From a critical review of the literature, it is concluded that the role of carbon dioxide in host-seeking by mosquitoes comprises two distinct actions. Firstly, it acts as an ‘attractant’, orientation towards the host being mediated by kinesis and optomotor anemotaxis. When tested in the absence of moving air currents, orientation to the source is not possible and only the kinetic or ‘activating’ effect is manifested. Moreover, in the absence of other host factors, sustained flight takes place only in response to intermittent pulses of carbon dioxide; this response is not elicited in uniformly permeated airstreams. Secondly, carbon dioxide has a combined action with warm moist convection currents at close range and with odour factors at a distance from the host.

At Nsukka in south-eastern Nigeria, nymphs of the wet-and dry-season generations of Zonocerus variegatus (L.) overlapped, both in time (January to March) and in space. Contrary to some previous suggestions, adults of the two generations also overlapped (mid-May to end-July), and copulation occurred between individuals of both sexes in the laboratory.

In experiments at Slough, southern England, one hundred tonnes of wheat at about 14% moisture content were divided between six similar metal bins, three of which were aerated during the winter. Observations were made on the mite and fungal populations and physical conditions for an uninterrupted storage period of three years. During the winter, the wheat in the aerated bins was 2–4°C cooler than that in the unaerated bins and it always had a moisture content 0·5–1% higher, except at the surface where it was usually drier. Aeration appeared to delay the increase of Acarus siro L. and Lepidoglyphus destructor (Schr.) for 4–6 months after harvest, but few individuals survived into the second year of storage in any bin. Cheyletus eruditus (Schr.) and Tydeus interruptus Thor were present after one year and were most numerous in the aerated bins. The distribution within the bins of the different species of mites varied with season. A greater increase in storage fungi occurred in the aerated bins than the unaerated. Members of the Aspergillus glaucus and A. restrictus groups, Penicillium spp. and Wallemia sebi were the commonest fungi.

The physiological age of female Stomoxys calcitrans (L.) caught biting horses during seven all-day catches and 20 catches in the morning or afternoon during the rainy season (January-July) in Manaus, Amazonas, Brazil, was determined by examination of their ovaries. Males and unmated females with undeveloped ovaries had similar biting patterns, with peaks of activity in the early morning and late afternoon, when the relative humidity was between 50 and 80%. Nulliparous inseminated females with ovaries at Stages II to V attacked throughout the day, with no pronounced peaks, whereas parous females showed a peak of biting in the late morning and early afternoon. The majority of parous flies had oviposited less than four times and had distended overiolar sacs, indicative of recent oviposition.

A single male and female were removed from a well-established laboratory colony of Glossina morsitans morsitans Westw. and became the parents of an inbred stock. In general, each subsequent generation comprised ten randomly selected females mated to one of three randomly selected males, both sexes being offspring of the preceding generation. The inbred stock was fed on the ears of rabbits for 40 generations, over a period of almost eight years. Performance, in terms of length of female life, female fecundity, number and weight of puparia produced, effective emergence rate from puparia and sex ratio of emerged flies showed little variation between generations. By generation 40, the inbreeding coefficient was 0·9347; over the same eight years, the inbreeding coefficient of the parent colony of G. m. morsitans was less than 0·0303. It is concluded that the risks of inbreeding having deleterious effects on laboratory colonies of Glossina are slight.

In studies in the Zambesi Valley, Zimbabwe, carbon dioxide alone dispensed at 2·5 to 15 litres/min, or acetone alone dispensed at 0·3 to 300 g·h, increased by up to six times the catches of Glossina morsitans morsitans Westw, and G. pallidipes Aust. from stationary biconical traps, stationary electrocuting traps used with and without a visual target, and a mobile party of hand-net catchers. Catches were increased further when the chemicals were dispensed together. Carbon dioxide at 2·5 litres/min plus acetone at 15 g/h was about half as effective as ox odour for enhancing the catches from an electrocuting trap plus target; the efficacy of carbon dioxide at 15 litres/min plus acetone at 300 g/h was not significantly different from that of ox odour. Several short-chain ketones, and also formaldehyde and propionaldehyde, were attractive. Several long-chain ketones, and also heptaldehyde and caproic acid, were repellent. Carbon dioxide was attractive for Tabanidae, Stomoxyinae and non-biting Muscidae. Acetic acid was repellent for Stomoxyinae and non-biting Muscidae.

