In laboratory studies of Dysdercus fasciatus Sign., populations were exposed to constant temperatures of 15, 20, 25, 30, 35 and 40°C. and a relative humidity of 60 per cent., and to 28°C. and 70 per cent. R.H. After hatching, the insects were supplied with cotton seed as food and water to drink. Development of eggs was incomplete below 25°C., of nymphs below 20°C., and of both above 30°C. To allow comparison of growth and rate of reproduction at temperatures outside the embryonic range, this stage was ignored in calculating values of the intrinsic rate of increase, r, and the mortality rate and length of life were measured from the time of hatching, the eggs being incubated under optimum conditions (those at 28°C.) and the freshly hatched nymphs then moved to the appropriate temperature. The value of r was found to increase with increasing temperatures up to 30°C., and to do so more rapidly between 25 and 28°C. than between 20 and 25°C. The age-schedule of deaths for populations living at 28°C. showed a distribution of deaths that was almost ideal, in that their highest frequency did not occur until the reproductive period was advanced. The principal deviation from this ideal was due to the high mortality rate found in the first instar. At 20°C., the death rate approached constancy throughout the life-span of the population. The interval between generations decreased with increasing temperature, the rate of decrease being approximately 4·6 days per 1°C. rise in temperature.

Further analysis of r was made by considering separately the growth and reproductive characteristics of the insect, and the effect of temperature upon them.

The rate of post-embryonic growth, as measured by live weight, increased with temperature, within the range of 20–30°C. At 15°C., growth did not proceed beyond the third instar, or beyond the fifth instar at 35°C. The principal cause of the increase in growth rate was the decrease and eventual disappearance of the periods between initial ecdysis and start of growth, and between the end of growth and final ecdysis, the rate at which growth actually took place differing but slightly.

The size of the insect just after the final ecdysis had an important effect on r because the number of eggs laid by small insects (mean weight 68·6 mg.) was only about half that of large ones (mean weight 100·2 mg.). Any decrease in size observed with increasing temperature was slight compared with that produced by restricting the insect's access to drinking water.

Copulation and oviposition occurred in adults maintained at any of the temperatures except 15 and 40°C. The percentage of females that laid eggs differed according to the temperature, the highest recorded being 90 per cent, at 28°C. and the lowest 30 per cent, at 20°C. The total time spent in copulation also varied with temperature, being least (9 days) at 28°C. and most (26·3 days) at 20°C. The change of weight of the female after moulting largely represented growth of the ovaries; at 15°C., this is slow and not completed before the female dies; at 40°C. the ovaries do not mature; at other temperatures tested (20–35°C.) growth is fairly rapid, the ovary being full grown in about four days.

The fertile female lays her eggs in batches, the maximum observed being six batches, at approximately three-day intervals. A few females survived the laying of the sixth batch of eggs by a period longer than their interoviposition period. At 28°C., the preoviposition period and the time spent in copulation were less, more egg-batches, and hence more eggs, were produced and a higher proportion of females mated, than at any other temperature. In the unmated female, the average life was twice that of the mated one, the preoviposition period was the same, the interoviposition period approximately three times as long, the egg-batches half as numerous, and the number of eggs per batch nearly the same. All fertile females were observed to lay eggs, but only 20 per cent, of the unmated ones did so. At 35°C., mated females produced one or two batches of eggs; unmated ones produced none, and although the ovary matured normally up to the fourth day, the yolk was subsequently reabsorbed, this process being complete by the 14th day.

These studies have indicated that in D. fasciatus the decrease in the value of r with decreasing temperature is caused by a rise in pre-reproductive mortality and a fall in reproductive capacity, as well as by the increase of the generation length, which other workers have found to be of predominating importance in the case of other insects.

In Trinidad, the only serious pod borer attacking pigeon peas is Ancylostomia stercorea (Zell.). This species breeds throughout the year. The eggs are laid on the young pods and the larvae feed on the developing seeds and later pupate in the soil. The complete life-cycle requires 26–32 days.

Eight species of parasites were reared from the larvae of Ancylostomia. Life-history studies and rearing techniques for the six commonest species are presented.

Apantelcs etiellae isolatus Mues. is a solitary endoparasite attacking first- to third-stage host larvae. It emerges from the fourth-stage host and constructs a white cocoon in the pod. The life-cycle takes 14–18 days.

