Five new species of Platygastridae associated with mango pests in India are described. Synopeas procon sp. n., S. temporale sp. n., S. mangiferae sp. n. and Inostemma oculare sp. n. parasitise mango leaf gall midges, Procontarinia spp. (Cecidomyiidae), while Inostemma apsyllae sp. n. is associated with the psyllid Apsylla cistellata (Buckt.). Notes on a further two species, the platygastrid Trichacoides indicus Jackson and the ceraphronid Aphanogmus sp., associated with Procontarinia are given. A key to separate these parasites as well as comments on their biology and distribution are presented.

In certain areas of the Kenya coast, Culex quinquefasciatus Say is unable to maintain itself in breeding sites (flooded pit latrines) which it has to share with C. cinereus Theo. The pattern of settlement of the two species and the replacement of C. quinquefasciatus by C. cinereus were studied from May to November 1980 by monitoring newly emerged males as they departed from two breeding sites located in a small village near Mombasa. C. quinquefasciatus was the first species to be recorded from both sites, soon after they were flooded by the early rains. C. cinereus came later and did not increase markedly until after the late rains. The pattern of replacement of C. quinquefasciatus by C. cinereus was similar in the two breeding sites; the former species was unable to maintain itself once C. cinereus started to increase. Studies in another village showed that, after displacement, egg laying by C. quinquefasciatus continued but at a much reduced level. It is suggested that this is an example of competition-mediated succession occurring annually, with C. quinquefasciatus being better adapted to exploit rapidly the newly flooded sites but unable to sustain later competition from C. cinereus.

Scolytus intricatus (Ratz.) is a potential vector of oak wilt and is distributed throughout Europe wherever oak (Quercus) occurs. Its biology was studied in England in Monks Wood National Nature Reserve, Cambridgeshire, Alice Holt Forest, Surrey, and the New Forest, Hampshire, in 1977–83. S. intricatus was univoltine. Oviposition occurred from June to September in the bark of cut or weakened oak (Q. robur) over 5 cm in diameter. Eggs were laid in a single batch in maternal galleries cut across the grain of the cambium and phloem. The mean egg batch size was 17–36. Eggs hatched after 10–14 days, and the larvae ate the phloem and underwent five, or occasionally six, instars. The beetle overwintered as third-fifth-instar larvae, which were cold hardy and were located in cells in the phloem or outer xylem. Pupation occurred in spring, in cells in the bark or outer xylem. Emergence occurred between mid-May and mid-July and spanned a period of 3–4 weeks. The sex ratio was 1:1. Males and females differed externally by the presence of a tuft of setae on the frontal-clypeal suture of the head of the male. Newly emerged adults fed on twigs of live oak, but twig feeding was not obligatory for sexual maturation. Mating was observed during attacks on new hosts, which occurred in June-September. The eulophid Entedon ergias Wlk. was an endoparasite of larvae while larvae of the dolichopodids Medetera and Dolichopus and woodpeckers were predators.

Tolerance of bioresmethrin, permethrin, deltamethrin and the natural pyrethrins with and without synergists (piperonyl butoxide and propyl prop-2-ynyl phenylphosphonate), and the frequency of kdr homozygotes (flies surviving a discriminating dose of DDT+FDMC (1,1-bis(4-chlorophenyl)-2,2,2-trifluoroethanol)) was investigated in 42 strains of Musca domestica L. collected on British pig farms and in one Canadian strain. Although all field strains were at least 4–10 times more tolerant of synthetic pyrethroids at the LD50 than the standard susceptible Cooper strain, and 27 strains (26 British + 1 Canadian) had detectable levels of kdr, pyrethroids failed to control flies on only nine farms where 10% of flies or more were homozygous for kdr and/or the LD50s (in μg/female) in bioassays equalled or exceeded 0·1 for bioresmethrin, 0·12 for permethrin, 0·012 for deltamethrin or 1·1 for pyrethrins. These figures correspond to resistance factors (Cooper strain = 1) of 20, 15, 30 and 4, respectively. Regression analyses showed a close relationship between the LD50s to pyrethroids and the frequency of kdr homozygotes. Cross-resistance to trichlorfon, which in part results in the 4–10-fold increased tolerance to pyrethroids observed in strains lacking kdr, was insufficient to cause control failure. The quantification of the relationship between the frequency of an insecticide-resistant genotype, levels of resistance as measured by bioassays and control failure in the field provides the means of forewarning when control failure is likely to occur and of confirming resistance as the cause when it has taken place.

The effects of chlorpyrifos resistance on fitness in Culex quinquefasciatus Say was evaluated in terms of life-span, fecundity, fertility and rate of development, and these parameters were integrated by calculating the intrinsic rate of natural increase. A chlorpyrifos-resistant strain from Tanzania had very significantly reduced biotic fitness compared to a standard susceptible strain, CfCA, from Sri Lanka. However, after five generations of backcrossing the resistant gene into the genetic background of the susceptible strain, fitness was found to be closer to that of the susceptible strain. The reduced fitness of the original Tanzanian strain therefore appears to be mainly due to background genetic factors rather than to the major resistance gene itself.

