Generalist predators and parasitoids are considered to be important regulators of aphids. The former not only feed on these pests, but might also consume parasitoids at all stages of development. This direct or coincidental interference affects the natural control of aphids, the scale of which is largely unknown, and it has rarely been examined under natural conditions. Here, molecular diagnostics were used to track trophic interactions in an aphid-parasitoid-generalist predator community during the build-up of a cereal aphid population. We found that generalist predators, principally carabid and staphylinid beetles as well as linyphiid spiders, had strong trophic links to both parasitoids and aphids. Remarkably, more than 50% of the parasitoid DNA detected in predators stems from direct predation on adult parasitoids. The data also suggest that coincidental intraguild predation is common too. Generalist predators, hence, disrupt parasitoid aphid control, although the levels at which the predators feed on pests and parasitoids seem to vary significantly between predator taxa. Our results suggest that taxon-specific trophic interactions between natural enemies need to be considered to obtain a more complete understanding of the route to effective conservation biological control.

Limburger cheese, previously shown to attract female Anopheles gambiae Giles, was solvent extracted and chemically fractionated into acid and non-acid fractions. The extracts and aliquots of headspace odour of the cheese were analysed by gas chromatography and electron impact mass spectrometry. Nineteen saturated and unsaturated aliphatic fatty acids, ranging in carbon chain length from C2 to C18, were detected. The most abundant acids (>1 mg/g of cheese) identified in the acid extract were ethanoic, propanoic, butanoic, hexadecanoic and 9-octadecenoic acid. The same compounds were identified in analyses of headspace samples but only trace quantities of the less volatile acids (C10 to C16) were present, whilst C18 acids were absent. Behavioural responses of female A. gambiae towards a range of dilutions of the acid extract (in diethyl ether) were recorded in a windtunnel bioassay. The undiluted extract was found to be repellent, but became highly attractive (P «0.001) at lower doses, and was still significantly attractive (P<0.001) when diluted 106times. A synthetic mixture of 12 of the more abundant aliphatic acids identified in the acid extract was found to be significantly attractive (P<0.001) when diluted 108 times. Electroantennographic (EAG) studies showed significant and reproducible responses to (saturated) Limburger cheese headspace. At doses higher than 0.1%, the synthetic mixture of 12 acids elicited significantly higher EAG amplitudes than the solvent control (paraffin oil). EAG responses were recorded from mosquitoes stimulated with C5 to C8 acids, that were characterized by significant dose-dependencies. Weaker, though significant EAG responses were obtained with the less volatile acids (C9 to C14). Only hexadecanoic acid did not elicit a detectable response. The electrophysiological and behavioural responses obtained with fatty acids isolated from Limburger cheese suggests that together they could act as a kairomone for female A. gambiae. The implications of this are discussed together with the occurrence and bacterial production of these compounds on human skin.

F2 traps of 53 different colours, selected from measurements of spectral reflectivities in the colour range visible to Glossina, were tested in a field study against G. morsitans morsitans Westwood and G. pallidipes Austen in Zimbabwe. Trap effectiveness depended mainly on reflectivity in four different wavelength bands, two of which, blue-green and red, were positively correlated with trap score; and two of which, ultraviolet and green-yellow-orange, were negatively correlated with trap score, the most important effects coming from the blue-green and green-yellow-orange bands. The ‘best’ trap material was a royal blue cotton, which reflected blue-green strongly but very little ultraviolet or green-yellow-orange. This material together with the lowest-scoring colours (green and yellow) gave results outside the range of a set of grey traps, indicating that the flies employ colour information and not intensity-contrast information alone in trap- orientated behaviour. No significant differences in colour preferences were found between sexes or species.

A method is described by which Culicoides variipennis (Coq.), C. riethi Kieff. and C. nubeculosus (Mg.) have been maintained as laboratory colonies for over five years. Techniques are given for the maintenance of adults, larvae and pupae; with some modifications these could probably be applied to a range of other species. Adult midges were held in waxed card pill boxes, and provided with sugar solution. Anaesthetised mice provided a blood-meal source. Larvae were reared in pans on a substrate of glass fibre in a medium which contained nutrient broth, grass meal and Bemax. The life-cycle of these species occupies 10–21 days at 23–25°C.

