To study the effects of plant density on populations of the cabbage root fly (Erioischia brassicae (Bch.) ) and the cabbage stem weevil (Ceutorhynchus quadridens (Panz.)), cauliflowers were planted in 24 concentric circles to achieve spacings of 10–90 cm at 22 plant densities (1·5–83/m2). Some plants were treated with a root drench of chlorfenvinphos. Each week female cabbage root flies laid approximately three times as many eggs per individual plant at the lowest than at the highest plant densities tested. This was equivalent to approximately 350 and 5000 eggs/m2, respectively. The numbers of cabbage root fly pupae produced ranged from 11/m2 at the lowest to 210/m2 at the highest plant density. In the absence of an insecticide, increasing the plant density considerably increased the absolute population of the pest without affecting cauliflower yield. Approximately seven times as many flies were produced per unit area of untreated mini-cauliflowers as from an equivalent area of plants growing at a conventional density. When chlorfenvinphos was not applied, damage by the cabbage stem weevil occurred in 30% and 70% of the plants grown at the lowest and highest densities, respectively.

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 technique, based on the release and recapture of marked females, was used to measure the mating competitiveness of sterile males of Culex pipiens fatigans Wied. in villages in Delhi Union Territory, India. Experiments were carried out with chemosterilised and cytoplasmically incompatible translocated (IS-31B) males simultaneously with prolonged release trials with these two types of male. The fertile males in the tests were the indigenous population and the females used were in most cases of wild origin. With each type of male, one test was conducted with a moderate (ca. 13:1) ratio of released to wild males and the other tests used high (ca. 40:1) ratios. The estimated mean mating competitiveness of IS-31B males was somewhat higher than that of chemosterilised males, but the difference was found to be non-significant using a specially devised method of testing statistical significance. In the four experiments 77–94% of the egg rafts laid by recaptured females were sterile, indicating that both types of sterile male were sufficiently competitive to induce a high level of egg sterility in an isolated wild population.

In two trials, at Chitedze, Malawi, in 1966–1967, the spread of rosette virus disease in groundnuts (Arachis hypogaea) intersown with field beans (Phaseolus vulgaris) was less than the spread in groundnut monocultures comprising plant populations equivalent to the number of groundnut plants and to the total number of plants in the intersown crop. In one trial, numbers of early rosette transmissions were related to numbers of alate Aphis craccivora Koch, the vector of the virus, found on groundnut plants. Immigrant alate A. craccivora settling on the intersown crop were trapped by the hooked epidermal hairs of the bean plants and the observed reduction of rosette infection in the intersown crop was attributed to this effect. Inter-sowing with beans is considered less effective than early-sown, high-density monoculture as a method of reducing groundnut rosette infections and yields of groundnuts from inter-sown crops may be lower than those obtained from high-density monoculture.

The diurnal flight activity of Simulium griseicolle Becker was determined at Shambat, Khartoum, by means of a suction trap and a vehicle-mounted trap; and the biting activity by means of a chicken-baited trap. Only incidental observations of mammal-biting activity were made. The three trapping methods indicated two peaks of activity, one in the morning and the other late in the afternoon. Fly activity was lowest in the early afternoon when temperature and light intensity were highest, wind speed was moderate and relative humidity was least. Females outnumbered males in all the catches, except in the early morning when more males were sometimes recorded.

Communication between adult male and female Spodoptera littoralis (Boisd.) was disrupted by spraying microencapsulated formulations of pheromone inhibitor (IIA) (Z)-9-tetradecen-1-yl-acetate on lucerne plots in north-west Crete. Polyurea-based microcapsules applied at the rate of 100 g/ha active ingredient caused a 97% disruption for a period of seven days, as measured by the reduction of catches in the treated area in traps baited with the pheromone attractant (III) (Z)-9, (E)-11-tetradecadien-1-yl acetate, compared with catches in control areas. At lower rates of application both the level of disruption after seven days and the subsequent persistence of the effect were reduced. When applied at a rate of 100 g/ha active ingredient, disruption of 80% and above was achieved for a period of three weeks. Slower release microcapsules containing IIA based on polyurea/polyamide appeared more effective in that a level of disruption was achieved at one-tenth the amount of active ingredient required for the polyurea-based formulations.

III dispensed in polythene vials caused 97% disruption when distributed at the rate of one vial per 9 m2, with lower levels of disruption at distributions of one vial per 25 m2 or 50 m2. IIA was much less effective in causing communication disruption at the same rates of distribution and no clear dose/response relationship was established.

