The duration of the aquatic stages of the mayfly, Povilla adusta Navás, in Lake Victoria, Uganda, has been determined by analysing larval samples from the stomachs of an insectivorous fish, Mormyrus kannume Forsk., and by culturing eggs in vitro. Emergence shows a well-defined lunar rhythm and, since adults live for only about one hour, duration of the aquatic stages must be an integral number of lunar months. Results indicate that a generation is usually completed in four or five months. Approximately the first two weeks of this period are spent in the egg.

The periodicity of reproduction imposes a feeding rhythm on certain species of fish in Lake Victoria. Some biological implications of the need for synchronisation are briefly discussed.

The varieties of the banana plant (Musa) on the Kenya coast, with particular reference to Aëdes simpsoni (Theo.), a species concerned with the transmission of yellow fever in East Africa, are described, and the species of mosquito larvae found in their leaf axils are recorded. A. simpsoni was virtually the only species present.

Details are given of the proportion of leaf axils that contain water and the percentage of these that produce larvae. Breeding was found to take place in all varieties, but to a much lesser extent in that known as Kibungala than in the others. Although there was often more water in the lower and upper axils than in the middle ones they produced less larvae individually than did the latter. Larvae were also found in old axils at the base of the stems in spite of the fact that these sites seldom appear to provide direct access for an ovipositing mosquito. Water was present throughout the year in the upper axils only.

It was found that the water content of axils varied from day to day and from morning to evening during dry periods and that the axils were often apparently dry for days at a time although the larvae were able to survive. It is suggested that the larvae are able to survive in the water film at the base of the axils, but that such unfavourable conditions may account for the retarded growth that has been observed.

The relationship between water content and number of larvae per axil is discussed, and the conclusion is reached that unless all measurements of water content for all varieties are made simultaneously each day, a comparison of average water content becomes impossible, and therefore no connection can be established from the data so far available.

Results are given of investigations on the effects of five post-treatment temperatures on the mortality of adults of Tribolium castaneum (Hbst.) sprayed with five or six concentrations of each of six insecticidal formulations, emulsified solutions of DDT, γ BHC, toxaphene, chlordane and parathion and a suspension of DDT.

With both emulsified solutions and suspensions of DDT and emulsified solutions of γ BHC the mortality of the insects decreased with the rise of temperature from about 14° to 30°C. and increased when the temperature increased from 30° and 40°C. On the other hand, with emulsified solutions of toxaphene, chlordane and parathion, the mortality of the test insects increased continuously with increase of temperature from 14° to 40°C. As a possible explanation for such divergent results with different insecticides it is tentatively suggested that whilst the inherent physiological resistance of Tribolium to DDT and γ BHC formulations which appear to increase with increase of temperature up to a certain point has been demonstrated, the technique has not been sufficiently critical in the case of the other formulations, and it is thought that physiological resistance has possibly remained masked by other factors and that the values of LC50 are not a true index of physiological resistance in the ease of these insecticides.

An essential similarity between the curve obtained by plotting values of LC50 against temperature in the case of DDT and γ BHC and those relating temperature to other physiological activities (published by various workers) has been stressed, implying a similarity between the resistance of the insect to insecticides on the one hand and its other physiological activities on the other.

Observations on the behaviour of Culex pipiens fatigans Wied. were made in 24 huts built and occupied by Africans on a sisal estate near Tanga, Tanganyika Territory. Catches were made in four huts each day, an exit trap being fixed on the window from 2 p.m. to 6 p.m. (evening trap) and replaced by another from 6 p.m. to 8 a.m. next day (morning trap), when a spray catch was made of the mosquitos still in the hut. Each hut was used only once a week, for 31 weeks, from December 1952 to July 1953. The females caught were sorted according to the stage of the gonotrophic cycle, as judged by external examination. The stages used were: I, no blood, no visible ovaries; II, stomach full of blood, ovaries small; V, little or no blood, ovaries fully developed; III and IV, intermediate between II and V.

An analysis of variance was performed on the results. Catches of both sexes showed a significant variation with time, which was not, however, correlated with rainfall. Significantly different numbers were taken in the traps and in the huts. Females were significantly most numerous in the hut catch, and males in the morning trap, the former result suggesting that most females spend more than one day in a hut. There were significant differences between the numbers of females in the different stages of the gonotrophic cycle, stages I and II together accounting for 80 per cent, of all females caught. The high proportion of stage I is attributed to delay between emergence and feeding, and of stage II to the taking of more than one meal during the gonotrophic cycle, later meals obscuring the state of ovarian development. There were significant differences between huts as regards the numbers of females caught, but not as regards males, and it is concluded that this is due to variations in the attractiveness of the inhabitants of the huts.