Reactions to Temperature

1. The reactions of Culex fatigans to temperature were studied by means of a new type of temperature gradient apparatus based on the same principle as the humidity alternative chamber.

2. Females at different stages were exposed to a range of 5°C. at different parts of the temperature scale, and it was found that the sensitivity was very much greater at high temperatures than at low ones.

3. The most striking feature of behaviour at all stages was the strong avoidance of high temperatures. This was strongest in the hungry females, less strong in the blood-fed females and those with mature ovaries, and least strong in the newly emerged females.

4. Newly emerged females showed avoidance of high temperature below 30°C., but not below 25°C. They also showed a weak avoidance of low temperature. At 29°C. they were sensitive to a difference of 1°C. or a gradient of 0·05°C. per cm.

5. Hungry females showed a strong avoidance of high temperature below 25°C., the reaction still taking place below 15°C. There was no avoidance of low temperatures.

6. Blood-fed females and those with mature ovaries showed a strong avoidance of high temperatures below 25°C., but below 20°C. they were unaffected by temperature differences. Blood-fed females were sensitive to a difference of 1°C. or a gradient of 0·05°C. per cm. at 23°C.

7. Except in the case of newly emerged females there was quite a close relation between the reactions to temperature and the effects of temperature.

8. Reasons are given for regarding the temperature reactions of Culex as of first importance in determining the behaviour of the mosquitoes when seeking a resting place.

Reactions to Humidity

9. The reactions of Culex fatigans to humidity were studied by means of the alternative chamber, in a dark constant temperature room at 25°C.

10. At all stages the strongest humidity reaction was an avoidance of high humidities above 95 per cent. R.H.

11. This reaction was strongest in the blood-fed females and those with mature ovaries, less strong in the newly emerged females, and weakest in the hungry females.

12. The avoidance of high humidity was strongest when there was a difference of 20 per cent. R.H., such as a 78–98 per cent. R.H. gradient. Near saturation point all stages except hungry females were sensitive to a difference of 1 per cent. R.H. or a gradient of ·05 per cent. R.H. per cm. Hungry females at this point were not sensitive to a difference of less than 3 per cent. R.H.

13. All stages showed a slight but regular avoidance of low humidities, provided a sufficiently large humidity range, not less than 40 per cent. R.H., was present.

14. Hungry females, despite the onset of mortality due to desiccation, showed no sharp avoidance of low humidities which were rapidly fatal to them.

15. Between 30 and 85 per cent. R.H. all stages were unaffected by humidity differences of as much as 40 per cent. R.H.

16. The avoidance of high humidities was equally strong in blood-fed females at 20, 25, and 30°C. At 35°C., greatly increased activity eliminated the reaction.

17. The reaction was much less intense in daylight and disappeared altogether after sundown.

18. Reasons are given for considering that the measure of humidity which determines the behaviour of the mosquito is relative humidity and not saturation deficiency, even though the latter is the important one in the water relations of insects.

The response to short photoperiod (10 h) of the F1 and F2 sexual generations of Myzus persicae (Sulz.) resulting from a cross between oviparae from a holocyclic clone and males from an androcyclic clone were examined and compared in experiments done at Imperial College Field Station, England. F1 and F2 progeny segregated into three distinct phenotypes; holocyclic, androcyclic and intermediate. Intermediate clones reared at 10 h photoperiod produced alatae which were physiologically intermediate between gynoparae and virginoparae, because their progeny consisted of oviparae, apterous virginoparae and intermorphs. Intermediacy was not affected by temperature and seems to be genetically determined. Segregation ratios in the F1 and F2 indicate that the androcyclic condition is induced by a recessive ‘ switch-gene ’ which completely suppresses the production of sexual females, and partially suppresses male production. This gene could be present in the heterozygous condition in a large proportion of parthenogenetic lines of the aphid, and thus confer a latent potentiality for anholocycly on populations even where conditions will not regularly permit this method of overwintering. Conversely where anholocycly is strongly favoured many aphids would be homozygous for the recessive, androcyclic character, but the potential for gamic reproduction could remain widespread.

