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.

Sticky traps were operated over sugar-beet crops at Rothamsted Experimental Station (Hertfordshire), Broom's Barn Experimental Station (Suffolk) and elsewhere for five years to gain information about the flight of the aphids that transmit beet yellowing viruses and to aid in the spray warning scheme for sugar-beet growers.

Numbers of Myzus persicae (Sulz.), Aphis fabae Scop, and of all aphids caught per week are given. Records of aphids trapped at Rothamsted over a period of 23 years have been published; but no repeating pattern of aphid abundance from year to year has been detected. M. persicae flew early in 1960 and 1961, when beet viruses spread extensively, whereas in 1962, 1963 and 1964, when alates of this species did not fly early but were trapped in relatively larger numbers later in the year, yellows spread much less. Large numbers of A. fabae flew in 1963, but beet viruses spread little.

Details are given of a cabinet, with a working space of 9 cu. ft., affording temperatures constant to within ± 0·5°C. over the range 5–25°C. and relative humidities constant to within ±2·5 per cent, over the range 40·85 per cent. The apparatus has electrically operated automatic controls. The only maintenance required is two-weekly renewal of the wet-bulb wicks and filling of the distilled-water reservoirs. Most of the construction was carried out in the laboratory. The cost of the cabinet and control equipment was approximately £170.

The effect of attack by the Coreid bug Pseudotheraptus wayi Brown on the yield of coconut palms was studied in Coast Province, Tanganyika, in 1957–60. Alternate plots in a line of six one-acre plots, each of 50 palms, were sprayed weekly with a mixture containing 0·1 per cent. DDT (to control P. wayi) and 0·1 per cent. malathion (to prevent any increase in scale insects). To facilitate collection of the immature nuts (vidaka) shed by the palms, the plots were kept cleared of surface vegetation. Since this is not a normal practice in local coconut plantations, its effect on yield was checked by leaving the vegetation untouched on six similar, unsprayed, plots immediately adjacent to the first six. All vidaka falling on the latter were collected and recorded daily, and the numbers showing damage by P. wayi were noted. The ripe coconuts on all twelve plots were harvested by climbers, and then counted, at eight-week intervals. Since the nuts take about 12 months to ripen, yields in the first year were in effect those of untreated plots.

The yields from unsprayed plots showed that removing the vegetation was beneficial; the three cleared plots produced 490 and 1,159 more nuts per plot in the second and third years, respectively, than their adjacent, uncleared, partners, whereas in the first year they produced fewer. The mean annual yields from these three cleared but unsprayed plots were successively 817, 2,134 and 3,129 nuts per plot. The corresponding yields from the three cleared plots that were sprayed were 1,102, 3,310 and 2,992. Thus, protection against P. wayi appeared to increase the yield in the second year, but to have no effect in the third, although vidaka damaged by P. wayi were fewer on sprayed plots throughout.

A series of estimates of ‘ total production ’, defined as the sum of the vidaka shed in any period and the ripe nuts subsequently harvested, was obtained by adding the total vidaka collected in successive eight-week periods to the ripe nuts gathered in the harvest taken 11½ months after the middle of each period. These showed that the initially greater yield from sprayed plots came about because a greater proportion of the ‘ total production ’ was converted into ripe nuts, that is, fewer vidaka were shed, doubtless as a result of the diminished attack by P. wayi. The subsequent drop in yield to about the level of the unsprayed plots was due not to any substantial change in this proportion but mainly to a drop in ‘ total production ’.

It is inferred that the number of ripe nuts produced by the palm is subject to an upper limit, which is determined by agronomic factors and greatly exceeded by the number of immature nuts formed. The excess nuts may be shed at an early stage, either for physiological reasons or as a result of biotic factors such as insect attack. Thus there exists a compensating mechanism whereby yields may remain constant under different levels of insect attack and yet show immediate responses to changes in soil or climatic conditions. This could account for the fact that, in the area studied, clearing of plots produced an apparently permanent increase in yield, and insect control only a doubtful and temporary one. It is concluded that, under present conditions, increases in coconut yields are more likely to result from improved methods of cultivation than from pest control with insecticides.

