The oviposition aggregation pheromone of six species or forms of the Simulium damnosum Theobald complex (Diptera: Simuliidae) from different sites in West Africa, was investigated by gas chromatographic analysis of hexane extracts of the ovaries from wild-caught flies, bloodfed and maintained until gravid in the laboratory. The two compounds previously shown to be released from fresh eggs and associated with mediation of oviposition aggregation were found in S. leonense Boakye, Post & Mosha (Sierra Leone), S. yahense Vajime & Dunbar (Ghana), S. sanctipauli Vajime & Dunbar (Ghana), S. sqnamosum; Enderlein (Cameroon), S. sirbanum Vajime & Dunbar (Ghana) and the Bioko form (island of Bioko, Equatorial Guinea). Coupled gas chromatography–mass spectrometry of the S. leonense, S. sanctipauli and the Bioko form extracts showed the two compounds to be identical in all three. Volatile emissions from freshly laid eggs of S. sanctipauli were similar to those previously described from S. leonense, and identical in chemical composition to gravid ovaries. No new compounds were detected in any ovary extracts or volatile emissions examined, demonstrating that the composition of the aggregation pheromone is similar throughout the S. damnosum species complex. Analysis of S. leonense adults of different age groups and physiological states showed that the compounds are detectable only in gravid ovaries at 2 or more days following the bloodmeal, suggesting that production of the pheromone occurs during egg development. Demonstration of an oviposition aggregation pheromone common throughout the species complex raises the possibility of developing an odour-baited trapping system for blackflies, which could be employed across the large area of Africa where they are the vectors of onchocerciasis.

In order to assess the potential effectiveness of DDT spray against mosquito larvae living under natural conditions and to determine the characteristics of the most effective form of spray, the variables considered were, area dosage of DDT, oil solutions compared with oil-in-water emulsions, concentration of DDT in the spray liquid, and drop size.

Spraying was carried out over small (20 ft.×40 ft.) areas of canal harbouring larvae of Anopheles maculipennis var. messeae, and A. claviger. The canal was densely packed with vegetation. The central channel was overgrown with Potomogeton natans, so dense that in some regions there was more area of leaf than of open water surface, and in places there were large masses of floating algae (a coarse species of Spirogyra). At the edge of the canal near the bank there was a margin of reeds averaging about 4 ft. wide, and from 1 to 4 ft. in height.

Spraying was carried out with a specially designed spinning disc atomiser giving drops of nearly uniform size and enabling drop-size and dosage delivered to be independently varied over a wide range. The range of DDT dosages investigated was from 4 g./acre to 80 g./acre, delivered in solutions or emulsions of approximately 0·5 per cent. and 5 per cent. concentration and drop sizes of 0·4 and 1 mm. diameter. Assessment of surface dosage in relation to delivered dosage, by spraying dyed solutions, showed that about 30 per cent. of the smaller drops were lost in the wind, but that there was no appreciable loss of the coarser spray.

For 5 per cent. oil solutions of DDT drop size in the range 0·4 to 1 mm. diameter had no effect on the kill, except at low dosages (< 10 g. DDT/acre) when the greater wind loss of small drops produced variable results. Tests on the effect of drop size were not carried out with emulsions.

From the point of view of larvicidal action, the experiments have not shown that is advantageous to distribute DDT in high dilution. 4·3 per cent. DDT oil solution sprayed at 10 g. DDT/acre actually gave a slightly higher mortality than 0·43 per cent, solution at the same dosage area of DDT, but the difference may not be significant owing to uncontrollable variables. Under the conditions of these trials, both oil solutions were superior to 0·43 per cent. AMSO emulsions. Experiments on the effect of concentration at constant area dosage were made only in the reed margin of the canal and data were not obtained for open water.

In the centre of the canal, mortalities greater than 90 per cent, were obtained for both oil solutions and AMSO emulsions at delivered dosages greater than 10 g. DDT/acre, the oil solution being slightly superior. In the reed margin the kill dropped sharply with AMSO emulsions at dosages below 40 g. DDT/acre, the fall-off was much less marked with oil solution. From considerations of the average mortality in all areas, a delivered dosage of 40 g. DDT/acre (small drops) or estimated surface dosage of approximately 30 g. DDT/acre, appears the optimum for economical usage of DDT.