Possible sources of adults of Spodoptera exempta (Wlk.) giving rise to outbreaks in East Africa at the beginning of the season were estimated by assuming downwind displacement and using the technique of backtracking. The accuracy of backtracks was limited by the availability of suitable weather data, but they provided a reasonably objective means of analysis. Eastern Kenya and eastern Tanzania were found to be the most likely source areas for moths. Migration from Ethiopia was very unlikely. Immigration from southern Somalia into Kenya, and from Malawi, Zambia or northern Mozambique into southern Tanzania was possible in a few years. In most years, there were likely to be sources in Kenya or Tanzania, probably of low density and in places suitable for the larvae to survive the dry season.

Insects and mites associated with each species in the Salvinia auriculata complex were recorded in Trinidad, Venezuela, Guyana, Brazil, Uruguay, Paraguay and Argentina. There was a consistent pattern of herbivore-plant association throughout the range of the complex. Field studies showed that three insects, the curculionid Cyrtobagous sp., the pyralid Samea multiplicalis Gn. and the pauliniid Paulinia acuminata (Deg.), together contained Salvinia molesta at a density slightly below the carrying capacity of the environment in coastal areas of Brazil.

In a field study of Sitobion avenae (F.) in winter wheat at Cranfield in southern England, the main predators were found to be the larvae of the staphylinid Tachyporus sp. and syrphids. Most predation occurred overnight. These predators were active during the period when the wheat crop was most suitable for aphid population increase, and in 1982 were apparently responsible for preventing an outbreak at Cranfield.

Population change in Myzus persicae (Sulz.) overwintering on spring cabbage in south-eastern England was studied in relation to meteorological and biological factors. Leaf surface wetness and temperature were correlated significantly with rate of population change, but rainfall and wind were not. Growth and development continued slowly throughout the winter, and the relationship with temperature is shown. Hymenopterous parasites, the fungus Entomophthora and predatory spiders did not affect winter survival.

‘Blind’ trials using laboratory-bred females that had completed 0–3 gonotrophic cycles showed that Polovodova's method of assessing parity, by noting the presence of follicular dilatations, is applicable to Lutzomyia flaviscutellata (Mangabeira) and L. furcata (Mangabeira). However, at the resolution of the techniques used, classification is limited to a simple division into nulliparous and parous flies. The presence of granules in the ovarian accessory glands was found to be an unreliable indicator of parity for both species.

Aphidius ervi Hal. parasitised natural populations of Acyrthosiphon pisum (Harris), Sitobion avenae (F.) and Microlophium carnosum (Buckt.) in Britain but parasitised few examples of S. avenae placed on trap plants in winter wheat, nettle-grass edge areas or lucerne-wheat strip crops. In laboratory experiments, Aphidius ervi reared from Acyrthosiphon pisum did not parasitise M. carnosum, and significantly fewer mummies were formed on S. avenae than on A. pisum. After rearing Aphidius ervi for 4–5 generations on S. avenae, similar numbers of mummies were formed on both hosts. The switch of hosts from Acyrthosiphon pisum to S. avenae was associated with the loss of certain parasitoid esterase enzyme bands revealed following electrophoretic separation of parasitoid proteins. Slow adaptation to new aphid hosts by polyphagous parasitoids such as Aphidius ervi may reduce the usefulness of reservoirs as a source of beneficial species.

Ivermectin injected subcutaneously into calves at the rate of 200 μ/kg body weight completely eliminated females of Psoroptes ovis (Her.) in 22 days. Injection of ivermectin also adversely affected the number and hatch of eggs and the proportion of adult males forming attachment pairs. The reduced number of eggs recovered in skin scrapings was apparently the result of a significantly lower fecundity among females that temporarily survived on treated calves. Females that were exposed to ivermectin for only three days did not recover their full reproductive potential even though they were transferred to calves not injected with ivermectin. The proportion of ovigerous females among survivors was not significantly affected five days after injection. Since the number of eggs recovered in skin scrapings was substantially reduced after only three days, the effect of ivermectin on female fecundity was not primarily gonadal. Reduction in the number of P. ovis eggs three days after treatment probably occurred because of a combination of mortality of adult females and reduced oviposition by ovigerous females surviving in the population.