In 1960–63, fifteen field trials were carried out on tea estates in Ceylon to find whether dieldrin at 1–5 or 3 Ib. per acre applied as a spray to the tea bushes immediately after pruning would afford control of the shot-hole borer, Xyleborus fornicatus Eichh. Koutine sampling by a method that is described was carried out for three years after spraying, and fluctuations in the numbers of live stages and galleries of the Scolytid were recorded.

In unsprayed plots, the beetle population left in the old wood of the tea bushes after pruning at first declined, but began to rise about nine months later. Sampling was then continued in the new wood that grew after pruning. In this, the numbers of galleries and live stages increased to a major peak late in the second or early in the third year and then declined; there was a smaller increase later in the third year in several of the trials. By comparison, dieldrin at 1·5 lb. per acre greatly delayed the build-up of attack and effected an average reduction in gallery numbers of 81 per cent, by the eighteenth month and 70 per cent, by the twenty-fourth month. The main peak of attack was delayed until the early part of the third year, and the maximum level averaged only about half of that on unsprayed plots; but control in the third year was less satisfactory and more variable than in the second year. Spraying with dieldrin at 3 lb. per acre did not give better control, and no difference in effectiveness was found between 1·5 lb. applied as a high-volume (90 gal. per acre) and a low-volume (8 gal.) spray.

Special sampling in two trials revealed that reinfestation of sprayed plots began at edges adjacent to infested unsprayed plots and continued progressively inwards. It is concluded that the duration of control from spraying will be influenced by the size of the area sprayed and the proximity of infested tea fields, and that on estates, where fields of 20–40 acres would be sprayed, the level of control will be at least as good as that observed in the trial plots of 5–10 acres.

The main drawback to the use of dieldrin is that it induces outbreaks of tea tortrix, Homona coffearia (Nietn.), by killing off the parasite Macrocentrus homonae Nixon. The possible use of less persistent insecticides is discussed, together with the timing of chemical control measures in relation to cultural practices.

The numbers of open galleries (entrances visible) were closely correlated with those of live stages of the beetle up to the time of peak attack and less closely afterwards, probably because the entrance holes healed up at varying rates. The proportion of immature stages (eggs, larvae and pupae) in the population fell from the first to the third year; the fall was most rapid in unsprayed plots after the second-year peak of attack. One-tenth of adult beetles counted were males, but the true proportion in the broods was estimated to be between one-third and one-fifth. The frequency distribution of gallery numbers showed that invasion of new wood starts at random and becomes increasingly over-dispersed (more uniform) as the density rises. This would be expected if there is a maximum density of galleries that is much the same in all the tea bushes. There was some evidence for a density-dependent regulation of borer numbers brought about by intra-specific competition for wood suited to gallery formation and brood-rearing. Other possible factors influencing density are discussed.

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.

In insecticide trials in 1962–63 in Rhodesia against woolly apple aphid, Eriosoma lanigerum (Hsm.), no appreciable control was achieved by applying ½ fluid oz. of a 40 per cent, emulsifiable concentrate of dimethoate per tree at 2- to 3-week intervals for 16 weeks in any of the following ways: painted directly on the lower trunk; absorbed in a cotton-wool band applied to the trunk, after being diluted 1:3 in water; applied to a furrow around the stem after being diluted in four gallons of water; injected into the soil with a nematicide injector after being diluted 1:4 in water.

A foliage spray of DDT (0·195% active ingredient) had a gradual controlling effect on the aphid and caused no upsurge such as might have occurred had the parasitic activities of Aphelinus mali (Hald.) been suppressed.

Activity of the ant Pheidole megacephala (F.) was immediately halted on trees sprayed with DDT and was suppressed on trees the trunks of which were painted with dimethoate and on those banded with a dimethoate-soaked barrier.

Over a fourteen-month period, the numbers of living aphid colonies fluctuated before decreasing at the same time as the activity of A. mali intensified.