When areas were sprayed the first two larval stages suffered a higher mortality compared with the later larval stages and pupae, and the proportion of pupae and later instars thus rose sharply.

There was no evidence that residual lethal effects of oil films extended beyond three days. The initial kill in these trials was followed by a very low population level, due, it is thought, to a natural decline in the reproductive potential of the population.

Chilocorus nigrita (Fabricius) is a well-known predator of scale insects. It has been widely used for biological control and has spread naturally beyond its previous native range over the last three decades or so. Three other Oriental species closely resembling C. nigrita can now be separated. Chilocorus melas Weise is redescribed and a lectotype designated. Chilocorus gressitti Miyatake is a junior synonym of C. melas. Chilocorus subindicus from the southern parts of the Indian subcontinent and C. gracilior from eastern Indonesia are described as new.

To determine whether host body size is the currency used by the aphidiine parasitoid, Lysiphlebus ambiguus Haliday (Hymenoptera: Braconidae), in assessing host quality, the aphid, Aphis fabae Scopoli (Homoptera: Aphididae), was reared at either high or low temperature to yield hosts of the same instar with different body sizes. Cohorts of A. fabae raised at 15°C and 30°C and exposed to individual female L. ambiguus in no-choice tests were successfully parasitized in all host stages from 1st instar nymphs to adults. However, younger and smaller aphids were more susceptible to parasitism than older and larger nymphs or adults, as measured by the number of mummies produced. For aphid cohorts reared at 15°C, the proportion of female progeny, progeny adult size, and development time all increased linearly with aphid size at the time of attack. In contrast, for aphid cohorts raised at 30°C, the proportion of female progeny and progeny adult size declined with aphid size, while development time remained unaffected. Through manipulation of host rearing temperature, we have shown that at cooler temperatures the koinobiont parasitoid, L. ambiguus, responds to host size in the same way as an idiobiont parasitoid, but that this response is compromised at higher temperatures. Our results suggest that differential mortality during development is likely to influence the observed secondary sex ratio in relation to aphid size for aphid cohorts raised at higher temperatures due to disruption of the activity of the host's primary endosymbiont and that such reduced nutritional quality of aphids cannot be compensated by increased development time.

Resistance to γ BHC and dieldrin in various insects usually gives a characteristic resistance spectrum, probably indicating a common defence mechanism. Resistant house-flies (Musca domestica L.) are slightly anomalous in showing greater tolerance of γ BHC than of endrin and isodrin, unlike other resistant strains. A possible explanation is that they can develop an additional defence, specific towards γ BHC, as well as the usual group resistance. This might well be enhanced enzymatic degradation of BHC, which is known to occur in flies, but was not found in resistant strains of Anopheles gambiae Giles or Cimex lectularius L.

To confirm this hypothesis the rates of BHC elimination were measured in normal and two resistant strains of flies and also in normal and resistant strains of Lucilia cuprina (Wied.) (which showed the more usual resistance spectrum). To avoid toxic effects, the non-insecticidal α BHC was used and its elimination after six hours measured in extracts by gas chromatography. The two resistant fly strains showed significantly increased degradation of BHC, correlated with their greater γ BHC resistance, whereas rates were about the same in normal flies and the two strains of L. cuprina.

The parasitic larvae of a number of Trombiculid mites are of economic importance as they include the vectors of scrub typhus, and scrub-itch mites of considerable nuisance value. Methods of trapping these mites and various field and laboratory observations on them are described. The methods were evolved and observations made during the course of work, sponsored by the Medical Research Council, in Imphal, Assam and Compton, Berkshire.

Live unfed larvae in the field may be concentrated and trapped by use of a low cover with a central light-admitting aperture and collecting apparatus. This method proved very efficient in trapping harvest mites (Trombicula autumnalis) in England. The rise in temperature within the trap can be made advantageous.

Guineapigs were chosen as bait animals for the collection of T. autumnalis at Compton, most of the larvae attaching near the anus and genitalia. The larvae fed for between 30 and 60 hours.

Engorged larvae may easily be collected as they leave their host (or dead animals and débris) by the funicular laboratory light-trap described.

Observations are made on the collection of adult mites, and to a lesser extent nymphs, from soil flotation in water. The vertical migration of adults in relation to soil moisture and temperature is discussed.

