Eight strains of Boophilus decoloratus (Koch) are described from farms in the High veld area of Rhodesia. All eight strains showed resistance to a number of organophosphorus ixodicides and four showed additional resistance to the carbamate, carbaryl. This is the first recorded resistance to these two groups of ixodicides in Rhodesia.

Biochemical studies on the Alicedale West Farm strain indicated a level of resistance between that of the Berlin strain of B. decoloratus and the Biarra strain of B. microplus (Can.).

Organophosphate resistance in Lucilia cuprina (Wied.) is shown, by the backcross and discriminating dose technique, to be controlled by two major genetic loci on chromosomes 4 and 6. Respectively designated Rop-1 and Rop-2, they are positioned on the known genetic map. Rop-1 has three resistance alleles and one of these, and the Rop-2 allele, demonstrated stable transmission and expression in the absence of insecticide. Expression of resistance was either intermediate or incompletely dominant depending on locus and stage of maturity. This, and interaction between the loci, suggests that they have different biochemical mechanisms.

Laboratory evaluation of alternative insecticides to replace persistent organochlorines in leaf-cutting ant baits is described, based on tests of 40 candidate compounds which were bioassayed with Atta cephalotes (L.) and Acromyrmex octospinosus (Reich). Insecticides having a suitable delayed killing action are listed, together with others which, although highly toxic to ants, had too rapid an action, but could feasibly be modified by using a controlled-release formulation.

A search was also made for alternative bait matrices to replace the expensive and often inadequate materials in current use. Horticultural grade vermiculite with sorbed orange juice as an arrestant was the best matrix tested, being at least as attractive as dried citrus pulp, which was the best previously known matrix.

Treatment of dried citrus pulp bait with propionic acid gave considerable protection against moulds, which spoil stored baits and baits placed in the field, and did not alter the attractiveness of these baits to ants.

Ten non-organochlorine insecticides which had shown promise in laboratory tests as formicides, because of their delayed toxic action, were field-tested in Brazil in experimental leaf-cutting ant baits and were compared with a mirex bait. Seven of these gave good control (similar to mirex) against Atta sexdens (L.) colonies. Several showed some success, at the concentrations used, against the larger Atta cephalotes (L.) colonies, but were not as good as mirex.

By microencapsulating some quick-acting and very potent insecticides it was shown that useful formicides could be produced, presumably because encapsulation delayed the toxic action.

Substituting vermiculite plus orange juice in place of dried citrus pulp as an attractive bait matrix gave successful results.

Anopheles implexus (Theo.) was studied at the Zika Forest near Entebbe, Uganda, from 1966 to 1971, with central reference to biting activities and host selection. Seasonal fluctuations of populations appeared to be correlated with lake levels, not with local rainfall. Results of biting, resting and nectar-feeding catches at various points across the forest floor indicated that diel activity patterns of man-biting were related primarily to the proximity of resting female A. implexus and only secondarily to the influence of environmental variables. Latent effects of moon phase on day-time man-biting activity patterns support this view. Blood-meal identifications showed that the great majority of blood-fed females resting in forest had fed on cattle, indicating that they left the forest at night. This was confirmed by direct catching from cattle outside forest, while the virtual absence of A. implexus resting near these bait animals, together with the fact that man is very seldom attacked away from forest, indicated that different kinds of host selection strategy were involved. The diel activity pattern of biting on cattle taken into forest was then found to be very different from that on man. Age-grading studies helped to substantiate these differences. Hourly sampling of A. implexus arriving at representative resting sites in forest indicated an exodus of most of the adult mosquito population from forest at dusk and a return shortly after sunrise. The two basic host selection strategies evidently involved (a) active or (in effect) ‘hunting’ flight, mainly outside forest with a tendency to restrict choice to most strongly attractive hosts, and (b) passive or opportunistic attack from rest, in which some of the unfed females sheltering may be activated by the proximity of a host which need not be strongly attractive. The latter situation was investigated further through analysis of short-term day-time patterns of attack on man in forest which are postulated to be a function of mosquito response delay (involving both resident and incoming elements of the sheltering population), which in turn determines depletion rates (involving only the resident element available at the time of the host's arrival). In A. implexus the response delay appears to vary according to time of day. Anomalous results are finally re-considered and it is concluded that the different patterns of active and passive host selection could arise from a single circadian rhythm of responsiveness, with flight characteristics and day-time inhibition modulating responses to specific and non-specific host stimuli in different ways.

The parasitic larvae of two species of water mites were studied on resting and biting Anopheles implexus (Theo.) from the Zika Forest near Entebbe, Uganda. Details are given of the mites' morphology, positions of attachment, growth stages and visible effects on hosts. Living larvae of the more numerous mite species (designated as species F, Limnesiidae) were only moderately reliable indicators of the nulliparous state of female hosts, whereas those of the other species (species G, Arrenuridae) were more reliable nullipar indicators, evidently owing to their far more rapid development. The presence of living larvae of either species not completely full-grown denoted the nulliparous state of female hosts with certainty. Male mosquitoes showed consistently lower infestation rates than females from the same resting samples, but the incidence of the different growth classes of species F indicated that these mites departed from hosts of either sex with equal facility and therefore regardless of whether the hosts returned to oviposition sites or not. Frequency distributions of species F on each host sex fitted most closely to highly clumped negative binomials, and biological interpretation of patterns of decline in mite numbers on females in successive Sella's stage groups, and other data, provided evidence of there being at most a negligible amount of mite-mediated host mortality.