Work at East Malling, Kent, between 1952 and 1963 on the biology of Harpalus rufipes (Deg.) (Carabidae), the strawberry seed beetle, is described in detail, and briefer notes are given on the life-histories of H. aeneus (F.), Feronia melanaria (Ill.) and F. madida (F.), which are less abundant but may also damage strawberries. Soil samples for larvae were washed over suitable sieves, those for pupae and adults were carefully searched in the field. Soil sampling showed that adults of H. rufipes colonised strawberry fields only during the fruiting period, weedy arable land and grassy situations being preferred at other times. By soil sampling, it was found that larvae of H. rufipes hatched from eggs laid in weedy soil in late summer, and evidence from pitfall trapping showed that the first two instars were sometimes active on the soil surface from August to December, before penetrating to a depth of 6–18 in. to overwinter. Development was resumed in April, but the larvae remained and the pupae were subsequently found at the overwinter depth in the soil, the larvae presumably feeding on the seed of fat hen (Chenopodium album) lodged in worm burrows. Third-instar larvae occurred from April to July, and adults emerged soon after. In the laboratory, adults lived for a further two years, hibernating in winter, and becoming active and breeding each summer. Laboratory observations on oviposition periods, fecundity and feeding were also made. Larvae, which in the field were mostly found associated with plants of fat hen, fed on germinating seeds of several plants in the laboratory but growth was most rapid when they were reared on the germinating seed of fat hen.

The life-cycles and habits of the three other species are briefly described and compared with those of H. rufipes, the seasonal occurrence of the different stages in the life-cycles of all species being shown in a table.

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.

Field and laboratory studies of virus disease in the armyworm Spodoptera exempta (Wlk.) were carried out in East Africa in 1962–64. A nuclear polyhedrosis virus was detected microscopically in pupae, prepupae and all larval instars except the first, and was found to be widely distributed in most areas subject to outbreaks of armyworm in East Africa. The signs and course of the disease in larvae of S. exempta are described. Attempts made in the laboratory to infect S. triturata and other species of Spodoptera with virus from S. exempta failed. In unsterile conditions of maintenance, almost all laboratory cultures from wild-caught female moths sustained heavy infections. The appearance of the symptoms of polyhedrosis was accelerated at higher temperatures, and the incidence was higher in more crowded cultures. Transmission took place from contaminated leaves to larvae and probably from one larva to another. There was evidence also of generation-to-generation transmission through the egg.

The effect on polyhedra of immersion in alkali solutions was investigated; it. was found that immersion for 15 minutes in 0·2 per cent. caustic potash effectively dissolved the matrix and inactivated the virus. When all equipment was sterilised in this way (or, later, with 0·4% caustic potash) apparently virus-free cultures were obtained by rearing the larvae from wild-caught females in isolation and breeding from those that survived to become adults.

The possible use of the virus for control of outbreaks of armyworm in the field is discussed; it is concluded that there is at present insufficient evidence to show whether such a measure would be effective.

The four commonest species of Sitona injuring leguminous crops in Israel were found during a survey in 1957–62 to be S. lividipes Fhs., S. hispidulus (F.), S. crinitus (Hbst.) and S. lineatus (L.). Adults of all four were collected in the field in December-January each year, at the termination of diapause, and kept in the laboratory for observations on their bionomics. Larvae and pupae did not survive in the laboratory, and therefore these stages were reared in the soil outside (where suitable food-plants had been grown) from eggs laid by the adults in the laboratory and kept at known temperatures until they were about to hatch. The soil was later examined daily for pupae.

Egg-laying began in December, larvae were found in January–March, pupae in March–April, and adults of the new generation in April–May. These adults fed freely but did not oviposit, and in June–July they sought shelter and entered diapause, which lasted until the close of the year. Feeding was then resumed, oviposition began shortly afterwards, and death occurred up to 250–300 days later.

