The occurrence of mosquitos in crab-holes is tolerably well known both in West Africa and in other countries. It is doubtful, however, whether these sources receive sufficient practical attention, and one hears too often when their presence is demonstrated the opinion expressed that the insects only shelter there and are not likely to use them as breeding-places when so many others are available. One has even found medical officers whose unbelief had to be assailed by demonstration of the larvae and pupae. Others again, though aware of the fact, perhaps think the occurrence of too trifling importance to justify the necessary steps to eradicate them, even when near a dwelling.

Solutions of six organophosphorus compounds, Sevin, and pyrethrins (alone or synergised with piperonyl butoxide) were applied by microburette in drops of constant volume (0·0216 μl.) to the dorsum of the thorax of young adults of Glossina morsitans Westw., 2–5 days old that had taken their first blood-meal the previous day. The solvents used were decalin (decahydronaphthalene), toluene and lighting kerosene, respectively.

Malathion, methyl-parathion, DDVP (dichlorvos) and Sevin were eliminated in preliminary tests as insufficiently toxic. Muscatox (coumaphos) was reasonably toxic but not readily soluble and was therefore not considered further. Diazinon and Baytex (fenthion) were fully evaluated; the former was about as lethal as DDT, the latter as γ BHC (LD50 about 0·004 μg.). The LD50 of diazinon for males (0·0115 μg.) was significantly smaller than that for females (0·016 μg.) but the LD95 was much the same for both sexes.

Pyrethrins were about equitoxic with dieldrin (LD50, 0·002 μLg.); when synergised with 15 parts of piperonyl butoxide to one of pyrethrins the LD50 for males was reduced to less than half this value, and there was a significant difference in susceptibility of the sexes, the LD50 for females being 1·4 times that for males. However, the slopes of the regression lines were such that at LD95 the difference between synergised and plain pyrethrins was too small to be of any practical use.

These results show that, judged by innate toxicity to young flies, none of these insecticides can compete with dieldrin or Telodrin for practical control, although Baytex is a useful reserve should Glossina acquire resistance to chlorinated hydrocarbons.

The origin of introduction of the cabbage root fly, Delia radicum Linnaeus to the north-eastern coast of North America in the 19th century has been assumed to be from Europe. From that point of introduction, D. radicum gradually spread westward to occupy available ecological niches. DNA fingerprinting and egg micromorphology were used to determine the most likely geographical origin of the North American populations of this species. Forty-five informative RAPD loci obtained from ten primers and three criteria for egg micromorphology were studied. These characters indicated a common origin for the North American populations and a high similarity between populations from North America and north-western Europe. The results suggest a single entrance point of D. radicum into North America, probably via the north-eastern coast (New York area) from north-western Europe. The implications of this study in assisting selection of natural enemies of this important agricultural pest are discussed.

Light-traps were used to sample populations of C. comutus De Meillon, C. pallidipennis G, I. & M. and C. schultzei (End.) gp. at sites at Embakasi, Kiboko and Makindu between 1971 and 1975. The samples were graded into age-groups by the degree of abdominal pigmentation, estimates of calendar ageing were made, and the seasonal variation in age-structure of the populations was recorded. Survival rates were calculated on the basis of a graphical model of the continually overlapping generations, and the survival rate of 0·8 was found typical. This rate is considered sufficiently high for C. cornutus, C. pallidipennis and C. schultzei gp. to act as vectors of bluetongue virus disease of sheep and/or ephemeral fever virus disease of cattle.

The natural predators of Culex pipiens L. and C. torrentium Mart, in artificial containers and ponds were studied in southern England, using serological techniques. The antisera were from rabbits immunised by injections of saline extracts of the species of Culex into the inguinal lymph nodes and made relatively more specific by absorption. The gut contents or whole individuals of 1098 potential predators were smeared on to filter paper and tested. The most important predators in the ponds were Odonata nymphs while those of artificial containers were larval Dytiscidae. Diptera and Araneae preyed on emerging adults. The length of time a mosquito meal remained detectable in the gut of predators varied from a minimum of 8 h for the newt Triturus vulgaris to 24 h for the zygopteran Ischnura elegans (van der Linden). The results of laboratory tests indicated that the anisopteran Sympetrum striolatum (Charp.) was potentially more important as a biological control agent for larval culicines in ponds than the zygopteran Coenagrion puella (L.).