Observations on the appearance of larvae of T. autumnalis on a chalk-down at Compton showed a sharp seasonal peak in September, 1946, and some evidence is adduced that this was related to a peak in oviposition.

Observations are made on attempts to rear T. deliensis, the scrub typhus vector in Assam, and notes are added on the behaviour of larval and nymphal mites.

For a study of population trends of Diarthrothrips coffeae, Williams, on coffee in Kenya, and to assess the value of sprays for its control, a method of sampling the population was required. This insect feeds on the leaves, green shoots, and berries ; but by far the greater part of the population lives on the leaves. Attempts to count the insects on the leaves in the field, by naked eye or with a hand lens, proved difficult and inaccurate. Two other methods were tried, those of E. A. McGregor (Pan-Pacif. Ent., 3, 1926, p. 29) and J. W. Evans (Bull. Ent. Res., 24, 1933, p. 349).The former proved unsatisfactory for several reasons such as the failure of the insects to forsake the leaves, the collection of debris on the grease tending to conceal insects, and the difficulty of counting the insects in the grease. The method of Evans was designed originally for obtaining the thrips from blossoms, but an examination of the method was made with the coffee thrips. Fairly consistent results were obtained with it, but the figures were low and it was clear that the sampling was not complete. It was found that a number of insects remained among the leaves and failed to reach the paper at the bottom of the cylinder. There are other disadvantages ; for example a large number of the cylinders are necessary to carry out a single spraying experiment, they are usually difficult to come by and the work of counting has to be done in the field, requiring a rather elaborate provision of tables and microscopes. Further it was found that even a light breeze was apt to cause loss of thrips during the counting.

Elaeidobius kamerunicus Faust (Coleoptera, Curculionidae) is one of the specific pollinators on inflorescences of the African oil palm Elaeis guineensis Jacquin. This derelomine weevil is native to tropical Africa. During the late 20th century, it was introduced into all tropical regions where E. guineensis is grown, in order to improve its pollination and fruit set. Despite an overall success, a decline in pollination efficiency has been documented in several regions. In this study, we reconstructed a multilocus phylogeography of the world populations of E. kamerunicus, in order to explore its genetic diversity in its native and introduced ranges. Our results showed that African populations of E. kamerunicus are forming two differentiated mitochondrial clusters in West and central Africa, forming a contact zone along the Cameroon Volcanic Line. The existence of this sharp contact zone along this weak altitudinal barrier suggests that other parameters, such as climate, may be driving the distribution of populations. A differential genetic structure between mitochondrial and nuclear genes, and the strong level of genetic structure of the mitochondrial gene, also suggest sex-biased dispersal in this species, with males dispersing more than females. The genetic structure inferred from Asian and South American populations suggests that they originate from populations of both western and central tropical Africa and that a bottleneck has probably been experienced by these populations.

Females of Stegobium paniceum (L.) produce a sex pheromone to which only males are attracted. Live females 4–5 days old attract males which first respond when they are 5–6 days old. Females extracted in diethyl ether showed the presence of pheromone immediately after eclosion (0 days) but secretion is delayed until 3–4 days just before emergence from the pupal cocoon (4–5 days). Mated females show a slight reduction in pheromone content and mated male response is significantly reduced, as is the response of males previously exposed to a pheromone extract. A series of pheromone concentrations ranging from 0·0005–l female equivalents was assayed, and the threshold level of male response estimated at about 0·0004 female equivalents.

Parasitoids are significant enemies of many economically important insects and there is some evidence to suggest that their actions have a role in terminating the outbreaks of forest Lepidoptera populations. In this study, we examined the impact of parasitoids on the pupae of the pine processionary moth, and highlighted the presence of several parasitoid species for this developmental stage. A higher rate of parasitism was found when the pupal density in the soil was reduced, but the rate of parasitism was not influenced by pupal morphological traits or by the presence or absence of a cocoon around a pupa. Of the external factors examined, a delay in the time of descent of larvae from the trees had a positive effect on the level of parasitism. Observational data indicated that dipteran and hymenopteran were the most abundant parasitoids to emerge from moth pupae. Our study highlights the complexity of the parasitoid–host dynamics, and stresses the importance of carefully determining environmental effects on host–parasitoid relations.

