A Chalcidoid egg-parasite of longhorn beetles of the genus Tragocephala, which damage shoots of cacao in West Africa, is attributed to the genus Aprostocetus Westw. (Eulophidae) and a new species, A. lamiicidus, is described for its reception. The morphological differences between this and some other African species of known economic importance are discussed and figured.

Descriptions are given of Orasema asscctator sp.n. and O. initiator sp.n. (Hym., Eucharitidae) from India, causing damage to the leaves of tea. For purpose of comparison, two species of the same genus are redescribed. The genus Semora Cameron is shown to be synonymous.

The so-called ‘sewing blight ’ of tea in Assam is an effect of oviposition in the young leaves by two species of Eucharitid, Orasema initiator Kerrich and O. assectator Kerrich. The affected leaves develop brown spots round the oviposition punctures, wither prematurely and adversely affect the quality of the made tea. Normally only a small proportion of bushes is affected and these are associated with the presence of nests of an undetermined species of Pheidole.

An account is given of the life-history of O. assectator, and the developmental stages are briefly described. The eggs are laid singly in incisions made by the ovipositor on the underside of the leaf in parallel rows arranged lengthwise. The newly hatched larvae exist as free-living planidia on the leaf surface, whence they are carried by unknown means into the ants' nests in the soil beneath the tea bushes. Here the planidium transfers to the last-instar larva of the ant and penetrates its body. There it remains inactive until its host reaches the prepupal stage, whereupon endoparasitic feeding and development start. After the host pupa has formed, the parasite larva emerges, establishes itself below the thorax of its host, and remains there, feeding ectoparasitically, through two further instars, completely consuming the contents of its host. The mature larvae remain scattered in the ant's nest and pupate a few days later; both larvae and pupae are cared for by the worker ants.

Blood-meals of two species of haematophagous insects, Glossina morsitans Westw. and Aedes (Stegomyia) aegypti (L.), have been ‘ marked ’ by allowing groups of adults to feed on an ox to which an aqueous solution containing 4 g. of trypan blue had previously been administered intravenously. The dyestuff is detected by a paper chromatographic procedure in which the blood-meal, mixed with 0·1N NaOH, is applied to a narrow strip of Whatman No. 1 chromatographic filter paper and the chromatogram is developed in 0·1N NaOH. Under these conditions, trypan blue remains at the origin, whereas the other coloured components of the blood-meal move away from the point of application. The duration of the mark in the ox and in the insects has been examined. The trypan blue was detected in four out of six fresh blood-meals of Glossina taken 38 days after injection of the dye into the ox, in six out of six examples of Glossina examined two days after blood-meals taken 24 days after the injection, in four out of six examples of Glossina examined eight days after blood-meals taken immediately following the injection, in six out of six examples of Aedes one day after blood-meals taken 14 days after the injection and in six out of six examples of Aedes two days after blood-meals taken immediately following the injection.

Members of the genus Tragocephala are widespread as pests of cocoa, and other tree crops, in West and also in East Africa. Those known to be associated with cocoa in West Africa are listed and observations are given on the biology of two of the more important, T. castitnia theobromae Entw. in Ghana and T. castnia cacaoensis Entw. in Nigeria, and a method of laboratory rearing and breeding is described.

The egg is laid in an unhardened stem and the oviposition behaviour is complex; the stem is first girdled at a point where it is less than one centimetre in diameter and an oviposition slit excavated above the girdle. The ovipositor is inserted into this slit and the egg is concealed inside the stem; the adult finally closes the oviposition slit with her mandibles.

The egg hatches after 11 days and the young larva bores upwards in the dead wood above the girdle. This phase appears obligatory and is followed by one in which the larva bores down into the living stem below the girdle. The mean larval period of T. castnia theobromae in the laboratory was 143 days (range, 70–228 days).

A pupal chamber is made by severing the stem beyond about 10 cm. above the end of the gallery and filling the aperture with shreds of wood. The pupal period, in the last half of which adult coloration begins to show, is about 20 days for T. castnia theobromae and 23 days for T. castnia cacaocnsis.