The eggs of all four species are creamy or yellowish white when laid but soon become glistening black. High humidity was necessary for hatching; no eggs of S. lividipes or S. hispidulus hatched at relative humidities of 76 per cent., or less, and virtually none of S. crinitus or S. lineatus at 56 per cent, or less. In favourable humidities, the percentage hatching was reduced at constant temperatures exceeding 25°C., except in S. lineatus, in which it was not affected up to 29°C. The threshold temperatures for development of eggs of S. lividipes, S. hispidulus, S. crinitus and S. lineatus were 4·8, 4·6, 5·8 and 6·5°C., respectively, and the thermal constants were 180, 211, 166 and 145 day-degrees C. The mean larval and (in brackets) pupal periods outdoors were 52 (23), 58 (34), 36 (25) and 38 (21) days, respectively. The average numbers of eggs laid were 843, 719, 519 and 1,113 per female, and the mean numbers laid per day were 10·2, 8·5, 9·6 and 17·5. These data were obtained by feeding adults on a variety of food-plants throughout their life in the laboratory. In another series of observations, adults were fed on the same type of food-plant throughout. Egg production of S. lividipes and S. hispidulus was greatest on clover (Trifolium alexandrinum) and least on broad bean (Vicia faba) and pea, respectively; that of S. crinitus and S. lineatus was greatest on pea and least on broad bean and clover, respectively.

Assessment of the effects of dichlorvos (DDVP), released from a Ciba XI dispenser, on females of Anopheles gambiae Giles and Mansonia uniformis (Theo.) entering a verandah-trap hut in the Umbugwe area of Tanzania was made over a period of two months in 1964. Of the numbers of A. gambiae that entered one treated and one untreated hut, 27 per cent, of those entering the hut treated with dichlorvos and 48 per cent, of those entering the untreated hut left again. Of the numbers leaving each hut, 38 per cent, left through the eaves of the treated hut as compared with 9 per cent, in the untreated one. In the case of M. uniformis, 88 per cent, of those entering the treated hut and 94 per cent, of those entering the untreated hut left again. Of the numbers leaving each hut, 59 per cent, left through the eaves of the treated hut as compared with 61 per cent, in the untreated one.

Over-all mortalities were 56 per cent, for A. gambiae and 34 per cent, for M. uniformis when the eave-egress fraction from the treated hut was taken into account, compared with 62 per cent, for A. gambiae and 43 per cent, for M. uniformis when the eave-egress fraction was ignored.

The results of bioassays and of chemical analyses showed that the problem of mortality from fumigation in situ was considerably less in verandah traps than indoors or in window traps fitted with funnels of cotton netting.

The taxonomy of African species of Antestiopsis, some of which are important pests of coffee, has hitherto been in confusion owing to the difficulty of finding decisive morphological characters. In the present study an attempt is made to clarify the relationships of the coffee pest species and some of their close allies by the use of both biological and morphological characters.

The species of Antestia and Antestiopsis occurring on coffee in Africa are differentiated in a key, and descriptions are given of the following: Antestiopsis orbitalis (Westw.), with three clearly distinguishable subspecies, orbitalis, bech-uana (Kirkaldy) and ghesquierei Carayon, several local colour forms of these, and a few variable populations that cannot be referred definitely to any one of the subspecies; A. intricata (Ghesq. & Carayon); A. facetoides sp.n. for the species hitherto known as “ faceta ” in eastern Kenya and Tanzania; A. crypta, sp.n. confined to Katanga; A. falsa (Schout.), a rare and imperfectly known species; A. lepelleyi sp.n., which does not feed on coffee; and A. littoralis sp.n., from the Kenya coast, known to the writer only from museum specimens.

Evidence for the arrangement adopted is discussed, and the taxonomic value of certain morphological characters is assessed. The distributions presented on maps are discussed, and it is concluded that the activities of man are unlikely to have obscured the natural patterns. A list is given of known host-plants, which, except for those of A. orbitalis orbitalis and form facetus, are with only a single other exception members of the Eubiaceae. The distribution on a local scale and recent changes of abundance of species in competition are discussed, and it is shown that A. orbitalis ghesquierei and A. o. bechuana appear to be spreading at the expense of A. intricata in Uganda and A. facetoides in Tanzania, respectively. Kesults of crossing East African species and forms show that those here regarded as species will not cross but that the subspecies of A. orbitalis will do so, producing intermediates that, when allowed to interbreed, are not as viable as pure strains. Finally an attempt to find morphometrical characters is discussed, and the results are given of a calculation of discriminant functions based on two characters. These, while, not conclusive, support the conclusions drawn from other evidence.