To elucidate how thrips feed, the mouthparts of Limothrips cerealium (Hal.) were examined in dead specimens by scanning electron microscopy and plasma-ashing, and in living specimens by cinematography as individuals fed through a transparent membrane on clear liquid containing small polystyrene latex particles that made its flow visible. Close contact with the food substrate was maintained by the labral pad. The single mandible was used to pierce the membrane and was then withdrawn rapidly and replaced by the maxillary stylets, which formed a tube with either a terminal or sub-terminal opening into which food was drawn by cibarial pumping at 2–6 pulsations/s. Oscillations in the surrounding fluid caused by such pumping were detectable up to 58 μm from the maxillary opening. Feeding persisted from a few seconds to up to half an hour, and when complete the stylets were withdrawn either rapidly and together, or more gradually by sliding one against the other. Whole chloroplasts up to 6 μm in diameter were ingested even though the diameter of the maxillary tube was about 1 μm. The thrips consumed the contents of ruptured plant cells at about 8·5 × 1O-5 μl/min, equivalent to almost 12·5% of their body weight per hour. Probing and feeding removed the surface wax from leaves, and the cuticle was so exposed that it often wrinkled. Leaf cells beneath a pierced epidermal cell were usually emptied completely, and little seepage from the wounded tissue occurred after stylet withdrawal. After intensive feeding, many mesophyll cells were totally destroyed and others showed extreme plasmolysis; grana sacks were contorted and large starch grains formed due to desiccation. Above such internal damage the epidermal cells collapsed, and the outer cuticle wrinkled and appeared silvery before turning yellow and brown.

Three French strains of Culex pipiens L. were compared at the fourth larval instar for tolerance to organophosphate and carbamate insecticides, with and without the addition of synergists (the oxidase inhibitors piperonyl butoxide and CGA 84708) (a propynyl compound) and the carboxylesterase inhibitors triphenyl phosphate (TPP) and S,S,S-tributyl phosphorotrithioate (TBPT). The S54 strain was resistant to all the organophosphates tested (chlorpyrifos, malathion, monocrotophos and profenofos) compared to the susceptible LA VIS strain but only slightly tolerant to the two carbamates (carbaryl and naphthyl phenylcarbamate). The MAURIN strain was resistant to all the insecticides, including the carbamates, at a higher level. The action of chlorpyrifos and malathion on S54 was very strongly synergised by TBPT, less strongly by TPP and not at all by piperonyl butoxide. In fact, resistance was enhanced by piperonyl butoxide, as was resistance to monocrotophos and profenofos by CGA 84708. No synergist had much effect on the MAURIN strain, although TPP slightly increased the toxicity of malathion, and piperonyl butoxide and CGA 84708 slightly increased the toxicity of carbaryl. The toxic effect of carbaryl was also increased by the addition of extra acetone. Electrophoretic studies showed that the carboxylesterase enzyme coded by gene Est-20.64 (which is in linkage disequilibrium withEst-3A and acts as a marker for it) was absent from LA VIS but present in the resistant strains; but, whereas S54 was monomorphic for the gene, MAURIN was polymorphic (frequency 0·5). It is concluded that organophosphate resistance in S54 was due to detoxification by carboxylesterase wherease organophosphate and carbamate resistance in MAURIN had a strong non-metabolic component, possibly an insensitive acetylcholinesterase.

The movement patterns of Glossina palpalis palpalis (R.-D.) around villages in Ivory Coast were investigated by means of mark-release-recapture studies at two different sites. At one site, Congo Aboisso I, there appears to have been a single fly population based on the village, with an asymmetric ebb and flow of flies between the village and the surrounding bush; flies tended to remain in or around the village once they had arrived there. At the other site, Degbézéré, on the other hand, there were two populations, one centred on the village and the other on a nearby lake, with considerable exchange between the two. It is suggested that flies go to Degbézéré Village and remain there to feed, primarily on domestic pigs, and females return to the lake briefly to larviposit; males stay longer at the lake, perhaps to increase their chances of mating with emerging females. Long-distance movement of flies between villages, and also an analysis of the spatial pattern of fly movement between Congo Aboisso I and the surrounding bush, shows that human activity may affect the pattern of tsetse movement. Flight activity, and the consequent fly movement, was related to the nutritional status of the flies; males with greater fat content undertook more flight activity and thus tended to move further away from the village. The implications of these results for attempts at local trypanosomiasis control are discussed.

A novel non-destructive method was devised for studying the development of insects hidden within individual wheat grains using a standard nuclear magnetic resonance (NMR) spectrometer. The development of Sitophilus granarius (L.) at 25°C and 70% RH was studied from egg-laying to emergence by NMR, X-radiography and weighing. The results of the three methods correlated quite well. Neither the NMR nor the X-radiation appeared to harm the insects. The NMR method did not usually detect the insects until they were in the third larval instars, but after that the areas of the two NMR peaks observed with each infested grain followed a pattern which was readily interpreted in terms of the insect development. The major NMR peak was found to be due almost wholly to water and the minor peak to lipid, and the size of the major peak obtained with adults was close to that expected on the basis of their water content. The movement of some of the insects within the grains was observed for short periods and appeared to be characteristic of each developmental stage. Preliminary work with a less sophisticated NMR machine showed that it is possible in a single scan to detect ten grains infested with S. granarius larvae in a batch of 500 grains, but further work is required to see whether single eggs can be detected. The results obtained in this study were sufficiently encouraging for a wide variety of other areas to be suggested in which use of NMR might help to solve some entomological problems.