Laboratory evidence suggests that there is a post-pupal resting phase in the pupal chamber followed by a free-living non-feeding period; in T. castnia cacaocnsis these lasted on average 6·5 and 4·2 days, respectively, and were followed by intensive feeding on green unhardened stems. The length of life of caged adults varied greatly but the mean was 57·0 and 55·5 days for males and females, respectively, of T. castnia theobromae and 32·0 and 28·5 days for T. castnia cacaoensis. The least preoviposition period noted for T. castnia theobromae was 20 days and previously unmated males and females of this subspecies were still fertile up to at least 76 and 162 days, respectively. Mating normally initiated the bark-ringing behaviour of females and the maximum number of eggs laid by a female of T. castnia theobromae was 146. Considering only individuals that laid 25 or more eggs, an oviposition rate (number of eggs laid per day between first and last oviposition) of 0·51 was recorded for this subspecies. Host plants alternative to cocoa are listed for T. castnia theobromae and T, castnia cacaoensis.

The oviposition activity of T. castnia theobromae was least in June, July, August, December and January, whilst for T. castnia cacaoensis very few eggs were laid in the main dry season (November to the following February).

The eggs of T. nobilis (F.), T. castnia theobromae and T. castnia cacaoensis, and of another species in the Congo Eepublic, are attacked by the Encyrtid Aprostocetus lamiicidus Kerrich, which in Nigeria appears to undergo a larval diapause in the dry season. Whilst only 5·5 per cent, of eggs were attacked in Ghana, over 50·0 per cent, were attacked in Nigeria. There was an average of 11·7 individuals per egg and the ratio of males to females was 1:2·7.

The Tachinid Billaea vanemdeni Fennah was parasitic on larvae of T. nobilis and T. castnia theobromae in Ghana, where its larval stage was in the region of 197 days and its pupal stage 23 days. Incidence of attack was highest from April to July and the two main adult emergence periods were June and September/ October.

An Ichneumonid, Nadia sp., is parasitic on either larvae or pupae of T. castnia cacaoensis in Nigeria. Scolytid species incursive in wood dying after being girdled destroy many eggs in Nigeria, where geckoes and ants are thought to be responsible for loss of larvae.

Tragocephala can be a locally important pest, especially of seedling cocoa and its numbers may increase considerably if unsuitable chemical control methods are used against other pests of cocoa.

The bark-ringing habit in Cerambycidae is discussed.

Series of 24-hour catches at different levels were made at Zika and Lunyo in the Entebbe area, Uganda, using fowls (White Leghorn cocks) as bait, and some comparative catches were made with man as bait.

Thirty-seven different mosquito species (including five species groups) were taken on the avian bait.

The vertical distributions and biting cycles of each of nine species (including one species group), Anopheles implexus (Theo.), Mansonia (Coquillettidia) aurites (Theo.) gp., M. (C.) fuscopennata (Theo.), M. (Mansonioides) africana (Theo.), Hodgesia cyptopus Theo., Aedes africanus (Theo.), A. apicoargenteus (Theo.), A. ingrami Edw. and Culex annulioris Theo. were similar on human and avian bait.

At Lunyo both A. africanus and C. annulioris had a marked diurnal peak, which had not been described previously.

Comparison of the numbers coming to avian and human bait indicate that species of Culex, H. cyptopus and most of the species of Mansonia (Coquillettidia) have a preference for birds.

The effect of DDT applied to cotton plants four times at 10-day intervals at a rate of 1 lb. active ingredient per acre per application against Hemitarsonemus latus Banks was studied at Serere Eesearch Station, Uganda. DDT applied as a 10 per cent, dust, or in a spray from a 50 per cent, wettable powder increased the damage caused by the mite, while DDT applied in a spray from a 25 per cent. miscible liquid decreased it.

Another trial using a DDT miscible-liquid spray applied at intervals of 10, 15 and 20 days at 1 lb. active ingredient per acre per application demonstrated partial control of the mite. However, when spraying ceased, tea-mite damage increased. At the final count all spray intervals showed significantly less damage than the control and there was an over-all significant difference between spray treatments and the control. In both trials the number of mite-infested plants increased in an exponential manner with time.

It is not considered that the present recommended practice of applying DDT four times, at 15-day intervals, in a spray from 25 per cent, miscible liquid at 1 lb. active ingredient per acre will cause an increase of the mite on peasant-grown cotton in Uganda, although it will only partially control any infestation of it that is present.

