Many West African mosquitoes fly at low levels when crossing open country. Experiments were therefore conducted in the Gambia on the effect of high fences on their dispersal. In the first experiment, a circular mosquito-proof fence 2·9 m high and with a radius of 18 m was constructed. Catches inside on human bait of Mansonia spp. were about 60% lower than catches outside the fence, whereas catches of Anopheles spp. in the two sites were not significantly different. In unbaited suction traps, catches of Mansoniainside the fence were significantly lower in traps 0 and 0· m above the ground, but not at 1 to 3 m, than in traps at similar levels outside. This suggested that, after flying over the fence, mosquitoes had not resumed normal ffight levels by the time they were trapped in the centre of the circle. In a second experiment, a much larger fence was erected, 6 m high and with a radius of 65 m. Catches were conducted in experimental huts in the centre of the enclosed area and at a distance of 70 m outside it when the fence was erected and again after its removal. Catches of Mansonia spp. on human bait in the hut inside were 46% of the total catch in the two huts when the fence was erected and 48% after its removal; catches of Anopheles spp. (A. gambiae Giles and A. funestus Giles) were 43% with, and 53% without, the fence. In calf-baited light-traps, catches of Mansonia were 41 % of the total with, and 38% without, the fence, and those of Anopheles 58 and 44%. Thus the presence of the 6·m fence had no significant effect on the density of mosquitoes in the centre of the enclosed area, and it is concluded that mosquitoes were flying freely over it. Due to the prevailing low winds in the area, passive transport of mosquitoes over the fence by the wind was not thought to be important.

The theory of phases of locusts put forward as a working hypothesis by the senior author (Uvarov, 1921) has led, as might have been expected, to further researches in that direction, but the results obtained have been in some cases apparently contradictory. A summary of the work done on these phases has been published recently in a book (Uvarov, 1928), and we do not propose to repeat it here, the purpose of the present joint paper being to discuss very briefly certain aspects of the problem in the light of new observations made by Predtechensky (1928) in Russia and by the junior author in Madagascar.

The paper deals with two members of the Simulium neavi Eoub. complex found at Amani in the forest of the Usambara Mountains, Tanganyika Territory. They have already been described but are at present termed the Amani unhanded and banded forms, scientific names being witheld until the taxonomy of the whole complex is better understood.

Some methods of study are described.

Pupae of the unhanded form constituted a large proportion of the total number found on the common local crab, Potamon (Potamonautes) lirrangensis Eathbun, which amounted to roughly one pupa to seven crabs. This form predominated in the lower and more open parts of the drainage system examined. The adults were not seen to bite man. This and the banded form were found at a much lower altitude than any hitherto reported for the complex, probably owing to the particular nature of the local climate. Neither form was abundant.

The larvae and pupae of the banded form, like the unhanded one, live externally on the crabs. The variability of wing size of the banded form is described. Observations were made on the internal anatomy of the adult with special reference to the ovaries in which the follicular relics are usually very large, indicating that the female probably bites soon after laying eggs. As in S. damnosum Theo. there is an easily recognisable class of old flies with clear Malpighian tubes. Nulliparous and parous flies have rather different biting cycles. The banded form bit man readily but only about five were taken per hour in good catching places and far fewer elsewhere.

Human onchorcerciasis has been reported from Amani but is not known to do any harm there. The existence of the disease in the presence of rather small numbers of Simuliids is of interest in relation to a belief that S. neavei is a more efficient vector of onchocerciasis than is S. damnosum. Out of 359 banded females dissected 41·2 per cent, were parous and 12·8 per cent, of these were infected with nematodes, at least some of which were not Onchocerca volvulus.

Taxonomy, the ovarioles and the Simuliid-crab association are discussed. The formation of the large follicular relics of the banded form is considered in relation to the history of the follicular epithelium before and after ovulation. The crab association is regarded as commensalism-, and it is suggested that the crabs benefit the Simuliids by carrying them a short distance to a suitable current and that they thus enable them to live in fast rivers and so extend their range.

A method is described for optimizing models by linking simulation procedures with a non-linear regression programme. It is then possible to work towards a parsimonious model which contains those, and only those, variables required for an optimum fit. Using the observed values, and the predicted values from each simulation, the optimizing routine calculates the value of an appropriate loss function. It then makes small changes in the parameters governing the simulation, recalculates the predicted values and the first and second derivative of the loss function with respect to each parameter. The algorithm uses this information to minimize the loss function for a given formulation of the model. The model is improved by adding variables which can be shown statistically to improve the fit, and by removing those which do not. The use of the technique is illustrated with reference to a series of weekly estimates of the total numbers, births and survival probabilities of a population of male and female tsetse flies Glossina morsitans morsitans Westwood. Simulation involved following the lives of cohorts of flies, and of all their progeny, from the time they were deposited as larvae. Development and reproduction were regarded as fixed functions of temperature, but mortality rates of pupae and of adult flies depended on meteorological and biological variables, plus the level of trapping imposed on the population. Potential factors were added singly and the model thereby improved in an objective, stepwise manner. The best fit was achieved when effects on adult survival due to maximum temperature, various modes of trapping, and an annual cycle were included in the model. The optimized simulation technique has been used here in improving a model which describes a biological population but it could equally be used to improve models in any situation where data are fitted using simulation procedures.