Phanerotoma bennetti Mues. is a solitary egg-larval parasite. The egg is laid in that of the host, but the parasite does not complete development until the host has reached the final larval stage and constructed a cocoon. A generation is completed in 20 to 28 days. A method of breeding this species on Ephestia cautella (Wlk.) is described.

Eiphosoma annulatum Cress, is a solitary endoparasite attacking first- to fourth-stage hosts. The parasites emerge from fifth-stage hosts which may be stunted in size but construct normal cocoons. The life-cycle is completed in 26–35 days.

Bracon thurberiphagae (Mues.) and Bracon cajani Mues. are gregarious ectoparasites of similar habit. They paralyse second- to fifth-stage larvae and deposit eggs on or near them. The life-cycle is completed in 13 to 16 days. A method of rearing field-collected immature stages is described.

Perisierola sp. is a gregarious ectoparasite. The adult enters the pod, paralyses a host, and attaches her eggs directly on to the caterpillar. Second- to fifth-stage hosts may be attacked but the larger hosts are preferred. The female frequently remains with her progeny until they have completed their development, which requires 11 to 15-days.

Hyperparasites attacking the parasite pupae are listed.

Details of a shipping container and methods of rearing and shipping parasites to Mauritius for trial against Etiella zinckenella (Treitschke) and Maruca testulalis (Geyer) are described. From a stock of more than 44,000 cocoons so sent two species, Bracon cajani and Eiphosoma annulatum, have been successfully established in Mauritius.

A population of Glossina palpalis (R.-D.) was studied for three years, between February 1954 and January 1957, at Ugbobigha, on the northern edge of the main rain-forest belt of southern Nigeria. A fly-round was laid out along the banks of a forested stream, running northwards from the forest belt into the savannah woodland, and was divided into four sections representing farmland, wide fringing forest, narrow fringing forest, and the edge of forest.

No major seasonal movements of the fly population from one section to another could be detected; it was found that open farmland and the edge of forest with good visibility always yielded the highest catches, whereas catches inside dense forest were always low. Data from other sources showed that at all seasons of the year G. palpalis may be found in small numbers throughout the savannah woodland, even in the absence of water. This species also occurs in very small numbers within the main forest belt, and in village clearings lying within this belt.

Apart from an increase in the second and third months of the rains (March–April) and a fall during the fourth and fifth months, the population tends to remain steady at a low level throughout the year. The increase in population is associated with a mean temperature of 79–80°F. (26·1–26·7°C.) and an average saturation deficit of 5·5 mb. These figures agree closely with those found to be optimal for G. palpalis by other workers. The decrease in population is associated with a falling temperature, but more especially with a mean saturation deficit that has dropped below 3 mb. These results agree closely with those found near the northern limit of the range of the species in Nigeria. The favourable period for increase during the wet season lasts for four months in northern Nigeria, but only two at Ugbobigha: this is believed to account for the much lower fly density found in the humid south.

Dissections of females showed no seasonal trend in the proportion that were pregnant, nor any cessation of breeding in the heavy rains (August–September). Of 3,130 flies caught, 45·5 per cent, were females, and of the 1,040 females dissected, only 3·6 per cent, were found to be virgin; in northern Nigeria, the comparable figures were 49·1 and 4·0 per cent., respectively. At Ugbobigha, there is no seasonal trend in the percentage of females amongst flies appearing to man. Among the non-teneral males caught, the mean monthly proportion that was hungry ranged from 8 to 22 per cent., but showed no seasonal trend, whereas comparable figures from northern Nigeria ranged from 24 to 43 per cent.; this suggests that G. palpalis requires food less often in the humid conditions of Ugbobigha, or possibly that game is more numerous.

Of 1,635 examples of G. palpalis dissected, 2·1 per cent, were found to have mature infections of trypanosomes; of the latter, about two-thirds belonged to the Trypanosoma vivax group and about one-third to the T. congolense group. There was no difference in the infection rates of males and females.

Very few pupae were found, owing to the low fly population and the extensiveness of the breeding sites under the equable climatic conditions. The temperature of the pupal environment is considerably higher here than in northern Nigeria.