Females in stage I were most numerous in the morning trap, those in stages II–IV were taken only rarely in traps, but there was no significant difference between numbers of stage V caught in huts and in the two window traps. These results arse attributed to restlessness in both hungry and gravid females, and sluggishness in fed ones. All stages except III were significantly more numerous in some weeks than in others and this might be due to variations in either rate of reproduction, or rate of loss of mosquitos from huts. There were significant variations in behaviour in different weeks. For females, this is attributed to changes in the proportions of the stages with time and the dependence of behaviour on stage. For males, there is some evidence of a relation between behaviour and humidity outside the hut. For females, the distribution of stages between different places of capture changes with time, stages II and III being most consistently associated with hut catches, while the most variable behaviour is shown by stage V.

The necessity for behaviour studies on mosquitos in the field is pointed out, especially in relation to field trials of residual insecticides.

Athalia lugens subsp. proximo (Klug) is a pest of cruciferous crops, and shows special preference for turnip. In the matter of selection of food, smell and taste of the food and the age of the plant are important factors. Epilachna vigintioctopunctata (F.) is a pest of solanaceous plants, particularly brinjal. In this insect only smell and taste are important factors in the selection of food.

The hydrogen-ion concentrations of the salivary gland, foregut, midgut and hindgut of the larva of Athalia are 6·4–6·6, 6·4–6·8, 6·6–6·8 and 7·0 and of the adults 6·2–6·4, 6·4–6·6, 6·4–6·6 and 6·6, respectively. The hydrogen-ion concentration of the salivary gland, foregut, midgut and hindgut of the larvae of Epilachna are 5·4, 6·4–6·8, 6·0 and 6·0 and of the adult 6·6–6·8, 6·2, 6·0 and 5·4–5·7, respectively.

The foregut and hindgut of the larvae and adults of Athalia and Epilachna do not secrete enzymes; the salivary glands of both larva and adult of Athalia secrete amylase, the midgut epithelium of both larva and adult of Athalia secretes amylase, maltase, invertase, lactase, lipase and protease. The salivary glands of the larva of Epilachna secrete amylase, but those of the adult do not, and the midgut epithelium of both larva and adult secretes amylase, maltase, invertase, lactase and protease. The midgut of both larva and adult of Epilachna secretes lipase also, although in the adult no more than traces are detectable. The proteases in both insects act in slightly acidic media.

Experiments were carried out in West Bengal to ascertain whether the Paddy Stem Borer, Schoenobius incertulas (Wlk.) could be controlled by “Tetrax” 1, a systemic insecticide containing technical schradan equivalent to approximately 42 per cent, octamethyl pyrophosphoramide + approximately 25 per cent, triphosphoric acid pentadimethylamide.

In a preliminary experiment, treatment had little effect on the damage caused by the borer but the yield of grain was higher from a treated plot than from a control plot.

A further experiment was carried out, the following year, in which the seed was soaked in a 0·1 per cent, water solution of “Tetrax” 1 for eight hours before sowing in the seed beds. The seedlings were lifted about 2½ months later and steeped in 0·1 per cent. “Tetrax” 1 for eight hours before transplanting into two plots, each 32 ft. × 32 ft. About three weeks later the plants were sprayed with a solution of the same strength. Two plots of similar size, in which the paddy had received no treatment, were maintained as controls.

Again there was very little difference, between the treated and untreated plots, in the damage caused to the ear heads by the pest, but the treated plots produced 108·68 lb. of grain as against 77·27 lb. for the untreated plots. The increase was largely due to an increase in the number of ear heads per plant.

The incidence of the borer was too low in both experiments to determine whether “Tetrax” 1 exercised any appreciable control, but the treatment did give rise to a higher yield of grain under the conditions of the experiments.

Continuous trapping of winged Aphids was carried out with Moericke trays and a suction trap for two years at a site at 6,850 ft. above sea level in Kenya, and with Moericke trays, for four months only, at a site at 1,200 ft. in southern Tanganyika.

The trap data show a marked seasonal periodicity of flight (three-quarters of the annual catch in two months) at the Kenya site. The large catch is a reflection of a large increase in population following the rains. A similar relation between size of catch and the period of the rains is indicated by the data from Tanganyika.

Successive hourly catches with a suction trap show no distinct diurnal double peak of aerial density such as occurs in Europe.

