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.

Some eggs of Ephestia cautella (Wlk.) and E. kuehniella Zell. hatched after exposure to near 100% atmospheres of nitrogen (N2) or carbon dioxide (CO2) for up to 5 days at 15°C, 3 days at 20°C and 1 day at 25°C. The most tolerant age at the start of treatment at 25°C in E. cautella was 7–24 h after oviposition for CO2 and 7–30 h for N2. Generally, hatch was lower in CO2 than in N2 whatever the exposure, and lower for E. kuehniella than for E. cautella. Considerably more eggs of E. cautella aged 30 and 42 h hatched after exposure to N2 than to CO2, showing a toxic effect of CO2 in the absence of oxygen. Eggs of both species treated with either CO2 or N2 hatched 1–2 days later than controls, regardless of age or percentage survival.

Severe defoliation of cassava by Zonocerus variegatus (L.) can occur every year during the dry season in southern Nigeria, but the effect of such defoliation on tuber yield was not known. Experiments simulating different forms of damage and direct observation on damage by Z. variegatus indicated that tuber yield is reduced significantly by defoliation only towards the end of the dry season after natural leaf regeneration has begun, when its effect is to delay regeneration so that damaged plants lag behind those which are undamaged. Continuous defoliation over six weeks at the end of the dry season caused a mean crop loss of 63%, and simulated debarking a mean loss of 49%. Z. variegatus confined in plots until the end of the dry season caused a mean loss of 36%, losses being less than those caused by simulated defoliation because cropping took place sooner after the end of defoliation. Defoliation during the dry season caused no significant crop loss when damage occurred before leaf regeneration at the beginning of the following wet season. Monitoring of natural defoliation by Zonocerus in successive years showed there were considerable differences in amount and timing. It is concluded that crop loss due to Zonocerus damage is significant only occasionally despite defoliation occuring every year.

A suction trap for sampling small insects in areas without mains electricity is described. The traps were operated from two 25-ampere-hour 12-V batteries connected in parallel, giving an average airflow of 329–355 m3/h over a 12-h period. The trap was used successfully to catch first-instar larvae of Cryptococcus fagisuga Ldgr. in a beech forest in England.

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.

Quantitative observations on the biting activities of Simulium simplicicolor Lutz and S. sanguineum Knab s.1. at Aripuanã, Mato Grosso, Brazil, and S. guianense Wise and S. sanguineum s.1. at Uru´, Par´, were made during the wet and dry seasons between June 1978 and August 1979. The species demonstrated characteristic attacking patterns regardless of abundance or environmental conditions. S. simplicicolor, S. guianense and S. sanguineum s.1. at Uruá demonstrated bimodal biting patterns with early morning and late afternoon peaks. S. sanguineum s.1. at Aripuanã, however, bit throughout the day with three peaks of activity. Evidence is presented for circadian control of the biting patterns which are subject to modification by exogenous factors outside of an optimal range. S. simplicicolor seemed to be most affected by light intensity, whereas the other species were affected by variable combinations of light, temperature and humidity depending on the species and population. Physiological age sometimes also modified biting activity in S. simplicicolor. This variable was not studied in the other species. S. simplicicolor and S. guianense preferred biting man on the legs and S. sanguineum s.1. at Uruá preferred the upper torso, but S. sanguineum s.1. at. Aripuanã did not demonstrate a consistent preference for sites above or below the waist. Average engorgement times for all of the populations except the Uruá population of S. sanguineum s.1. were between 4·3 and 5·3 min.

The numbers of Glossina pallidipes Aust. and G. morsitans morsitans Westw. flying in and out of a large clearing in Zimbabwe were estimated from catches on unbaited electrified nets placed on the perimeter of the clearing. By estimating the numbers of flies that would encounter visual and olfactory attractants in the middle of the clearing, and from measurements of the numbers caught responding and estimates of the efficiency with which responding flies were caught, it was calculated that 80–100% of flying tsetse responded to stimuli they encountered. The importance of flight as a means of encountering host stimuli in woodland and open areas, and with mobile and stationary baits, is discussed.

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.