Several species of Dynastid beetles are serious pests of yam (Dioscorea) in Nigeria, the adults attacking the setts and new tubers underground. The base of the yam vine and the roots are not generally damaged. The most important species is Heteroligus meles (Billb.).

H. meles does not breed in the yam fields, and the adults fly to them from breeding grounds that are distinct, and to which they return later.

The cultivation and growth of the yam plant in Nigeria are briefly described. Small tubers, or cut pieces of tubers (setts) are planted. The earlier the date of planting and of emergence of the vine from the soil, the heavier the vine and the new tuber.

An account is given of observations on the infestation, in relation to crop growth, of a plot of yellow yams (D. cayenensis) planted near Benin, in Western Nigeria on 29th March 1958.

Adults of H. meles were taken, from 3rd April to 26th June and again from 8th to 21st November, between 7 and 9 p.m., at a light-trap placed at a distance of ¼ mile from the plot.

Beetles entered the soil of yam hills within six inches of the vine, usually before 7 a.m., on mornings following evening flights, the entry holes usually being identifiable. The first vines were seen in the experimental plot on 19th April. Beetles did not enter a yam hill unless the vine had emerged.

The longer the exposure to flying beetles, the more likely were plants to be attacked, and bigger vines attracted more beetles than did smaller ones. Later planting decreased beetle damage, but a lower yield resulted.

At first the beetles fed on the sett, making and increasing the size of fewer lesions than later on the new yam. About the time that the flying period ended, the setts were starting to rot, and the beetles left the immediate vicinity of the yam plant, as no acceptable food was available. Most moved deeper into the soil, but a few left the plant altogether and flew away. After the new tubers had begun to develop, the beetles returned in early August from their positions deeper in the soil to feed on them, constantly making new lesions, more numerous but smaller than those made in the setts, averaging about 4 g. of yam eaten.

During late August and again in late September, a few beetles moved underground from the original plants attacked to others. In mid-November, the beetles left the yam fields altogether, presumably returning to the breeding area.

The reasons why the beetles fly away from the yam fields remain uncertain, but they may include the seasonal decline in rainfall, the maturation of the yam tuber and the development of the gonads.

Factors that can affect the rate of attack are the dates of planting and harvesting in relation to the period during which the beetles fly, the method of cultivation and the variety of yam planted.

The genetics of diazinon resistance in an Australian strain of Musca domestica L. was investigated by means of two series of repeated back-crosses of the hybrid resistant form to the susceptible. Resistance was maintained through nine and eleven generations in the separate studies. The ratio of susceptible to resistant hybrid flies found in the progeny of each cross was approximately 1:1.

In the second series, the frequency data were supported by dosage/response information on the relationship between dosage of insecticide and mortality. Together with the result of a previous study, the data furnish strong evidence that a fully dominant factor is responsible for the diazinon resistance in the Perth strain of house-flies resistant to organic phosphate insecticides.

Observations were made in Fiji on the ecology and control of two Delphacid planthoppers on rice, Sogatella furcifera (Horv.) and Nilaparvata lugens (Stål), the latter species having apparently been responsible for a devastating outbreak in 1959. The studies covered three rice seasons, 1961, 1962, and 1963, most of the research being done at Koronivia in the south-eastern part of Viti Levu. Samples were taken of planthoppers and their natural enemies in dryland (drilled) and wetland (transplanted) rice, as well as in rice seed-beds and areas with grass or mixed rice and grass. Insecticides applied at standard dosages were tested against the planthoppers.

It was shown that S. furcifera was most common on young rice and that N. lugens predominated on older rice. Sogatella kolophon (Kirk.), long placed in the genus Sogata and confused with Sogatella furcifera, was abundant only in grassy areas. Populations of N. lugens and, to a lesser extent, of S. furcifera, were apt to reach damaging levels on transplanted rice growing in pools of standing water after a dry period. In drilled fields, the predatory Mirid Cyrtorhinus lividipennis vitiensis Usinger provided effective control by destroying eggs of N. lugens, and, by the time the rice was six months old, it usually outnumbered the females of N. lugens. Parasitism of planthopper eggs by Mymarids, Trichogrammatids, and Eulophids was very low. Parasitism of adults of S. furcifera and S. kolophon by Elenchid Strepsipterons averaged about ten per cent, and that by Dryinid wasps less than one per cent. Adults of N. lugens were virtually free from parasitism but were sometimes infected by fungi. Factors influencing outbreaks are discussed. These include the amount of rainfall, the type of cultivation, the age of the rice crop, the species composition of the planthopper populations, and the relative abundance of Cyrtorhinus.