Inside enclosures of 10 100 and 1 000 m2 fenced by single-strand polythene impregnated with IIA at the rate of 1 mg/5 cm and maintained at a height of 0·5 m, a high level of disruption in excess of 93% was achieved for the first five days. The effect persisted in the smaller enclosures in that disruption in excess of 80% was maintained for a period of 40 days. In the 1 000 m2 enclosure the effect declined much more quickly.

When IIA and III were dispensed together in WT traps the inhibitory effect persisted for at least 60 days. Similarly the polyurea-based microcapsules containing IIA together with III in WT traps maintained an inhibitory action for periods of 30–40 days. Polyurea/polyamide formulations of IIA were generally less effective, probably because loss from these slow releasing formulations became too low. Small numbers of mostly unmated female moths were attracted to the traps when IIA was exposed together with III, either when dispensed in the polythene vials or in microencapsulated formulations.

Experiments were carried out to determine the optimum temperatures and photoperiods for inducing diapause in the cabbage root fly, Erioischia brassicae (Bch.). The induction of diapause occurred at certain receptive stages between the first and third instars of larval development. When developing larvae were subjected to 20±1°C and a 16-h photoperiod for 7–14 days followed by 13±0·5°C and a 10-h photoperiod for 28–35 days, diapause was induced in 84–97% of the pupae; 88–99% of pupae entered diapause when developing larvae were subjected to 13±0·5°C and a 10-h photoperiod for 28–42 days followed by 20±1°C and a 16-h photoperiod for 11–18 days. Similar results were obtained when developing larvae were subjected to 13±0·5°C (day)/7±0·5°C (night) and a 6-h photoperiod. The fecundity of flies from the diapausing pupae was not adversely affected. Application of these results should enable cabbage root fly to be cultured economically for intermittent use.

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.

In this survey of distribution and prevalence of adult ticks (Acarina, Ixodoidea) parasitising domestic animals in the northern regions of the Somali Democratic Republic, 26 species were identified. The ten most common species were widely distributed with Hyalomma anatolicum anatolicum Koch, H. dromedarii Koch, H. erythraeum Tonelli-Rondelli, H. impeltatum Schulze & Schlottke and Rhipicephalus sanguineus group more common in the drier vegetation zones, and H. marginatum rufipes Koch, H. truncatum Koch, R. e. evertsi Neum., R. pravus Dön. and R. pulchellus (Gerst.) more common in the wetter woodland, evergreen and forested zones. Four species, Amblyomma gemma Dön., A. variegatum (F.), Boophilus decoloratus Koch and R. simus Koch, were confined to the wooded zones above 1200 m altitude. Species collected less frequently were Argas persicus (Oken), Amblyomma falsomarmoreum Tonelli-Rondelli, H. anatolicum excavatum Koch, H. m. marginatum Koch, H. m. turanicum Pom., H. punt Hoogst., Kaiser & Pedersen, Ornithodoros savignyi (Aud.), R. armatus Pocock and R. longicoxatus Neum. Ambylomma lepidum Dön. was represented only by a few specimens introduced on nomadic livestock.

Nearly 60% of the total number of ticks collected were R. pulchellus. This species is considered to be the main vector of Nairobi sheep disease (NSD) virus in northern Somalia. NSD is the most important tickborne disease in sheep and goats and causes considerable economic losses to the Somali livestock industry. A. gemma and A. variegatum are probably the vectors of Cowdria ruminantium (heartwater) in sheep and goats in the western highlands. These two ticks are also incriminated in the spread of Dermatophilus congolensis infection (streptothricosis). R. e. evertsi may be the vector of Babesia motasi in sheep and goats. Boophilus decoloratus is probably the vector of Babesia bigemina in cattle in the western highlands. Various tick species may be associated with bacterial abscesses of feet and lymph nodes in sheep and goats.

Ticks were collected from 2136 small mammals, comprising 5 bats (5 species), 14 elephant shrews (3 species), 84 Crocidura shrews (5 species), 25 hares (1 species), 10 small carnivores (3 species), 3 hyraxes (1 species) 1998 rodents (33 species), and from 41 birds (19 species) at various localities in Zambia. From these hosts 6568 ticks (4384 larvae, 1686 nymphs, 317 males and 181 females) were recovered. Twenty-three species were positively identified and nineteen other species were assigned to genus or species-group. Host and tick records are tabulated by regions collected and for each of the two regions with the largest collections, the records are tabulated by months. The ticks collected in the high montane area near the Malawi border differed significantly from collections in other areas studied, reflecting host and climate differences. In the two areas tabulated by month, most of the immature ticks were recovered in the cool dry winter months (April to August).