Observations are reported on diapause and laboratory breeding of Phlebotomus perniciosus Newst. and P. ariasi Tonnoir, the two phlebotomine sandflies incriminated as vectors of visceral leishmaniasis in southern France. Previous field studies had suggested that both species are univoltine in southern France, but the present laboratory investigations showed that diapause is obligatory for neither species. Temperature (both species) and photoperiod (P. perniciosus) were found to affect diapause-induction, and diapause was commonly determined before the overwintering stage (the fourth-instar larva). The results showed that P. perniciosus can be mass-reared for at least three uninterrupted generations each year if it is maintained at 28°C in LD 17:7. Further investigations are needed if P. ariasi is also to be bred in sufficient numbers for epidemiological experiments; its colonisation was prevented primarily by low fertility, and attempts at forced insemination were unsuccessful.

Among collections from natural microhabitats in coastal forests in Kenya, larvae of Eretmapodites quinquevittatusTheo. and E. silvestris conchobius Edw. were recovered almost exclusively from water-filled snail shells, while those of E. subsimplicipes Edw. were found in tree holes, snail shells, leaf pools, cavities in fungi and most often in fruit husks. E. quinquevittatus oviposited in shells of Achatina fulica set as traps during periods when E. s. conchobius was not abundant, thereby reducing niche overlap of these two species in this microhabitat. The eggs of all three species were moderately drought-resistant. In the laboratory, larvae of E. subsimplicipes preyed upon larvae of Aedes aegypti (L.) but pupated sooner when offered particulate food instead. E. quinquevittatus failed to complete development on a diet consisting only of prey larvae. Mating and oviposition of all three species was achieved in the laboratory, and blood-feeding was not a prerequisite for insemination of E. subsimplicipes.

Nocturnally active mosquitoes are attracted visually to large (1·5 × 2·4 m) unpainted plywood suction traps. Such traps, which discharge air horizontally in one direction only, were placed in an open field in Florida in various patterns to study the flight behaviour of mosquitoes. When four traps were placed 15 m apart in a column, the two end traps captured 83 or 53% more mosquitoes than the two inner traps, depending upon whether the air discharged from the traps was perpendicular to, or in line with, the trap column. When the traps were spaced 30 m apart, the end traps captured only 13% more than the inner traps, indicating that at this distance visual competition between traps was small. When 16 suction traps were spaced 15 m apart in a grid of four columns of four traps each, the traps at the four corners of the grid captured about 2·1 times, and traps between the corner traps along the edge of the grid 1·5 times, as many mosquitoes of most species as traps within the grid. Subsequently, four additional traps were placed 15 m beyond the corner traps, and these traps captured 3·3 times as many mosquitoes as traps inside the grid. Traps within the grid had four adjacent traps while traps at the edge, corner, and beyond the corner had three, two and one adjacent traps, respectively. The numbers captured by a trap at a particular location in the grid were inversely related to the number of adjacent traps, viz., suction-trap catches were decreased by about 33% as the number of adjacent traps were increased and thus each trap acted as a competing visual attractant on nearby traps. It was estimated that an isolated suction trap would capture approximately five times as many mosquitoes as a trap inside the grid. Assuming these differences between trap collections were caused by the distance at which mosquitoes respond to the traps and thus would be proportional to the visually unobstructed area about each trap, it was calculated that most adults responded visually to the traps from distances of approximately 15·5 to 19 m. Aedes vexans (Mg.) and Psorophora columbiae (D. & K.) were most responsive, followed by Culex nigripalpus Theo. and Culiseta melanura (Coq.) and then by Anopheles crucians Wied., P. ciliata (F.) and Uranotaenia lowii Theo. Only U. sapphirina (O.S.) and Culex quinquefasciatus Say appeared to possess visual ranges of 7.5 m or less. Visually conspicuous objects can serve as long-distance attractants. Low air velocities caused appreciable reductions in trap collections. At a distance of 15 m, the velocity of air discharged from the traps was only 0·6 m/s, but catches from a trap downstream of an adjacent trap were reduced by 17%. Catches from rows of traps downstream from one, two or three rows of traps were reduced by 15, 36, and 51%, respectively. Estimates of mosquito population densities in a natural environment will be affected by the differing visual attractiveness of objects of irregular distribution and sizes and their effect upon wind velocities.