The diurnal rhythm of activity of G. palpalis was investigated both in the dry season and the wet. In both, activity increases steadily between 7 and 10.30 a.m., as the temperature rises, and falls steadily between 3.30 p.m. and dusk; peak activity occurs at various times between noon and 3.30 p.m. The numbers caught before 11 a.m., expressed as a percentage of the day's catch, increases at seasons when the temperature is higher. The flies are equally active in overcast weather and full sunshine, but rain reduces activity by more than a half.

In the British Solomon Islands Protectorate, the incidence of the immature nutfall of coconuts that is caused by species of Amblypelta depends upon the distribution of (1) the species that are concerned, which determines on what islands nutfall occurs, and (2) certain species of ants, which affects the local distribution of nutfall on those islands. A. cocophaga China is the most important member of the genus as regards responsibility for nutfall; A. cristobalensis Brown and to a less extent A. costalis Van Duzee also frequent the coconut palm and cause nutfall, but not on a serious scale; A. gallegonis Lever rarely, if ever, attacks coconut.

The current view that Oecophylla smaragdina (F.) protects coconuts against Amblypelta, and that Pheidole megacephala (F.) and Iridomyrmex myrmecodiae Emery give little or no protection, is accepted, but evidence is brought forward showing that Iridomyrmex appears to give some protection against A. cristobalensis on San Cristobal. Most attention has been given to a fourth species of ant, Anoplolepis longipes (Jerd.), the relation of which to nutfall has hitherto been in some doubt; evidence from various sources shows that, at least on Guadalcanal and Malaita, it gives nearly, if not quite, as much protection against Amblypelta as Oecophylla does.

A method based on crop estimation is used to give some indication of the losses due to nutfall in the European plantations that have been surveyed. The accuracy of the method is discussed in an Appendix. Varying numbers of nuts survive to maturity in nutfall areas, depending on the intensity of attack. In addition to the loss caused by the failure of nuts to survive to maturity, Amblypelta attack causes further losses by reducing the amount of copra obtainable from surviving nuts, and by rendering plantations where the attack is sufficiently severe unprofitable to work, so that they become, in effect, a total loss, even though a proportion of the nuts may survive attack.

An attempt is made to evaluate and compare the fraction of the crop lost on some of the principal islands, but it is impossible to give an even approximately accurate figure for the losses due to nutfall in the islands as a whole, because essential data, comprising the planted acreage of each plantation and island, and, except for a very few plantations, details of annual production figures over a period of years, are often lacking; also, limited time has made it impossible to survey many of the plantations in sufficient detail for an accurate assessment of nutfall.

A list is given of the species of ants recorded from coconut plantations during the present work.

Observations were made on Glossina tabaniformis Westw., G. fusca (Wlk.), G. nigrofusca Newst. and G. medicorum Aust., which all occur near the field station of the West African Institute for Trypanosomiasis Research at Ugbobigha in southern Nigeria. Identification of these species by the use of external characters has not been found possible between the females of G. tabaniformis and G. fusca, but is fairly simple between males of these two species and between both sexes of G. nigrofusca and G. medicorum. A simple key, based on external characters, is given. When necessary, females of G. tabaniformis and G. fusca were separated by dissection. G. tabaniformis, G. fusca and G. nigrofusca usually rest in a vertical position, with the head downwards, at a height of 4–6 ft. above ground (possibly lower for G. nigrofusca), on tree trunks, climber stems, etc., having a diameter of 5 in. or less.

A fly-round was started using a Zebu bull as bait. G. tabaniformis and G. fusca were caught in good numbers, G. tabaniformis forming 83 per cent. of the catch. There appears to be a decrease in population in the late dry season (January and February) in both these species. Females comprised 56 per cent. of the total catch of G. tabaniformis and 47 per cent. of that of G. fusca.

The vegetation of the fly-round, which is typical secondary rain-forest as found in southern Nigeria, was analysed; both G. tabaniformis and G. fusca prefer old forest with an absence of a lower stratum, beneath a continuous middle stratum and good upper stratum, that is to say, where visibility beneath the trees is good. G. nigrofusca comprised only 1·1 per cent. of the catch on the fly-round, although at first it was believed to be common in the area. G. medicorum does not inhabit the main forest belt, but is confined to riverine vegetation and forest islands in savannah.