The suitability of ten diets for the development and reproduction of Franklinothrips orizabensis Johansen, the key natural enemy of Scirtothrips perseae Nakahara, a pest of California grown avocados, was determined in the laboratory. The experimental diets evaluated were: (i) irradiated Ephestia kuehniella Zeller eggs; (ii) irradiated E. kuehniella eggs and avocado pollen; (iii) Tetranychus pacificusMcGregor eggs; (iv) T. pacificus eggs and avocado pollen; (v) irradiated E. kuehniella eggs and T. pacificus eggs; (vi) irradiated E. kuehniellaeggs, T. pacificus eggs and avocado pollen; (vii) Scirtothrips perseae; (viii) Heliothrips haemorrhoidalis (Bouchè); (ix) avocado pollen; and (x) a young avocado leaf. Franklinothrips orizabensis larvae were unable to develop to adulthood on diets 9 and 10. The remaining eight diets supported complete development of F. orizabensis, but only diets 1, 2, 5, 6, 7 and 8 produced fecund females. On diet 5, F. orizabensis exhibited high larval to adult survivorship (90%), mated females exhibited highest daily and lifetime fecundity, and the progeny of mated females were female biased (53%). Analysis of jackknife estimates of net reproduction (Ro), intrinsic rate of increase (rm), and finite rate of increase (λ) were all significantly greater for F. orizabensisreared on irradiated E. kuehniella eggs and T. pacificus eggs (i.e. diet 5) than corresponding values for other diets on which female F. orizabensiswere able to complete development and reproduce. Incorporation of avocado pollen into diets had an adverse effect on demographic statistics for F. orizabensis, and low quality diets resulted in male biased sex ratios for this predator.

A method of estimating the damage inflicted on the developing fruit of the coconut palm by Pseudotheraptus wayi Brown is needed in order to assess the efficacy of measures for the control of this Coreid. The insect lives in the crown of the palm, populations are small in relation to the damage they cause, the adults take wing readily and the nymphs are agile and secretive. Direct estimation of populations by hand-collection, trapping, the use of knockdown sprays and marking-recapture methods, using paints or radioactive materials, were all unsuccessful, and indirect methods of estimation were therefore studied.

The growth, flowering and fruiting habits of the coconut palm are described. There is a single growing point, at which the leaves are produced in succession. From 12 to 18 inflorescences are formed each year; each is borne in a leaf axil and carries male flowers distally and female flowers proximally; the latter open, and are fertilised, almost together, after all the former have fallen off, and some 3–4½ weeks after the inflorescence has emerged from its spadix. All subsequent stages in the development of the fruiting body are dated from the latter event.

The young nut at first elongates rapidly and in the first six months attains over 80 per cent. of its final length; it is ripe at about a year.

In the absence of damage by insects, from 20 to 80 per cent. of the fruiting bodies are shed as nutlets, 1–2 weeks after fertilisation, the proportion depending on the variety of the palm and being less in those that bear few flowers and large nuts, but very few are shed at any other stage of their development. When an adult or a late-instar nymph of P. wayi feeds upon a developing fruiting body a characteristic lesion develops at the site of the puncture, which is concealed by the calyx, and if the fruiting body is less than three months old at the time (in which case it is locally termed a kidaka, plural vidaka) it is normally shed 4–7 days later. As the nut develops, it becomes less likely to be shed following attack by P. wayi, although the lesion formed may be invaded by fungi or by the weevil, Diocalandra frumenti (F.). Fruiting bodies attacked by the latter insect cease growth but are not shed. Experiments and field observations show that where damage by P. wayi is prevalent, a proportion of the vidaka are shed in the pre-fertilisation stage, even though they show no evidence of attack by the insect. The extent and implications of this phenomenon are not yet understood.