Delayed and immediate oocyst rates; parous rates and sporozoite rates were obtained in Anopheles gambiae Giles, A. arabiensis Patten and A. funestus Giles from two villages in the Kilombero Valley, southern Tanzania during the wet season of 1991. Collection methods included light trap, indoor resting collection and nets with holes cut in their side. Mosquito survival estimates from parous rates obtained from light trap collections, were compared with estimates from capture–recapture experiments and from that obtained during a population decline. Methods of estimating the proportion of feeds infectious to mosquitoes, K, were also compared. This proportion varied between villages and species and was highest in the village with the greatest proportion of A. gambiae. We propose that absolute estimates of K should be obtained by determining the immediate oocyst rate and measuring the parous rate using the same host seeking mosquitoes. This estimate was only available from one village and ranged from 1.9% for A. gambiae s.l. to 3.4% for A. funestus.

The effects of ambient temperature on all component life cycle stages of the sheep blowfly Lucilia sericata Meigen were examined under controlled conditions. The critical base temperatures and the number of day-degrees required for completion of each stage were determined. Using these data a simple simulation model was developed to evaluate temperature effects on the seasonal pattern of L. sericata abundance. The number of flies estimated by the model to be available for capture, together with the temperature over each capture period determining adult activity levels, were able to account for 77% of the variance in L. sericata abundance observed over a season.

It is a matter of general agreement that atmospheric humidity is often of great importance in limiting the times or places at which insects are abundant. But though one may collect facts which suggest that a particular degree of dryness or dampness favours some stage of an insect, it is not easy to devise experiments which will give unassailable facts. Some of us feel that the precise study of water relations and water balance may lead to greatly increased knowledge of the living insect, and therefore to results of economic value ; and it is certain that a fuller understanding of these matters is delayed because few know the methods appropriate for measuring and controlling humidity.

The purpose of the present paper is to make known a number of practical methods, which might be of service to a worker even in a remote country. As this is my objective, I shall include material which is already well known to physicists, and as our concern is with the conditions in the places where insects are actually living, I have given particular attention to unorthodox devices which can be used in small spaces and which are portable; among the great variety of methods, I have endeavoured to show what is good and bad in each.

This is an account of laboratory experiments made with the tsetse Glossina palpalis. The results deal mainly with the effects of climatic conditions, temperature and humidity in particular, on the metabolism and life-cycle. Some work was also done on the activity and behaviour of the fly, but this is very incomplete, though it shows the importance of the problem and the need for further study.

The work was done during a visit of just over a year to East Africa, in 1935-36, as Wandsworth Scholar of the London School of Hygiene and Tropical Medicine. I spent most of the time at the Human Trypanosomiasis Institute, Entebbe, Uganda, and also visited tsetse areas in Kenya and Tanganyika. I am grateful to all those who helped to make my visit profitable. Among others, to the Directors of Medical Services of the East African territories, in particular the Hon. W. H. Kauntze of Uganda, and many members of their departments. To Mr. C. B. Symes, Medical Entomologist, Kenya, and to Mr. W. H. Potts, of the Department of Tsetse Research, Tanganyika. I am especially grateful to Dr. H. Lyndhurst Duke, Director of the Human Trypanosomiasis Institute, for many kindnesses. Considerable assistance was received from Mrs. Helen Mellanby, who was working on allied problems at Entebbe. And mention must be made of the intelligent and conscientious help of my laboratory assistant, Omw. Bonaventure Semalwadde.

Recent experimental evidence has shown that learning occurs in the host selection behaviour of Helicoverpa armigera (Hübner), one of the world‘s most important agricultural pests. This paper discusses how the occurrence of learning changes our understanding of the host selection behaviour of this polyphagous moth. Host preferences determined from previous laboratory studies may be vastly different from preferences exhibited by moths in the field, where the abundance of particular hosts may be more likely to determine host preference. In support of this prediction, a number of field studies have shown that the ‘attractiveness’ of different hosts for H. armigera oviposition may depend on the relative abundance of these host species. Insect learning may play a fundamental role in the design and application of present and future integrated pest management strategies such as the use of host volatiles, trap crops and resistant crop varieties for monitoring and controlling this important pest species.