Laboratory experiments with juvenile hormone analogues on Cydia pomonella (L.) showed that Cecropia C17 juvenile hormone (methyl 10,ll-epoxy-3,7,ll-trimethyl-2,6-dodecadienoate) was the most active of the 28 compounds tested. When applied to four-hour-old eggs at 0.1 μg/egg, the hormone caused 100% failure in embryogenesis, while the other compounds were at least five times less effective. Depending on the time since ecdysis and the dose, juvenile hormone mimics applied to last-instar larvae resulted in a wide range of intermediate forms. Against three-day-old last-instar larvae, the Cecropia C17 hormone gave 100% inhibition of development at a dose of 1 μg/larva, while three other compounds (methyl 10,11-epoxy-3,7,11-trimethyl-2,6-dodecadienoate, ethyl 11-chloro-3,7,11-trimethyl-2-dodecenoate and ethyl 3,7,11-tri-methyl-2,4-dodecadienoate) gave the same effect at 2–5 μg/larva. Against newly emerged adults, the last two compounds at 10–50 μg/insect reduced fecundity and fertility to 0–81% and 0–50%, respectively, of their normal levels.

A method of calculating survival rates and population size from mark-recapture experiments for bait-caught haematophagous insects is presented. The method fits the data to a series of simultaneous equations. This procedure is not affected by the cyclical nature of the recapture rate experienced in this type of experiment. Methods are presented which allow estimates of the confidence limits on the estimated parameters. Unlike earlier methods based upon a regression analysis of the log (number recaptured), this method allows estimates of the population size in addition to the survival and length of the feeding cycle of the mosquitoes. The methods have been applied to data collected in Papua New Guinea and give estimates of the total number of Anopheles feeding per night in different villages ranging from 3000 to 46 000.

The Asian long-horned beetle (ALB), Anoplophora glabripennis (Motschulsky), is a highly polyphagous invasive pest with a broad range of host species, but showing relevant differences between infestation areas. Host preference and host colonization (female fecundity, egg and larval survival) were assessed in a population in Northern Italy by choice and no-choice experiments conducted in both field and laboratory conditions. During 5 years of field observations, ALB was found to infest seven genera of trees: Acer, Aesculus, Betula, Populus, Prunus, Salix and Ulmus. However, Acer, Betula, Ulmus and Salix resulted to be the preferred hosts corresponding to 97.5% (1112) of the 1140 infested trees. In both laboratory and field trials carried out on these four host genera, no-choice experiments recorded the highest host colonization of A. glabripennis on Acer trees, with the highest number of laid eggs and the lowest egg and larval mortality. Ulmus and Salix showed a lower number of laid eggs during laboratory choice test, but egg and larval mortality had mean values similar to Acer. On the contrary, despite the high number of Betula trees felled during the eradication plan carried out in the infestation area, this tree species showed the lowest beetle suitability in terms of number of laid eggs and insect survival. An overestimation of the number of infested Betula occurring during the tree survey may explain the discordance between high number of infested Betula and low beetle suitability. Instead, the large number of infested Acer recorded in the field was probably due to the high abundance of these trees occurring in parks and gardens within the infestation area and to the low adult dispersal of A. glabripennis. Overall, results from this study confirm that host species affects both beetle colonization and breeding performance. The study shows ALB host preference and host suitability varying between tree species, suggesting an ALB acceptance even of sub-optimal hosts.

The host range and aspects of the biology of Hispine beetles recorded from plants in the genus Lantana is reviewed. The host specificity of Octotoma scabripennis Guér. and Uroplata girardi Pic was studied in Hawaii where these insects had been imported and established for biological control of the important weed L. camara. New techniques were employed in which feeding and oviposition behaviour was studied in field and simulated-field experiments embracing a wide range of plants interplanted amongst an abundance of the Hispines' normal host. Eesults indicated that both species are restricted almost entirely to L. camara, and subsequently these insects have been imported into and established in Australia. Both insects are particularly well suited to use as biological control agents and should be extremely useful in many countries where L. camara is a weed.