Fallen vidaka rot quickly and those that are found will reflect the damage that was inflicted 7–10 days previously. By collecting a sample of freshly fallen vidaka, removing the calyces and determining the percentage of them that shows damage by P. wayi, a measure is obtained that is termed the Vidaka Damage Rate (V.D.R.). The method advocated is to collect at random and at weekly intervals a sample of at least 100 vidaka per ten acres, excluding any with an overall length exceeding three inches. This size is reached at about 2½ months; older fallen nutlets invariably show damage from P. wayi or other causes. No significant differences have been found between values of the V.D.R. based on such collections and those based on collections from below individual palms, or rows of palms, taken at random. No significant difference was found between vidaka in the pre-fertilisation stage and those in the stage at which normal nutfall occurs as regards the proportion showing damage by P. wayi, and the former are therefore not excluded.

Comparison of the numbers of nymphs of P. wayi found by two trained entomologists at weekly intervals on 12 palms in each of two areas, one of which was treated with an insecticidal spray at monthly intervals and the other left untreated, and the V.D.R. determined a week later in the same area but on a larger sample of palms, showed a curvilinear association between the two quantities; the association between the logarithms of the quantities was linear but the correlation was not quite significant. In more detailed investigations, two 100-acre areas were used, one of which was undergoing insecticidal treatment, and in each a large but variable number of palms (from 100 to over 900) was examined during each week over a period from mid-October 1956 to the end of March 1957 by a team of climbers who had been trained to search for P. wayi. There was less variability in the data from the control than from the treated area; the latter showed a curvilinear relationship between the observed population of nymphs of P. wayi and the V.D.R. from the whole area one week later, but the correlation between the logarithms of the two variables was not significant.

If counts of first- and second-instar nymphs, which cause very little damage, were excluded from the data, together with any week in which no individuals were recorded, and the values of the V.D.R. were computed from that part of the area in which the insects were counted, then, when both variables were converted to logarithms, the transformed data showed a straight-line relationship with a highly significant correlation coefficient of −0·975. The regression equation indicates that where the number of palms that it would be necessary to search in order to find one 3rd- to 5th-instar nymph is 10, 100 or 1,000, the corresponding value of the V.D.R. would be 84, 13 or 2·4, respectively. It is concluded that where the V.D.R. is below 20, the population density giving rise to such a rate of damage is so low that its accurate determination by direct counts is unlikely to be possible.

Data on V.D.R. and yield were collected from a number of experimental plots and control areas; values from the latter were too uniform to give rise to significant correlations, but when a quarterly estimate of the V.D.R. in an experimental area, obtained from the totals of damaged and of undamaged fallen vidaka collected during successive three-month periods, was compared with the figure for yield obtained from harvesting the same area during the corresponding quarter the following year, a linear relationship was found between yield and V.D.R., the coefficient of correlation being significant in each of the five areas considered, and ranging from −0·7 to −0·984, and the values of a and b in the regression equation Y = a + bX, where Y is the yield in nuts per palm per harvesting and- X is the quarterly value of the V.D.R., ranged from 13·65 to 19·8, and −0·141 to −0·287, respectively. It is concluded that the V.D.R. is a good measure of expected yield, provided that the rate does not rise unduly in the interval between assessment and harvest; in such circumstances, the increased population of P. wayi that is reflected in the increased V.D.R. may damage the nuts at a later stage of their development and so reduce the yield below that expected.