An island of 4·5 km2 in Lake Kariba, Zimbabwe, was stocked with cattle and infested with Glossina morsitans morsitans Westwood and G. pallidipes Austen in 1979. From February 1980 to April 1981, the tsetse populations, estimated by mark, release and recapture, increased about ten times, to contain about 3000 males of G. m. morsitans and 2000 males of G. pallidipes. From May 1981 to May 1983, six traps, with carbon dioxide and acetone as odour attractants, were used to capture 0·1–0·3% per day of the G. m. morsitans population and 1–4% per day of the G. pallidipes population. Captured flies were retained and killed, or were automatically sterilized with metepa and released. In May 1983, when the populations of G. m. morsitans and G. pallidipes had declined by about 90 and 99%, respectively, the traps were replaced by 20 targets with acetone and 1-octen-3-ol as attractants. The targets were coated with dieldrin or, later, deltamethrin and killed about 2% per day of G. m. morsitans and 5% per day of G. pallidipes. Both populations then declined rapidly, G. pallidipes disappearing in 11 weeks and G. m. morsitans in nine months. Targets offer a cheap, simple and effective means of eliminating isolated populations of tsetse.

The genetic polymorphism and the biotype identity of the tobacco whitefly Bemisia tabaci (Gennadius) have been studied in population samples taken from different localities within Greece from cultivated plants growing in greenhouses or in open environments and from non-cultivated plants. Two different approaches were used: sequencing of the mitochondrial cytochrome oxidase I (mtCOI) gene and genotyping using microsatellite markers. Analyses of the mtCOI sequences revealed a high homogeneity between the Greek samples which clustered together with Q biotype samples that had been collected from other countries. When genetic polymorphism was examined using six microsatellite markers, the Greek samples, which were all characterized as Q biotype were significantly differentiated from each other and clustered into at least two distinct genetic populations. Moreover, based on the fixed differences revealed by the mtCOI comparison of known B. tabaci biotype sequences, two diagnostic tests for discriminating between Q and B and non-Q/non-B biotypes were developed. Implementation of these diagnostic tools allowed an absence of the B biotype and presence of the Q biotype in the Greek samples to be determined.

Methods for dispensing tsetse attractants using sealed polyethylene sachets and bottles were studied in the laboratory and field. 1-Octen-3-ol (octenol), 4-methylphenol and 3-n-propylphenol were dispensed singly or as blends from sachets 25–200 cm2 in surface area and with a wall thickness of 0.06–0.32 mm; butanone was dispensed from polyethylene bottles. The release rates of attractants, assessed gravimetrically or by GC analysis of volatiles released, were independent of the amount present. The rates were related directly to surface area, inversely related to wall thickness and increased exponentially with temperature. With blends of the attractants, the release rates of the two phenols were directly proportional to the concentration present, but that of octenol showed an exponential dependence. A similar exponential effect was seen with blends of the attractants and an involatile diluent. For mixtures of chemicals, the ratio of the released components was not affected significantly by temperature, sachet size or wall thickness. Release rates from polyethylene sachets and bottles in the field varied 100-fold according to temperature differences related to the time of day, season, and degree of insolation. Day-degree models to predict the losses of attractants from a polyethylene sachet in shade or in full sunlight were highly correlated (r2 = 0.84 and 0.81 respectively) with observed losses. The practical implications of these findings are discussed.