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.

During 1972–74, 13 865 female mosquitoes of 25 species from eight genera were collected at the Kisumu heronry using light-traps, chicken-baited traps and battery-driven aspirators. A total of 3298 of these were engorged and 2169 were subjected to precipitin testing in order to determine their food sources. A high percentage of feeds on birds was recorded for Coquillettidia karandalaensis (Wolfs) (96%), Culex poicilipes (Theo.) (82%), and C. univittatus gp (65%); Mansonia uniformis (Theo.), M. africana (Theo.) and C. antennatus (Becker) were found to feed on birds occasionally. Results from catches in CDC light-traps set at various heights in trees with nesting birds indicated that C. univittatus gp, C. poicilipes and Aedomyia africana Nev.-Lem. were active in the upper levels of the canopy. Further analysis of blood-meals from birds indicated that C. univittatus gp mosquitoes were feeding principally on ciconiiform birds. Any mosquito which feeds regularly on birds and man must be considered as a potential vector of arboviruses; the results indicate that the most important vectors at Kisumu are probably C. univittatus gp mosquitoes.

Adult behaviour and oviposition patterns of Cacoecimorpha pronubana (Hb.), Phlogophora meticulosa (L.), Autographa gamma (L.), Mamestra brassicae (L.) and Lacanobia oleracea (L.) were studied by introducing laboratory reared pupae into glasshouses. Adults emerging from these pupae were located by direct visual searching of chrysanthemum plants and of the greenhouse structures for up to three weeks after emergence.

In small houses (2·9×3·3×2·5 m), 49 adults of C. pronubana emerged. At least 15 stayed inside the house and laid 1 750 eggs. With P. meticulosa, A. gamma and L. oleracea, 262 adults emerged and escaped from the houses without laying eggs inside.

In a large glasshouse (9·8×13·1×5·1 m) with automatic ventilators, 840 adults of P. meticulosa, A. gamma and M. brassicae emerged and many were prevented from escaping when the ventilators were closed during the moths' flight period. Moths were inactive in daytime and most were found on the highest parts of the aluminium framework, mainly on the sides which received most external light overnight. None were found on the glass. Only 27·3% of the P. meticulosa were found on the plants. Moth distributions probably result from moths flying until they reach a barrier, which they then tend to follow, with directional responses to gravity, light, settling site, food plant and oviposition site superimposed in varying degrees on this basic pattern. About 30 470 eggs were laid, more in outer than in inner beds and more in the outer than in the inner rows of a bed. P. meticulosa and A. gamma laid eggs only on plants. M. brassicae laid about 1 854 eggs on the undersides of leaves and 2 972 on glass and framework, mainly in the direction of external light.

All five species can cause serious damage to crops. Initial infestations can be controlled by sprays of chemical insecticides or Bacillus thurin-giensis. Usually a few larvae survive a single spray and, in the absence of further control measures, they may produce a troublesome second generation, although in certain circumstances further control measures may not be required. If biological control of other tomato pests becomes widespread, steps should be taken to prevent L. oleracea again becoming an important pest.

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.

Experiments in Malawi showed that the (log) number of males of Diparopsis castanea Hmps. attracted to sex pheromone traps was linearly related to the (log) number of virgin females used as attractant. Virgins remained sexually attractive for up to 31 days but were maximally attractive three nights following emergence; 97·7% of light-trapped females were mated, a small proportion having mated four times. Numbers of matings were directly correlated with temperature at 22.00 h, but relative humidity had little effect. Mean fecundity of mated females was 152 ± 10·3 eggs, multiple mating influencing egg fertility rather than total oviposition. Potential fecundity was linearly related to body weight on emergence. Peak oviposition of unfertilised eggs by virgins occurred at about nine nights following emergence. Of emerging females 2% were barren. Only 1·4% of females mated twice in one night when confined outdoors with males, and there was no difference in the abilities of newly emerged males or males up to four days old to mate with newly emerged females or females up to four days old. Although outdoors males mated on average 0·8 times per night throughout their life, and were capable of mating twice per night, mating propensity of males under laboratory conditions was much lower. Males responded to female sex pheromone throughout the calling period of the female, individuals completing up to 143 orientations during a night without the occurrence of lasting physiological habituation to the pheromone. The importance of this in any control programme aimed at disrupting pheromone communication between the sexes is discussed.