A method is described by which a continuous supply may be produced, efficiently, of large numbers of adults of Drosophila melanogaster Mg. of known age and sex for microbioassay tests.

Equal numbers of male and female flies were introduced into breeding jars containing a nutrient medium and maintained at 24–25°C. and 60–80 per cent, relative humidity. They were removed ten days later, just before the emergence of their progeny.

It was found that the physical conditions in the culture jars exerted an appreciable influence on several aspects of the breeding of Drosophila. Thus, in trials in which the surface of the nutrient medium was flat and unbroken, with a pad of cotton-wool laid on it to provide suitable sites for pupation, and with or without a layer of cotton-wool beneath it, or in which the medium was broken with irregular lumps, laid on a layer of cotton-wool and arranged with a space, filled with cotton-wool, at the centre, the best results were obtained with the last modification.

Under these conditions, emergence of adults began earlier and reached its peak earlier, a most constant sex-ratio and a higher number of progeny per female, and consequently a higher yield of flies per culture jar, were obtained.

A special device, which takes advantage of the positive phototropism of the flies emerging from a group of culture jars enclosed in a darkened box with an exit funnel leading into a collecting jar, made it possible, by daily replacement of the collecting jar, to remove practically all newly emerged flies within 24 hours, so that the known age of any batch is accurate within the limit of one day.

Male flies have been found to be twice as susceptible as females and give a greater response to differences in dosage of toxicant. For this reason male flies only are to be preferred for use in bioassay experiments.

Using another device, the flies were therefore sexed, and the required number of batches of males collected. This device consists of a glass-covered container through which a gentle continuous stream of CO2/air is passed over the flies, which have already been anaesthetised with CO2. The male flies are taken up individually with a small aspirator and passed direct into test tubes where they are collected in batches.

By means of a laboratory spraying technique, ten comparisons were made of the resistance to rotenone of samples of adult apterous viviparous parthenogenetic females of the Pea Aphid, Acyrthosiphon pisum (Harris), reared on broad bean and on clover, respectively. In nine of the tests, the Aphids from clover were more resistant than those from broad bean, the ratios ranging from 1·1 to 2·5. These differences were not all significant. In the remaining test the Aphids. from broan bean showed a very small increase in resistance over the Aphids from clover which was not significant.

The Aphids from the clover were generally smaller than those from broad bean. Figures are given to show that while the total amount of poison retained by the larger individuals from broad bean was more than that retained by the smaller individuals from clover, the amount of poison retained per unit body weight was greater with the smaller individuals. It appears, therefore, that while the results obtained might be due, at least partially, to the greater total weight of poison retained by the larger individuals from broad bean, the difference in resistance between the insects from broad bean and clover, respectively, might be even greater if the poison were applied on the basis of equal weight of poison per unit of body weight. Since the difference in resistance between the Aphids from the two host-plants did not appear to depend primarily on difference in size, the assumption might be made that it is due to difference in nutrition. It was found that Aphids reared on clover had a significantly higher proportion of dry matter in their composition than those reared on broad bean, which may be taken as evidence that differences due to nutrition are being produced. These may lead to differences in resistance.

An experiment has been undertaken in Northern Nigeria to ascertain whether the felling of the trees forming the overhead canopy and the deliberate blocking, with trash, of the stream-bed to obstruct the tsetse's flight-line, would result in the eradication of Glossina palpalis (R.-D.).

Obstructive clearing was employed on approximately 3¾ miles of stream. The results suggest that, provided the experimental reaches are adequately isolated, obstructive clearing does lead to the eradication of G. palpalis.

It is noteworthy that if, owing to inadequate isolation, the cleared stream becomes re-infested in the rains, conditions for at least the first two dry seasons are so unfavourable that flies cannot persist.

The immediate effect of obstructive clearing is to increase greatly the hunger of the few surviving flies.

Records suggest that obstructive clearing leads to a considerable reduction in the number of human hosts visiting uninhabited parts of the stream, presumably because of the destruction of forest produce. The duiker (Sylvicapra and Cephalophus) population also becomes greatly reduced, especially in the vicinity of hamlets. The hunger observed in the surviving fly population may therefore be in part due to an actual reduction in the number of hosts, as well as to the altered environment, which prevents free movement, under shade, of the hungry tsetse that is searching for food; instead, the tsetse is forced out into the open, where the climate in the dry season is intolerable, and presumably the unsuccessful fly rapidly succumbs from water-loss.

