A study of wing fray and ovarian age in females of Glossina morsitans centralis Machado in Botswana confirmed that although the relationship between the two was strong it varied from month to month. The rate of wing fray with age was greatest in the hot dry season, and in both very young and very old females it was affected by humidity. Both age and activity are manifested as fraying of the wings, but it is considered unlikely that wing fray could be used as a reliable measure of either. It is suggested that wing fray may impose a physiological limitation on the lifespan of tsetse flies and may consequently be a factor in population regulation.

Groups of Coptotermes acinaciformis (Froggatt) originating from six colonies, three taken from each of two widely separated localities in northern Australia (Townsville and Darwin), were kept at population densities of 0·005, 0·001 or 0·020 g termites/ml. Survival and wood consumption of the groups after eight weeks followed a similar pattern in the colonies from both collection areas. Groups exhibited least vigour at the lowest population density, most vigour at the middle density and slightly less than maximum vigour at the highest density. However, the actual values for survival and wood consumption varied widely between colonies, irrespective of their origin. The implications of these and related results for laboratory experiments which rely on survival and wood consumption as indicators of termite vigour are discussed.

A vehicle-mounted net was used to study the circadian flight activity of several species of Simulium in a northern Guinea savanna area in Nigeria during the dry season. The sampling method yielded large numbers of both sexes of Simulium squamosum (Endertein) of the, S. damnosum Theobald complex, S. hargreavesi Gibbins, S. vorax Pomeroy, S. adersi Pomeroy, S. hirsutum Pomeroy and other species. The main peak of activity of all species recorded occurred just after sunset and there was a smaller peak just before sunrise. Flies continued to be caught at a low level 2·5 h after sunset when sampling ceased. Differences in the activity patterns of S. squamosum males and females and of the other species were analysed. Of the S. squamosum females caught, 12% were blood-fed; these and gravid females were mainly active in the evening, while the blood-thirsty flies had a high level of activity throughout the day. Differences between species in the relative activity of blood-thirsty and gravid flies, and nulliparous and parous flies are noted.

The effect of quantitative and qualitative differences in maize leaf fed to larvae of Spodoptera exempta (Walker), and of larval density, on flight duration in female moths was investigated using a tethered-flight technique. Neither food deprivation nor diets of water-stressed maize influenced the proportion of moths flying for long periods. However, a significant increase in the incidence of long flights was recorded in moths from larvae reared at high densities. Significant differences were observed in the weights and sizes of moths from the different larval treatments. Wing-loading was shown to be a function of moth weight, with lighter moths having lower wing-loadings. However, wing-loadings of long-flying moths and those of short-fliers were similar, and it is concluded that the migratory potential of females of S. exempta cannot be predicted from moth weight or morphometric data. A feature of the results was the variable proportion of long-flying moths in the test and control groups, irrespective of larval treatment. Re-examination of the data showed that a high incidence of long flights was evident in the experimental insects at approximately one-generation intervals, and it is suggested that there is a major genetic component in the determination of flight capacity in this species.

The existence of a genetic component in the determination of flight capacity suggested by the results of previous experiments on the effects of environmental factors on flight performance in Spodoptera exempta (Walker) was confirmed by successful selection for and against the capacity for prolonged flight. The results of selection experiments were consistent with those expected when a polygenic character is subjected to directional selection. Heritability estimates for flight duration were 0·4 for overall heritability (mean offspring on mid parent regression) and 0·5–0·9 for single sex offspring on female and male parent regressions, demonstrating that flight capacity has a substantial additive genetic component. Although there can be no doubt that genetic factors play a major role in the control of migration in S. exempta, it is not yet clear whether flight capacity is a continuously varying character or whether discontinuous variation in the form of a genetically controlled flight polymorphism is involved. It is suggested that the life-history strategy of S. exempta is adapted to maximise dispersal in the rains when a massive extension of favourable habitat occurs, and to maintain populations in those habitats which remain favourable in the dry season. The present evidence suggests that this strategy is achieved by cyclic selection of genetically determined variability in potential flight capacity.

