A series of 24-hr. catches of Glossina from bait-oxen was carried out during 16 months in 1962–63 at Lugala, Uganda, where G. pallidipes Aust., G. palpalis fuscipes Newst. and G. brevipalpis Newst. occur. Female flies were dissected to determine their physiological age and the presence or absence of trypanosomes. Five age-categories were distinguished, depending on whether a fly had ovulated 0, 1, 2, 3 or more (4 + ) times. Flies remained in each of the first four categories for about 11 days and the fifth therefore comprised those over 40–50 days old. Trypanosome infections were classified as brucei-type, vivax-iype or congolense-type (i.e., attributable to trypanosomes of the groups of Trypanosoma brucei, T. vivax and T. congolense) according to the sites in which they were found.

In all three species of Glossina, vivax-tjpe infections were commonest and alone showed seasonal fluctuations in incidence. Infections of the brucei-type were rare. The total infection rate (all types) in G. pallidipes and G. palpalis fuscipes was highest in or immediately after months of greatest rainfall and relatively lower in dry months; the highest infection rates in G. brevipalpis occurred a month later than those of the other two species. Over 80 per cent, of infections in all three were found in category 4+ flies, the percentage of which in the catches varied in much the same way as the total infection rate, suggesting not only that the flies live longest during wet periods but also that fluctuations of infection rate are largely due to changes in mean age. The regression of total infection rate on percentage of category 4 + flies was significant for G. palpalis fuscipes over 14 months, and for G. pallidipes over 12 months, but insignificant for G. brevipalpis.

The age-composition of catches of G. pallidipes and G. brevipalpis but not G. palpalis fuscipes varied during the day. In G. pallidipes, the percentage of older flies was higher in the middle of the day than in the early morning and late evening, and these contrasts were reflected in the infection rate, which was highest in samples taken in the middle of the day. In G. brevipalpis, the percentage of oldier flies and also the infection rate were lower during the night than during the day.

Estimates were made of the mean number of bites by infected females that would be received by one ox in one day. The number varied from month to month, with peaks shortly after periods of high rainfall, mainly as a result of changes in fly density and relatively little as a result of changes in infection rate. G. pallidipes, the most numerous species, was responsible for most of the potentially infective bites.

The persistence of DDT deposits on vegetation in the Northern Guinea Savannah zone of Nigeria was studied by chemical analysis of leaf samples and by bioassay tests with teneral females of Glossina palpalis (R.-D.). Two formulations of DDT were used, one (A) made by mixing a 75 per cent, wettable powder with water to give a 5 per cent, suspension, the other (B) made by adding a household detergent to A at the rate of 3·8 g. per gal. suspension. They were applied to foliage by knapsack sprayer in August 1964, about the middle of the rainy season.

It was noted that the particles deposited from B were finer and more evenly distributed over the leaf surface than were those from A. Chemical analysis of leaf samples showed that the deposit from B was initially the higher. Both deposits declined greatly during the first six weeks after application, coinciding with the period of heaviest rainfall. Those from A and B reached 49·8 and 46·2 per cent., respectively, of their initial levels at the end of the second week, and 9·2 and 5·2 per cent, at the end of the sixth. From then to the end of the sixteenth week, when the observations ended, no further decline was observed. In the tests with G. palpalis, deposits from A and B caused mortalities of 60.3 and 66.8 per cent., respectively, in the fourth week and 79·4 and 82·8 in the fifth, no mortalities below the latter being subsequently observed up to the tenth week.

It is considered that rainfall was the main factor responsible for removing the deposits from foliage. After the end of the rainy period, losses of the deposits became negligible. Deposits from B at first declined faster than those from A. It is considered that this was due to the faster removal by rain of the smaller particles.

Heavily weathered deposits were highly toxic to G. palpalis under the test conditions, and it seems likely that under natural conditions of contact they would have exerted still greater toxicity.

Some effects on the adult of environmental conditions during the larval and pupal stages of Spodoptera littoralis (Boisd.) were investigated in the laboratory in Israel. The conditions studied were temperature during larval life, temperature and humidity during pupal life and the density at which larvae were kept, and their effects were found by varying one of them at a time. Except for such variations, larvae were reared in batches of 30–50 at 22–24°C. and 60–70 per cent, relative humidity, pupae were kept at 23–24°C. and 70–80 per cent, relative humidity, and adults were kept in pairs at 20–21 °C. and 75–85 per cent, relative humidity. Larvae were fed on clover leaves and adults on sugar solution.

