In investigations made in January to November 1962, Anopheles parensis Gillies was found biting man in large numbers in a zone near Malindi, Kenya, in which house-spraying with DDT had been carried out between March 1961 and October 1962. Densities were greatest just outside villages, less so on the verandah of a house and least indoors. In one open type of unsprayed house, however, moderately large numbers were caught. The monthly average catch per night by two men was greatest (over 200) outdoors in July and August.

Biting activity reached two peaks during the course of the night, catches in all situations being greatest during the two hours following sunset and the three hours preceding sunrise. The evening peak was highest in the outdoor catches, and the late-night peak in the indoor collections. A distinct influence of moonlight on the catches was observed, the early evening peak under certain conditions being greater during the moon's first quarter and the late-night peak during its last quarter.

Numbers of examples were caught biting cattle, but owing to the absence of large herds of stock it is believed that most feeding took place on man. The proportion of nulliparous females was 64 per cent, in the sprayed zone and 50 per cent, in an unsprayed village, and in the latter the nulliparous rate in females resembling A. funestus Giles (the majority of which would have been that species) was 24 per cent. No specimen of A. parensis infected with sporozoites was found in the sprayed zone. In the unsprayed village, no infected glands were found in a small series dissected. Thus no evidence was obtained that A. parensis was acting as an exophilous vector of malaria in the sprayed zone. Moreover, in view of the high nulliparous rate observed in the unsprayed area, this species is considered unlikely to be of any importance under normal conditions.

The insecticidal activities of 13 triphenyltin compounds having the general formula (C6H5)3Sn X were compared with those of other organotin compounds and DDT by exposing adults of Sitophilus oryzae (L.) for 48 hours on filter paper impregnated with 1 per cent, solutions of the compounds in benzene, and by allowing larvae of Tineola bisselliella (Humm.) to feed for 14 days on pieces of woollen cloth impregnated with 1 per cent, by weight of the compounds. The triphenyltin compounds were ineffective as contact insecticides, virtually all the Sitophilus adults surviving, whereas all were killed by DDT. Their effectiveness as stomach poisons varied with the nature of the Group X, mortality after 14 days amongst the Tineola larvae ranging from 76 per cent., for triphenyltin thiophenoxide, down to zero, for hexaphenylditin. All except the latter and triphenyltin sulphide were highly effective moth-proofing agents, the weight lost by the test pieces being less than 5 per cent, of that lost by the untreated control. Tetraphenyltin afforded no protection against Tineola, but tributyltin oxide caused 100 per cent, mortality, apparently by contact action, since none of the test piece was eaten.

Observations in three areas in northern Tanganyika on the day-time resting sites of adults of Glossina swynnertoni Aust. showed that the most important of these was the underside of branches of trees. The number of flies seen on this site represented about one-third of the total population as calculated from the apparent density, and about half of them were on branches 4–9 ft. above ground, 1–4 in. in diameter and at an angle of less than 35° from the horizontal. It is suggested that were an insecticide to be applied to branch sites within these limits, then, since any fly must make six or more flights in the first 18 days of its life, it would be expected to alight on a treated surface at least once in this period. Were a lethal deposit maintained for twice this period, plus the pupal period, control could be effected.

Pyrethrum spray-sheet collections in a small village in Northern Nigeria showed that there was no significant difference in the numbers of Anopheles gambiae Giles and A. funestus Giles caught at different times in the early morning. In this village, huts at the edge nearest to the only breeding site attracted considerably more adults than those further away from the edge, and some huts were consistently more attractive to mosquitos than others. There was a positive correlation between the numbers of A. gambiae and A. funestus in the huts. Although significant differences were found between numbers of mosquitos caught in the huts occupied by different numbers of people, no simple relationship could be discovered between the combined densities of the two species and the number of hut occupants. It is concluded that there is need for further investigations into the factors influencing densities of the Anophelines in village huts.

The toxicity of naturally weathered deposits of 21 chemicals to larvae of the codling moth, Cydia pomonella (L.), was assessed by spraying apple trees in the orchard and testing samples of the fruit picked at various intervals after treatment. Each apple was placed in a separate glass container with one first-instar larva from a laboratory culture, and larval mortality and damage to the fruit (defined as removal of a portion of the skin) were recorded after three days in a constant environment.