Baseline responses of United Kingdom field populations of Macrosiphum euphorbiae (Thomas) and Brevicoryne brassicae (L.) to demeton-S-methyl were investigated using the FAO-recommended dip-test bioassay. Dose-response lines were produced, and discriminating doses for the two species were derived from the results (320 and 500 mg a.i./litre, respectively) and validated by testing further field populations at those single doses. Of the 1620 individuals of M. euphorbiae and 330 of B. brassicae tested, none survived the discriminating doses.

Breeding of Simulium damnosum Theobald s.1., the vector of Onchocerca volvulus, had been eliminated by 1977 from about 654 000 km2 of the Onchocerciasis Control Programme in the Volta River Basin Area (OCP) of West Africa. Nevertheless, migrating adult females continually invaded the controlled area, being blown on the prevailing south-westerly winds from uncontrolled breeding sites beyond the south-western border of the OCP area. Graphs of numbers of females caught per man per day (the daily biting rate) throughout the wet season, March to October, at 16 sites in 1977 within the OCP controlled area were remarkably similar in pattern from site to site over a range of about 500 km downwind. In 1978, only seven sites within the OCP area were similarly monitored, and the graphs were different in pattern from those in 1977, when they each consisted of three or four well-defined waves or cycles of daily biting rate which could be easily identified and traced across country, their times of occurrence lagging increasingly as the distance of the site from the south-western border of the OCP area increased. Four methods were used to demonstrate and estimate the lag: visual comparison of seasonal graphs; comparison of the mean dates of cycles at different sites and the regression of these dates on distance from the south-western border; the dates when particular cumulative percentages of the total season's catch occurred at each site and their regression on distance; and principal coordinate analysis of the data and its relation to distance from the south-western border. Statistically significant lags were demonstrated and averaged one day for every 10–30 km from the border in 1977, which indicated an average speed of migration across country. In 1978, a rate of one day per 7–35 km was indicated. Where some graphs at outlying sites were anomalous, possible alternative sources of immigrant flies are considered. The possible behaviour of flies in causing the lag is discussed.

Detailed studies were conducted over a five-year period at a rice farm in the Philippines on the flight activity of Nilaparvata lugens Stål) and Sogatella furcifera (Horváth). Suction traps were used to measure aerial density, and catches included immigrants, emigrants and insects undertaking trivial flight. Activity was partitioned using a variety of other trap types. Emigration was effectively monitored using net canopy traps and immigration was best measured using green water traps. Yellow water traps also measured immigration, but when macropterous adults were being produced within the plot, insects undertaking trivial flight were also caught. The light-trap caught immigrant and over-flying migrant insects.

Energy-dispersive X-ray spectrometry was used to make quantitative determinations of the elemental composition of plasma-ashed apterous individuals of Rhopalosiphum padi (L.) and Metopolophium dirhodum (Walker). R. padi was reared on 24 plant–soil combinations and M. dirhodum on nine plant-soil combinations. Analyses were done for 12 elements: Na, Mg, Al, P, S, Cl, K, Ca, Mn, Fe, Cu and Zn. Principal components analyses of individuals showed no distinction, in either aphid species, between insects reared on any plant–soil combination, whether all elements, elemental sub-sets, soil sub-sets or host-plant sub-sets were considered. When group means (mean for all individuals from a particular plant-soil combination) were used in principal components analyses, five groups of R. padi could be distinguished from the other 19, although neither set could be further separated. Four of the five distinguishable groups were from plants that grew particularly poorly, and the fifth was from plants in a soil in which all host-plants grew less well than in other soils. There were no distinct separations between groups of M. dirhodum, though there were slight indications that soils were distinguishable. In both R. padi and M. dirhodum, elemental differences involved the minor elements, particularly Mn, Fe, Cu and Zn. The uniformity of elemental content in the apterae of both aphid species may be a consequence of genetic uniformity within clones of parthenogenetically reproducing species.

