Anopheles minimus Theobald was studied in four villages that had experienced differing levels of DDT application during malaria control operations in the foothills of northern Thailand. During times of high population level, the behaviour of the mosquito was assessed with respect to man-biting indoors and outdoors and feeding from domestic bovids. Its responses in villages recently treated with DDT differed from those in villages that had not been treated for several years, so that the insecticide had little direct lethal effect. Furthermore, the influence of the insecticide on the behaviour of the insect was considerably longer than is the lethal effect of the chemical. There was a suggestion that the taxon A. minimus may include two or more morphologically-cryptic species.

The development of Onitis caffer Boheman in cattle dung was studied in the laboratory. The larvae feed on the dung in which the eggs are laid. Egg to adult development at 25°C was completed in 24·7 weeks by a strain from a winter rainfall (WR) area of South Africa and 29·4 weeks by a strain from a summer rainfall (SR) area, and occurred without diapause. Maximum larval dry weight was achieved mid-way through the third larval instar, after which the larva emptied much of its gut to form a protective faecal shell, in which pupation occurred. At 20°C, 20% of WR larvae developed without diapause and the adults emerged after 33·5 weeks, whereas the remaining 80% of adults emerged after 80·1 weeks. In the SR strain, 70% emerged after 37·1 weeks without having entered diapause, while the remaining 30% emerged after 83·8 weeks. Thus, the period of diapause for both strains was 47 weeks and occurred in the third larval instar. At 15°C, 74% of WR larvae had pupated by 153 weeks, with a mean development time of 121·8 weeks. Zero development temperatures were 10·4°C (WR) and 10·1°C (SR), and day-degree requirements for development without diapause at 20°C were 2251 (WR) and 2571 (SR).

The citrus pest Scirtothrips aurantii Faure shows a positive phototactic response to yellow surfaces, particularly fluorescent yellow with peak reflectance at about 525 nm. A fluorescent yellow sticky trap was devised. Impact of individuals on the trap surface was principally random. Taylor's power law gave a generalized value of 1·42 for slope of b. Widespread geographical locations gave similar values for biologically significant values of b. Habitat differences within one geographical area influenced b, which was highest in natural vegetation and lowest in certain citrus monocultures. Three traps per orchard (>5000 trees) were practicable, and produced statistically realistic results. The period during which S. aurantii can damage fruit was divided into a longer risk period and a shorter, central critical period. Where S. aurantii was present on the traps at less than nine individuals per set of three traps throughout the central critical period and 20 during the late risk period, the percentage of fruit so damaged as not to be of export grade was less than 1·0. This method of monitoring was sufficiently robust to allow for some human error in reading the traps under commercial conditions, and to permit variability in placement of the traps in the orchard.

In order to understand how the malaria vector Anopheles arabiensis Patton exists in the extremely hot and arid environment (mean annual rainfall 21 mm) in Northern Province, Sudan, regular sampling from breeding places and resting sites was undertaken during 1978 and 1979 at four villages along the River Nile downstream (i.e. northwards) from Dongola. The population density of A. arabiensis was lowest during the flood season (July—October) and increased as the river flow decreased during November—June. Thus there was an inverse relationship between the Nile water level and A. arabiensis production. Prolific breeding in riverside pools was the main source of A. arabiensis as the river receded. During the annual flood, when riverside pools were all inundated, A. arabiensis continued breeding at low densities in sheltered sites such as wells and pits. Breeding also occurred in all months in association with the weed Potamogeton crispus in slow reaches of the river. Adult females fed regularly on blood, with gonotrophic concordance in all months, and there was no evidence of aestivation. Outdoor biting activity occurred throughout the night, with a peak between 2100 and 0500 h. Daytime searches indoors and outdoors indicated that resting females A. arabiensis are almost entirely endophilic in the study area.

A malathion-resistant strain of Oryzaephilus surinamensis (L.) was subjected to selection with malathion for ten generations at three doses, 65, 260 and 390 mg/m2. The relative fitness of the resistant homozygote, the heterozygote and the susceptible homozygote were estimated at each dose and in an untreated control population by comparing the change in frequency of the susceptible homozygote from generation to generation. In the absence of the insecticide, the resistant genotypes had a fitness coefficient of 0·82 compared to the susceptibles, whereas following selection at the highest dose of malathion, the fitness coefficient of the susceptible homozygote was 0 and that of the heterozygote 0·4, compared to the resistant homozygote. With selection at the highest dose of malathion, the frequency of the resistance gene rose from 0·5 to around 1·0 during the experiment, and this was accompanied by a 2·3-fold increase in the resistance factor at the ED50. A model is provided to show how the data collected in these experiments can be used to predict the increase in resistance under various treatment regimes. The model shows that although resistance would be delayed longest at the lowest dose, such a dose would fail to control the pest population. Using the data from these experiments, the model predicts that the best combination of control and delay of the spread of resistance would be achieved by using the highest dose of malathion while allowing the maximum acceptable proportion of beetles to remain untreated.