1. The only biting fly of common occurrence in Mauritius is Stomoxys nigra.

2. The method of transmission of surra by Stomoxys nigra is direct, i.e., it occurs when flies take a meal on a surra-infected animal, with trypanosomes in the peripheral blood, and immediately afterwards feed on a healthy animal.

3. Trypanosomes are found active in the proboscis of Stomoxys from one to ten minutes after a meal, when the temperature of the room is between 25 and 27° C.

4. No active form of trypanosomes can be found in the gut, Malphigian tubes or salivary glands of the fly 24 hours or longer after a meal on an infected animal.

5. For successful transmission the interval between the feeding on the infected and on the healthy animal must not be more than ten minutes.

6. Trypanosomes in the gut of Stomoxys are active from one minute to one hour after a meal on a surra-infected animal.

7. Trypanosomes are partially disintegrated, the cytoplasm becoming more granular and the flagellum disappearing, 24 hours after an infected meal.

8. No developmental forms of trypanosomes have been found in the salivary glands, gut or Malphigian tubes of Stomoxys nigra 24 hours or more after an infected meal.

9. When trypanosomes could not be found in the peripheral blood of a surrainfected animal, transmission could not be effected.

This paper is concerned with certain Mymaridae from crop pests in the Far East and the Ethiopian region. Anneckia oophaga gen. et sp.n. was reared from eggs of Sexava in New Guinea, and a key is given for the separation of the genus from other members of the tribe Anagrini. Acanthomymar nigrum gen. et sp.n. is associated with pests of coffee in Uganda and the genus is placed close to Chaetomymar Ogloblin (tribe Mymarini). Gonatocerus brevifuniculatus sp.n. reared from an unidentified scale on Albizia sp. in Pakistan and from Indonesia, Polynema oophaga sp.n. from Tettigoniid eggs in Malaysia, and the previously unknown male of Platypatasson fransseni Ogloblin are described. The original description of Erythmelus helopeltidis Gahan is extended by means of illustrations and Ophiomyia lantanae (Froggatt) is cited as an additional host record. Identification of material from Tanganyika showed the range of Chaetomymar lepidum Annecke & Doutt to extend to that country.

Bucculatrix parthenica Bradley sp. n., a moth native to Mexico, is described. It has been released and established in Queensland, Australia, as a biological control agent for its host plant, Parthenium hysterophorus. The moth oviposits on leaves of its host. First and second instar larvae are leaf miners, and later instars feed externally on the leaves. The life cycle occupies about 25 days under field conditions. B. parthenica was narrowly oligophagous in host-specificity tests. In Mexico the insect is scarce but in Queensland it has become abundant enough to cause extensive defoliation of its host plant at some sites. Its rapid increase in Queensland is attributed to the absence of parasitism.

Studies on the egg diapause of Teleogryllus commodus (Wlk.) in southern Victoria, and the effect of latitude on the intensity of diapause in Teleogryllids have led to the concept of population suppression by the genetic elimination of diapause. The method is based on the finding that males of the closely related T. oceanicus (Le Guillou) transmit the non-diapausing trait when crossed with T. commodus females. An additional suppressive factor is imposed by sterility in the progeny of the cross. An evaluation of the feasibility of this approach has been carried out in small-scale trials using field enclosures in which known populations of both types were studied. With a 10:1 ratio of non-diapausing/diapausing males, a mean of 73–8% of the eggs from the T. commodus females were hybrid, and with a 5:1 ratio 50–8%. The practical application of the method will not be attempted until the relative suitability of a number of candidate non-diapause biotypes has been determined.

The cuticular hydrocarbon profiles of wild caught, male Phlebotomus argentipes Annandale & Brunetti from Kandy, Sri Lanka, and Calcutta, India, were significantly different. Using discriminant functions based on three peaks from a gas-liquid chromatogram, 89% of specimens were correctly allocated to their parent sample. These results correlate with previously reported morpho-metric differences in this species from different parts of its range. Following laboratory colonization of the Kandy strain, the cuticular hydrocarbon profiles showed a progressive change, so that wild-caught and F5 generations could be completely distinguished by discriminant function anaysis, with the F1 and F 2 as intermediates.