High temperature during the larval stage reduced fecundity; whereas at 22°C. the resultant females laid about 1,200 eggs each and 12·5 per cent, produced non-viable ones only, at 30°C. they averaged about 700 eggs each and 50 per cent, produced non-viable ones only. Temperature during the pupal stage affected fecundity similarly and life-span to a lesser extent; at 20 and 34°C., 40 and 5 per cent, of the resultant adults lived 15 days or more, the percentages of females laying only non-viable eggs were nil and 70 and the mean numbers of eggs laid were about 1650 and 700, of which about 60 and 2 per cent, were viable, respectively. High temperatures were directly inimical to pupae, less than half of which survived at 26°C. or over.

The effects of humidity during the pupal stage were in general less than those of temperature. The mean life-span was longest in adults from pupae kept at an intermediate humidity of 76 per cent., as also were the proportion of barren females and the mean number of eggs laid; the percentage of viable eggs was reduced only amongst those from females kept as pupae at over 95 per cent, relative humidity. Pupal mortality was affected only by low relative humidities, which raised it.

Larvae reared singly tended to be brighter in colour than those reared in batches of 30–50; fewer died and the subsequent pupae were heavier and longer. The mean life-span of the resultant adults was longer, and they laid more eggs.

The results are compared with those of other workers on S. littoralis and other insects.

The distribution on cotton plants of the eggs, nymphs and to a lesser extent the adults of Empoasca lybica (de Berg.) was studied on the varieties Bar XL1 and BAJ 7/57 in the Sudan during 1961–64. Counts of jassid nymphs in the process of hatching from eggs buried in the leaf veins showed that hatchlings were most numerous on the third to fifth expanded leaves from the main-stem apex and that most eggs had been laid either close to the point of insertion of the petiole into the leaf lamina or about half-way along the length of the veins on the underside of the leaves. The greatest number of hatchlings was found in the central leaf vein. It was concluded that eggs are most frequently laid in this position on newly expanded leaves at the apices of the main stems or side branches.

The distribution of the early instars on the main-stem leaves was peaked, with maximum numbers occuring on or about the fifth expanded leaf from the apex; a similar distribution with a less prominent peak nearer to the apex leaf was found on side branches. The later instars, being more mobile, had a more even distribution. In the over-all distribution of nymphs on a typical cotton plant, a combination of the patterns found on main-stem and side-branch leaves, the greatest numbers of jassids occurred in the upper half or upper third of the plant. Co-variance analyses showed that the relation between numbers of jassids per zone and number of leaves per zone was not close and that the manner in which the plants were divided into zones for analysis of the relation greatly affected the correlation coefficients obtained.

Regular counts of nymphs and adults on the upper surface of leaves throughout a period of two complete days showed that both nymphs and adults moved to the upper surface of leaves each day between 1400 and 1800 hr. local time and returned to the under surface at about 0300–0400 hr. Neither the environmental factor that stimulated this movement nor the way in which it benefited the insect was clear.

Pupae of Glossina morsitans Westw. collected in the Zambezi valley near Kariba, Rhodesia, were brought to the laboratory, and the effects of the chemosterilant tepa were investigated by observations on the resulting adults. In the standard test, 25 pairs of adults were caged together for 28 days at 79°F. and 70 per cent, relative humidity and fed on guinea-pigs, and the survival of both sexes, the numbers of pupae and adults produced and (in some tests) the insemination rate of the parent females were recorded. With untreated flies, the insemination rate was 94 per cent, or more, averages of 28 pupae and 26 adult progeny per cage were produced, and 72 and 77 per cent, of males and females, respectively, survived for the 28 days. These results were compared with those obtained when the flies of one sex in the cage had been treated with tepa either as pupae or as adults.

Injection of 1 μg. tepa into the thorax of young males produced complete sterility. Dipping the pupae in 5 per cent, tepa solution for one minute caused complete sterility of adults emerging during the first two post-treatment weeks and partial sterility of males emerging during the third week. Adults emerging from dipped pupae washed one day after treatment were fertile. Dipping pupae in solutions containing 1 or 0·5 per cent, tepa did not completely sterilise the resulting adults. Contact exposure of adult males and females of various known ages usually resulted in complete sterility (99·7%) after exposures ranging from 15 to 240 min. to deposits on glass of 10 or 50 mg./ft.2 tepa. Males exposed for 240 min. to 10 mg./ft.2 tepa retained their sterility throughout a 42-day test period and, in special tests, competed well with untreated males for the females, but their life length was reduced by 25 per cent, when unmated and by 33 per cent, when mated. Males exposed for 60 min. or less survived as well over a 42-day test period as untreated males, but those exposed for 15 min. recovered an undesirable degree of fertility. No treatment affected the ability of the male to inseminate the females. Sperm from treated males were motile and appeared normal in their behaviour in the female spermathecae. Dominant lethality induced by tepa was usually expressed during the embroyonic stages, but occasionally was delayed until the pupal stage.

