which females of S. albiclavus become mature was investigated at three temperatures and it is shown that the rate of maturation of the ovaries is a function of the temperature.

At 25°C., females of S. albiclavus are unable to lay eggs until the third day after emergence. The number of offspring produced then falls off with increasing age of the female and very old females, although attacking hosts, are unable to oviposit.