Catches of Glossina morsitans morsitans Westw. and G. pallidipes Aust. were made on electric nets baited with the odour of one ox, in deciduous and riverine woodland in the Zambesi Valley of Zimbabwe. Catches of teneral and mature flies of both sexes and species declined sharply during the hot dry season (September to November) in the deciduous woodland. In the riverine woodland, catches of mature G. m. morsitans increased during this period; catches of mature G. pallidipes rose rapidly to a high level in June (early in the cool dry season), which was maintained for most of the dry season. Catches of teneral flies in the riverine woodland were fairly constant from June to September (the cool dry season and start of the hot dry season) and then declined, though not as sharply as in the deciduous woodland. The percentage of tenerals in the catch showed a minimum at the end of the hot dry season (October–November); at that time there was also a dramatic rise in the female: male ratio in the deciduous woodland, but no such change occurred in the riverine area.

The efficiencies of five mechanical traps and an electric trap for tsetse flies were measured by estimating the numbers of flies which approached the devices but were not captured by them. With this method, it was possible to discern significant differences in efficiencies even if the means differed by as little as 25%. Three biconical traps had estimated efficiencies of 40–70% for Glossina morsitans morsitans Westw. and 50–80% for G. pallidipes Aust. when used in the presence of the odour of one ox. The efficiency of a small electric net was estimated at 70–75% for all tsetse under this test condition, and a modification of one of the biconical traps had an estimated efficiency of 55–85%. The efficiency of this trap increased by a factor of 1·2–2·2 when used with the odour of six oxen, compared to the efficiency in the absence of host odour. Preliminary results suggested that, when used in the presence of ox odour, the efficiency of this trap for teneral tsetse was at least as high as for mature flies.

The duration of flight by Nilaparvata lugens (Stål) of tropical origin from field and laboratory populations was studied. Field insects (from the third generation on rice) flew longer and more readily than laboratorybred insects. The longest recorded flight, of 10·75 h, was by a female from the field. Laboratory-reared insects performed poorly even after only one generation in the laboratory. Flights that were started in the morning lasted longer than those started in the afternoon. Lift production varied between individuals and during a continuous flight. Individuals flying for over 150 min tended to produce more lift for a longer proportion of the flight than those flying for less than 10 min. The pattern of lift production appeared to be similar in successive flights, except in those following very long flights when the insect appeared to be exhausted. There was no tendency for the first flight to be the longest. Up to 28% loss of body weight was recorded (in a flight lasting 512 min) during flight. The results indicate that individuals from tropical field populations of N. lugens have the capacity for long range migration.

Counts were made of the numbers of Oscinella adults caught in water traps in plots of grass and oats and in a suction trap in north-eastern England in 1969 and 1970. The numbers of eggs laid by O. frit (L.), O. vastator (Curt.), O. nitidissima (Mg.), O. hortensis Collin and O. maura (Fall.) on their respective host-plants were also counted. In both years, there were two generations of O. nitidissima and O. nigerrima (Macq.) and one of O. maura. In 1969, there were two generations of O. frit and one of O. hortensis and O. vastator. In 1970, there were partial second generations of O. hortensis and O. vastator and a partial third generation of O. frit. O. nigerrima was the first species to appear in the spring, followed by O. frit and O. nitidissima. O. hortensis, O. vastator and O. maura emerged later, and these species dominated the trap catches in July. The proportions of O. frit and O. nitidissima increased in August, and by late September these species again dominated the catch. The proportions of O. vastator and O. hortensis in the suction-trap catches were much lower than in the water-trap catches. Adults of all species were always found in the grassland water traps before they were found in the suction trap. The migratory requirements of other species in the genus, in particular O. maura and O. vastator, may be less than those of O. frit. The oviposition period on particular grass species was relatively long, and thus control of Oscinella spp. on grassland would be difficult.