Indigenous cattle are trekked, along well defined routes, from the north of Nigeria to markets in the south of the country. A major route crosses the River Niger at Jebba and proceeds south through Ilorin, Ogbomosho and Oyo towns. In 1912 the tsetse fly Glossina morsitans submorsitans Newst. was absent from this route south of Jebba. The species appeared mid-way between Jebba and Ilorin in about 1935, reached Ilorin by about 1950 and Oyo by, or before, 1967. The rate of southwards advance, if linear, was about 5·4 km per year or 104 m per week.

The Jebba-Oyo infestation may have originated, not as a southwards extension of a fly belt north of the River Niger at Jebba (now termed Belt 24), as generally believed, but by immigration of flies from Eastern Ilorin Province, known to be heavily infested as early as 1912. Several cattle routes from that area converged north of Ilorin before the present route became predominant.

G. m. submorsitans was eradicated from the route south of Ogbomosho by insecticide spraying in January 1970. The rate of re-invasion of this section was measured for the next three years and found to be about 5·13 km per year or 99 m per week, proceeding faster during dry than during wet seasons.

The calculated rates of advance, both long and short term, were about half the figure (180 m per week) proposed by other workers as the dispersal rate of individual flies, which is believed to determine rates of advance. The relative slowness of the present advance was probably related to the equability of the climate, in which seasonal increases and decreases in fly population were slight.

The population dynamics of the desert locust, Schistocerca gregaria* (Forsk.), in Africa, the Middle East and Asia from 1966 to 1969 have been analysed to determine the causes of the beginning and the abrupt end of the plague of 1968. Evidence indicates that in 1966 there were no persistent sequences of breeding by gregarious populations, but in 1967 and early 1968 there were four sequences of breeding by initially solitary behaving locusts, each resulting in a substantial increase in numbers and density. These events led to a plague that ended by mid-1969.

The threshold rainfall requirement for successful breeding, defined as an increase in numbers from mature adults of the parent generation to filial fledglings, has been related to the rainfall required for the germination of ephemerals and their growth to sizes that can provide food and shelter for hoppers throughout their development. It is suggested that the minimum quantity of rainfall required initially over a large area is 25 mm. This requirement is usually met in the summer breeding areas. Rainfall in the winter-spring breeding areas is more variable, and falls exceeding the threshold are most commonly associated with deep troughs in the mid- and upper-tropospheric westerly winds in winter and spring. A season in which many such troughs occur may be essential for plague development. It is also suggested that the timing of successive periods of rainfall allowing successful breeding is critical in determining the occurrence of upsurges.

Control against non-gregarious infestations failed to contain the upsurge, but later control measures against hopper bands and swarms contributed to the plague decline. The most economical strategy for plague prevention might be one of upsurge elimination, that is to say control in selected areas against gregarious locusts only. The implications of adopting such a strategy are discussed.

In a series of field trials at Chitedze, Malawi, groundnuts were sown at spacings of 30 cm, 7·5 cm and 2·5 cm within rows 90 cm apart. Contrasting sowing dates were approximately 1 December and 1 January. Immigration of alatae of Aphis craccivora Koch, monitored on observation plots, commenced 5–6 weeks after the emergence of early-sown groundnuts. Numbers of immigrant alatae were significantly greater on late-sown or open-spaced than on early-sown or close-spaced groundnuts, and were correlated with numbers of randomly distributed primary rosette virus infections. During observations, more alatae landed on 56–60-day-old plants than on 85–112-day-old plants. Similar numbers landed on 11–26-day-old plants at 30-cm and 2·5-cm spacing, but significantly more aphids settled on 30-cm spacing. The incubation period of rosette virus was consistently longer in 2·5-cm than in 30-cm spacing, and increased with plant age at inoculation. The virus was transmitted from a low proportion of infected plants before the appearance of rosette symptoms, and from a high proportion of plants snowing symptoms. The rate of spread of virus transmissions from inoculated sources within the crop varied significantly with spacing as 30 cm > 7·5 cm > 2·5 cm. Secondary spread of rosette varied, approximately, with the numbers of aphids per infected plant.

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.