Insecticidal concentrates tested against both S. furcifera and N. lugens included malathion 50 per cent, emulsifiable concentrate, diazinon 20 per cent, e.c., Bogor 30 per cent, e.c., DDT 20 per cent, e.c., dieldrin 15 per cent, e.c., and Sevin 80 per cent, wettable powder. Dieldrin-resistant strains of N. lugens appeared during 1961, the third season in which dieldrin and BHC had been widely used. The other five materials gave good results, DDT being the least expensive and the most persistent, although it took more than 24 hours to reduce the plant-hopper populations. It was concluded that rice should be closely watched from its third to the end of its sixth month and that 50 oz. of DDT 20 per cent. e.c. in 50 gallons of water per acre, or an equivalent formulation of some other insecticide, should be sprayed on the rice stems if the planthopper density should exceed 10 per stem. Other possible measures for controlling rice planthoppers would include the introduction of Dryinid wasps parasitising N. lugens, the development of rice varieties resistant to planthopper attacks, and the use of controlled flooding in high-bunded fields, but on present evidence the first two appear to hold little promise of success.

Notes are given on the use of a chloral hydrate solution for clearing sandflies (Phlebotomus). Descriptions are given of three new species of sandflies from Uganda and Kenya (Phlebotomus (Sergentomyia) edwini, P. (Sergentomyia) kitonyii and P. (Sergentomyia) teesdalei spp. n.) and of the male of P. (Sergentomyia,) multidens Heisch, Guggisberg & Teesdale. Supplementary descriptive notes are given on Phlebotomus (Phlebotomus) rodhaini Parr., Phlebotomus (Sintonius) graingeri Heisch, Guggisberg & Teesdale, with illustrations of the spermatheca in both species, and the occurrence of morphological variation in the male genitalia of Phlebotomus (Sergentomyia) schwetzi Adl., Thdr. & Parr, in Kenya is discussed in relation to season. Data are given showing natural infection rates with flagellate Protozoa in populations of Phlebotomus (Serigentomyia) garnhami Heisch, Guggisberg & Teesdale in part of the Kitui district of Kenya.

The persistence of DDT deposits, derived from dilutions of an emulsion concentrate, Arkotine D.25, on the leaves of riverine vegetation in the Northern Guinea Savannah vegetation zone of Nigeria was studied in the laboratory by a bioassay method using teneral females of Glossina palpalis (R.-D.) as test insects. Irrespective of whether sprayed in the dry or wet season, deposits derived from sprays containing 5.0 per cent. DDT produced by the Warley knapsack sprayer were still reasonably toxic one year after spraying. Deposits derived from sprays having a concentration of DDT varying from 1·25 to 5·0 per cent. DDT were equally toxic when young, but those from the lower concentrations were weathered much more rapidly than those from the 5·0 per cent, sprays. Young deposits produced by Warley and Motoblo sprayers were equally toxic, but deposits from the Motoblo deteriorated more rapidly than those of the Warley.

The toxicity of the DDT deposits on leaves varied regularly with the seasons. The various climatic factors that it is thought influenced the variations in toxicity are discussed. Accumulations of wind-blown dust on the leaves during the late dry season and low evaporation rates at the height of the rains appear to be responsible for reduced toxicity at those times; in the early wet season, the occasional violent storm probably washes off the leaves the dust accumulated during the dry season and makes the insecticidal deposits once more available. Heavy rainfall is important in removing the insecticidal deposits from the vegetation, and leaf decay and refoliation are important in reducing the availability of the deposits. The implications of these variations in toxicity and factors that reduce the availability of the deposits are discussed in relation to the eradication of riverine tsetse.

Great differences in the rates of foliage decay and refoliation occur between different riverine plants, and it is suggested that a thorough study of this feature in riverine plants and of resting sites favoured by tsetse flies might reveal information that would enable tsetse to be eradicated by selective spraying of certain plant species only.