Invasive organisms can have major impacts on the environment. Some invasive organisms are parthenogenetic in their invasive range and, therefore, exist as a number of asexual lineages (=clones). Determining the reproductive mode of invasive species has important implications for understanding the evolutionary genetics of such species, more especially, for management-relevant traits. The willow sawfly Nematus oligospilus Förster (Hymenoptera: Tenthredinidae) has been introduced unintentionally into several countries in the Southern Hemisphere where it has subsequently become invasive. To assess the population expansion, reproductive mode and host-plant relationships of this insect, microsatellite markers were developed and applied to natural populations sampled from the native and expanded range, along with sequencing of the cytochrome-oxidase I mitochondrial DNA (mtDNA) region. Other tenthredinids across a spectrum of taxonomic similarity to N. oligospilus and having a range of life strategies were also tested. Strict parthenogenesis was apparent within invasive N. oligospilus populations throughout the Southern Hemisphere, which comprised only a small number of genotypes. Sequences of mtDNA were identical for all individuals tested in the invasive range. The microsatellite markers were used successfully in several sawfly species, especially Nematus spp. and other genera of the Nematini tribe, with the degree of success inversely related to genetic divergence as estimated from COI sequences. The confirmation of parthenogenetic reproduction in N. oligospilus and the fact that it has a very limited pool of genotypes have important implications for understanding and managing this species and its biology, including in terms of phenotypic diversity, host relationships, implications for spread and future adaptive change. It would appear to be an excellent model study system for understanding evolution of invasive parthenogens that diverge without sexual reproduction and genetic recombination.

Some of the structures illustrated here have already been noticed in two previous papers (Jackson, 1948a & b). All the present drawings were made by one of us (E.B.) from living material of Glossina swynnertoni Austen. The eggs and the first- and second-instar larvae were dissected from wild female flies and examined in saline under the microscope; the third-instar larvae were obtained by keeping females in captivity until larviposition occurred, normally in the late afternoon.

The potential of the mirid predator Dicyphus hesperus Knight (Heteroptera: Miridae) as a biological control agent of the sweetpotato whitefly, Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae) and the potato psyllid, Bactericera cockerelli Sulcer (Hemiptera: Psyllidae) in tomato was investigated in two experiments. The first experiment focused on the study of the life history traits of D. hesperus when fed on nymphs of the potato psyllid compared with the factitious prey Ephestia kuehniella Zeller (Lepidoptera: Pyrallidae) eggs. Although reproductive and development rates were higher on E. kuehniella eggs, the predator exhibited a good intrinsic rate of natural increase (rm) when feeding on B. cockerelli nymphs (rm: B. cockerelli 0.069 ± 0.0001; E. kuehniella 0.078 ± 0.0001), thus reflecting good potential as a biocontrol agent of this pest. The second experiment focused on the efficacy of D. hesperus as a biocontrol agent of the potato psyllid and the sweetpotato whitefly in a tomato greenhouse. Prey species were offered individually or together in a series of five treatments in greenhouse cages. Results showed that the predator was able to establish and suppress populations of both pests inhabiting tomato plants when pests occurred alone or together. Thus, D. hesperus was demonstrated to be a suitable biocontrol agent of these two important pests that could be used in tomato greenhouses.

A laboratory-reared British strain of Myzus persicae (Sulz.) did not readily accept the artificial diet that has been used to maintain North American strains. All components of this diet were re-tested in factorial tests and a modified diet was developed which contained increased amounts of alanine, leucine, phenylalanine, serine, folic acid, calcium pantothenate and pyridoxine, while omitting arginine, glutamic acid, histidine, tryptophan, valine, ascorbic acid, choline chloride, nicotinic acid and riboflavin. This diet, although less adequate nutritionally than the original diet, could maintain M. persicae for several weeks and more than two generations. It was readily accepted by aphids with few deaths in the first generation, so that it should be more suitable than the Californian diet for bioassay of systemic insecticides and for studies on substances that might influence aphid behaviour.

A method for collecting flying insects is described, developed for studies on the dispersal of Simuliidae. The apparatus consists of a net mounted on the roof of a motor vehicle, leading to a catch-segregating apparatus within it, such that the catches over any desired distance at speeds up to 48 km/h can be segregated without stopping until 50 catches have been obtained. The volume of air filtered is measured with a counter anemometer mounted in the net mouth. Specimen results for one day are given as an illustration of the efficiency of the method.