The study confirms the usefulness as well as the limitations of the presence of parasitic water mites as a rapid means of age-grading female mosquitoes, and suggests several new applications.

The suggestion that mosquitoes can discriminate ABO blood group status in man was re-examined and an attempt made to determine recognition mechanisms.

Host choice was assessed in the laboratory by recording landings on and blood-meals taken from the forearms of pairs of human volunteers in a 10-min exposure to 20 females of species A of the Anopheles gambiae complex, and an alternative procedure, which did not involve mosquitoes probing the host's skin, was developed and evaluated. The presence of weals on the host's skin was found to be an unreliable indicator of probing or feeding activity by mosquitoes. The effect of thermally induced sweating was also investigated.

No effect of ABO blood group status on host choice was found. Mosquitoes did, however, show a highly significant preference to land and feed on a subject when thermogenic sweating was induced. Secretor substances in the sweat did not influence host selection.

The predictive value of host variables such as MN blood group, skin temperature and humidity, skin colour and forearm hair density in determining host choice was examined. Very little of the observed variation in mosquito activity could be accounted for by these host variables within the ranges used.

Saliva was obtained by applying capillary tubes to the mouthparts of the cattle tick, Boophilus microplus (Can.), after the subcuticular injection of pilocarpine hydrochloride. Acid-lipid extracts of this saliva showed prostaglandin (PG)-like activity on bioassay. Chromatographic studies confirmed this activity as being due to PGE2. Extracts from homogenates of B. microplus larvae and salivary gland tissue also showed prostaglandin-like activity. A role for PGs in B. microplus feeding mechanisms is discussed.

Two techniques have been developed to investigate the incidence of multiple feeding by mosquitoes. One system detects the ABO blood group substances and can be used up to 24 h after feeding in the case of Anopheles stephensi List. and 30 h for Aedes aegypti (L.). It is limited by cross-reactions which develop between blood group substances as digestion occurs in the stomach of the mosquito. The second system detects the serum protein haptoglobins (Hp) and it is possible to detect the Hp type of blood in single feeds 20 h after feeding for Ae. aegypti and 16 h for A. stephensi. Multiple feeds taken within a short time of each other can be identified up to 16 h after completion of the meal. The minimum amount of blood necessary to effect an identification in a fresh two-part meal is 0·1 mg, which is approximately one-tenth of the total amount of blood taken. It is now therefore possible to measure multiple ‘cryptic meals’ taken from man, if they are of different Hp types. Identification of Hp from A. gambiae sp. A blood-meals has been successfully carried out using material sent from the tropics. Limitations of the techniques as applied to field collections are discussed.

The effect of host movement on multiple feeding by Aedes aegypti (L.) was observed in a laboratory experiment and the value of techniques developed to measure multiple meals was assessed. Multiple feeding on the arms of two human volunteers was significantly increased when both hosts moved their arms. If only one host was moving, a slight increase in multiple feeds over the level obtained with no movement was noted, although in such cases the majority of meals were taken from the stationary host. Statistical analyses of the results showed that the association between host movement and multiple feeding was highly significant.

In a country-wide survey of Culicoides in Nigeria 31 species were caught in light-traps set on the eaves of livestock pens. Three species, namely C. imicola Kieff., C. schultzei (End.) and C. milnei Aust., were most numerous and were found in all parts of the country. C. austeni C., I. & M. was predominant in mangrove swamps, C. schultzei in the hot Sudan zone and C. milnei was dominant on the plateaux. C. imicola and C. milnei were predominant in the forest zone while C. schultzei and C. imicola were dominant in the savanna zones. C. quinquelineatus Goetgh. was a southern species and was replaced in the north by C. moreli Clastrier. Peak catches of most species were between 01.00 and 05.00 h and a large proportion of the Culicoides were engorged with blood. The presence of large numbers of engorged Culicoides, especially C. imicola and C. milnei, around livestock indicates the danger of bluetongue virus transmission.

A branchlet-mining scolytid beetle, Hylurdrectonus araucariae Schedl, has invaded the hoop pine (Araucaria cunninghamii) plantations at Bulolo and Wau in Papua New Guinea. A study of the infestation pattern in a plot of 184 young (5–6 year-old) trees at Bulolo from February 1968–August 1972 revealed four major phases: (i), a relatively prolonged but small build-up of the population on most trees over a period of 12–18 months following the first attack; (ii), a dramatic upsurge in the infestation over the following 12–18 months, reaching a peak infestation with the severe attack of nearly all trees in the plot; (iii), a sharp decline in the number of attacks and population over the next 12–18 months due to a lack of nest sites and food and (iv), a slow decline over a protracted period. The variation (313 to 6220) in the maximum number of infested branchlets on the trees in the plot at peak attack was great, due to the differing amounts of foliage and size of the trees, but it usually represented an estimated 85–95% of the foliage.

