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.

The control of Simulium has always relied largely on the use of insecticides against the larvae, and this is the case in the current large-scale Onchocerciasis Control Programme against the vector S. damnosum Theobald in West Africa. Resistance to temephos has occurred in some vector species, and it is necessary to find alternatives to this preferred larvicide. In order to provide a frame of reference for the development of new larvicides or formulations, the literature relating to larval filter-feeding behaviour is first reviewed in detail. Then the physico-chemical conditions in larval habitats are outlined. The types of formulations and classes of insecticide used in Simulium control are considered, with particular attention being given to emulsifiable concentrate formulations and the reasons for their effectiveness. Particulate formulations, which have been recommended on environmental grounds, are also discussed. Techniques used in the screening of larvicides are considered, and it is concluded that flow-through systems are necessary; mini-gutter tests conducted using water and fauna from rivers to be treated are to be strongly preferred, followed by stream trials. Knowledge of Bacillus thuringiensis var. israelensis as a Simulium larvicide is reviewed in detail. The environmental impact of control of Simulium larvae, both in the tropics and the temperate zone, is extensively reviewed. Throughout, key features which might lead to improved larvicide formulations and testing procedures, together with serious gaps in our knowledge are emphasized.

Examination of the polytene chromosomes and cross-breeding data confirmed the specific status of Anopheles dirusPeyton & Harrison within the complex of A. balabacensis Baisas. The data also strongly suggested that A. dirus itself is a complex of at least two species, one of which, a hitherto unrecognized species, provisionally designated A. dirus species B, previously known as the Perlis form, occurs in northern Peninsular Malaysia. A distinct population from Thailand was designated A. dirus species A. The mosquitoes studied also include material from natural populations in Sabah, here provisionally designated A. balabacensis s.s., and may represent the first genetic analysis of this species. The Sabah material is distinct from either of the A. dirus forms. Hybrid males from crosses of A. balabacensis × A. dirus species A and of A. dirus species B females × A. dirus species A males were sterile. Chromosome studies also showed that reproductive isolation was accompanied by genetic changes in both the autosomesand X chromosome in the hybrid larvae.

Sitophilus oryzae (L.) is a pest of stored cereals and, because most populations are unable to survive on yellow split-pea and other legumes, admixture of legume with cereal has been suggested as a control method. However, some geographical strains have been found able to feed and breed on yellow split-pea. The ability is heritable and known to be controlled in one strain by a single recessive, autosomal gene. The inheritance pattern of the ability was investigated in three different geographical strains, two of which could feed and breed on yellow split-pea and one which could not. The genetic mechanism controlling the character in these strains was not a simple recessive allele, but differed between the two pea-breeding strains and was co-dominant with the inability to feed on yellow split-pea inthe non-pea-breeding strain. The results indicate there is considerable between-strain genetic variability for the character, which may render cereal-legume mixture of little value as a control method against S. oryzae.

A simple Perspex and stainless steel device is described suitable for rapid, simultaneous homogenization of numbers (60) of small insects individually for electrophoresis. Since this device significantly decreases the time taken for preparation of samples (commonly a rate-limiting stage in electrophoretic studies), it may be of value to other workers in entomology and insect population genetics.

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.

Reduction in growth of saplings of Eucalyptus deglupta resulting from die-back caused by Amblypelta cocophaga China was studied in forestry plantations in the Solomon Islands. At a standard spacing of 10 × 3 m, a comparison was made of tree growth and incidence of A. cocophaga attack on saplings planted in strips 2 m wide cut through secondary forest, with those from which all inter-row vegetation was cut back prior to planting. Initially, a greater proportion of trees was infested on the cleared than the uncleared plots, but at the end of the first year, at which time the attack was at its peak, no differences could be detected. From the fifth to the thirteenth month after planting out, uninfested trees on the cleared plots increased in height at an average rate of 60 cm per month. For every week that at least one A. cocophaga was recorded on a tree, this rate was depressed by 1·3 cm. On the uncleared plots, the average rate of increase of uninfested trees was only 42 cm per month and this was reduced by 1·0 cm for every week that an insect was recorded. By the end of the first year, an estimated 37% (in cleared plots) and 41% (in uncleared plots) of the potential stand was rendered useless for future timber production due to A. cocophaga damage. In terms of total stem volume (not log production), about 1 m3/h out of a potential 3 m3/h was lost in the uncleared plots and 0·2 m3/h out of a potential 0·6 m3/h in the uncleared ones. Whilst clearing did not reduce the incidence of A. cocophaga attack, the advantage of clearing in terms of increased tree growth was considerable.