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

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

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

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

A large–scale mating disruption trial for the control of Pectinophora gossypiella (Saund.) was carried out in the Fayoum Province of Egypt during the 1981 cotton season. Two areas, each of 50 ha, were sprayed with a microencapsulated formulation of the sex pheromone (a 1:1 mixture of (Z, Z)- and (Z, E)-1, 11-hexadecadienyl acetate) as the sole means of controlling this pest. Five applications of 10 g a.i./ha were made during the season using fixed-wing aircraft. The pheromone treatments were compared with conventional insecticide spray treatments in two other 50-ha areas of cotton. From comparisons of treatments in terms of various plant damage criteria including the percentage of rosetted flowers, percentage boll infestation, gross yield of seed cotton and lint quality, it was concluded that the pheromone treatment was equal in effect to the insecticide sprays.

Engorged Culicoides specimens were collected in light-traps from 16 sites in Kenya. The precipitin test was used to identify the blood-meal source of 682 specimens of 21 species over a period of five years. Culicoides pallidipennis C, I. & M. and C. schultzei (End.) were shown to feed mainly on cattle and to a lesser extent on sheep, and thus could be involved in the transmission of bluetongue virus. C. cornutus De Meillon, C. milnei Aust. and C. zuluensis De Meillon are probably not common enough as feeders on cattle and sheep to play more than an incidental role as vectors of bluetongue. C. schultzei is probably also important in the transmission of ephemeral fever. No groups of vertebrates other than Bovidae were implicated as virus reservoirs.

During the past fifteen years the attention of Economic Entomologists in Central America and the West Indies has been increasingly directed to the damage done by species of the genus Brassolis to the foliage of coconut and other palms. In some of the scattered papers (q.v. Review of Applied Entomology, Series A, 1913–22) dealing with these ravages one finds references to the natural control exercised by Hymenopterous parasites. So far as I am aware the only writers to mention by name any of these enemies are C.Schrottky (1909) and G. E. Bodkin (1917), who list four species between them. Since the spring of 1920 I have examined two small collections of Hymenopterous parasites of Brassolis from Trinidad and British Guiana respectively. In each of these the same one of Schrottky's species is represented, and in all I am now able to list seven species. Two of these have not been seen by me, and two more (Brachymeria and Spilochalcis) are probably recognisable from extant descriptions. In the case of the Telenomus it is hoped that the figures given may facilitate recongnition. Though Ashmead's description of this species is very incomplete, I have forborne for the present to supplement it, since the diagnosis of these minute parasites for any particular geographical area can be attempted best in a comparative key. only the Anastatus has been fully described.

Apterous adult Myzus persicae (Sulz.) of a glasshouse strain differed greatly in their ability to colonise sugar-beet according to the plant on which they and their forebears were cultured. Those from Chinese cabbage (Brassica pekinensis) settled least readily on beet, whilst aphids from broad beans (Vicia faba) produced larger populations than those cultured on sugar-beet. When reared wholly on groundsel (Senecio vulgaris) young adults differed in their ability to colonise Chinese cabbage, sugar-beet and broad bean according to their parents' culture host species, and these differences were detected in a second generation reared wholly on groundsel. The responses of clones isolated from cultures maintained continuously on Chinese cabbage and broad bean were similar, showing that the effect was caused by the aphids' host-plant experience, and was not due to fixed, heritable characters of the sub-cultures. Some, but not all clones of M. persicae collected from the field showed enhanced colonising ability after culture on broad bean as compared with Chinese cabbage. This was apparent on sugar-beet and lettuce (Lactuca sativa). These effects of former hosts on the ability of M. persicae to colonise plants may be important both in work on resistance to aphids and in the epidemiology of aphid-borne diseases.

As stated in my previous paper on the Ethiopian species of Dacus, the Oriental forms of this genus show much more variation in their structural and ornamental features. They may be therefore divided into no less than five well defined genera, only one of which is common to both faunal areas. Reserving for later publication a third paper on the Oriental (and Australian) species, I will give here some notes on the classification and feeding habits of the species from British India.

Experimental huts fitted with window traps, of the same basic design as those described by Thomson (1948), modified for Malayan conditions, were used in studying the behaviour and mortality of A. maculatus in relation to DDT and BHC. Other species of Anophelines formed a large proportion of the human bait trap catch but rarely entered the huts.

In untreated huts, A. maculatus fed at all hours of the night with a peak between 9 p.m. and midnight. The large majority left before 8 a.m. in search of outdoor resting places, at least 50 per cent. before dawn. It appeared that attraction to light was the strongest, but not the only factor influencing exit from the huts.

Large numbers of Culicines (mostly Culex fatigans) were recovered. In untreated huts about 80 per cent. were blood fed ; 28 per cent. were in the window traps.

DDT (33 per cent.) and BHC (“ Gammexane P530 and P520 ”) water dispersible powders were tested.