A comparative study of seedling resistance of the two major plantation species, hoop pine and klinkii pine (Araucaria hunsteinii) was carried out at Bulolo in 1967 using seedlings from the local nursery and placing them in cages with large quantities of infested foliage. Over a two-month period, no colonies of H. araucariae were established in the klinkii pine seedlings and only three of 32 attacks recorded in the hoop pine seedlings had produced brood. Infestation of seedlings was extremely rare in the plantations and natural stands. On the other hand, most trees aged 2·5 to 12 years in the plantations at Bulolo and Wau were susceptible to severe infestation. Older trees were seldom severely attacked. Klinkii pine has proved non-susceptible to attack. In studies of impact in three plots of 1000 trees at Bulolo from 1967–1971, least growth increment and highest mortality was recorded in the plot that had been initially severely affected by the scolytid. In contrast, good growth and low mortality was recorded in the plot of healthy trees. They were later exposed to severe infestation from the adjacent plantation of young 3–4 year-old trees, but escaped relatively unscathed. In another study of impact at Bulolo from 1967–1972, the effect of two levels of pruning on subsequent growth and re-infestation was examined. The results indicated that site also strongly affected the situation, with little growth and high mortality evident on poor sites. Secondary insects, notably the weevil Vanapa oberthueri Pouillaude, were an important factor contributing to mortality among the stressed trees.

Monthly observations were made of the numbers and nutritional state of Glossina morsitans morsitans Westw. and the numbers of game animals in an 11 km2 block of woodland in Rhodesia. After 31 months the block was enclosed by a warthog-proof fence and nearly all of the warthog inside were removed rapidly. Tsetse diet switched from 80% warthog to 40–80% bovid (mainly kudu), 20–50% elephant and 0–20% warthog. Six months later elephants were driven from the block and bovids then formed about 90% of tsetse diet for the next year. Although the selective removal of hosts produced a clear stress, it had no drastic effect on the numbers and nutritional state of tsetse when compared to these features of a control population. Movement of tsetse into the enclosed area can account partly, but not fully, for this. The effects of routine hunting operations on a tsetse population are also reported.

Male and female Glossina morsitans morsitans Westw. which emerged from puparia produced by animal-fed and in vitro-fed colonies in England were marked distinctively with non-toxic paint and released into a natural habitat of G. morsitans and G. pallidipes Aust. in Rhodesia. Concurrently, adults of both species which emerged from locally-collected puparia were marked and released. Recaptures from artificial refuges, odour attractants and mobile baits at periods up to 59 days after release and at distances up to 1800 m from the release site indicated no clear differences between native G. morsitans and the two laboratory-reared groups in respect of body size, amount of fat present at emergence, survival, dispersal, availability to a range of baits, diet, speed of taking a first meal, wing damage and insemination rate. Although the blood-meal identifications for marked female G. morsitans were similar to those for both sexes of unmarked flies, blood-meals from marked males showed a relatively high proportion of bovid identifications. Unmarked flies caught were generally older than marked catches. The ratio of females to males in unmarked samples (1:1 for G. morsitans, 2:1 for G. pallidipes) was roughly double that in marked catches.

The distribution and seasonal abundance of Stomoxys nigra nigra Macq. and S. calcitrans (L.) in Mauritius was determined by field surveys in 1973–74. S. nigra, the species of major importance, is most common throughout the wetter, higher elevations where it becomes a major pest of cattle. S. calcitrans occurs throughout the island to a much lesser extent. Coastal areas with less than 60 inches of rain are generally free of damaging infestations of both species. Seasonal infestation levels were determined by making counts of flies feeding on animals and of flies on resting surfaces. Populations of up to 200 S. nigra per animal were highest during the warm, wet, sugar-cane cropping season but declined to generally non-damaging levels during the cool season. S. calcitrans increased up to 145 flies/animal during the cool, drier season and virtually disappeared during the wet season. S. nigra accounted for up to 98% of the total Stomoxys infestation with S. calcitrans making up 62 % of the total at one study site during the study.

Sugar-cane debris in fields was found to be the primary breeding source for 5. nigra, whereas decaying manure and organic matter provided the source for S. calcitrans. Generation-to-generation increases were usually below five-fold for both species. Both species exhibit two feeding peaks throughout the day at temperatures of 14°C or above.

The biology of Hydrotaea irritans (Fall.) has been studied at Weybridge since 1973. The flies have failed to mate in cages and only those which have been fertilised before capture have laid viable eggs in the laboratory. In experiments in 1975–76 flies in the field emerged from June onwards but development of the ovaries (noted in seven stages) to the point of ovi-position was not completed until September. Some 1400 larvae were established in culture and, although they had reached a maximum size by January, they continued to feed until 14 March. Pupation lasted for 25 to 32 days during 6 May to 12 June and a total of 185 flies emerged from 4 June to 9 July. The results of these experiments confirm that H. irritans does not diapause and that the species is univoltine.