The hymenopterous parasite, Aphidius sonchi Marshall, has been introduced into Australia as a biological control agent of the sowthistle aphid, Hyperomyzus lactucae (L.), the principal vector of lettuce necrotic yellows virus disease. Some aspects of its biology were studied in the laboratory. Females reared at 22°C contained a mean ± s.e. of 179·4 ± 10·26 eggs on emergence, and more eggs were formed during adult life. Unmated females produced male progeny only; mated females produced progeny of both sexes. At 22°C, both males and females mated within 12 h of emergence. Virgin females could mate successfully after having commenced oviposition and switch to producing progeny of both sexes. At 20°C, both virgin and mated females started oviposition within 7 h of emergence. The female oviposited in all nymphal instars and both apterous and alate adults of the host. Only one egg was laid per insertion of the ovipositor. Superparasitization was common, but only one parasite per aphid survived to the adult stage. Females at 22°C and LD 12:12 oviposited during both the photophase and the scotophase; the proportion of eggs laid in the scotophase was correlated with the availability of hosts. Adult females lived longer in the absence of hosts than in their presence and lived longer than males, and those supplied with water and honey lived longer than those without. Facultative diapause occurred. The integumental coloration of adults varied according to the temperature during their immature stages. Females of A. sonchi oviposited readily in Macrosiphum euphorbiae (Thomas), but their progeny did not develop beyond the egg stage. A. sonchi was parasitized by Alloxysta ancylocera (Cameron), Pachyneuron aphidis (Bouché) and Dendrocerus carpenteri (Curtis) in the field.

In the Zambezi Valley of Zimbabwe, the numbers of Glossina morsitans morsitans Westwood and G. pallidipes Austen electrocuted on grids placed across their flight paths as they arrived at various natural and synthetic odour sources demonstrated that ox odour comprises two broad fractions of attractants. One fraction can be trapped by a charcoal filter and, in part, consists of 1-octen-3-ol. A more volatile fraction passes through the filter and, in part, consists of carbon dioxide and acetone. Levels of acetone and 1-octen-3-ol in ox odour varied considerably, up to maxima of 24 mg/h and 0·025 mg/h, respectively. Catches were roughly doubled when octenol at 0·5 mg/h was added to ox odour, but declined when the dose was increased to 50–500 mg/h. A synthetic odour consisting of 2 litres of carbon dioxide/mm, 5 mg of acetone/h and 0·05 mg of 1-octen-3-ol/h, was nearly as effective as ox odour for G. m. morsitans but only half as effective as ox odour for G. pallidipes. Increases to the doses of each attractant in the synthetic odour increased the catches, to roughly double those with ox odour. Data for other Diptera are also presented.

In mature Valencia orange trees at three sites in the Transvaal lowveld, there was a variable differential between levels of Aonidiella aurantii (Maskell) in the upper and lower parts of the trees. At one site there were high scale levels in the crowns of the trees as a result of past poor chemical spray procedure. In recent years, pest management has maximized on the use of natural enemies, especially Aphytis spp. However, the natural enemies have not been able to ameliorate the crown problem. At generally high levels of Aonidiella aurantii, the natural enemies were ableonly, more or less, to maintain the average overall level of the scale from one year to the next; they could not bring it down. This arose each year from too many scales escaping parasitism and reaching the relatively invincible adult stage early in the season. As the behaviour of the parasitoids was inversely density-dependent at these relatively high scale levels, this led to a greater increase in scale numbers, leading eventually to up to 90% of the population (excluding crawlers) being composed of adult females. The inverse density dependence was also partly because the majority of single scales escaped parasitoid attack. In the lowveld, it is a prerequisite that the density of A. aurantii first be lowered by an introduced natural enemy (e.g. the coccinellid Chilocorus nigritus (F.)) that attacks the adult stage and/ or by chemical means before maximal use is made of the regulatory influence of the existing natural enemies, particularly Aphytis spp.

Nine types of plastic ear tags impregnated with organophosphorus, amidine or synthetic pyrethroid compounds were applied to both ears of groups of five Maasai zebu cattle in Narok District, Kenya, and grazed together with five untagged cattle to which no acaricides were applied. Most of the tag types gave highly efficient control of Rhipicephalus appendiculatus Neumann attaching to the head and ears of the cattle, which lasted up to 160 days after application and often completely prevented tick engorgement. All the chemical groups were effective. The most effective tag was a combination of amitraz and permethrin which gave better control than either chemical on its own. Control of Boophilus decoloratus (Koch), Amblyomma cohaerens Dönitz, A. variegatum (F.) and R. evertsi evertsi Neumann attaching to the bodies of cattle was less effective, although most of the tags exerted some effect. Rainfall appeared to reduce the degree of control by the tags. A role for such impregnated ear tags for the control of cattle ticks in Africa is suggested.