The site of entry of the larvae was shown to vary with fruit size, calyx entries decreasing and side entries increasing with increase in the surface area of the fruit.

The relationship between larvicidal activity and age of the spray deposit for periods up to ten weeks after spraying is illustrated graphically; data are presented for fruit damage caused by larvae applied one and three weeks after spraying.

On the basis of larval mortality and fruit damage recorded in tests on deposits up to three weeks after application, a spray containing 0·1 per cent, carbaryl was the most effective, followed by 0·05 per cent, fenthion, while Bayer 5024, Zectran, DDT, DDD (all at 0·l per cent.) and 0·04 per cent, azinphos (as the methyl or ethyl homologue) were only slightly less effective. Deposits from 0·1 per cent. Kepone, 0·02 per cent, diazinon, 0·11 per cent, malathion, 0·01 per cent, parathion and 0·05 per cent, carbophenothion, dimethoate and ethion also caused 90–100 per cent, mortality when fresh, but were less persistent. Fresh deposits from 0·1 per cent, endosulfan, 0·04 per cent, dioxathion, 0·05 per cent, phenkapton, 0·02 per cent, phosphamidon, 0·2 per cent, lead arsenate and 0·6 per cent, ryania only killed 50–88 per cent, of the larvae, and their residual toxicity was proportionately low.

Heavy rain soon after spraying caused a large reduction in deposits from wettable powders but the accompanying reduction in larvicidal activity was shown to be greater in the case of carbaryl than for DDT or DDD.

The toxicity and persistence under natural field conditions of deposits of dieldrin and isobenzan, derived from dilutions of emulsion concentrates, on the leaves of riverine vegetation in the Northern Guinea Savannah vegetation zone of Nigeria were studied by a bioassay method, using teneral females of Glossina palpalis (R.-D.) as test insects. Although deposits of both insecticides were extremely toxic when first sprayed, neither product was found to have a long residual action, and isobenzan was found to be approximately half as efficient as dieldrin. It is suggested that because of its poor residual action isobenzan will be little used in tsetse control campaigns in areas similar to that in which the investigations were performed.

A key is given for the separation of a group of allied species of Eulophidae comprising Elachertus nigritulus (Zett.), E. geniculatus (Eatz.), E. olivaceus (Thoms.), E. scobiciae Erdős, and a species here described as E. pallidus sp. n. Biological data for each species are given. E. nigritulus and E. geniculatus have previously been regarded as synonymous; the latter parasitises Laspeyresia strobilella (L.), a pest of conifers, whereas E. nigritulus, and also E. pallidus, attacks Lepidoptera associated with fruit trees.

Populations of the leaf-miner Leucoptera meyricki Ghesq. and its parasites, of which Zagrammosoma variegatum (Masi), Achrysocharella ritchiei Ferriére and Parahormius leucopterae Nixon were the most abundant, were studied for 40 consecutive weeks during 1960–61 in Kenya, in four experimental blocks of coffee (Coffea arabica), two of which received several applications of parathion sprays and the other two none. Each week eight different trees within each block were covered with a tent, pyrethrum spray was atomised within, and the adult moths and parasites were recovered from the polyethylene sheeting used as a floor to the tent. Fortnightly, counts of leaves, mined and unmined, and collections of leaves with leaf-miner larvae and parasites within them were made. These intensive studies were supplemented with two special spray tests, in which different dosages of insecticides were used, and with collections of leaves made periodically over a rather extensive area in Kenya, from which adult leaf-miners and parasites were reared to gain information on the parasite/host relationships over a wide range of ecological conditions.

Parathion used at 1 lb. 20 per cent, wettable powder in either 65 or 80 gal. water per acre appeared to kill all adult leaf-miners and parasites present. Possibly between 50 and 75 per cent, of the leaf-miner larvae, and appreciably fewer of the immature stages of the parasites within the mines, were killed. The sprays apparently had even less effect on the leaf-miner prepupae and pupae and the parasites within the cocoons, which are usually formed in the litter and in crevices in the soil.