A serially numbered list is given of plant species, both cultivated and wild, with the insect species found associated with each in Harar Province, Ethiopia, during 1960–64. In a second list, the insect species are arranged under orders and, alphabetically, under families and genera, the plant species with which they were associated being indicated by numbers referring to the first list.

Fresh evidence is described which supports the theory that moths of the Noctuid Spodoptera exempta (Wlk.) (the adult stage of the African armyworm) are migratory. The evidence comes from four main sources: a study of fluctuations in numbers of moths caught in a network of light-traps operated in East Africa; the fertilisation rates in samples of females as shown by dissection; the sex ratios in samples of moths caught in light-traps; and a study of the behaviour of moths in the field during the period immediately following emergence. In certain of these features S. exempta is compared and contrasted with the related S. triturata (Wlk.), in which the evidence points against extensive migration.

It is concluded that migration occurs in S. exempta, probably on an extensive scale, and that it therefore has an important bearing on the occurrence and distribution of outbreaks of the larvae.

The life-history of Contarinia nasturtii (Kieff.), a gall-forming pest of swedes, was investigated in northern England in 1958–60, particular attention being paid to the influence of temperature and moisture on development in the soil. Most of the observations were made under controlled conditions in the laboratory, although much of the material came from the field.

The adults emerge from the soil, mate, and live 1–3 days. In laboratory conditions, each female developed about 95 eggs, laid in batches of 2–50 on the young leaves of the host plant, and produced 78·7±11·4 unisexual larval progeny. The eggs require moist conditions, and hatched according to temperature after 1–10 days at 30–10°C. The larvae fed for 7–21 days at 25–15°C., producing a gall.

The full-grown larvae burrow into the soil. It was found that they either pupated in oval-shaped cocoons just below the surface, producing adults 10–48 days later (at 25–12°C.) or become dormant in spherical cocoons. At 32·5°C. the pupae died, and below 32·5°C. males developed faster than females by about 24 hours.

Dormancy is caused either by diapause, in which case the larvae require prolonged chilling before development can be resumed, or by drought, in which case development is resumed immediately in response to wetting.

The incidence of diapause increased regularly during the summer generations, probably in response to decreasing day-length, and the larvae tended to avoid diapause when placed in high temperatures (e.g., 25°C.). The firmness of diapause appeared to vary according to the conditions experienced by the feeding and full-grown larvae, but, in general, the larvae completed diapause development after 100 days at 2–5°C. followed by 30 days at 20–25°C., i.e., after exposure to conditions similar to those experienced by the diapause larvae during winter and spring.

Dormancy due to drought (quiescence) affected both non-diapause and post-diapause larvae; the former became quiescent on entering dry soil (pF>3·5–4·0), and the latter remained inactive if kept in dry or even in moist soil (pF 3·4) after completing diapause. In both cases, the termination of dormancy occurred immediately in response to a thorough wetting of the soil. The larvae left their spherical cocoons, moved to the surface, re-entered the ground and pupated in oval cocoons as if entering the soil for the first time.

Factors that delay pupation of C. nasturtii similarly delay the development of its Hymenopterous parasites and hence synchronise the emergence of the adult parasites with the host's feeding stage.

Experiments are described on the aerial application of very low volumes (0·5 gal./acre) of oil solutions of DDT to control two pests, Heliothis armigera (Hb.) (bollworm) and Acanthomia horrida (Germ.) (brown bug), of the seed-bean crop in northern Tanzania. The method was compared with an improved variant of the standard commercial method of aerial control, in which DDT emulsion is applied at 1·85 gal./acre. This improved variant was also compared with a standard commercial treatment. Very-low-volume (solution) treatments were made with rotary atomisers, normal volume (emulsion) treatments with boom-and-nozzle equipment. The results were assessed, by measuring the amount of DDT deposited on filter papers and on the leaves of the crop and by estimating pest mortality from counts made immediately before and 48 hours after spraying.

A direct comparison of very-low- and normal-volume treatments under identical conditions was not possible, but it was established that under similar conditions the proportion of DDT emitted that was deposited at crop level (percentage recovery) was much the same for the two methods, varying between 41 and 62 per cent, according to conditions. The lower leaves of a fairly young crop of an open variety received about 60 per cent, of the deposit on the upper leaves, but in a mature crop of a tall dense variety this percentage fell to 35.

Standard commercial practice, with the aircraft flying very close to the crop, gave a recovery of about 55 per cent, in moderately good conditions but with a variation in deposit density across the swath of over 7:1. An identical application from 10 ft. above crop, as in our method gave in rather better conditions a recovery of 62 per cent., with the deposit-density variation reduced to 2:1. This performance was much the same as that achieved by the type of emulsion application used in the other experiments described.