G. tabaniformis is unlikely to be of economic importance, since the rate of infection with trypanosomes is low (3·7%) and this fly is confined to the forest. G. fusca and G. medicorum are both of economic importance, since their infection rates are high (14·9 and 15·4%, respectively) and they travel out into the savannah grassland. G. nigrofusca has a yet higher infection rate (26·7%), but it is confined to the forest at Ugbobigha; where, as in Ghana, it frequents the savannah, it is potentially dangerous. Females of G. tabaniformis and G. fusca are more heavily infected than males.

Females of G. tabaniformis were examined (by dissection) for pregnancy; 82 per cent. of the females were pregnant and 4·3 per cent. unfertilised. No seasonal fluctuations in the rate were apparent.

The biting behaviour of East African species of Aëdes in the subgenera Aëdimorphus, Banksinella and Dunnius, as shown in numerous series of 24-hr, catches made predominantly in Uganda, is discussed. It is shown that with the single exception of A. (A.) natronius Edw., which is arboreal, all the species encountered have been most prevalent at ground level. They bite mostly by day, but A. cumminsi (Theo.) shows a marked peak of activity from just before to just after sunset, and A. natronius is crepuscular. When, however, samples were obtained in environments less favoured than the forest floor, and in which the mosquito concerned was less abundant, the biting cycle might be altered. Thus various species which were essentially diurnal at ground level in forest might be nocturnal in the canopy or in banana plantations.

In some cases there seemed to be a tendency towards a group pattern of behaviour. For example, in the abnormalis (Theo.) and tarsalis (Newst.) groups of Edwards it was found that at least three species showed very similar biting cycles. A fourth species, A. nigricephalus (Theo.), which occurs in Nigeria, is reported there to differ in its biting habits, and is also strikingly different in appearance and in the structure of the terminalia.

Members of all three subgenera have been involved in various isolations of virus, but it is not possible to prove that they, rather than other species of Aëdes included in the infected lots, were the vector mosquitos, except in the case of the A. tarsalis group, from which there have been two definite isolations of Rift Valley fever virus, and in that of A. circumluteolus (Theo.), which has been shown by recent work in South and East Africa to be of major importance, well over 20 isolations of virus having been made from this species. So far as is known at present, seven separate viruses and one distinct variant have been isolated from A. circumluteolus, and other members of the subgenus Banksinella also appear to be involved in transmission.

The development of the khapra beetle, Trogoderma granarium Everts, and the cycle of movement of insects between the food and hiding places has been studied at 30°C. The results have been correlated with observations at maltings, its chief habitat in Britain.

In populations at 30°C., many larvae delay pupation and enter diapause, the remainder spending most of their time in the food and completing development quickly. The diapause larvae leave the food in the fourth and in later instars in search of hiding places. Disturbing the food stimulates the larvae to leave it a little earlier. Larvae resting in diapause moult occasionally, and at long and irregular intervals they emerge, presumably to replenish their food reserves by feeding, after which some pupate and the rest hide again.

The hidden diapause larvae can persist for a very long time; in cultures, 16 per cent, remained after four years. Apparently, as the food stored in the fat-body is depleted, they become readier to emerge from the crevices to feed. Replacing stale food by new food causes some larvae to emerge and the effect of disturbing the larvae is variable. After feeding, some of these larvae complete development and the resulting adults breed, presumably producing both quick developing and diapause larvae among their offspring.

When denied a hiding place, the diapause larvae remain inactive in the food without increasing their rate of pupation. However, they feed more, producing heavier beetles, an effect also obtained by regularly providing fresh food.

It is concluded that when a malt store is loaded, some diapause larvae remain in the fabric of the store and others emerge and feed; after feeding, some larvae re-enter crevices and others complete development and breed; the offspring contain some diapause larvae, which accumulate in the crevices and on the walls just below the malt surface; after the malt is unloaded, diapause larvae may persist in empty stores for a number of years, because they can restore their food reserves by occasionally eating grain residues.

In the second of this series of papers on the losses caused by the Coreid, Pseudotheraptus wayi Brown, to coconuts in Zanzibar, descriptions are given in summary form of a number of Government-owned plantations of coconuts on the island, together with the yields recorded over the 12 years, 1944–55. The variation from year to year in any group of plantations is not large, and over all those considered does not exceed 25·8 per cent, of the 12-year mean.