The effect of obstructive clearing on the vegetation is as follows. Within a few weeks the mound of trash is overgrown with creepers, Mucuna pruriens becoming dominant. In the first year's heavy rains the mound of trash tends to sink down in the stream-bed; on larger streams, spates do some temporary damage to the creeper growth and gaps may appear in the obstruction. The impression gained is that the blockage will persist for many years on small tributaries, but will disintegrate within a few years on larger streams. In very hilly country, with a rapid run off, the obstruction is likely to be displaced. In perennial streams of the type dealt with, the annual fires make only small inroads into the obstruction.

The technique evolved for the obstructive clearing of streams is described. The cost of this method worked out at 390 man days per mile, which is about half the cost of the present methods.

Should large-scale undertakings in the field confirm the efficacy of this new method, the biggest saving will be the elimination of the present necessity to re-slash streams that have been partially cleared. Observations will be continued to ascertain how long it will be before the vegetation again becomes suitable for G. palpalis.

Results are given of laboratory trials of insecticides, carried out in Kenya, against two pests of agricultural crops in East Africa. Against Epilachna hirta (Thnb.) (Col., COCCINELLIDAE), the adults and larvae of which feed on the foliage of wheat and other crops, dusts containing 0·5 or 2 per cent, parathion, applied at rates to give 0·74 to 2·97 mg. active ingredient per sq. ft., were the most rapidly effective against the adults. A 5 per cent. DDT dust, at rates giving 0·36 to 5·82 mg. technical DDT per sq. ft., was less rapid in action but produced very good results by the end of three days. A proprietary BHC dust, used at rates giving deposits of from 0·23 to 1·04 mg. γ isomer per sq. ft., was less effective and, at the highest rate used, only reached 100 per cent, mortality after eight days.

Several insecticides were tested in emulsified solutions against Cylas puncticollis Boh. (Col., CURCULIONIDAE), one of the important sweet-potato weevils of East Africa. All the insecticides were applied at concentrations of 0·02, 0·1 and 0·5 per cent, active ingredient, and at a deposit rate of 0·813 mg. of spray per sq. cm. DDT was the most effective after 18 hours, but γ BHC was only slightly inferior.

Experiments with second-, third- and fourth-instar larvae of Aëdes aegypti (L.), as well as pupae, were carried out to determine their behaviour in temperature and light gradients in an experimental trough.

When second-instar larvae are subjected to a temperature gradient from 42°C. at one end of the trough to 8°C. at the other, the majority of larvae aggregate over the range of temperature 23–32°C. Third- and fourth-instar larvae and pupae, however, show a marked preference for the range of temperature between 28–32°C.

When subjected to a light gradient from 1·08 log foot-lamberts to log foot-lamberts, second- and third-instar larvae show no marked preference for any one light intensity. The majority of fourth-instar larvae, however, aggregate in the darkest region of the trough, and this negative phototactic reaction is very pronounced in the pupae. This behaviour is probably correlated with the development of sense organs as the larvae grow. In the case of light gradients, it is likely that the increasing negative phototactic reaction is due to the increasing sensitivity of the imaginal compound eye which starts developing in the early larval instars and reaches an advanced stage in the pupa.

Three aerial applications of the n-butyl ester of 2,4,5-trichlorophenoxyacetic m acid (2,4,5-T) in diesel oil were made at intervals of six weeks to an isolated woodland community on a peninsula in Lake Victoria, Kenya. The woodland contained two species of tsetse fly, Glossina pallidipes Aust. and G. palpalis (R.-D.) (subsp. fuscipes Newst.). The object of the treatment was to defoliate the woodland in order to ascertain whether the reduction in shade would control the tsetse fly. It was also desired to obtain further information on the effect of the spray applications on the woody plant species.

The first application, at an estimated actual dosage of 2·2 lb. 2,4,5·T per acre, resulted in a rapid defoliation of 13 out of the 15 observed leafy species, eight of, which subsequently died during the following nine months. Two succulent species of Euphorbia also died during this period. Of the remaining two species, one was fully defoliated only after the third application but recovered slowly, while the other, Lecaniodiscus vaughaniae, was but slightly affected at any time.

No significant reduction in the numbers of tsetse fly was observed during the nine-month period following the first spraying. The following factors probably account for this lack of effect: the varying rate of defoliation of the different plant species, the resistance to the spray of one locally abundant species, the persistent shade cast by the stems of the thick vegetation after defoliation and the relatively humid climate during the period of maximum defoliation. These factors allowed an environment favourable for the tsetse fly to exist in one part or another of the peninsula in spite of the severe effects on the vegetation.