Amblyomma lepidum Dön., previously incriminated as a vector of heartwater (caused by Rickettsia ruminantium) among sheep and goats, and possibly camels, in southern Kassala Province, Sudan, is apparently the only Amblyomma species in this area. Systematic collections of all ticks infesting domestic animals were carried out in November 1959, just after the rains, in five ecologically differing areas in the region most severely infected with heartwater. Though rare in desert scrub (north of 16°N. latitude) and only moderately numerous in semidesert grassland (Butana area), incidence of A. lepidum is high in wooded savannah (River Atbara) and in the cultivated Gash Delta, and highest (15·5 per host) in the Acacia seyal savannah of the River Gash. Chief hosts of adults are cattle. Sheep are secondary hosts, and camels, donkeys, and goats are less heavily infested. Two males were taken feeding on humans. Mating (breeding) activity is only slight following the rains (November). Few larvae and nymphs were found during this period; those present were mainly on sheep and goats, with a few on cattle, and these were usually feeding on the hoofs of their hosts.

Rhipicephalus s. sanguineus (Latr.), the most numerous and widely distributed tick here, infests chiefly sheep and goats, is common on cattle, and also occurs on camels and donkeys. Mating activity of this species is high in November. Hyalomma dromedarii Koch is equally widely distributed and follows R. s. sanguineus in numbers, but is most frequent on camels, common on cattle, and rare on donkeys and sheep; goats were uninfested. Mating is moderately active at this season. The incidence of H. impeltatum Schulze & Schlottke, which occurs in each zone, equalled that of A. lepidum. Cattle are the chief hosts and camels are secondary hosts; donkeys, sheep, and goats are less frequently infested. Mating activity is moderate in November.

Other more or less common tick species on these domestic animals are Boophilus decoloratus (Koch), R. e. evertsi Neum., R. simus Koch, H. anatolicum excavatum Koch, H. truncatum Koch and H. marginatum rufipes Koch, evidence for the status of which as a subspecies of H. marginatum Koch is to be presented in a subsequent paper. Several other rare species are also recorded.

Results are presented of 15 experiments made in north coastal districts of New South Wales from 1957 to 1961 with insecticides against the weevils Amnemus quadrituberculatus (Boh.) and A. superciliaris (Pasc.), the larvae of which have been reported as pests attacking the roots of clover (Trifolium repents, T. pratense and T. subterraneum) there. The adults live above ground, and single surface applications of insecticides were made to pastures in the form of dusts, granules or dilutions of emulsifiable concentrates in January, when maximum numbers of weevils were present and before significant oviposition had taken place. Insecticidal control was assessed by soil sampling for larvae in July–August, during the following winter. Pasture cuts were made in an attempt to assess the effect of treatments on the yield of clover.

Dieldrin at rates of 2 and 4 lb. per acre gave near eradication of Amnemus for one year, and satisfactory control was obtained with 1 lb. per acre. Aldrin, endosulfan (Thiodan) and BHC were less effective, and limited tests with heptachlor suggested that it was inferior to dieldrin. The scanty results available suggest that dieldrin is effective against Amnemus for only one year, but it is doubtful if annual applications are warranted. Owing to the patchy distribution of clover in the pastures, only one experiment showed an increased yield of clover associated with the reduction in numbers of larvae of Amnemus brought about by the application of 1 lb. dieldrin per acre. Similarly, poor persistence of clover on all plots prevented assessment of any residual effect on yield in the second year.

No method was found by which accurate estimates could be made of the density and distribution of adults of Amnemus in pastures to which insecticides were to be applied. Treatments, therefore, were replicated more frequently than was needed statistically in order to ensure that measurable levels of larval infestation were present at sufficient sites.

Small plots (500–700 sq. ft.) proved of little value, and this is attributed not only to contamination of control plots but possibly also to the death of weevils that moved from untreated into treated plots. Large plots (13,000–21,000 sq. ft.) gave the most consistent results in assessment of insecticides.

Control of Amnemus did not increase the productivity or persistence of clover, and it is concluded that any benefits from control are unlikely to be significant unless other factors, such as competition from grasses, drought, floods, nematodes and diseases of clover, which affected the density and persistence of clover in these experiments, are not limiting.