An antiserum was prepared against carboxylesterase E4, the enzyme conferring resistance in Myzus persicae (Sulzer) to a wide range of insecticides, and the immunoglobulin G (IgG) fraction was purified from it by affinity chromotography. Interactions of the antiserum and IgG with aphid homogenates and the purified esterase proteins were studied by immune diffusion, immunoelectrophoresis and enzyme-linked immunosorbent assay (ELISA). In M. persicae, the interactions were specific for E4 and its closely-related mutant form, FE4, and except for Phorodon humuli (Schrank), there was no cross-reaction with homogenates of the nine other aphid species examined. These studies confirmed the quantitative changes in E4 protein previously reported and established that the increased esterase activity in P. humuli also arises from the production of more protein, or proteins, homologous to E4. Resistance of M. persicae could be characterized by immunoelectrophoresis even after preservation of the insects in 30% ethanol. Although ELISA could also be used to identify resistance, a simpler immunoplate assay was developed based on measuring the esterase activity of E4 retained when the enzyme bound to IgG. This assay discriminates well between the three resistant M. persicae variants common in the field in the UK, and its simplicity allows the study of large numbers of insects.

The cryptic species Middle East-Asia Minor 1 (MEAM1), formerly referred to as ‘B biotype’, of the whitefly Bemisia tabaci complex entered China in the mid 1990s, and the Mediterranean (MED) cryptic species, formerly referred to as ‘Q biotype’, of the same whitefly complex entered China around 2003. Field surveys in China after 2003 indicate that in many regions MED has been replacing the earlier invader MEAM1. The factors underlying this displacement are unclear. We conducted laboratory experiments and field sampling to examine the effects of insecticide application on the competitive interactions between MEAM1 and MED. In the laboratory, on cotton, a plant showing similar levels of suitability to both whitefly species, MEAM1 displaced MED in five generations when initial populations of the two species were equal and no insecticide was applied. In contrast, MED displaced MEAM1 in seven and two generations, respectively, when 12.5 and 50.0 mg l−1 imidacloprid was applied to the plants via soil drench. Field sampling indicated that in a single season MED displaced MEAM1 on crops heavily sprayed with neonicotinoid insecticides but the relative abundance of the two species changed little on crops without insecticide spray. We also examined the effects of host plants on the competitive interactions between the two species in the laboratory. When cohorts with equal abundance of MEAM1 and MED were set up on different host plants, MEAM1 displaced MED on cabbage and tomato in five and seven generations, respectively, but MED displaced MEAM1 on pepper in two generations. As field populations of MED have lower susceptibility than those of MEAM1 to nearly all commonly used insecticides including imidacloprid, insecticide application seems to have played a major role in shifting the species competitive interaction effects in favour of MED in the field across China. Host plants may also shape competition between the two species depending on the relative levels of plant suitability.

Mosquitoes of the Anopheles maculipennis group were collected in five districts of Romania (Constanta, Giurgiu, Ilfov, Mehedinti and Suceava) between March 2000 and June 2003. Two hundred and ninety-seven specimens were identified by molecular methods. Nuclear rDNA ITS2 sequences of 178 specimens were compared with GenBank sequences for nine known Palaearctic species of the group, and 119 specimens were identified using an ITS2 PCR–RFLP assay developed during the study. Five genetically distinct species of the group were identified: A. atroparvus van Thiel, A. maculipennis Meigen, A. melanoon Hackett and A. messeae Falleroni and a previously unrecognized species. The new species, herein formally described and named A. daciaesp. n., was collected in the Black Sea coastal region and plains adjacent to the Danube River in southern Romania. Anopheles daciae is most similar to and sympatric with A. messeae. It is contrasted with A. messeae and characterized on the basis of unique nuclear ITS2 and mitochondrial COI DNA sequences and morphological characters of the eggs. The larval, pupal and adults stages of the two species were also compared, but no reliable characters were found to distinguish them. It seems likely that A. daciae is more widespread in eastern Europe and the Balkan States, and could be responsible for malaria transmission in these regions that is currently attributed to A. messeae. Anopheles melanoon is reported from Romania for the first time.