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.

Four species of hypogeic mealybugs are known to infest African violets (Saintpaulia spp.). These are Rhizoecus americanus (Hambleton), R. cacticans (Hambleton), R. dianthi Green and R. saintpauliae sp. n. The last species has some striking characters and is described here from specimens from S. ionantha in a nursery in Thailand. None of these species is known to occur on plants in their natural habitat, the mountainous areas of Kenya and Tanzania, where the survival of most of the 20 species of Saintpaulia is threatened. Although infestations of R. dianthi on African violets may be severe, the mealybugs only affect these and other potted plants in the extensive horticultural trade. A key is provided to separate the four species.

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.

In Zimbabwe, the catches of Glossina morsitans morsitans Westwood and G. pallidipes Austen in traps were increased by up to three times by releasing 1-octen-3-ol at 0·05–50 mg/h or acetone at 5–5000mg/h near traps, but in some circumstances 1-octen-3-ol at 5–50 mg/h reduced catches. Carbon dioxide at 0·02–20 litres/min increased catches by up to ten times. A mixture of all three chemicals increased the catches by up to 60 times. Each of the three chemicals attracted both species of flies from a distance; carbon dioxide also enhanced trap-entering and alighting responses. Acetone with 1-octen-3-ol can increase by several times the numbers of flies that contact visual baits suitable for exposing them to insecticide. Data for other Diptera are also presented.

Laboratory experiments showed that 4°C, rather than 6°C as used previously by most authors, was a suitable base temperature for calculating the number of day-degrees C required to predict the time of emergence in the spring of Delia radicum (L.); 1 February was an appropriate date to start the accumulation, as more than 50% of the pupae had completed diapause by this time and were therefore able to proceed with their development.The time of 50% fly emergence in the spring was estimated more accurately from accumulated day-degrees 6 cm deep in the soil, the average depth of overwintering puparia, than from accumulated air day-degrees calculated from standard meteorological measurements of air temperature. At Wellesbourne, England, approximately 179 ± 8 soil day-degrees above 4°C or 230± 10 air day-degrees above 4°C were required for 50% emergence in the spring. In general, males emerged 25–50 day-degrees above 4°C (4–8 days) before females. A further 60–170 day-degrees above 4°(2–5 weeks) then elapsed before maximum fly activity occurred in new host crops.

Mating disruption of Cydia molesta (Busck) was attempted by treating, with pheromone, all orchards in a small but discrete peach-growing district in New South Wales for two successive years. In the final year of the trial, two former control orchards were also treated with pheromone. The efficacy of the treatment was examined by monitoring fruit and shoot damage, male captures in pheromone traps, captures of both sexes in feeding lures, mated status of wild females and numbers of immature stages in trap bands. It was concluded that mating disruption was a viable alternative to conventional insecticides.

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.

An assay based on recovery rates of released laboratory-reared flies was used to compare the field performance in Australia of a series of strains bearing compound chromosomes with that of wild-type strains of Lucilia cuprina (Wiedemann). The compound chromosome strains tested all performed less well than the wild-type strains. Four of the former were recovered on average 0·37 times as readily as the average wild-type strain, and one was recovered 0·65 times as readily. The compound chromosome strains differed in the selection pressure they had been exposed to in the field, which had selected among the various compound chromosomes in an original strain and in the extent to which their non-compound chromosomes had been replaced by recently collected field material. The strain that performed best had been exposed to the most severe selection pressure, overwintering in the field, and had had much of its non-compound genome replaced. Among the group of strains with similar performance, some had had their non-compound genome replaced with field genetic material.

Regular catches of males of Spodoptera exempta (Walker) were made in 41 pheromone disc traps scattered throughout Malawi in 1978–82. Each trap had a vial, replaced monthly, containing 2 mg of a 13·3:1 mixture of two sex-pheromone components of the female. Over the five-year period, males were caught every month at a majority of sites throughout the country, suggesting that they came from populations resident in Malawi. Sites at which moths were regularly caught had areas with green grass throughout the year which could have sustained larvae within their vicinity. A few sites at which moths were caught only occasionally had very dry immediate surroundings in the dry season, and it is suggested that moths caught at these sites are primarily migrants from either within or outside Malawi. There was no obvious relationship between site elevation, monthly rainfall and monthly moth catches or whether moths were caught persistently or irregularly. The results strongly suggest that some of the moths captured throughout the year in Malawi developed locally while some originate in other countries such as Mozambique.