In a long series of experiments with Lasioderma serricorne (F.) carried out at 30°C. and 60 per cent. R.H. it was established that shortage of food prolongs development and reduces survival of the immature stages and also reduces the weight of the resulting adults. Competitive effects between larvae over and above those caused by food shortage alone were not detected. Larvae ate eggs and pupae only in the complete absence of any other food, and they did not appear to eat one another. There was no trend in the performance of the immature stages attributable to the age of the female parent at the time of oviposition. Variation between the times taken by different individuals to attain a subsequent stage was positively skewed. Adult females weigh more than males, this difference in weight first occurring during the third (penultimate) larval instar. There were no significant differences in the developmental periods of the sexes.

Estimates of the size of populations of the red locust, Nomadacris septemfasciata (Serv.), in their outbreak areas have been made in Tanganyika from counts of adults caused to fly up by the approach of a slowly moving vehicle. For research purposes it was desirable both to improve and estimate the accuracy of such assessments. For control purposes it was desirable to devise an objective aerial assessment technique which could be used in areas where ground methods were either impracticable or expensive. The errors involved in both ground and air estimates can be divided into those concerned with the ratio of locusts counted in the sample area to those actually present, and those concerned with the distribution of the locusts.

It was found that a Land-Rover moving at five miles an hour, with the wind blowing from a rear quarter, flushed a high and virtually constant proportion of locusts during most of the day and in the most important grasses of the Rukwa outbreak area, throughout the dry season. Variation in locust density and in the state of the grass had little effect, if any, on the value of the equivalent strip (e), i.e., a strip whose width is such that the number of locusts in it is equal to the number flushed by the vehicle in a strip equal in width to its own. The change with time, and thus presumably with locust behaviour, in the value of e, estimated as recommended, was small but significant.

Counts by various observers in one vehicle gave similar results and it seems likely that, even with high numbers, there was no systematic mis-estimation. This is almost certainly true for counts of under a hundred locusts flushed per 0·1 mile. With upwards of one thousand 0·1-mile counts in each assessment, it is believed that the random errors due to mis-counting of the locusts flushed will be negligible.

The locusts are always distributed in an over-dispersed manner, consequently normal techniques for ascertaining the standard error of estimate cannot be used. Three assessments were made by the methods recommended, using a grid of two-mile squares; in one case, where the distribution was very gregarious, the most densely populated sector was more intensively sampled. The standard error of assessments laid out in this way was estimated. The method of analysis overestimates the standard error to some degree. Alternatively, the standard error resulting from the nature of the locust distribution can be computed for assessments where the 0·1-mile counts can be shown to be distributed log-normally.

Provided the population assessment is carried out under the conditions stipulated above, the additional errors will be minor. The effect of such errors will be likely to be so small that the estimated standard error, derived from the lognormal or assessment-grid analysis, may be regarded as a valid estimate of the standard error of the population estimate.

An attempt was made to estimate populations of the red locust in part of an outbreak area from locusts flushed by a ‘ Prospector ’ aircraft. The trials suggested that, given a clear rear view, red locusts which were flushed could be identified as such. Further, the number of locusts flushed could be counted at low densities, and it is thought likely that a reasonably objective technique could be developed for estimation at higher densities.

Flushing appeared to be most effective at an aircraft height of 20 ft. or less and when the direction of flight was with the wind. However, the majority of locusts present failed to take off and the proportion which did rise varied very greatly. The spraying of concentrated ammonia under pressure increased the efficiency of flushing.

A large-scale comparison of air and ground assessments suggested that, under the prevailing conditions, a considerable proportion of the locusts could be flushed only from the dense concentrations. At all densities the proportion of locusts which the aircraft caused to rise was a small fraction of those present. With flushing of such a low level of efficiency, little idea could be obtained of the size of the locust population at a moderate or low density.

The facultative larval diapause of the khapra beetle, Trogoderma granarium Everts, is initiated extrinsically by temperature, crowding, and very low or very high humidity. In crowded populations, in tubes of wheat, the proportion of diapause larvae varies from very low (2 to 3 per cent.) in the upper part of the insect's temperature range to 100 per cent, in the lower part. Diapause larvae become more frequent with increasing population density, the frequency becoming noticeable at a density of about ten larvae per gramme of wheat (about 10 times their minimum food requirements). Accumulation of faecal pellets is a factor that induces diapause in crowded conditions. Many larvae that are kept singly enter diapause when fed on old culture food from which pellets have been removed: possibly in the old culture the pellets impart to the food a substance that initiates diapause. The availability of a suitable refuge, in which larvae can cluster, has no consistent effect on the proportion of diapause larvae. Factors that induce diapause also slightly increase the developmental period of non-diapause larvae.