Leaf-miner populations within the sprayed blocks were somewhat lower than those in the unsprayed blocks, but the fluctuations were remarkably similar. In general, this was also true for the parasites.

Assessment of the effects of the sprays on the efficiency of the parasites was made on the basis of the ratios of adult parasites to moths obtained from tented trees and from infested leaf samples held for adult emergence, as well as in terms of percentages of larvae parasitised in the samples dissected. It was found that the sprays killed a greater proportion of the leaf-miner larvae than of parasites within the mines, and thus increased the ratios of living parasites to leaf-miners immediately following the spray applications. During the period from October to January, when the sprays in the Eukera plots were synchronised with the peak populations of the moth, parasitisation was significantly higher in the sprayed plots than in the unsprayed plots. Furthermore, in the special spray tests, where different dosages of parathion and diazinon were used, parasitisation within the surviving populations was higher in the plots that received the higher dosages. These findings suggest that with proper timing of spray applications the efficiency of leaf-miner parasites may be improved.

Adults of Zonocerus variegatus (L.) collected in southern Nigeria in January to May 1963 were found to be parasitised by larvae of Blaesoxipha filipjevi Rohd. Of 1,691 adults of Z. variegatus dissected, 43 contained from one to six larvae of B. filipjevi, but none was found in 167 nymphs dissected mostly in January and February. No parasites were found in 155 examples of 11 other locally occurring species of Orthoptera. Full-grown larva left their hosts through the cervical membrane; they pupated within 48 hours, probably in the soil in natural conditions, and the adult Sarcophagid emerged 9–10 days later. No larva was observed to undergo diapause. The presence of the parasite restricted the ovarian development of the female host, but the species is considered to be of negligible importance in the control of Z. variegatus because of its low incidence.

Two types of population history shown by Lasioderma serricorne (F.) are described, one when the food was renewed at regular intervals, the other when there was no food renewal. Initially, both of these populations increased together to a high level, the former continuing at this level until the observations were discontinued, the latter declining and eventually becoming extinct. Stage-specific properties, which relate the numbers in each stage to those a unit of time previously and which are functions of the survival, developmental and fecundity rates, were estimated for each type of population; they are compared as between the two types and with the corresponding properties of a population given effectively unlimited space and food. It is shown that the effect of the limiting conditions produced a decrease in survival, developmental and fecundity rates. From this, together with other evidence, it appears that food shortage, not space shortage, was the primary cause. After the initial increase in numbers, the stage-specific properties shown by the species in both populations imply that there was a regular oscillation in the developmental, survival or fecundity rates, which would result in corresponding fluctuations in numbers.

Descriptions are given of 24-hour biting catches, made in and around Faza, a village on Pate Island, off the north-east coast of Kenya, East Africa.

Aedes pembaensis Theo. was the predominant mosquito in these catches but fair numbers of Aedes mombasaensis Mattingly were also taken; the biting cycles of these two are discussed. Six other species were taken in small numbers.

For Ae. pembaensis, biting cycles calculated on catches grouped for site, moon phases, neap tides and spring tides show that both moon and tide and light intensity influence the biting behaviour. Different but recurring patterns occur with various combinations of these factors.

For Ae. mombasaensis, the cycles have a very constant biphasic pattern. Catches grouped for moon phases, tides and catch sites, as for Ae. pembaensis, show that more biting females are taken at neap tides than at spring tides. Two patterns of behaviour occur, one associated with spring tides and the other with neap tides. An even level of biting activity occurs during the night with intense and prolonged moonlight; otherwise moon-phase cycles have little effect on biting behaviour.

It is felt that 24-hour biting catches can give useful information on behaviour patterns but it is desirable to have a long series of catches to analyse. For the purpose of calculating biting cycles, the results of catches showing similar modifications in behaviour should be treated separately.

The paper includes a description of studies on Anopheles gambiae Giles in the insecticide-free Umbugwe area of Tanganyika, and the results of dissections of A. gambiae and A. funestus Giles for sporozoite infections.