In the plantations on poorer soils, predominantly occupied by the ants Anoplolepis longipes (Jerd.) or A. custodiens (F. Sm.), the vidaka damage rate (V.D.R.) during 1955 varied from 60–80. The plantations on better soils are occupied predominantly by a complex of Oecophylla longinoda (Latr.) and Pheidole punctulata Mayr and the V.D.R. determined on a part of these in 1955–56 varied from approximately 41 to 55, with a mean of 47·1. The mean value of the V.D.R. calculated from 200 localities taken at random in Zanzibar during June–August 1955 was 60·6. Taking a value of 50 as a conservative estimate of the V.D.R. for the whole island, and inserting this in the regression equation Y = a + bX relating yield (Y) with V.D.R. (X), derived in the first of this series of papers, together with the average values of the constants a and b obtained therein, it is shown that about two-thirds of the potential crop of coconuts is lost as a result of damage by P. wayi.

Comparison of the yields from palms occupied by Oecophylla in two of the plantations on better soil with those of the whole of those plantations suggests that about one-half of the potential crop is being lost.

The annual value of the total exports of unconverted nuts and coconut products (copra and coconut oil) varied from £636,254 to £1,008,194 during 1949–56, and the annual value of the total production of nuts, calculated from the estimated total acreage (104,000), the number of palms per acre (50), the 12-year average yield per palm on Government-owned plantations (22·5 nuts per annum) and the market price in 1948–56 (Shgs. (E.A.) 90–150 per thousand nuts), is £526,500 to £877,500. Taking into consideration the lower and upper estimates of the amount of crop lost and of the value of what remains, the minimum and maximum estimates of the financial loss caused by P. wayi in Zanzibar are of the order of £500,000 and £2 million, respectively.

The bean fly, Melanagromyza. phaseoli (Coq.), the larvae of which tunnel in the stems of Phaseolus vulgaris, is a pest of this crop in Tanganyika. Field trials there in 1956 on haricot-type beans showed that dressing the seed with chlorinated-hydrocarbon insecticides could prevent attack for at least 30 days after germination; organophosphorus insecticides were less effective. In four further field trials (A-D), in 1957, the insecticides and types of formulation used were aldrin (wettable powder and emusifiable concentrate (EC)), endrin (EC), γ BHC (dry dressing and EC), dieldrin (dry dressing and EC) and a proprietary organophosphorus systemic (dry dressing). Wet dressings were applied by treating the seeds with the liquid and drying immediately, and in one treatment aldrin as a wettable powder was applied dry and the seeds then damped and dried at once.

Damage was assessed on an arbitrary scale on trials A and B, and yields measured on trials A, C and D. Results varied between insecticides and under different growing conditions, but wet dressing with endrin at 213 mg. per 100 g. seed, of which about 50 per cent, was retained on the seeds, resulted in the lowest damage, amounting to 7·7 compared with 52·6 for the control (no dressing), and the highest yield, amounting to 13·5 units compared with 8·6 for the control. All treatments, except that with the organophosphorus dust, reduced the damage significantly below that in the control. Wet dressings were usually more effective than dry dressings with the same insecticide, as regards both yield and reduction in damage. This may be associated with the better retention of wet dressings, which was shown by the results of chemical analysis of the residues on the seeds left in the drill hopper after sowing.

An undesirable effect of using a dust containing 0·4 per cent, lindane for the control of Pseudotheraptus wayi Brown on coconut palms is the eradication of Oecophylla longinoda (Latr.), a species of ant inimical to this Coreid, and in the search for a more suitable preparation, formulations were tested in Zanzibar that contained DDT, with synthetic resins to prevent its absorption through the treated surface of the palm. One such formulation, prepared by dissolving 23·5 lb. of a proprietary coumarone indene resin and then 235 lb. 80 per cent. p,p′DDT in a mixture of 100 gal. power kerosene and 100 gal. diesoline, heated to 40–45°C., is here termed 10 DRDK and its properties described.