Nine months after the first spraying, between a third and a half of the vegetation was destroyed during the dry season by an accidental fire. The effect on G. pallidipes was almost immediate, and two months later the population had been reduced to a fairly low level, which was maintained for the last 16 months of the experiment. The fire hardly affected the environment of G. palpalis and the main effect of defoliation was to cause this species to concentrate near the shady lake shore, where the dominant tree was Lecaniodiscus vaughaniae.

There is little doubt that the destruction of the vegetation by fire was made possible by the effects of the spray applications, as the hitherto evergreen thicket would normally have been unburnable. While this suggests a possible new technique for bush clearance, further trials have indicated several factors which may make difficult a satisfactory burn following defoliation.

Details are given of the assessment of the spray droplet performance both in calibration trials and during the applications to the peninsula.

A comparison is made of the populations of mealybugs, ants, predators and parasites on cacao growing in dense secondary bush and under well-cultivated conditions in Ghana, West Africa. The percentage of cacao trees infested (termed the infestation rate), the number of colonies and the populations of the vectors were similar under the two cultural conditions. Populations of ants of the genus Crematogaster and of COCCINELLIDAE were higher in bush areas than in cultivated ones. Populations of ants of the genus Pheidole, though smaller than those of Crematogaster, were greater in areas of well-maintained cacao.

Correlations of infestation rates and populations were compared under the two cultural conditions for mealybugs, ants, predators and parasites. The field data showed an exponential relationship between these factors, which was rendered linear by suitable transformations. The correlation of mealybug populations with infestation rate and with populations of parasites and predators was equally high in both habitats. The correlation of mealybug populations with those of Crematogaster was closer in the bush than in well-maintained cacao, but the implications of this are not fully understood.

There was a higher infestation rate of cacao during the first three months of the year. In contrast with previous work, the present survey has demonstrated significant changes in the vector population during the year, of a five- or six-fold order. These seasonal changes are based on mean mealybug populations per infested tree, and were largely the result of changes in the numbers of colonies; populations showed a decline during the first six months of the year and then rose to a maximum during October–November. The data suggest that these trends may be brought about largely by changes in the abundance of predators and parasites.

Trials were carried out, at two places in Tanganyika, on the underground storage in sealed pits of maize of high moisture content. The average moisture content of the maize when placed in the two pits was 16·9 and 14·8 per cent., whilst the general level of insect infestation was very light and fairly light, respectively. The predominant species was Calandra oryzae (L.); Oryzaephilus surinamensis (L.) and Tribolium castaneum (Hbst.) were also present.

The maize was kept in the sealed pits for 144 and 374 days, respectively. Samples taken at intervals showed that the insect infestation died out early, and there was no increase in insect damage. Other changes, unconnected with insect infestation, took place, and conditioning and admixture of a more palatable maize was necessary before grain from the pits could be offered to the public.

It is concluded that long-term underground storage of maize of high moisture content is not a practical proposition under tropical conditions owing to the deterioration that occurs in the grain.

Samples of aquatic stages, taken from a small lowland stream near Durham, England, showed that the blackfly, Simulium ornatum Mg., emerged in quantity from April to October (7 months) and that oviposition took place between May and October. Oviposition was confined to the period between sunset and dusk.

Flies emerging in the early summer of 1952 were smaller than those emerging in the spring and late summer of that year.

S. ornatum landed on cattle from dawn to dusk, with usually a small peak 2–4 hrs. after dawn, and a large peak between sunset and dusk on warm, sunny days. On cool, cloudy days the number of flies landing showed irregular fluctuations throughout the day.

The number of flies landing on untethered cattle was not markedly dependent on air temperature or saturation deficiency. Winds of over 5 m.p.h. markedly decreased or inhibited landing activity.

On average about 70 per cent, of all blackflies landing spent less than 10 min. on cattle after landing, and this interval sometimes decreased as the total number of flies landing per unit time increased.

Of the flies which landed, some 8 to 25 per cent, were calculated to bite the cow, and the proportion which bit varied significantly from day to day. The number of bites sustained by cattle in the district appeared to cause no ill-effect, apart from the formation of scar tissue in the navel region where most bites were inflicted.