The densities of A. gambiae and A. funestus were assessed in houses by pyrethrum spray catches in 90 houses distributed in ten villages in the Umbugwe area between March 1960 and February 1962. A. gambiae was seasonally abundant, a sharp increase in density being associated with periods of rain. A. funestus type form was scarce in houses throughout the year, although a larval survey showed it to be the most common member of the complex of A. funestus in the area.

The average ratio of fed to gravid individuals of A. gambiae was 2·3:1 from June 1960 to November 1961, with peaks reaching 7:1 in March 1960 and 7·5:1 in January 1962. The peaks were attributed to rapid increase in production of adults during the limited period of the rainy seasons that followed very dry conditions.

Thirteen per cent, of recently fed individuals of A. gambiae were found in the exit window traps of experimental huts, having attempted to leave the huts on the night of feeding.

Two distinct types of huts are commonly found in the area, the tembe, which is large, divided into an average of five rooms by walls that are usually incomplete at the top, and accommodates large numbers of cattle as well as humans; and the banda, which is smaller, divided only into two rooms and seldom housing any domestic animals. Precipitin tests showed that whereas only 20 per cent, of individuals of A. gambiae taken in tembe had fed on man, in banda huts the percentage was 77. It was also shown that there was a dispersal of A. gambiae within a hut shortly after feeding. In a tembe. one-third of the individuals positive for man, and one-quarter of those positive for cattle had moved to rooms other than those in which they had fed.

A sporozoite rate of 1·47 per cent, was found among 3,746 specimens of A. gambiae dissected. Of the total number of 55 sporozoite-positive females of A. gambiae, 39 were found among the 424 individuals dissected in February 1962, thereby indicating unusually heavy transmission during the early part of 1962. A. funestus type form appeared to be of virtually no importance in malaria transmission in the Umbugwe area. Transmission by A. gambiae was highly seasonal, for although the percentage of gland-positive specimens was slightly higher in the long dry season than in the rainy season, the much larger mosquito population in the latter led to a higher number of infective bites in the rainy seasons. The highly seasonal transmission by A. gambiae was reflected in the results of examination of blood-films of people attending the Government dispensary.

Bagged maize stored in large stacks on the Kenya coast is subject to reinvasion by stored-products pests following successful fumigation with methylbromide, and treatment of the stack surfaces with insecticidal sprays has been unsatisfactory in preventing reinfestation.

Further tests are described of different methods of applying insecticides to small experimental stacks, each composed of ten 200-lb. bags of maize, exposed within a warehouse, after fumigation, to reinfestation from a large bulk of maize heavily infested with Tribolium castaneum (Hbst.). Populations of adults and pre-adult stages of T. castaneum were recorded from samples of grain obtained by a sampling spear from each bag at intervals.

In the first of two experiments, single applications of malathion in a spray at 100 and 150 mg. per sq. ft. to the entire external surface of each bag during the construction of the stack did not give good control of reinfestation in the six months after fumigation, but were not significantly worse, respectively, than a dust containing 1 per cent. lindane similarly applied to the upper surface of each bag and, four weeks later, to the outside of the stack at the rates of 3 and 6 oz. per bag. When the malathion treatments were followed by 24, 12 or 8 applications, at intervals of 1, 2 or 3 weeks, respectively, of sprays containing malathion to give 100 and 150 mg. per sq. ft. over the whole external surface of the stack, good control of T. castaneum was obtained with all treatments.

Mean residues of malathion in the outer inch of maize in the bags six months after the start of the experiment varied from 3 to about 19 p.p.m., according to treatment, suggesting that little penetrated through the bag wall and that after thorough mixing of the grain before use the malathion content would not exceed the permissible limit.

In the second experiment, an admixture of malathion dust with the maize before bagging to give 8 p.p.m. active ingredient gave almost complete control of larvae and pupae, and application of 3 oz. 0·5 per cent, malathion dust, or a spray affording 400 mg. malathion per sq. ft., to the upper surface of each bag during stacking gave highly significant reductions in numbers of T. castaneum in the pre-adult stages. The last of these treatments, followed, after fumigation, by malathion applied in a spray at 150 mg. per sq. ft. every three weeks to the external surfaces of the stack, is recommended for large-scale trial.