Esterase-based resistance in the peach-potato aphid, Myzus persicae (Sulzer), is generally due to one of two alternative amplified carboxylesterase genes, E4 or FE4 (fast E4). The E4 amplified form is distributed worldwide and it is correlated with a particular translocation between autosomes 1 and 3, whereas the FE4 form, which has hitherto not been found to be associated with chromosomal rearrangements, is typical of the Mediterranean regions. In this study, we present for the first time cytogenetic and molecular data on some M. persicae parthenogenetic lineages, which clearly show a chromosomal A1-3 translocation associated with esterase FE4 genes and unrelated to high levels of esterase-based resistance.

An account is given of work carried out since that of Wootten & Sawyer (1954) on the pick-up of spray droplets by flying locusts. The same species, Schistocerca gregaria (Forsk.), was used. The values given in their work for the amounts of spray collected were confirmed, but when observations were extended to cover smaller droplets (less than 50-μ. diameter), locusts were found to collect these much less efficiently.

Other factors affecting pick-up were sex (females collected more spray than males) and flying speed (faster-flying locusts tended to collect less spray per unit of distance flown). When the angle of approach of the droplets to the flying locusts was varied between 1 and 11° from the horizontal no difference in the pick-up of spray could be detected.

For droplets between 60- and 300-μ diameter, the dose of insecticide collected by the locusts is given by the formula 9xPC μg. for males, and 11·5xPC for females, when the locusts fly through a concentration of spray of C ml. per cu. m. for a distance P m. and the spray solution contains x per cent, (w/v) of insecticide.

The possibilities of migrations in the West African species of Dysdercus are discussed and a hypothesis of long-range migrations associated with the Inter-Tropioal Convergence Zone and its wind systems is proposed. Catches of adult Dysdercus in four light-traps distributed from south to north of the Ivory Coast showed that the phenology of assumed migratory activity in D. voelkeri Schmidt differs with latitude and may be correlated with particular types of weather; stainer migrations taking place during the warm, wet and sunny part of the year. The whole life cycle of the insects as well as their flight activity occur under these climatic conditions, prevailing in a belt of 600–900 km width, situated immediately to the south of the Inter-Tropical Front. Colonisation of newly available habitats is thus only possible when climatic factors allow: (i), migratory flight activity and (ii), survival in the colonised area. A close examination of the timing of both migrations in the two main species, D. voelkeri and D. melanoderes Karsch, and of annual movements of the I.T.F. leads to the only logical hypothesis that the transportation of migrating insects is effected by atmospheric convergence, prevailing wind currents and air mass displacements.

Females of Callosobruchus spp. are known to produce sex pheromones that attract males. These sex pheromones cannot be adopted for use in pest management without first investigating the responses of the males in the windless conditions of storage environments. Consequently, behavioural bioassays of Callosobruchus subinnotatus Pic males were conducted in an olfactometer in the absence of air-flow. Under these conditions males were found to be able to follow odour trails to the source. However, the latency period was longer in diffusional bioassays than for insects in a Y-tube olfactometer that provided directional wind cues. The highest percentage of males reached the pheromone source when components of the pheromones, (E)-3-methyl-2-heptenoic acid (E32A) and (Z)-3-methyl-2-heptenoic acid (Z32A), were formulated in a 50:50 or 25:75 ratio. Males of C. maculatus (Fabricius) responded to sex pheromone of C. subinnotatus, but males of C. subinnotatus did not respond to that of C. maculatus. The two sex pheromone components of C. subinnotatus are also constituents of C. maculatus sex pheromone. These two components may be potentially useful in monitoring the populations of both species in stored beans. It is postulated that (Z)-3-methyl-3-heptenoic acid (Z33A), the major component of the sex pheromone of C. maculatus, must have acted as an antagonist inhibiting response of C. subinnotatus to the sex pheromone of C. maculatus.

Geromyia gen.n. is erected to accommodate the millet grain midge, Itonida penniseti Felt, 1920, a species that attacks developing grain of bulrush millet, Pennisetum typhoides and other species of Pennisetum. Cecidomyia penniseti Felt, 1920, Itonida seminis Felt, 1921 and Cecidomyia pennisetoides Barnes, 1956 are synonymised under G. penniseti. The male, female and larva are described and illustrated in detail and the life-cycle and seasonal biology are described from field observations at Bambey, Senegal. G. penniseti is recorded from P. typhoides in India, the Sudan, Nigeria, Senegal, Niger and Upper Volta and is provisionally recognised in collections from P. polystachyon and P. pedicellatum in Ghana, Uganda, Madagascar and Nigeria.