In malted barley, more larvae enter diapause than in wheat, probably due to the intensification of crowding by the confinement of larvae to a few malt grains.

The relative importance of the factors that induce diapause is discussed. These factors help to explain observations in stores and conflicting results in the literature. The main function of diapause seems to be in assisting the larvae to survive periods of food shortage; diapause may also improve the survival of larvae in a cold winter and synchronise the emergence of adults. Of the factors inducing diapause, accumulation of faecal pellets precedes food shortage and falling temperatures precede the cold of winter, but the role of high and low humidities in this connection is difficult to assess. Diapause larvae play a major part in the dispersal of the species. The diapause of T. granarium is compared with that of other arthropods.

Resistant and normal colonies of the blowfly Chrysomyia putoria (Wied.) were obtained from the Congo and cultured in London. By selection and inbreeding, sub-colonies homogeneous for resistance to (a) the BHC/dieldrin group of chlorinated insecticides and (b) malathion, were obtained. Homogeneous resistant colonies were markedly less fertile and were difficult to perpetuate.

Toxicological investigations of the BHC/dieldrin-resistant colony revealed a characteristic resistance spectrum similar to that of six other insect species. Genetical experiments with the BHC/dieldrin-resistant strain indicated inheritance by a single gene pair, intermediate in dominance, very similar to that reported in nine other insect species.

Toxicological investigations of the malathion-resistant colony, including tests with 19 organophosphorus insecticides, showed a resistance largely specific to malathion and malaoxon. This was rather similar to malathion-resistant strains of two other species, for which data were available. It is known that the toxic action of malathion on mammals can be potentiated by prior treatment with small doses of certain organophosphorus compounds, which inhibit an aliesterase that detoxifies malathion by carboxylic hydrolysis, and furthermore that potentiation has been found in malathion-resistant strains of the house-fly, Musca domestica L. Accordingly, the phenomenon was investigated in C. putoria by adding non-lethal amounts of EPN or tri-o-cresyl phosphate (TOCP) to malathion. It was found that specific malathion-resistance was virtually abolished by this means, a result that suggests that such resistance in this species depends on a carboxyesterase. Genetical experiments with the malathion-resistant strain indicated inheritance by a single gene pair, with nearly complete dominance, similar to that in three other insect species.

It is concluded that both types of resistance in C. putoria have much in common with those occurring in analogous strains of other insect species.

The ecology of the adult mosquitos of the Northern Guinea Savannah was studied from 1960 to 1962 in the Kaduna area mainly in two Hausa villages, Anguwun Rimi and Kangimi, and in nearby Fulani settlements. A description of the area and various types of village huts is given together with an account of the climate and meteorological data. Emphasis was on the Anophelines and their relation to malaria but at the same time information on the Culicines is presented.

Biting catches, in which mosquito scouts acting as human bait collected adults in test-tubes, were performed for over a year in A. Rimi. A total of 38 species was caught in these collections, but many appeared only infrequently. By far the commonest mosquito biting man was Anopheles gambiae Giles which had its peak density towards the end of the rains, in September, and although its population was greatly reduced during the dry season it however remained the principal anthropophilous species. In the area in which the catches were performed A. nili (Theo.) was the second commonest mosquito, and with the exception of March it was more abundant than A. funestus Giles. In other areas it was not so common, and in Kangimi A. funestus was almost as abundant during the rains as A. gambiae, and at the beginning of the dry season it became the main Anopheline. Most of the other Anophelines that were taken at bait were only caught in any numbers during the latter part of the wet season; for the remainder of the year they were virtually absent. Mansonia uniformis (Theo.) was abundant in October, but for the rest of the year it was rarely taken; M. africana (Theo.) was found to be uncommon in the area. Due to the close proximity of Kaduna to A. Rimi, Culex pipiens fatigans Weid., a species now associated with urbanisation and not with villages, was common. Both bait catches and pyrethrum spray-sheet collections in houses showed that it greatly increased in numbers at the beginning of the rains, but that this high level of density was not maintained, and during the greater part of the wet season the species was less common than in the early rains. Aedes aegypti (L.) sens. lat. was rare both in houses and in bait catches; the two principal Aedes species were Ae. vittatus (Big.) and Ae. furcifer (Edw.); the latter species is confined to the Savannah zones. The biting cycles of the three main Anophelines were characterised by maximum feeding occurring after midnight. In both A. gambiae and A. nili there were two main peaks, between 2400 and 0100 and between 0300 and 0400 hr.; in A. funestus, maximum biting occurred between 2400 and 0200 and between 0300 and 0400 hr.