Mosquito larvae have been shown to respond to water-borne kairomones from nearby predators by reducing their activity, and thus visibility. If they can identify the predator, they can then alter their response depending upon the associated predation risk. No studies have shown that mosquito larva may also detect water-borne vibrations from the predator. Final instar larvae of three mosquitoes: Culiseta longiareolata, Culex perexiguus and C. quinquefasciatus, were exposed to recorded vibrations from feeding dragonfly nymphs, to dragonfly kairomones and the combined effect of both. Predator vibrations caused C. longiareolata to significantly reduce bottom feeding and instead increased the more passive surface filter feeding. The larvae also significantly increased escape swimming activity. These behavioural changes were not significantly different from the effect of dragonfly kairomones, and there was no synergistic or additional effect of the two. C. perexiguus gave a smaller (but still significant) response to both dragonfly vibrations and to kairomones, probably due to a different feeding behaviour: when lying on the bottom, it was an inactive filter feeder. C. quinquefasciatus did not respond to either vibrations or kairomones and during these experiments was entirely an inactive surface filter feeder. Both C. longiareolata and C. perexiguus were thus able to detect and identify vibrations from feeding dragonfly nymphs as an anti-predator strategy. The lack of response in C. quinquefasciatus is probably a result of living in water that is highly polluted with organic material, where few predators can survive.

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.

1. Two huts were selected which were surrounded by dense bush, which varied in height from 4 to 15 feet. After elimination of this bush within a radius of 140 yards from these huts, the proportion of the population of ♀ A. funestus and ♀ A. gambiae attracted to them was at least 90 per cent. of the proportion which reached them before the bush clearance. This result indicates that bush clearance is not a justifiable measure for reducing Anopheline infestation. Even the male Anophelines entered the cleared area in the same proportion as they did before clearance.

2. While bush clearance was in progress there was a temporary sharp reduction in the infestation, and the proportion of the female Anopheline population attracted declined to between one-third and one-quarter of the proportion attracted before clearance. The proportion of males dropped by one-half. At the same time the ♀ Anophelines were apparently much less able to discriminate between quantitative olfactory stimuli. Both effects are attributed to masking by an obscuring odour from the cut and withering bush.

3. There was no difference between the numbers of A. melas attracted to a hut screened by a 10 yard thick belt of dense high bush and the numbers attracted to an identical hut in the adjacent clearing 25 yards away.

The population genetic structures of Culex pipiens Linnaeus were evaluated in China over a 2000 km transect that encompasses the two subspecies, C. p. pallens and C. p. quinquefasciatus. Four polymorphic allozyme loci were investigated in 1376 mosquitoes sampled from 20 populations across four provinces. These loci were not statistically dependent with no apparent heterozygote deficit or excess. On a regional scale (intra-province), a low (Fst=0.007–0.016) and significant genetic differentiation was found, with no clear geographical pattern. On a wider scale (inter-province), the genetic differentiation was higher (Fst=0.059), and an isolation by distance emerged. The results are compared with previous population genetic surveys of this mosquito species in different geographic areas over the world. The overall pattern suggests that Culex pipiens requires considerable distance (500–1000 km) to show isolation by distance, irrespective of the subspecies (C. p. pipiens, C. p. quinquefasciatus and C. p. pallens) or the geographic location.

1. This report continues the account of the experimental field work carried out by the Tsetse Investigation in Northern Nigeria from May 1926 up to the end of 1929. G. morsitans and G. tachinoides are the tsetse concerned. The main object of this work was to attempt to control tsetse by the destruction of primary and secondary foci by the clearing of all fringing forest, the general woodland being left untouched. Two main experimental areas have been dealt with, the Sherifuri area described previously and the Matyoro experimental area.

2. Methods of clearing and dealing with re-growth are described in detail. Records show that re-growth although very rapid the first year, then slows down to such an extent that it may not be economical to re-slash more often than every third year. The effect of clearing on tsetse was controlled by collecting fly week by week from certain fixed foci. These flies were dissected and the following factors noted : the sex proportion in the catch, the rate of catching, the state of nutrition, the proportion of very young flies, the blood content of the gut with classification of the kinds of blood found, and the trypanosome infection.

With G. morsitans, clearing of fringing forest only up to 800 yards from the collecting centre had no apparent effect on the wet season extension but at four miles it was reduced to one-sixth of its old figure.