The inheritance of black pupa in Lucilia cuprina (Wied.) was investigated by means of a series of back-crosses through five generations. Since an approximate 1:1 ratio of reddish brown to black pupae was observed throughout, it is concluded that the character black pupa is due to a single recessive gene (bp).

A test for the existence of a linkage group containing genes for black pupa and dieldrin-susceptibility was then made. The exposure of females from reddish brown and black pupae derived from back-crosses to discriminating levels of dieldrin, and the pattern of mortality observed with scalar concentrations of dieldrin, indicated that genes for black pupa (bp) and dieldrin-susceptibility (rdi) are on different chromosomes.

In laboratory studies of Heliothis armigera (Hb.) in Western Tanganyika, where it may attack cotton severely, pairs of newly emerged adults, derived from sixth-instar larvae collected in the field and allowed to pupate in the laboratory, were confined separately and provided with sucrose solution. The mean number of eggs laid per female fell from 1,226 in March-May to 198 in June—July 1962. Peak egg laying occurred in the fifth to eighth nights after emergence. In April, the mean length of life of adults of either sex was about 11 days and the maximum one month. The mean incubation period of 1,436 eggs laid in March was 2·78 days, and 66 per cent. of them hatched. The mean period from hatching to pupation of 42 larvae reared on cotton squares in April was 21·1 days; each passed through six instars and required three squares in the first 14 days and a further 10 thereafter; only 22 per cent. of the dry weight of the squares was consumed and of this only nine per cent. was converted to pupal dry weight.

Pupation occurs in the soil. The mean pupal period of males increased from 16 days in March to 18 in July, and their pupal weights fell from about 0·27 to 0·23 mg. over the same period, although at any given time pupal period was positively correlated with pupal weight. Female pupae were lighter than male pupae and had a shorter pupal period.

From March to July, a small but progressively increasing proportion of the pupae formed entered diapause; the proportion averaged less than four per cent. in June to July 1962–64. The pupal period ranged from 30 to 171 days, being less in later-formed pupae, so that a general emergence occurred in September–late October.

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.

Factors affecting the susceptibility of seeds of sorghum (Sorghum vulgare) to attack by Sitophilus oryzae (L.) were investigated in the laboratory. It was known that varieties in which a majority of the seeds have a predominantly vitreous endosperm (vitreous varieties) are less attacked than those in which the majority have a predominantly mealy endosperm (mealy varieties). A method of measuring the relative amounts of vitreous and mealy endosperm in a seed was devised, and was used to classify samples from ten varieties of sorghum that had been grown in East Africa. The varieties ranged from vitreous to mealy, and the seeds from them formed the test material.

Adult weevils confined singly in tubes with seeds of either a vitreous or a mealy variety consumed more per day of the latter than of the former (about 0·2 and 0·15 mg., respectively, per mg. body-weight of weevil). When females were allowed to oviposit in seeds and the next-generation adults were counted, greater numbers were obtained from mealy than from vitreous varieties, the extreme results from a range of five being in the ratio of about 20:1. Seeds of vitreous varieties have a lower moisture-content than those of mealy ones at the same humidity, but this was not the cause of the differing numbers of adults, for the results were similar when the experiment was repeated with seeds of a vitreous and a mealy variety treated so that the moisture contents were identical. Attempts to compare the numbers of eggs laid in seeds of these two varieties gave inconclusive results; it was shown that none of the methods used was entirely reliable; in two experiments, no difference could be detected, but in a third, in which the seeds were examined by means of X-rays as well as by other means, significantly more eggs were laid in seeds of the mealy than of the vitreous variety. There was no evidence of a preference for any particular size of seed of either.