When 10 DRDK was applied by pneumatic hand-sprayers to the centres of palm crowns, small species of ants (Pheidole spp., Crematogaster spp., Paratrechina longicornis (Latr.)) and Anoplolepis longipes (Jerd.) were eradicated from such sites, whereas O. longinoda increased in numbers and other large species (Camponotus spp., Polyrhachis spp., etc.) were unaffected. Although 10 DRDK was lethal to all species when applied as an aerosol in the laboratory, the residual deposit from it killed only the smaller species, apparently because their bodies make contact with the DDT crystals whereas those of the larger species (except A. longipes) are held clear. Under Zanzibar conditions, this deposit, which is at first gummy, gives rise within 2–3 weeks, or following mechanical disturbance, to needle-like crystals of DDT, 10–120 μ long × 2–10 μ wide projecting from the sprayed surface and forming clumps up to 1·5 mm. high.

In field tests, paper bands dipped in 10 DRDK and attached round palm trunks prevented the passage of A. longipes for six months, and of Pheidole for nine months, despite heavy rain; that of the larger species of ants was unaffected. Determinations of the deposit on a sample band selected each week at random showed great variability but fell from 392–478 μg. DDT per sq. cm. initially to 92–176 μg. after 31 weeks. In concurrent tests of similar bands exposed in the laboratory, the deposit fell only to 282 μg. per sq. cm. over approximately the same period.

In tests of 10 DRDK applied topically to the dorsum of Pseudotheraptus wayi, complete mortality of adults was obtained within 48 hours with droplets 85 μ in diameter (containing 0·31 μg. DDT) and the size required diminished progressively, the earlier the stage treated. When individuals of P. wayi were allowed to walk for one minute on glass plates bearing known deposits from 10 DRDK, complete mortality of all stages, from 2nd-instar nymphs to adults, followed within 24 hours of exposure to 2·7 mg. DDT per sq. ft., but not to 1·6 mg., except in the case of recently moulted adults, 5th- or 4th-instar nymphs.

Two experimental areas totalling some 1,000 palms, of which 10 per cent, had Oecophylla nesting in them in October 1952, were sprayed with a commercial formulation containing DDT from November 1952 to June 1953, and the percentage fell to 2·5; the areas were then treated with 10 DRDK by hand-sprayer until January 1954 and by machine for the rest of 1954. The percentage of palms having Oecophylla, in October 1953, October 1954 and February 1955 increased to 7, 15 and 38, respectively. In a control area one mile away, the percentage rose from 23·5 to 36 over the same period. In a third area, 12 applications of 10 DRDK totalling 10 gal. per acre were made by machine during 1953, 12 totalling 33 gal. in 1954 and 9 totalling 30 in 1955, and the percentage of palms colonised by Oecophylla rose from nil to 21·7 in 1953, to 26·1 by March 1955 and to 30 by April 1956, while the percentage colonised by A. longipes fell over the same period from 90 to 1.5. In the control areas, A. longipes remained dominant and no Oecophylla became established.

The addition of lindane to 10 DRDK to give concentrations of 0·1, 0·5 or 1·0 per cent, adversely affected the selective properties of the formulation, and although the highest strength gave a good kill of P. wayi and other insects, apart from Coccids, which increased considerably, it reduced Oecophylla to a greater extent than it did other species of ants. No advantages are obtained by the addition of dieldrin, endrin, pyrethrins or rotenone.

The importance of certain species of Stomoxys in Uganda, the possibility that these species may be responsible for the mechanical transmission of trypanosomiasis, and the effects of severe biting of Stomoxys on cattle causing loss in milk yields and weight in beef animals, is pointed out.

A satisfactory method is described for rearing large numbers of Stomoxys calcitrans (L.) under the conditions that prevail in East Africa.

A description of special cages for keeping the adults and for egg production is given, together with a technique for supplying the adults with 0·2 per cent, citrated bullocks' blood.

A satisfactory egg-laying and breeding medium contained 9 oz. of dried cow dung, 5 oz. of dried blood granules and 1 oz. of sugar.

A detailed description of the construction and working of a constant-temperature and humidity room for rearing larvae and pupae is given, the temperature and relative humidity of the room being maintained at 90°F. and 90 per cent., respectively.

The maximum number of eggs that can be introduced into 1-lb. and 2-lb. Kilner jars without causing overcrowding and subsequent under-nourishment in the later larval instars was found to be 200 and 400, respectively.