An application of 100 mg. DDT and 20 mg. γ BHC (P530) per sq. ft. was unsuccessful, due in part to the small numbers of mosquitos recovered. No conclusions are drawn from the results.

DDT at 200 mg. and BHC (P520) at 40 mg. γ isomer per sq. ft. were both effective for at least 12 to 16 weeks against A. maculatus. With DDT, 63 per cent. initial, and 83 per cent. 24-hour corrected mortalities were recorded over 16 weeks. With BHC, though the initial mortality dropped from 100 per cent. in weeks 1–4 to 19 per cent. in weeks 12–16, the 24-hour mortality, almost 100 per cent. for weeks 1–10, was still 88 per cent. for weeks 12–16.

DDT apparently had little effect on the feeding of A. maculatus ; with BHC there was a reduction in the percentage fed.

DDT was relatively non-lethal to C. fatigans, but had a marked irritant effect driving them into the light trap and the biting rate was reduce to 45 per cent. BHC killed all C. fatigans which entered for 2 weeks but most of its toxic effects were lost by the eighth week. The biting rate was reduced to 27 per cent. for weeks 1 to 8 and the majority of mosquitos were recovered in the light trap.

Ants, cockroaches, spiders, etc., were found to affect the number of mosquitos recovered and special precautions had to be taken against losses.

The results suggested that BHC when freshly applied acts as a repellent to mosquitos.

Mansonia uniformis was shown to be susceptible to both DDT and BHC residual deposits.

Egg populations of the Pea Aphid, Acyrthosiphon pisum (Harris), overwintering on lucerne and hop trefoil have been followed. On hop trefoil the overwintering mortality of these eggs was 83 per cent. Although the mortality was apparently less on lucerne, a wide discrepancy existed between the two crops in the ratio between the total numbers of eggs at the beginning of eclosion and the number of Aphids which successfully established themselves the following spring. The peak number of fundatrices on lucerne was three times the egg total at the beginning of eclosion whereas on hop trefoil it was only half. Many more eggs than were recorded were undoubtedly laid on the lucerne plants and the high number of fundatrices subsequently found must have emerged from eggs that had fallen or been knocked off the host-plant.

The biting habits of Chrysops centurionis Austen and its distribution in Uganda are discussed. This species is everywhere arboreal and mainly crepuscular. The absence of loiasis in man in Uganda is, it is suggested, due to differences between the biting habits of this species and those of the known vectors, C. silacea Austen and C. dimidiata Wulp, which are closely allied to C. centurionis.

The peculiar biting-cycle of another Tabanid, Haematopota nefanda Edw., is described briefly.

Short notes on the biting habits and distribution of some other Uganda Tabanids are given.

The insect fauna of a block of Amelonado cocoa trees at Tafo, Ghana, partly shaded by Gliricidia sepium and partly unshaded was sampled. Crematogaster clariventris (Mayr) and Oecopyhlla longinoda (Latr.) were the most numerous species of ants, the former occurring on 84% of the trees and the latter on 17%. There was a considerable overlap in the distribution of the two species. Thirty-two other species of ant were collected by pyrethrum knockdown sprays from the cocoa canopy, and 47 species were collected from leaf litter beneath the trees. More species of ant were recovered from litter on shaded plots than on unshaded ones. There was some avoidance of trees occupied by O. longinoda by certain canopy .ants. A greater number of Lepidoptera larvae, Orthoptera and the mirid Sahlbergella singularis Hagl were collected by pyrethrum knockdown sprays from unshaded plots than from shaded ones, whereas Diptera and Hymenoptera other than ants were more numerous on shaded plots. The most abundant coccid was Stictococcus sjostedti Ckll., a species tended for its honeydew by both dominant ants; it was more common on shaded plots. Mealybug species, of which Planococcoides njalensis (Laing) was the most common, were more abundant on unshaded plots.

Pieces of netting and sheeting of various types were impregnated by dipping them in permethrin emulsion. Bioassays were performed in which three species of mosquitoes were exposed to the impregnated fabrics for periods of between 15 s and 8 min. When pieces of netting and sheeting were dipped in permethrin emulsion at ambient temperature, the amount of insecticide absorbed was generally proportional to the weight of liquid taken up, i.e. there was no evidence of selective absorption. Diffusion of permethrin did not occur between pieces of netting and sheeting sewn together. The LD50 on cotton nets was found to be about three times as great as on nylon nets. Aedes aegypti (L.) was found to be more susceptible than Anopheles gambiae Giles, which was more susceptible than Culex quinquefasciatus Say. Although for most other groups of insecticides variation in time and dose have equivalent effects, for permethrin on netting this was not found to be true, i.e. on having the exposure time the LD50 was less than doubled.