The breeding sites used by three species of the Anopheles gambiae Giles complex were investigated in northern Natal, South Africa. Those used by the two freshwater species, A. arabiensis Patton and A. quadriannulatus (Theobald) were similar, immature stages of both being collected from the same pool at five out of seven localities from which A. arabiensis was recorded. A. quadriannulatus was the most extensively distributed species of the complex and was found in association with A. arabiensis at only five of 49 localities. The difficulty in locating the breeding sites of A. arabiensis is a product of their low density, presumably as a result of the intra-domiciliary, residual insecticide spray programme. A. merus Dönitz larvae and pupae were recorded only in water with a salinity greater than 5 p.p.t. The pH, dissolved oxygen, pool size, turbidity, shade and association with vegetation of water bodies containing A. gambiae s.l. were also recorded and showed no difference between the three species. The importance of distinguishing between winter and summer breeding sites is discussed, as well as the need for entomological consultation prior to agricultural development in endemic malarious areas.

Mononychellus tanajoa (Bondar), a spider mite new to Africa, was discovered on cassava in Uganda in 1971. This exotic mite of Neotropical origin has since spread to 27 countries, causing an estimated 13–80% reduction in cassava yield. The history of its introduction and spread in Africa is reported, and present knowledge on the taxonomy, biology, ecology and pest status of the mite, and the evolution of strategies to control it are reviewed. While attempts have been made to control M. tanajoa, it remains a serious pest in most areas. The prospects for classical biological control as an appropriate control strategy are discussed.

Records of hourly trap catches of Helicoverpa armigera (Hübner) in a light trap and two pheromone traps in Andhra Pradesh, India, were used to assess the influence of moonlight and weather on trap performance. The environmental factors that were considered were mean hourly temperature, relative humidity, wind speed and maximum hourly percentage moon illuminance. The mean number of adults caught per hour reached a peak at 03.00 h in the light trap and at 02.00 h in one of the pheromone traps. The environmental factors were not sufficiently severe to produce any marked activity thresholds, although zero catches were recorded in the light and pheromone traps on occasions when the mean hourly temperature was 11°C. Despite there being obvious relationships between hourly light and pheromone trap catches with temperature, relative humidity and wind speed, it was not possible to determine whether these were causally related or merely coincidental relationships. Some of the observed relationships could not be explained in terms of known physiological or behavioural characteristics of the insect. It was evident that the light trap performance was influenced by the level of moon illuminance because this affected both the timing and size of the peak catch.

Tomato plants in Nigeria were subjected to foliar sprays of Bacillus thuringiensis subsp. kurstaki (formulated as Dipel and Thuricide) and Baculovirus heliothis (Elcar), to which carbaryl, plus the adjuvants Tenac and Gustol were on occasion added, to test their effectiveness against Helicoverpa armigera (Hübner) and other lepidopterous larvae. H. armigera larvae were found susceptible to both pathogens. The 0·5 kg/ha and the 1·0 kg/ha applications of Bacillus thuringiensis gave good field control of the larvae, similar to that of carbaryl at 1·5 kg/ha. Bacillus and virus were compatible but not significantly more effective when combined than when applied separately. Combinations of bacillus and virus with carbaryl were also not significantly more effective than the pathogens applied separately. B. thuringiensis at 0·5 kg/ha applied with carbaryl at 0·5 kg/ha was as good as carbaryl at 1·5 kg/ha. Gustol and Tenac did not significantly increase the effectiveness of the pathogens.

Multivariate analysis was used to demonstrate that specimens of Planococcus collected from yams (Dioscorea spp.) in both the West Indies and Africa can be differentiated from the similar P. ficus (Signoret) which occurs on figs, grapevines and pomegranates in the Mediterranean Basin, Pakistan, South Africa and Argentina. The specimens from yams are considered here to be a distinct species, to which the name P. halli Ezzat & McConnell is applied. Examination of material of both species reared on potato tubers at various temperatures showed that the differentiation is not a host-induced effect. Independent canonical variates analysis of the field-collected and reared material each showed clear differentiation of the two groups. However, the coefficients obtained for each character differed markedly between the analysis of the field-collected material and that of the reared material, and thus could not be used to assign individuals to groups. This difference in the values of the coefficients is considered to have been due to the peculiarities of individual populations, as the field-collected material included many genotypes while only three genotypes were represented by the reared material. A key and illustrations are provided for the separation of the two species.