The larvae of two species of swift moths, Hepialus humuli (L.) and H. lupulinus (L.), live in the soil and are common under grass in the British Isles, but do not usually have any obvious effect upon the grass. The larvae of H. humuli are polyphagous and when they occur under agricultural or horticultural crops they may cause damage by feeding on the roots. Lettuce, strawberry and chrysanthemum are most frequently damaged.

The adults, which are described, fly at dusk, the female seeking the male. The female lays between 200 and 1,600 eggs, with a mean of about 600, over a period of four days. Sweep-net catches showed the ratio of the sexes to be approximately equal, and mercury-vapour light-trap catches showed that the flight period in southern England is principally in June.

In the laboratory, never less than 80 per cent, of eggs hatched, even in dry air, and the shortest incubation period, between 11 and 24 (mean 18) days, was at 20°C. At 5°C. they did not hatch, but remained viable for at least six months.

The larvae were reared in small cells drilled in blocks of plaster of Paris, which were stood in a tray of water, or in vials containing a layer of moist plaster of Paris, and were fed on pieces of carrot.

The growth of the larval head capsules was geometric and allowed 12 instars to be distinguished at 15°C.; at higher temperatures there may be more.

The growth curve of the larvae was S-shaped with a very distinct fall in weight in each instar for several days before moulting. The daily intake of food was weighed, and the conversion rate shown to be small, ranging from 0·00058 to 0·04, as compared with 0·205 to 0·49 recorded for other Lepidopterous larvae.

At 5°C., larvae did not develop beyond the second instar, nor beyond the fourth at 10°C. The optimum temperature for their development (mean period 224 days) was 15°C., although mortality was high. They developed at 20°C. more rapidly (mean 197 days) but more died. Larvae kept in a container sunk in the soil outdoors developed more slowly than those at 15°C. and had only reached the eighth instar by February (239 days after hatching). This evidence, together with that from an artificially infested plot in the field and general field observations, suggests that the usual life-cycle lasts two years.

The three-dimensional pattern of dispersion of five species of grain-infesting beetles was analysed in a 12-in.-cube bulk of wheat, kept in darkness at 25°C. and 14 per cent, moisture content, and built up of four layers, each of 16 three-in.-cube bags of Terylene net; the net retained the grain but allowed passage of insects. One hundred adults were placed in the centre of the upper surface of the topmost layer and after two weeks the entire bulk was broken down and the number of insects in each bag was determined. Five replicates were used for each species. More recoveries of Sitophilus granarius (L.), Tribolium castaneum (Hbst.), Rhyzopertha dominica (F.) and Cryptolestes ferrugineus (Steph.) were made from the top quarter of the bulk than from any of the lower layers. The vertical dispersion of Oryzaephilus surinamensis (L.) was homogeneous. Lateral dispersion was homogeneous with T. castaneum, R. dominica and C. ferrugineus, but with S. granarius and O. surinamensis relatively more recoveries were made from the corner units of the bulk than from elsewhere. The dispersion pattern assumed by a species in a uniform bulk is affected by locomotory activity, boundary response and intragroup stimulation. Thigmotaxis was demonstrated in S. granarius, persisting at relatively high densities; thus, following dispersal, individuals collect along habitat boundaries and then move up them as a result of intragroup stimulation. The positive response to boundaries shown by individuals of T. castaneum in isolation breaks down in crowded conditions, producing movement back into the bulk of grain and thus homogeneous lateral dispersion. O. surinamensis shows a positive response to habitat boundaries but no movement up them. Dispersal is slow in R. dominica, but the ultimate pattern of vertical dispersion is homogeneous. C. ferrugineus shows a tendency to form clumps, even in conditions free from marked physical gradients. The data are discussed in relation to ecology of the species, low-density populations, aggregation behaviour and a dynamic concept of population dispersion.

Details of the insect and mite infestation encountered on food commodities imported into Britain from the United States of America between 1953 and 1961 are given. Twenty-eight species of insects and nine species of mites, thought to have been introduced with the goods are listed together with a further 35 species of insects thought to have been derived from ships' holds. Emphasis is laid on the dangers of foodstuffs acquiring infestation either by cross-infestation or from infested residues in the holds.