The hardness of the seeds of all ten varieties was estimated by grinding equal quantities in a mill and weighing the amounts that then passed through a 60-mesh sieve. This was done twice, with seeds at 10 and 14 per cent, moisture content. The order of hardness was not appreciably affected by moisture content, and was clearly correlated with the proportion of seeds with predominantly vitreous endosperm; the more vitreous varieties had harder seeds than the more mealy ones. It is inferred that hardness of the seed is the principal factor responsible for resistance to weevil attack.

When fasting fifth-instar larvae of Rhodnius prolixus Stål were poisoned with a lethal dose of DDT, the rate of oxygen consumption increased from the onset of hyperactivity, reached a marked peak shortly after knockdown, and then declined. For some days after the peak the oxygen consumption was markedly in excess of that prior to poisoning with DDT. Eventually, the oxygen consumption fell below the pre-teatment value and continued at this low level for some days, although the insect was then undoubtedly dead and in one case had been bisected. There was no marked discontinuity in the declining phase of oxygen consumption and therefore there is no indication of when death occurred. It is concluded that the time of death in DDT-poisoned larvae of Rhodnius cannot be determined by measurements of oxygen consumption.

The total oxygen consumed from poisoning until death was always less than that consumed in the normal use of all metabolic reserves by the fasting insect, and these experiments do not support the hypothesis that death in DDT poisoning is due to total exhaustion of metabolic reserves. However, it is pointed out that, in Rhodnius, some of the metabolic reserves are contained in the undigested residue of the blood-meal and in the massive endocuticle and that there is no reason to think that either digestion of the remaining blood-meal or resorption of the endocuticle could be speeded up during DDT poisoning. Hence there is a strong possibility that, in DDT-killed Rhodnius, death is brought about by exhaustion of the available reserves.

The peak rate of oxygen consumption during poisoning was greatest in very recently fed larvae and decreased as the interval between moulting and DDT-treatment was increased. This suggests that knockdown occurs when the fuel demands of the DDT-induced activity exceed the rate at which the fuel can be mobilised from the metabolic reserves.

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.

In Western Tanganyika, Heliothis armigera (Hb.) occurs as a major pest of cotton from February to April, but also feeds on many other host plants. The dry season (August–October) is spanned usually by diapause pupae, the moths emerging from which oviposit on a species of Gleome, on which the first generation develops, giving rise to adults in November–December. Larvae of the second generation feed mainly on early-sown maize, and it is usually those of the third and fourth generations that attack cotton. Two subsequent generations occur on a variety of host plants, including late cotton, maize and legumes. The increasing severity of the attacks of Heliothis on cotton has accompanied the replacement of sorghum by maize in recent years. Maize is not only an intermediate host on which Heliothis builds up before it attacks cotton but also a source of diapause pupae later in the season.

In studies of the natural control of H. armigera, based on regular sampling of eggs and larvae on host plants in the field, the most important parasites were the Tachinids Drino imberbis (Wied.) and Goniophthalmus halli Mesnil, and field observations suggested that a species of Chrysopa (Neuroptera) was the main predator. Increasing use of insecticides may be reducing the effectiveness of natural control. A polyhedral virus was common, mainly found in larvae of Heliothis feeding on maize. The control of Heliothis on cotton by cultural methods was attempted by banning early sowing of maize and by sowing strips of maize in cotton fields as trap crops. Neither method is practicable on a large scale. Early sowing of cotton appears to be the best means of withstanding attack by Heliothis, for the local strains of cotton are able to compensate by later growth even for a very heavy Heliothis attack, provided they are sown early enough to utilise the late rains.

In cotton that was subject to a heavy attack by H. armigera, five applications at 2-week intervals of DDT at 1 lb. per acre gave good control of the larvae and increased the yield from about 200 lb. seed cotton per acre to about 500 lb., the difference being mainly in the early pickings. The addition of toxaphene increased the yield, probably by controlling Earias spp., but neither toxaphene alone nor carbaryl appeared to control Heliothis. The numbers of eggs laid were higher on cotton treated with DDT than on untreated cotton.