By the use of mosquito nets baited with humans, both inside huts and out of doors, the relative attractiveness, to the anthropophilous Anophelines, of man in the two situations was assessed. It was found that A. nili was equally attracted to man in both situations, and although slightly greater numbers of A. gambiae and A. funestus were found biting out of doors, for practical purposes man is equally attractive in both places. Certain species, notably A. coustani Lav. sens, str. and A. hancocki var. brohieri Edw., were rare or absent in the inside and outside bait-net collections, whereas they were readily taken in both situations in test-tube catches performed in the same locality on the same nights. In fact, more specimens of A. coustani sens. str. were taken in the outside test-tube catches than of either A. funestus or A. nili, and A. hancocki var.brohieri was commoner than A. funestus.

Catches of adults from mud walls and thatch roofing of typical round village huts showed that there was generally no appreciable difference in the attractiveness of these two surfaces to either A. gambiae or A. funestus, but as the thatch only comprised about 34–44 per cent, of the internal surface area of the huts the absolute number resting on the walls will be greater than on the roof.

Spray-sheet collections showed that besides large numbers of A. gambiae and A. funestus resting; during the day-time in normal mud-walled living huts of the Hausa, high densities of these species were found in the Fulani huts, which do not incorporate any mud in their design, and moderate numbers were also caught in Hausa villages in the zaures (huts resembling living ones, but without doors, furniture or fires and not normally slept in at night). Collections from outdoor resting places demonstrated that considerable day-time resting occurred in uninhabited huts, under eaves of huts, both inside and under eaves of goat stables, in kitchens, amongst the tightly woven grass mats termed ‘ zana ’ matting, in rodent holes, tree holes, pots, near wells, amongst grass and vegetation and underneath and under the eaves of grain bins. Surprisingly few examples of A. nili were found in any of the outside resting shelters examined, despite the fact that both exit traps and spray-sheet collections showed that it bit freely in huts but rarely stayed in them. The large number of A. gambiae and A. funestus found out of doors, coupled with the exodus of blood-fed individuals from huts, showed that an appreciable amount of exophily occurred in both species. Entrance traps fitted to village huts caught, in addition to unfed, both blood-fed and gravid (taken to include half-gravid and full-gravid) females of A. gambiae and A. funestus, suggesting that a certain amount of exophagy and re-entry of gravid individuals was occurring. Numerous precipitin tests were made on blood-meals obtained from A. gambiae, A. funestus and A. nili. and a few also from most of the other species. Results showed that the three principal Anophelines were strongly anthropophilous but the exophilous population of A. funestus and A. gambiae showed some deviation to other vertebrates. Most of the other Anophelines, e.g., A. rufipes (Gough) sens, lat.,A. hancocki var. brohieri, A. flavicosta Edw. and A. longipalpis var.domicolus Edw., found resting in goat shelters and other outdoor sites had fed mainly on other vertebrates.

On account of the already available information on the infectivity of both A. gambiae and A. funestus in Northern Nigeria, dissections for estimation of sporozoite rates were only carried out on their exophilous populations, and in both species these were shown to contribute to malaria transmission. Attention was concentrated on dissecting the other Anophelines, special attention being paid to A. nili. Only two species were found with infected salivary glands. A. flavicosta had a crude sporozoite rate of 2·74 per cent, of the 73 dissected, and from 998 examples of A. nili a crude sporozoite rate of 0·80 per cent, was obtained. It was thought that as A. flavicosta was mainly zoophilous it was possible that the sporozoites in the glands were of malaria not of human origin. It appeared that where A. nili was common it could become a secondary vector, and on account of its marked exophilic nature it might prove difficult to interrupt transmisssion by this species.

The relatively recent increase in towns of C. p. fatigans and the almost virtual disappearance of C. nebulosus Theo., formerly the predominant Culicine, and the possibility that this change might have been initiated by the practice in recent years of using DDT larvicidal formulations and not oil, is discussed.