With the decline in production of new insecticides, the development of resistance is likely to become more of a problem than at present. Models of the spread of resistance genes may become integral parts of many management programmes. A critical examination is made of the classical theory of inheritance of resistance, i.e. the spread of a single resistance- conferring allele through a population. The theoretical considerations suggest that simple Mendelian inheritance is unable always to account for the development of resistance. It is suggested that some resistance factors may be under multigenic control and that such inheritance could account for the rate at which resistance sometimes develops. Following on from the theory, an analysis was made of time to knockdown and dry body weight in Sitophilus oryzae (L.). A half-sib experimental design was employed which enabled quantitative analyses of the characters to be made. Both characters had substantial heritabilities and were phenotypically correlated. The analysis also indicated a positive genetic correlation between the characters. The implications for the development of tolerance in the light of the genetic analysis are discussed.

Females of Anopheles minimus Theobald at a site in northern Thailand that were caught on man or domestic bovids and were released showed a significant tendency to return to the type of host upon which they were first caught (P = 0·03). From a total of 3526 individuals marked and released, 51 were recaptured. A simple explanation is that the taxon is in fact a mixture of two or more morphologically cryptic species, a suggestion already indicated by previous studies.

The status and taxonomy of the west Palaearctic Pyrus-feeding psyllids are reviewed, and keys for the identification of adults and larvae are given. The species, now referred to the genus Cacopsylla, have been much confused. They are shown to comprise seven distinct species: C. pyrisuga (Förster), C. pyri (L.) (summer form pyrarboris, winter form pyri), C. pyricola (Förster) (summer form pyricola, winter form simulans), C. bidens (Šulc) (summer form vasilevi syn. n., winter form bidens), C. notata (Flor) sp. rev., C. permixta sp. n. (= simulans sensu Loginova and Gegechkori nec Förster) and C. fera (Baeva). Psylla horvathii Šulc and P. vicina Šulc are synonymized with C. pyricola; P. picta is regarded as a nomen dubium. Information is given on the host-plants and distribution of each species.

Six hundred and twelve anthropods from 11 families collected in and around cattle dung in south-western Australia were screened using a general antiserum against all developmental stages of Musca vetustissima Walker with gel precipitin and immunoelectroosmophoresis (IEO) tests. Positive results were found in Staphylinidae (65%), Histeridae (64%), Carabidae (12%), Dermaptera (21%) and Lycosidae (27%). The relative proportions of predator species varied in different sites, but three staphylinids (Leptacinus socius (Fauvel), Philonthus longicornis Stephens and P. subcingulatus MacLeay) and one histerid (Saprinus sp.) were widespread and numerous and consistently had a high proportion of positive results. Compared to precipitin tests, IEO was found to extend detection times for a single meal from two to five hours for small staphylinids and from 24 to 36 hours for larger carabids. In subsamples of P. subcingulatus and Saprinus sp. collected on the same day at one site, the relative proportions of positive results using IEO and gel precipitation, respectively, were 74 and 23% for P. subcingulatus and 95 and 53% for Saprinus sp.

A key is provided to distinguish the three species of Planococcus occurring in the Mediterranean Basin, P. citri (Risso), P. ficus (Signoret) and P. vovae (Nasonov), and their nomenclatural histories are reviewed. Notes on economic importance, host preferences, distribution and taxonomy are given for each species. Pseudococcus citrioides Ferris is synonymized with Planococcus ficus (Signoret), Pseudococcus lindingeri Bodenheimer is transferred to Planococcoides, Pseudococcus inamabilis Hambleton is synonymized with Planococcus vovae, and Allococcus Ezzat & McConnell is regarded as a subjective junior synonym of Planococcus Ferris. A new genus, Delottococcus, is erected to contain a group of species previously placed in Allococcus.