An investigation into the seasonal abundance of Zonocerus variegatus (L.) around Ibadan, Nigeria, showed that hatching occurs between October and March and peak abundance is in late November. Adults occur almost throughout the year. Oviposition takes place between March and October or possibly November, with a peak in April. Eggs laid in March and April hatch in October and November after a diapause, while those laid from June onwards do not appear to enter diapause. Thus eggs laid in June and July hatch at the same time as those laid in March and April. Parasitism by the sargophagid fly Blaesoxipha filipjevi (Rod.) during March and April results in a rapid decline in adult numbers which may be followed by a secondary peak in adult numbers when nymphs, which are present at the same time and are rarely parasitised, reach adult stage. Oviposition resulting from such a peak does not produce a secondary peak in hatching as this coincides with hatching from earlier layings. The fungus Entomophthora grylli plays an important role in controlling the abundance of nymphs and adults during the dry season despite the intermittent nature of the attacks. During the wet season, the fungus is able to germinate and disperse more readily, thus keeping the numbers of the insects low. It is concluded that there is one generation of Z. variegatus a year, with a peak in population coinciding with the dry season (November-March). It is suggested from the results that the grasshopper may have originated in the semi-arid zones of the north.

Photoperiod was shown to be the principal factor regulating the induction of a facultative egg-diapause in Chortoicetes terminifera(Wlk.). All developmental stages from first-instar nymphs to immature adults were sensitive to photoperiod. At constant photophases, the insect exhibited a short-day—long-day response, with the upper and lower critical photo-periods for induction approximating to LD 15·5: 8·5 and 11:13, respectively. These correspond to the range of photoperiods experienced by the insect under natural conditions. The maximum inductive response occurred at about the mid-point of this range, i.e. LD 13·5: 10·5. In experiments in which insects experienced a change in photophase at the end of the nymphal stage, the incidence of diapause varied with the direction of change (long to short or short to long) and indicated that diapause induction was prevented by an increase in photophase but enhanced when the photophase was reduced. The size of the inductive response associated with a decrease in photophase appeared to depend less on the size of the decrease than on its position within the inductive range, such that the maximum effects were observed when the sequence of light regimes were close to or spanned the most inductive constant photophase. Temperature was also important in determining the induction of diapause. In the upper portion of the inductive range (15·5 to 12·5 h light), insects subjected to high temperatures or to an increase in temperature during development showed a lower incidence of diapause than those subjected to low temperatures or to a decrease in temperature. In the lower portion of the inductive range, the effects of temperature were reversed, with high temperature or an increase in temperature being more inductive than low temperature or a decrease in temperature.

The sexual competitiveness of males of Ceratitis capitata (Wied.) carrying a chromosomal translocation and a morphological mutation was compared to that of a wild-type strain. The competitiveness was evaluated by calculating from progeny data the proportion of females that mated with each male type. Males were introduced into the test population in varying proportions. The chromosomal translocation did not affect the competitiveness of the males. The presence of an eye-colour mutation (apricot) reduced the sexual competitiveness of the males bearing the translocation. The results showed evidence for a minority effect (an inverse relation between genotype frequency and mating success). The genetic background of the females in the test populations influenced the competitiveness of the participating males.

The natural predators of larvae and pupae of the complex of Simulium damnosum Theo., most probably S. soubrense Vajime & Dunbar and S. sanctipauli Vajime & Dunbar, in the River Marahousé in the Ivory Coast were identified by serological methods. Rabbits were injected with cell-free saline extracts of S. damnosum larvae to produce S. damnosum antiserum, which was used in interfacial capillary ring tests. A total of 1648 gut smears was made from various aquatic invertebrates and tested, and Trichoptera larvae were identified as the most important predators.