The rate of oocyte development in Spodoptera exempta (Walker) was investigated in the laboratory and in the field in Kenya. Stages and rates of development were examined in relation to moth size and timing of mating and oviposition. The stage of oocyte development was established by measuring the widths of the second or third oocyte at the distal end of one ovariole. Data from moths of known age showed that oocytes were partially developed at eclosion and that a linear progression in development occurred up to 30 h after emergence, by which time the oocytes had reached approximately half their mature size. Oocyte development continued unbroken in some moths up to the time of oviposition on the second night after emergence, whilst the remainder arrested oocyte development for a varying number of days. Mating occurred after midnight, but only once the oocytes had reached a certain size, irrespective of whether development was continuous or arrested. In the latter case, this stage was reached immediately after development resumed. Oviposition usually occurred the night after mating, mainly around midnight and with a second peak towards dawn. The dawn peak derived from mature moths which mated and oviposited on the same night. It is suggested that moths arrest oocyte development to minimize wing loading during migration and that, since moths stay in arrested development for varying lengths of time (thought to be genetically regulated), dispersal is greatly enhanced.

The braconine Palabracon diatraeaphilus gen. et sp. n. is described and illustrated from a unique female collected in Ecuador. The new species was reared as a parasitoid of an undetermined species of Diatraea.

A description is given of the use of a video camera to estimate light-trap efficiency in the field. This camera relies on the extra light sensitivity provided by the Newvicon detector tube to enable insect track discrimination. Recorded insect flight tracks were classified into three distinct categories, new arrivals, passers by and local flights, the numbers of which were compared to the moth catch in a Robinson mercury vapour light-trap. Calculations of efficiency were made using two methods, the best-estimate efficiency, obtained by comparing the new-arrival tracks to the light-trap catch, and the worst-estimate efficiency, obtained by comparing new-arrival tracks plus passer-by tracks to the light-trap catch. Preliminary results indicate that efficiency varies with windspeed but with a maximum of 39%, obtained in virtually calm conditions, suggesting that some aspect of moth behaviour limits trapping efficiency. It is suggested that the speed of migration of screening pigment from the dark-adapted state to the light-adapted state in superposition eyes may have a bearing on the catching mechanism of a light-trap.

Standard curves for the regression of pteridine fluorescence in the head upon chronological age were constructed for laboratory-reared Glossina adults. Of the five species investigated, the technique was a reliable predictor of age in G. morsitans morsitans Westwood, G. pallidipes Austen, G. palpalis palpalis (Robineau-Desvoidy) and G. tachinoides Westwood, but was not reliable for G. austeni Newstead. Field-caught tenerals of both sexes of G. p. palpalis, field-caught teneral females of G. pallidipes and tenerals of both sexes of G. m. morsitans released on an island in Lake Kariba, Zimbabwe, had significantly higher pteridine fluorescence levels than tenerals hatched in the laboratory. However, the regression of fluorescence on age produced similar slopes for both laboratory-reared and field-caught flies. From this, it is concluded that estimates of the ages of field-caught flies can be corrected by simply subtracting the difference in fluorescence values between field-caught and laboratory-reared tenerals. In practice, this amounts to shifting the frequency distribution of different age categories to bring the youngest age group back to day zero. A comparison of the fluorescence technique and the ovarian dissection method of determining the ages of females showed that over a wide range of ages the former was at least as accurate as the latter and should be the technique of choice for most field investigations.

The attack rate by the parasitoid Apanteles glomeratus (L.) on laboratory-reared larvae of Pieris rapae (L.) exposed for 3–4 day periods in a kale field in Massachusetts was greater when five larvae rather than two were placed on plants. The attack rate was greatest if host larvae were in the first instar when placed in the field, and little or no attack occurred when second- or third-instar larvae were exposed. The co-occurrence of unoccupied P. rapae larval feeding sites on plants where larvae were exposed reduced attack rates. Parasitism rates in trap-host larvae and in field-collected larvae (counting only cases in which the parasitoid was still in the egg stage) did not differ as estimators of recruitment to the population of parasitized hosts either in terms of total recruitment achieved per host generation or in the temporal pattern of the recruitment. In both simple and multiple linear regressions, the density of young P. rapae larvae (either parasitized or not) was the strongest correlate of parasitoid recruitment for the whole season, whereas average air temperature was the strongest correlate in the last month of observations (September).

Four models are presented which represent the four combinations of two trap types (food-baited or pheromone-baited), each containing either insecticide or chemosterilant. These were then modelled in combination to determine which combinations might be useful for controlling arthropod pest species in which the virgin females produce sex pheromone which attracts males. The most promising results occurred in combinations involving different trap baits but the same pesticide type, i.e. where one trap contains food bait while the other contains sex pheromone, and both contain either insecticide or chemosterilant. This conforms to the principle of complementarity of control methods and at the same time avoids the interference which would occur if insecticide was used in one trap type and sterilant in the other.