In Zimbabwe, catches of Glossina morsitans morsitans Westwood and G. pallidipes Austen in traps baited with acetone and 1-octen-3-ol were increased by the addition of the synthetic mixture of eight phenols found in cattle urine to a level equal to or greater than those with natural urine. The addition of natural urine to the synthetic mixture did not increase catches further, indicating that the phenols account for essentially all the attractiveness of cattle urine. 4-Methylphenol and 3-n-propylphenol were shown to be the naturally-occurring components essential for attractiveness, and 2-methoxyphenol was found to reduce attractiveness. 4-Methylphenol alone was slightly attractive to both species, but only for males, increasing catches by approximately 30%. Catches of both species were increased by approximately 50% by 3-n-propylphenol. The addition of 4-methylphenol increased catches of G. pallidipes by up to a further four times, but catches of G. m. morsitans were decreased. Of 14 other phenols tested, phenol, 3-methylphenol and 4-ethylphenol increased the attractiveness of 3-n-propylphenol to G. pallidipes without decreasing the attractiveness to G. m. morsitans; (E)- and (Z)-3-(1-propenyl)phenol, potential contaminants in 3-n- propylphenol, did not reduce the attractiveness of mixtures of 3-n-propylphenol and 4-methylphenol, and the E and, to a lesser extent, the Z isomer could substitute for 3-n-pro-pylphenol in these mixtures. Mixtures of phenols which increased the attractiveness of traps to tsetse showed similar effects with targets but at a slightly reduced level.

Investigations of the feeding activity, resting behaviour and seasonal distribution of Glossina morsitans Westw. were carried out at Lusulu Veterinary Research Station, Rhodesia, in 1961–63. Nine principal sampling sites were used, one in each of five distinct vegetation types and four at places where various pairs of types met. At each site, from dawn to dusk on several consecutive days in each of four seasons, tsete flies that had engorged naturally on a tethered ox were caught, marked and released, and meterorological readings were taken. Daylight observations of resting flies, both marked and unmarked, were made by searching the vegetation from ground level to a height of 25 feet (with the aid of ladders) and also by placing nets over inaccessible resting places, such as ant-bear holes, at the hottest time of day, thus trapping the flies that emerged later. Attempts to determine the night resting places by releasing flies marked with reflecting paint were unsuccessful.

The results showed that the feeding activity of G. morsitans was restricted to temperatures between 18°C., below which the flies were inactive, and about 32°C., above which they echibited a negative reaction to light. Feeding ceased abrupthy with the onset of darkness, and these was some evidence that activity was reduced by very high light intensity during the middle hours of sunny days. The diurnal pattern of feeding activity varied considerable from season to season but relatively little between vegetation types. A sex ration near equality was observed amongst flies caught feeding on oxen. The proportion of marked flies recaptured (i.e., feeding a second time on a bait-ox) was low, ranging from 0 to 12 per cent. according to vegetation type and season: it was higher for males than for females.

During daylight, the boles and branches of trees were used as resting places in all vegetation types, branches (especially horizontal ones) being preferred at most seasons. When temperatures rose above 32°C., however, the flies removed to resting places in deep shade, e.g., ant-beat holes, rock crevices, tor holes in trees and the fluted boles of dark-barked trees. Searching at night with electric torches failed to reveal the resting places used at that time.

The catches of feeding flies indicated that a wide range of vegetation types at Lusulu were inhabited by G. morsitans at all seasons and that, with the exception of males in riverine vegetation in the hot dry season, vurtually no concentration of flies took place in any specific vegetation at any time of year. These findings are discussed in relation to control by discriminative clearing.

In an inland area of the Gambia the density of flying mosquitoes at successive distances from a pair of bait-calves or an equivalent source of carbon dioxide was measured with ramp-traps to determine the maximum range at which orientation towards the bait was initiated. Thirty-six traps were operated at intervals of 7·5 m up to a distance of 60 m from the bait, on 66 nights. Anopheles ziemanni Grünb., Mansonia uniformis (Theo.) and Aedes spp. were responding to the presence of the baitcalves from a distance of 22·5–30 m; with carbon dioxide as bait the same species showed a clear response at 15 m but, with the doubtful exception of M. uniformis, not at 22·5–30 m. M. africana (Theo.) responded to both calf and carbon dioxide baits at 15 m but not at more distant ranges. Culex thalassius Theo. and C. univittatus Theo. showed a response at 7·5 m but not at any greater distance. C. decens group showed no response to either bait even in the nearest traps (7·5 m). The parous rate in Mansonia spp. varied with distance from the bait. Similar variation in the proportion of females infested with mites was not detected.