Landing site preferences of fed males of Glossina morsitans morsitans Westwood were measured in ca 50-cm-wide arenas in the laboratory. Flies were presented with simple black shapes of 225 cm2 against a white back-ground. Preference ran in the order: circle < square < triangle (whether the targets were black shapes on white or white on black). However, the triangle on its side (i.e. rotated through 90°) or the square presented as a diamond (i. e. rotated 45°) were both greatly preferred over their original orientations, whereas inverting the triangle (by rotating it 180°) greatly decreased its attractiveness. These preferences were retained whether the targets were compared paired or singly. The most obvious correlation was between preference and the relative lack of horizontal features in the target. When the diamond (the most attractive target) was split horizontally by a narrow white band, its attractiveness was reduced by ca 60%, whereas when split by a vertical band the attractiveness was reduced by only ca 25%. Similarly, when an additional narrow black bar was placed horizontally beneath the diamond its attractiveness was cut by 47%, whereas when the bar was placed vertically beside it the attractiveness was cut by only 28%. These reductions occurred even though the targets should have been more attractive because of their greater edge length and area. When the effect was tested with a series of rectangles, the greater the ratio of the vertical:horizontal edge length, the greater the attractiveness. The relative inhibition of landing by the presence of horizontal features in a laboratory-tested landing site thus seems clear, notwithstanding that horizontal resting sites in nature are the most preferred.

The nerve sheath of the thoracic ganglion of the house-fly (Musca domestica L.) is readily permeable to diazoxon but is impermeable to acetyl choline and acetyl thiocholine. Acetone and other lipoidal solvents, but not formaldehyde, were found to destroy the barrier to entry of the substrates, acetyl choline and acetyl thiocholine, and it is inferred that the barrier is lipoidal. At − 16°C., acetone does not destroy the cholinesterase of the ganglion.

Cholinesterase associated with the ganglion could be divided into three regions which showed different inhibition characteristics: (a) ‘ superficial ’ enzyme outside the nerve sheath, inhibited by 3·3 × 10−8M diazoxon; (b) ‘ peripheral ’ enzyme in the cellular region of the ganglion, inhibited by 3·3 × 10−8M and 3·3 × 10−9M diazoxon; (c) ‘ central ’ enzyme in the synaptic area, inhibited by not less than 3·3 × 10−7M diazoxon. Using inhibition of cholinesterase as an indicator of penetration, no difference in permeability was found between the ganglia of the susceptible and resistant strains. No difference was found in the inhibition of cholinesterase by diazoxon in the ganglia of susceptible and resistant strains.

It is concluded from this and previous work that if inhibition of cholinesterase of the nervous system is the cause of death there are no differences between the ganglia of the susceptible and resistant strains which affect resistance; and, furthermore, that inhibition of cholinesterase in the thoracic ganglion is unlikely to be the cause of death.

The flight potential of Nephotettix virescens (Distant), the most important vector of rice tungro virus disease, was assessed using tethered flight techniques. Most individuals tested were not willing to fly in response to stimulation, or flew for very short times. A small proportion of leafhoppers flew for long periods and one female flew for almost 7 h, indicating the potential for long distance dispersal of insects and inoculum. Few individuals flew before four days of age and thereafter flight profiles were similar for insects aged between four and 12 days. Mature females were more flight willing when kept as adults in mixed groups with males than when caged separately. There was no consistent effect on flight performance when insects were reared on rice varieties with different levels of leafhopper resistance. The flight activity of N. virescens was greater when leafhoppers were reared on mature, compared with young, rice plants. Leafhoppers reared through one generation on tungro-diseased rice plants were less willing to fly than individuals maintained on healthy plants of the same age and variety, whereas those tested after a 24-h access period to tungro-diseased plants were more flight-willing. The results are discussed in relation to the spread of tungro and to management interventions for the control of the disease.