Ninety-two individuals of Sitobion avenae (F.) collected throughout Britain in 1979 and 1980, were cloned and investigated genetically by electrophoresis of 14 enzymes representing 26 loci. Percentage polymorphism (P) differed considerably between years, 64% (16/25 loci) in 1979 and 19% (5/26) in 1980, whereas average heterozygosity () was low (ca. 2%) in both years and confined mainly to one locus, EST-1. The prevalence of homozygous allozyme variation supports ecological findings suggesting S. avenae to be largely anholocyclic in Britain. In 1981 and 1982, large populations, sampled from 11 sites in Britain and Spain, were examined at 13 loci. ranged from 2 to 7·6%, with heterozygosity restricted again mainly to EST-1. Some alleles were unique to certain geographical regions (including Britain or Spain); others showed significant spatial, and in two British populations examined in successive years, temporal frequency differences. Calculating Nei’s genetic identity (I) and distance (D) coefficients for each population pair mostly gave I>0·8, D<0·2 with overall means (± s.e.m.) of 0·896 ± 0·006 and 0·111 ± 0·006, respectively, which are comparable with geographical population values for other insects. D was poorly correlated with geographical distance, although values were slightly greater (ca. 0·025) for international population comparisons and did not overlap on a principal coordinates plot. The overall population similarity suggests substantial inter-population gene flow; geographical barriers may have restricted movements but seemingly have not led to allopatric race formation. P and values resemble those for many other aphids, but H values are lower than typically found in other insects. Possible causes of this heterozygote deficiency are discussed.

Ways in which the bionomics and dynamics of populations of Musca domestica L. can influence the development of insecticide resistance, and how resistance genes spread within and between farms was investigated in a three-year study of the biology and movement of flies on 63 pig-rearing farms in south-eastern England. House-flies survived winter only on 12 ‘overwintering’ farms where they bred in heated pig-rearing houses (‘closed buildings’) throughout the year. In late spring they appeared out doors, and their descendents founded populations on neighbouring ‘summer’ farms where pigs breed only in unheated (‘open’) buildings. There, flies reached peak numbers in August–September and died out by mid-November. Gene flow within and between farms was studied indirectly by mark-release-recapture of colour-marked adults, and directly by monitoring the diffusion of the visible marker gene bwb (brown body) introduced into indigenous house-fly populations. Although movement between open buildings within a farm was unrestricted, dispersal between farms was limited, and gene flow between even adjacent closed buildings was indirect, and required more than one generation. Likewise, indirect and gradual gene flow during summer probably accounted for the similarity in type and frequency of other independent genetic markers of local overwintering populations. Thus closed buildings played a key role in house-fly ecology and population genetics. Unfortunately, control with persistent insecticides in these buildings ensures efficient resistance selection, ultimately resulting in its spread to all pig farms. Less selective control practices are needed at these sites.

The black markings on larvae of Cactoblastis spp. can be used to separate different biotypes or species. These markings are figured, together with host and locality records for ten distinct biotypes or species, at least five of which are undescribed. Past introductions of C. cactorum (Berg) and Cactoblastis spp. to Australia and elsewhere are reviewed, and it is suggested that some of the undescribed biotypes might be of value in the biological control of Opuntia spp.

Genetic (electrophoretic) variation was examined in the two pest species of Heliothis found in Australia, H. armigera (Hübner) and H. punctigera Wallengren. They could be differentiated by seven loci which enabled identification of individual eggs and small larvae not normally distinguishable by their morphology. The traditional criteria for distinguishing the larger larvae of the two species were shown to be unreliable. The genetic distance between the two species was 0·34 ± 0·02. The percentage of loci polymorphic in both species, 32%, and the mean heterozygosities, 11·3% for H. armigera and 10·8% for H. punctigera, are lower than those reported in the American species, H. virescens (F.) and H. zea (Boddie). Populations throughout Australia were differentiated from each other, but there did not appear to be a marked geographic pattern to the variation. Genetic distances between populations of H. armigera were low (<0·01). It was concluded that the effective population size of Heliothis is large and that significant gene flow probably occurs between widely separated regions.