A sandwich enzyme-linked immunosorbent assay (ELISA) test was developed to detect blood-meals in insects and identify the host fed on. The test proved both sensitive and specific. Very small quantities of fresh blood (about 0·02 μl) can be detected; in practice, this enables blood in mosquitoes which are about three-quarters gravid to be identified. In trials in both Zambia and Britain, positive reactions were easily identified visually; consequently, this enabled the ELISA technique to be used as a routine field test. In addition to those of mosquitoes, blood-meals of a few Culicoides species were also successfully identified.

Three populations of Aonidiella aurantii (Maskell) were studied on orange trees at two sites in the hot Transvaal lowveld in South Africa. The first two were on the same trees, which had severe scale in the tree crowns and a low infestation in the bottoms. The third population, at a second site, was high and relatively evenly-spread over the whole tree. In previous years, the parasitoids Aphytis africanus Quednau and A. melinus DeBach had been unable on their own to reduce the high scale populations. Once a certain scale density level on the tree framework had been breached, a proportionately large number of susceptible scales escaped parasitism and reached the gravid female stage, which is invulnerable to attack. The ineffectiveness of parasitoids in these circumstances, resulting partly from their narrow niche breadth, was compounded by peak numbers only being reached late in the season. By this time, the large number of adult scales had already rendered the fruit unmarketable. In both sites, the predator Chilocorus nigritus (F.) was introduced and the trees also received commercial applications of petroleum oil. In one site, this oil treatment was restricted to the tree crowns. Although overall parasitism of vulnerable stages was relatively unaffected by these abiotic and biotic controlling factors, there was a shift to increased percentage parasitism of the virgin female away from the other susceptible stages. In addition, it was confirmed that the broad attack niche provided by C. nigritus, which preys on all developmental stages of the scale, readily complements parasitoid activity and can be of major economic importance.

In Zimbabwe, the catches of Glossina pallidipes Austen and G. morsitans morsitans Westwood in traps were roughly doubled by the presence of two bushpig bedding sacks or jars containing 200 ml of urine from ox or buffalo. The main effect of these residues was to increase the trap-entering responses of tsetse once they reached the trap; in addition, the urine brought G. pallidipes to the traps. The efficacy of the residues persisted for at least two months after initial exposure, although urine on soil was ineffective after two days. Efficacies were not affected by the presence of 1-octen-3-ol, acetone or butanone as additional attractants but were lower in the presence of carbon dioxide and lower with electrified visual targets than with traps. A ten times increase in dose caused no clear increase in catches, ten jars of urine being repellent, but catches increased when the urine and sacks were used together.

An attempt to eradicate Glossina pallidipes Austen from the Lambwe Valley of western Kenya by sequential aerial application of endosulfan aerosol spray is described. The operation was ultimately unsuccessful, even after nine sprays of relatively heavy dosages of insecticide. Survivors were present throughout after each spray, and females mated and bred between sprays. The population was reduced by over 99·9% in main habitats of thicket and woodland and by about 90% in conifer plantation. The outcome of a model of spray effectiveness suggested, however, that the final reduction in population size was the cumulative effect of only about a 90% kill per spray application. Post-spray monitoring showed that the tsetse population in thicket returned to its pre-spray level in little more than 12 months and became stabilized thereafter. Elsewhere, recovery was much slower and more variable. Evidence was found for population regulation by density-dependent emigration of flies. Calculations of population growth rate gave an instantaneous rate of increase of 0·0148/day, equivalent to a finite rate of increase of 1·568/month or a doubling time of 47 days. This permitted a 90-fold increase in population size over a ten-month period of unrestricted growth. The failure to achieve eradication is discussed in terms of certain operational shortcomings and environmental constraints which exist in the Lambwe Valley.

Indirect and direct measures of parasitoid activity were taken in grassland and autumn-sown cereals in southern England between 1979 and 1981. Studies of anholocyclic aphid populations in the winter months were followed through to parasitism of the main pest species, Sitobion avenae (F.), during the period of population increase in April and May. Aphidius spp. parasitized artificially-established colonies of cereal aphids in ryegrass in every month between December and May of both seasons, but there was no Aphidius activity until March-April in winter cereals sown early enough to receive an autumn input of aphids and parasitoids, apparently due to the small amount of physiological time that accumulates before temperatures drop in the winter months. A. rhopalosiphi De Stefani Perez and A. picipes (Nees) were completely dominant over other parasitoid species in the winter and spring period. Natural populations of Aphidius adults and parasitized aphids were low (<2/m2) in both winters, and percentage parasitism of S. avenae measured by dissection in March and April did not exceed 11·7%. Rates of S. avenae parasitism in many winter wheat fields peaked in May, before the peak and rapid decline in aphid populations. The significance of winter and spring parasitoid activity to the survival of the parasitoid and effects on pest aphid peaks are discussed.