Seed treatments of calomel, DDT, dieldrin and aldrin were compared in three seasons′ field trials for use against onion fly, Delia antiqua (Mg.). Excellent control and also improved germination were obtained with 0·5 oz. actual dieldrin per lb. of seed applied with a sticker, with or without thiram. Similar results were obtained with 0·1 and 1·5 oz. actual dieldrin per Ib. of seed, but 3·2 oz. reduced germination. Aldrin at the same rates gave excellent control but reduced germination. DDT at 1·5 oz. and 3·2 oz. gave good control early in the season, but was not sufficiently persistent and seriously reduced germination. Calomel gave little control, although it improved germination.

Although kerosene used as a sticker for a dust was satisfactory, it was liable to reduce germination seriously when used alone, except at very low rates.

Seed treated with DDT, dieldrin or aldrin may be stored safely for a month or two in unsealed containers but not in sealed containers.

There was close correlation between the percentage of plants attacked and the yield per 100 plants in the original stand. For every 10 per cent. of plants killed by onion fly there was a 10 per cent. loss of the potential yield.

Even where the onion-fly attack was heavy, comparatively few plants showed symptoms of damage at any one time, which suggests that the level of attack is frequently under-estimated.

Cashew, Anacardium occidentale, an increasingly important cash crop in the coastal region of Tanganyika, is damaged by two widely distributed species of Helopeltis, H. anacardii Miller and Helopeltis sp.

At Bagamoyo, in June 1955, the period from egg to adult for H. anacardii occupied 35·9 days; that for Helopeltis sp. occupied 39·2 days.

Damage is caused to the leaves, shoots, buds, young fruits and to the cashew apple. Damage in a young tree is more marked than that in an old tree and may result in its being malformed or stunted.

The build-up of Helopeltis populations on cashew follows the main growth period of the crop which begins shortly after the end of the main rains in May. The insects are readily found from July to October-November, when the crop matures.

Application of a 0·5 per cent, γ BHC dust and a 5 per cent. DDT dust to two-year-old trees increased the amount of crop but the increase was not economic owing to the fact that the trees were coming into bearing for the first time. Cross-infestation from untreated plots may also have reduced the effectiveness of the treatments.

Three or four applications by a knapsack-type power duster of 0·5 per cent. γ BHC dust at 15-day intervals previous to flowering of the main crop gave promise of successful control in the field.

The life-history and seasonal cycle of the Lepidopterous borer, Busseola fusca (Fuller), the most serious pest of maize in Southern Rhodesia, have been studied there.

There are two generations in the year, the majority of the full-grown larvae of the second entering diapause, in which condition the dry season is passed in the maize stem, but a proportion of the second-generation consists of short-cycle individuals that give rise to moths irregularly during the dry season.

In the field, the egg stage lasts about 7–11 days, according to the time of year. In the laboratory, there are six, very occasionally seven, larval instars in the first generation, occupying about 37 days, and the pupal stage lasts about 17 days. In the second (diapausing) generation there may be one or two additional moults without appreciable change in size, and there is considerable variation in the length of instars and in the date of entry into diapause, but by mid-June the bulk of the larvae that will survive are in diapause. The majority of diapause larvae pupate in early November, the pupal stage lasting about 23 days.

The feeding habits of the larvae are described and reference is made to other food-plants.

The length of life of the adult, in cage conditions, averages 6–7 days, but there is great variation. When provided with diluted honey, adults were not observed to feed, and absence of such food did not appear to impair egg-laying. The sex ratio was 1:1, but in catches at a light-trap the ratio of males to females was 5:1. Copulation takes place shortly after emergence, and oviposition may begin within 24 hours of emergence.

The average number of eggs laid per female in cages was 360 over an average of four days, one female laying 1,032. Several batches of eggs may be laid in one night. A single mating appears to be sufficient, but males may copulate with more than one female. Eggs laid by virgin females do not hatch.

Diapause is thought to be induced by larval feeding on drying food. Continuous rearing of non-diapause generations can be achieved by feeding the larvae on fresh, green maize. Similarly, in the field, irrigated out-of-season maize will support non-diapause generations and constitute a source of infestation that may render ineffectual the normal routine destruction of all plants of the previous dry-land farming season.

The main parasite is the Tachinid, Sturmiopsis parasitica (Curr.), which may destroy more than 33 per cent, of the larvae in either generation.

Observations were made at Dorimon in the extreme north-west of Ghana, during the hot months of March and April 1954, of the infectibility of Glossina palpalis (R.-D.) and G. tachinoides Westw. with Trypanosoma vivax.