In similar conditions, both very-low and normal-volume treatments gave very similar mortalities of Heliothis. Acanthomia was present in only one experiment and was less readily controlled; it required deposits at crop level of about 0·4 lb./acre to give satisfactory mortality, whereas in the same experiment 0·25 lb./acre gave 96 per cent, mortality in a relatively young Heliothis population containing only 10 per cent, of sixth-instar larvae.

Older Heliothis larvae required higher dosages, 0·4 lb./acre at crop level killing only 53 per cent, of a population containing 62 per cent, of sixth-instar larvae. It was shown that there is a regular decrease in the kill inflicted by a given dosage on the successively later instars (from 92 per cent, of the third to 66 per cent, of the sixth) with a recorded deposit of 0·63 lb. DDT per acre.

Except in the first experiment, mortalities were much below those claimed for commercial treatments, even at lower rates of DDT per acre. The reasons for this are discussed, together with the advantages to be expected from a change to the very-low-volume technique with solutions.

Populations of the red locust, Nomadacris septemfasciata (Serv.), can build up to large numbers in certain of the grass plains of south-central Africa. Adult populations are always under-dispersed, and estimates of their size can be made economically only by counting the locusts flushed on line traverses of considerable length. It is necessary, in such traverses, to determine the width of the strip swept, the proportion of the locusts in it that are flushed, and the accuracy with which these are counted. Investigations into the use of a three-seat Hiller helicopter for this purpose were carried out in south-west Tanzania in 1964–65. It proved possible to cause virtually all the locusts in a strip the width of the rotor blades to rise ahead of the machine, provided it was flown at a height of about 10 ft. and at less than 10 m.p.h. and neither in the early morning nor in the late evening. A comparison of estimates of the size of the population in a 1-sq.-mile plot made by Land-Rover traverses with those made by helicopter, both when the traverse strip was marked on the ground and when it was assessed from within the helicopter, showed no evidence of systematic errors in estimating from the helicopter either the number of locusts flushed or the width of strip. Further, two observers simultaneously counting locusts rising from one strip achieved very similar results. Thus, estimation of the size of a complete outbreak-area population by means of a helicopter is clearly possible.

It has been suggested that nuclear radiation might be used for locust control, but insufficient knowledge has hitherto been available to decide whether such a measure is feasible. In this paper, the results of some laboratory experiments on the effect of γ-radiation on eggs of the desert locust, Schistocerca gregaria (Forsk.), are described.

After a single dose of γ-radiation, the resulting mortality among the eggs was correlated with the size of the dose received and the age of the egg at the time of irradiation. The dose of radiation required to kill the older eggs was 40 times greater than that required to kill young eggs; thus, a dose of 144 rads caused almost complete inviability among eggs deposited one or two days before irradiation, but a dose in excess of 5,500 rads was required to kill eggs deposited eleven days earlier. For comparison, the lethal dose of γ-radiation for humans is estimated to be 400–700 rad.

When the irradiation dose was applied in three small fractions, with intervals between them, the percentage of eggs killed was less than when the same total dose was given in one exposure. This difference was presumably due to tissue recovery during the inter-radiation periods. The temperature to which the eggs were exposed during the inter-radiation periods also affected survival, recovery being greater at higher temperatures.

The possibility of using γ-radiation to control locust egg-fields, the cost of the equipment needed and the hazards involved are discussed. It is concluded that control by this method not only offers no advantage in terms of cost, effectiveness or convenience as compared with conventional insecticide treatment but would be very impractical and dangerous to operators and the inhabitants, human and domestic animal, of the treated area. It is possible that other control techniques utilising radiation, such as sterile-male release or attractant traps treated with a sterilant, may be useful against certain species of locusts after further work on the development of chemical attractants has been carried out.

An economical method of tsetse control aimed at reducing fly numbers to a low level prior to human settlement was tried in northern Tanganyika in 1964–65 in an area containing Glossina morsitans Westw., G. swynnertoni Aust. and small numbers of G. pallidipes Aust. The major central part of the infested area, about 7½ square miles, was sprayed four times at three-weekly intervals with endosulfan from an aircraft, and the remaining peripheral parts were sprayed from the ground. In the aerial applications, the volume of spray averaged 0·0121 gal./acre per application and the amount of endosulfan averaged 0·0242 Ib./acre (a total of about 1 Ib. per 10 acres for the whole operation). The results indicated that the tsetse population was probably eradicated in the part sprayed from the air. Though the ground spraying of the surrounding parts was not completely satisfactory, the tsetse population in the whole area a year later was only about ten per cent, of its original level. The cost of the air-spraying was £88 per sq. mile.