A radioimmunoassay (RIA) was developed that utilizes 125I-linked Protein A as a tracer to detect the presence of antibodies to an antigen of Mansonia larvae. Antiserum was made by periodic injections of ground gut of fourth-instar larvae of M. dyari Belkin, Heinemann & Page into a rabbit, bleeding the rabbit by cardiac puncture and separating the serum. Using the rabbit antiserum at various dilutions, the specificity of the antibody to Mansonia was examined in tests with seven other mosquito species of different genera. Although there was low-level cross-reactivity with all the other species, the differences in reactivity between those and Mansonia larvae ranged between 2·5 and 8·4-fold; therefore, positive identification was possible. Furthermore, one fourth-instar Mansonia larva could be detected within a predator (fourth-instar larvae of Toxorhynchites rutilus rutilus (Coquillett) 48 h after consumption using the RIA.

Spodoptera exempta (Walker) occurs very widely in Africa south of the Sahara and in south-western Arabia, and more intermittently in the eastern Indian Ocean and Pacific areas. Throughout its range, the extent and frequency of its attacks have increased markedly, especially in the last 10–15 years. In parts of Africa and in south-western Arabia it is now regularly a seasonally important pest; examples are given of monthly distribution maps of the frequency of its attacks in this region. Maps such as these provide a useful and wide-based perspective for those concerned with prediction, survey and control of S. exempta in a more limited area and with little or no access to information from other territories. Year to year variations within the general patterns derived from many years' records are illustrated by the distribution of outbreaks in three recent seasons, in all of which there were outbreaks in at least seven countries of central and eastern Africa, in two years in Arabia, and in one year also in southern and western Africa.

Since Maconellicoccus hirsutus (Green), a pest of many plants including Hibiscus, was introduced into Egypt in 1908, probably from the Oriental Region, it has spread to much of tropical Africa. There is little information available on its control, but the encyrtid Anagyrus kamali Moursi is known to give good control in Egypt. The ladybird Cryptolaemus montrouzieri Mulsant is a voracious feeder on M. hirsutus in Egypt, but it does not survive the Egyptian winter, although it may be useful in the tropical areas. M. perforatus (De Lotto) is synonymized with M. hirsutus, and the distribution and host-plants of this species in Africa are discussed. A lectotype is designated for M. ugandae (Laing), a species now known to occur throughout tropical Africa, especially on coffee and cocoa. It is illustrated and redescribed and compared with M. hirsutus. M. bardus De Lotto, known from South Africa only, is excluded from the study because it probably belongs to the genus Chorizococcus.

Five strains of Culex pipiens L. (four resistant and one susceptible) were compared at the fourth larval instar for tolerance to organophosphate, carbamate and pyrethroid insecticides, with and without the addition of three synergists (piperonyl butoxide, triphenyl phosphate (TPP) and S, S, S-tributyl phosphorotrithiote (TBPT)). The DAR/D strain from Tanzania showed the highest levels and broadest range of resistance (temephos 37 ×, malathion 579×, propoxur 3032× and permethrin 100×). A strain from Rangoon and two from France (S54, BLEUET) showed lower resistance, restricted to organophosphates. Temephos and malathion resistance in the RANGOON strain was strongly inhibited by TBPT but not by TPP or piperonyl butoxide. Temephos and permethrin resistance in the DAR/D strain was slightly inhibited by TBPT and permethrin resistance by piperonyl butoxide. The DAR/D, RANGOON and CfCA (susceptible) strains were also compared for general esterase activity and phosphatase activity, both of which were higher in the resistant strains. It is concluded that resistance in RANGOON is associated with high production of an esterase sensitive to inhibition by TBPT but with little or no sensitivity to TPP, resembling but not identical in properties with the enzyme in strain S54 investigated earlier. Resistance in DAR/D was also associated with some increase in esterase activity, but the basis of resistance was different from that in S54 and RANGOON, having a much lower sensitivity to inhibition by TBPT.

Rastrococcus invadens sp. n. has been accidentally introduced to West Africa where it is causing considerable damage to many plants, especially mango and citrus, in Togo and Ghana. The origin of the mealybug is the Oriental Region, where it is known from a wide area, but it has always been mistaken for R. spinosus (Robinson), a closely related species. Serious outbreaks on mango in some areas of the Oriental Region suggest recent introductions also, although records from other parts of the Oriental Region are as early as 1900.