Pupae were obtained from the Black Volta where shade temperatures ranged from 70 to 98°F. and the flies that emerged from them were kept singly in small glass tubes in the laboratory at a temperature of 85 to 95°F. and a relative humidity of 60 to 80 per cent. They were given several feeds on infected goats. The following percentage rates of infection were observed.

Labrum and (or) hypopharynx: General rate, 56·1; males of G. palpalis, 72·2, females, 34·6; males of G. tachinoides, 68·4, females, 56·8.

Labrum only and labrum & hypopharynx: General rate, 37·4; males of G. palpalis, 27·8, females, 15·4; males of G. tachinoides, 68·4, females, 40·9.

Early infection is the rule but late infections occurred. Some flies appear to be uninfectible. Thus, out of 107 flies, 47 remained uninfected in spite of having had on the average 10·6 infective meals per fly. A high percentage of flies lost their labrum infection.

The following percentage loss of labrum infection was recorded: General rate, 48.8; males of G. palpalis, 66·7, females, 62·5; males of G. tachinoides, nil, females, 43·8.

G. tachinoides appears to be more tenacious of infection than G. palpalis. Feeding infected flies on goats in the negative phase and (or) on spurwing goose (Plectropterus gambensis) did not appear to have any adverse effect on the colonies of trypanosomes in the labrum.

In experiments with Aëdes aegypti (L.), fourth-stage larvae bred at 30°C. survived exposure to 0·5°C. for 7 hours, but none recovered after exposure for 17 hours, although nearly all those from the same culture that had been acclimatized for one hour to 18 or 20°C. did so. No such effect followed acclimatization at 10°C., at which larvae are in chill coma. Larvae acclimatized at 18°C. survived exposure to 5°C. for longer than did those from 30°C. Earlier work showed that the thermal death point, for a one-hour exposure, was 42°C. for larvae acclimatized at 30°C. but rose to 44°C. for larvae acclimatized to 37°C. It is concluded that the effects of high or low extremes of temperature may be substantially modified by a brief period of acclimatization at a less extreme temperature.

Records are given of the species of mosquitos captured at Mombasa in the years 1943–44 and 1949–52. They were caught by four different methods, namely: (1) day-time net catches in the bush, (2) window-trap catches, (3) diurnal (bait) biting catches in the bush and (4) twenty-four hour (bait) biting catches in three different situations. Sixty-six species were taken in the day-time net catches and nine others which did not figure in the net catches were taken in one or other of the remaining three methods.

The habits of the commonest species, as indicated by these catches, are discussed in some detail.

Culex pipiens fatigans Wied. occurred in large numbers in biting catches, net catches and window-trap catches. In 24-hour catches most biting occurred after midnight, but, in the window traps, activity was greatest between 18 and 21 hr.

Aëdes simpsoni (Theo.) was not taken in window traps or houses. Seasonal occurrence, as indicated by larvae in banana axils, net and biting catches in the bush, is discussed. Twenty-four hour catches confirmed earlier findings that this mosquito bites almost solely during daylight.

Aëdes pembaensis (Theo.) occurred throughout the year with little seasonal variation; this is thought to be connected with its breeding in crab-holes. It is often found in fair numbers in houses when these are near the breeding grounds. Window-trap catches show that most activity takes place at night though some also occurs during the day. The biting rhythm as shown by 24-hour catches in houses, bush and on tree platforms is discussed.

Aëdes albicosta (Edw.). Previously this mosquito may have been confused with Aëdes albothorax (Theo.) and Aë. lineatopennis (Ludl.). It can occur at times in great numbers when it may bite viciously both indoors and outside.

Anopheles gambiae Giles and A. funestus Giles were not evident in large numbers. In window traps most activity took place at night although some also occurred during the day. In 24-hour catches, A. gambiae fed mostly just before dawn though biting occurred also from midnight onwards. A. funestus appeared suddenly and in fair numbers in window traps but was absent for much of the year.

Aëdes aegypti (L.), though fairly common, is recorded only in Tables and in one figure as its bionomics have already been discussed elsewhere.

Notes are given on other species, which include Culex duttoni Theo., C. nebulosus Theo., C. tigripes Grp., Aëdes metallicus (Edw.), Aë. albocephalus (Theo.), Eretmapodites subsimplicipes Edw. and E. quinquevittatus Theo.