Residues of pirimicarb or deltamethrin plus heptenophos on potatoes in field cages in southern England reduced artificial infestations of susceptible and insecticide-resistant strains of Myzus persicae (Sulzer) introduced up to 14 days after treatment. Deltamethrin plus heptenophos gave better control than pirimicarb, particularly of nymphs, but also selected more strongly for very resistant (R2) aphids. Susceptible (S) aphids survived the treatment with deltamethrin plus heptenophos better than moderately resistant (R1) aphids, probably due to a different or more pronounced behavioural response to the pyrethroid. However, the combination of the greater persistence of deltamethrin plus heptenophos and the high resistance of M. persicae to the pyrethroid led to more prolonged selection for R2 aphids, which is sometimes associated with a resurgence in aphid numbers.

Survivorship curves for the pre-adult stages of Pieris rapae (L.) on kale in Massachusetts exhibited two patterns. Early season generations showed a linear decline with mortality in all stages, whereas late season generations showed reduced losses in larval instars 2-4 and a concentration of mortality in the fifth instar. Ratios of direct measurement of recruitment of P. rapae and its parasitoid Apanteles glomeratus (L.) to their first larval and egg-plus-larval stages, respectively, indicated that losses to parasitism for five host generations were 86·1, 9·1, 58·O, 71·7 and 40·3% for the 1985 third generation and the 1986 first to fourth generations. Patterns of percentage parasitism within single generations were determined by higher rates of mortality in parasitized than healthy older larvae (instars 3-5) and, in some cases, by higher rates of host than parasitoid recruitment towards the end of the generation.

Using several methods, claims that stem-borers, especially Scirpophaga incertulas (Walker), cause serious crop loss in deepwater rice were tested in Bangladesh. Insecticides were used to control different borer broods. Early season, pre-flood applications reduced infestation, but did not affect yield. One to three mid- to late-season applications of monocrotophos at 250 g a.i./ha significantly reduced infestation and/or whitehead numbers, with yield savings (7-10%) similar to those which earlier workers obtained by applying diazinon 20 times in a season. In each of six years, tiller populations peaked before flooding, then steadily declined until harvest, but stem-borer infestation varied, remaining low until late season in two of the years. In 1981, infestation lower than 24% pre-flood and 42% at harvest did not affect yield. In 1982, eighty-four correlation calculations showed no consistent significant effects of infestation (27-60%, C.V. 40%) on yield (25 000 stems were dissected). Anatomical studies of elongated stems revealed S. incertulas feeding neither causes significant structural damage nor seriously interrupts nutrient flow; also, the passage of a larva through a nodal septum is not detrimental. Irrespective of stem-borer attack, the submerged lower internodes commonly die, the fibrous remains anchor the upper stem, and nodal roots take over nutrient uptake. Studies of panicle-bearing stems (n = 838) showed that, even with 97% stem infestation, most yield loss results from infestation of the terminal internode and is manifested predominantly as whiteheads. In a specific study, 94% whiteheads (n = 205) were associated with terminal internode infestation, where larval feeding in the narrow stem had disrupted food conduction, so preventing grain-filling. The apparent tolerance of S. incertulas by deepwater rice varieties is consistent with their being a primitive group of cultivated rices.

From March to October 1984, targets consisting of black cloth and netting, baited with 1-octen-3-ol (released at about 0·5 mg/h), and acetone (about 100 mg/h) or butanone (15 mg/h), and coated with deltamethrin, were deployed at 3–5/km2 in 600 km2 of the Zambezi Valley of Zimbabwe where Glossina morsitans morsitans Westwood and G. pallidipes Austen were initially abundant. About 3 000 000 adults of G. pallidipes and 200 000 of G. m. morsitans originally present in the area as adults or pupae were killed by targets or removed by sampling procedures between March and December. At the end of this period, the tsetse populations in the centre of the block had declined by at least 99·99%. The targets dealt adequately with a strong invasion pressure from initially dense infestations nearby, partly because the targets reduced the abundance of tsetse up to 5–10 km outside the block. At 18 months after the start of the study, the targets were badly faded; this was corrected by spraying them with a black dye and an ultraviolet-light absorber that protected the dye and insecticide, but by then the targets had deteriorated and were without adequate odour attractant, and many were no longer being maintained. Tsetse then invaded further into the block, but only in small numbers. Tabanids and muscoids were not strongly attracted to targets; their population densities in and near the block did not change greatly. Targets offer a simple and ecologically clean method of controlling tsetse and preventing invasion.