Further observations and trials were conducted with insecticides against larvae of Culicoides impunctatus Goetgh. on Soutra Hill, Midlothian. The analysis of the data was complicated by a large natural reduction (76%) which occurred in the untreated plots. Nevertheless, it appears that the following dosages of insecticidal preparation were still active two years after application:—(a) 50 and 200 mg. p,p′DDT/sq. ft. applied as a dust, wettable powder or water-miscible concentrate (99% control), (b) 50 and 200 mg. γ BHC/sq. ft. as a wettable powder or 200 mg. γ BHC/sq. ft. as a water-miscible concentrate (95% control), (c) dieldrin at 25 mg./sq. ft., which gave 97 per cent, control and (d) chlordane at 50 mg./sq. ft., which gave 84 per cent. control.

The effect of spray volume on insecticidal effect was investigated by applying 25 mg. and 50 mg. p,p′DDT/sq. ft. in the following spray volumes:—5, 10, 15, 25, 50 and 80 gals./acre. The effect of 50 mg./sq. ft. at each volume was less marked than in the previous work, when only one concentration was used. Weather conditions in the present season were unusual, but there were indications that moderate spray volumes (15 and 25 gals./acre) give the best results at this dosage of insecticide. The combined results for 50 mg./sq. ft. at all volumes gave only 43 per cent, residual control, while those for the lower dosage showed no residual control.

The results are discussed with reference to the effect of rainfall on residual control. It is concluded that the volume of spray applied is unimportant provided the droplets of insecticide are closely and evenly distributed on the mossy vegetation that overlies the peat. Subsequent prolonged rain, of the order of 20 inches, is required to attain the most effective distribution of the insecticide, which is at the surface of the peat, where the eggs are laid and the newly hatched larvae will come in contact with the poison.

By the method of attacking flying swarms of locusts with insecticides sprayed directly into the swarm by relays of light aircraft, a proportion of the swarm receives a sub-lethal dose from each sortie. For successful operation it is essential that a substantial contribution to the final mortality should be produced by the accumulation of these sub-lethal doses on individual insects over a period of time. The object of the present experiments was to determine whether such doses applied at intervals are wholly additive in their effects. The poison used was dinitro-o-cresol (Mk. IV DNC solution) and to shorten the experimental procedure, the locusts, Schistocerca gregaria (Forsk.) and Locusta migratoria migratorioides (R. & F.), were dosed by means of a single drop of poison applied to the ventral surface of the abdomen by a micro-drop syringe.

When locusts are given regular daily doses of DNC the doses are not wholly cumulative in their effect. After the second or third day the lethal effect of each dose becomes steadily less, and after the fourth or fifth day it tends to zero, representing a steady state in which the rates of application and loss of insecticidal activity in the survivors are equal.

When the dose is applied in two halves with various time intervals between them, the cumulative effect during the first 24 hours is less in S. gregaria than in L. migratoria. In the latter species it is possible that sensitisation occurs. After three days, the first half-dose has fallen to an estimated 20 per cent, of its initial effectiveness in each species.

These two species are equally susceptible to a single dose expressed as μg. DNC/g. body weight. The females are more resistant than the males to daily doses (relative susceptibility in S. gregaria, 1·54) but probably not to single doses (relative susceptibility, 1·09).

Resistance to a daily dose correlates roughly with resistance to a single dose, the total dose required to produce 50 per cent, mortality in four days being about twice the LD50 for a single dose.

If flight activity does not materially alter the present results, it is evident that the non-cumulative effects of sub-lethal doses could cause a serious loss in the efficiency of an air-spray operation if it were unduly prolonged. Thus a quantity of insecticide sufficient to kill over 99 per cent, of the locusts if applied as a single dose would kill less than 40 per cent, if the application were spread over four days.

It is estimated that in 1953, as a result of attack by Wheat Bulb Fly, Leptohylemyia coarctata (Fall.), 59,000 acres of wheat were re-drilled and 58,000 acres were patched with spring-sown wheat; another 85,000 acres were affected without any action being taken by the farmer. The cost of new seed and the reduction of yield of spring wheat as compared with winter wheat represent a minimum financial loss of about £1,200,000. With the aid of maps it is shown that the distribution of damage is similar to the distribution of wheat and to the area with less than 30 in., rainfall annually. In districts where over 5 per cent. of the combined crops and grass acreage is in potatoes, there is a tendency for the amount of damage by Wheat Bulb Fly to increase with increasing potato acreage.

It is tentatively suggested on circumstantial evidence that high rainfall on the west side of the country is partly responsible for the absence there of damage by Wheat Bulb Fly. Many of the variations in the distribution of damage on the eastern side of the country could be accounted for by differences in cropping.

In Scotland, the distribution of the fly is also confined to the eastern side. There are a few records of the fly in the Republic of Ireland.