A relationship between mean development rate, temperature and saturation deficit was derived for the egg stage of Lucilia cuprina (Wied.). Development rate increased linearly with temperature between 10 and 40°C at constant saturation deficits. Increasing saturation deficits between 0 and 10 mm Hg caused non-linear decreases in development rate. At zero saturation deficit, temperatures between 15 and 40°C had no effect on egg survival. Survival in the egg stage declined rapidly with increasing saturation deficits, primarily through the inability of the larvae to rupture the chorion of the egg. The aggregation of single eggs into compact egg-masses during oviposition appeared to afford no additional protection against desiccation. The ecological implications of the results are discussed.

The courtship of Spodoptera littoralis (Boisd.) was studied in closed cages containing an excess of the female sex pheromones (Z,E)-9, 11-tetradecadienly acetate (III) or (Z)-9-tetradecenyl acetate (IIA). High levels of III or IIA were obtained by using polyethylene vials loaded with 5, 1 or 0·1 mg of pheromone. Vials containing 10 or 1 μg released low levels of pheromone. Excess pheromone reduced mating; at high levels of III and IIA, only 15% and 42% of pairs, respectively, mated, compared with 92% of control pairs. Some 45% of courtships in control cages did not end in copulation, and in half of these the female rejected the male by giving a rapid flick of the wings. A detailed examination of unsuccessful courtships showed that an excess of III or IIA disrupted female courtship behaviour. At the higher levels of pheromone, no female wing-lifted to show acceptance of the male and only a few rejected the male by wing-flicking. Significantly more females took to flight in cages containing III, whilst in cages with IIA females either took to flight or remained still. These changes in behaviour were still apparent in courtships where the female was calling and the male gave a full brush display. It is suggested that both III and IIA block olfactory reception of the male brush pheromone. An excess of either pheromone increased the proportion of male courtships of non-calling females. IIA had no other appreciable effect on male behaviour, but III also significantly reduced full brush displays during courtship, increased the period of flight preceding hovering and increased partial brush extension during flights that did not lead to courtship.

The physiological age-structure of populations of the malaria vector Anopheles darlingi Root, collected biting man, was determined from collections made from March to June 1979 at the end of the rainy season in the village of Aripuanã, Mato Grosso, Brazil. The number of mosquitoes biting increased during the transition between the wet and dry seasons, but adult survival remained low at all times. Only seven of 1596 females dissected had laid eggs four or more times, and thus the proportion of females that could be potentially infective with malaria sporozoites was 0.4%. The mosquitoes rested in the vicinity of the host for periods of up to 10 min before biting. The results are compared to those obtained during a study on A. darlingi on the Manaus-Boa Vista Highway, 1000 km to the north. In this area, peak numbers were collected at the beginning of the rainy season and adult survival was longer than at Aripuanã.

Reports of the presence and absence of biting by Simulium damnosum Theo. in the Volta River Basin in 1962, 1966 and 1975 were used to identify occasions when sites were invaded by parous and nulliparous females. Circumstantial evidence suggests that this insect is a wind-borne migrant, and the weather before and during some of these invasions was examined. Although most invasions studied took place south of the Inter-tropical Convergence Zone, for the first time evidence is presented suggesting that migration also takes place to the north of this zone. Immigrants were captured at the invaded sites only when light winds or calms were present. This cannot, however, be used as proof that S. damnosum migrates and lands only where winds are light or it is calm because host-seeking is inhibited by high winds and the time of arrival, as opposed to capture on a host, is unknown. Until the factors initiating emigration, as well as the height, duration and number of flights in each gonotrophic cycle and the time of immigration are known, the present findings cannot be tested rigorously nor can wind records be used to trace the source of immigrants.