The importance of colour in the attraction of Glossina palpalis palpalis (Robineau-Desvoidy) to trapping devices was investigated in the Ivory Coast. Biconical traps were tested with the normally royal blue lower cone replaced with one of 25 differently coloured cloths. Royal blues were consistently the best colours for traps; yellow and orange were the worst, catching less than 1% as many as the best royal blue. Modelling trap data from the spectral reflectivities of the colours used showed that blue wavelengths contributed positively, and ultraviolet and green-yellow-red negatively, to trap performance. The responses to screens were studied using electric nets, deployed to catch flies both circling around and landing on the screen. The overall catch (of circling and landing flies) was greatest for royal blue screens, intermediate for yellow and green ones, and lowest for screens highly reflective of ultraviolet light; the total range of variation between colours was much smaller than was the case with traps. The relationship of catch to spectral reflectivity was similar to that described for trap score. An achromatic series of screens (black, white and greys) all attracted significantly fewer females than did royal blue screens, implying that attraction to blue depends on colour discrimination and not on intensity contrasts alone. For most colours, the majority of flies circled the screen without landing; with materials strongly reflecting ultraviolet, however, a high proportion of flies (especially females) landed.

Epidinocarsis lopezi (De Santis) was found to parasitize and complete development in all developmental instars of its host, Phenacoccus manihoti Matile-Ferrero. However, parasitoid mortality was high (15·8%) when development took place in the first nymphal instar of the host. Complete development from egg to adult emergence was prolonged in smaller hosts, and developmental periods recorded were 18·8, 17·4, 16·1 and 14·9 days for the first, second, third and fourth nymphal instars, respectively. Irrespective of the age of the host parasitized (with which size is strongly correlated), E. lopezi completed only one life-cycle during one life-cycle of P. manihoti. Oviposition commenced within 24 h of emergence and lasted effectively for six days, during which 95% of its eggs were laid and 10·8 large hosts were killed through host feeding. Unmated females of E. lopezi are arrhenotokous, laying only male eggs; eggs laid by mated females produced males and females in the ratio of 1:3 in favour of females.

Age structures and reproductive anomalies of two field populations of Glossina pallidipes Austen in Zimbabwe were compared. One population was treated with insecticide sprayed on odour-baited targets, while the other was left undisturbed. Both populations were sampled with F3 prism-type traps. Capture probabilities were higher for females in early stages of pregnancy than for those in later stages. Per-capita mortality rates were estimated from age distributions which had been corrected for rate of increase. The mortality rate steadily increased over time in the insecticide-treated area but remained roughly constant in the undisturbed area. Estimates of mortality had wide confidence intervals, and the mortality model is critically reviewed. No evidence was seen in the treated population for an increased incidence of abortion or other reproductive anomalies, or for a decrease in insemination rate.

A spray trial of a nuclear polyhedrosis virus (NPV) as an insecticide for Euproctis chrysorrhoea (L.) is described. The trial was carried out indoors in the spring on third-instar larvae emerging from overwintering nests onto small potted hawthorn trees (Crataegus sp.); the equipment used was the Turbair Fox Ultra Low Volume Sprayer. Dosages applied ranged from equivalents of 1 × 1011 to 1 × 1013 polyhedral inclusion bodies (PIB) per hectare. Infection was first detected in samples of live larvae after ten days and indicated rates of infection consistently lower than the final mortality attained. Larvae began to die of NPV infections 11 days after spraying, and mortality due to the virus ceased after ca 20 days; most larvae died in the fourth instar. Over the range of virus doses from 1 × 1011 to 5 ×10 12 PIB/ha mortality levels rose with dose, to a maximum of over 90%. Increasing the dosage to 1 × 1013 PIB/ha elicited no further increase in mortality. This preliminary trial suggests that the virus has considerable potential as a control agent, and field trials are, therefore, in progress.

A survey for ticks on livestock with emphasis on ticks parasitizing cattle was conducted below 16°N lat. in Mali. Seventeen species of ixodid ticks were recovered from cattle, 12 from sheep, five from goat, four from horse, one from donkey and four from camel. Amblyomma variegatum (F.), Boophilus geigyi Aeschlimann & Morel, Hyalomma marginatum rufipes Koch and H. truncatum Koch were widespread, and could each be collected as adults from cattle throughout the year in certain regions. A. variegatum was most numerous from the tropical woodlands to the Sahelo-Sudanian steppe. The prevalence of B. geigyi in Mali confirms an extended distribution of this species in West Africa. B. annulatus (Say) and B. decoloratus (Koch) were prevalent in the inland delta area and in south-western Mali. H. m. rufipes and H. truncatum were most numerous in the Sudanian and Sahelo-Sudanian steppe. H. dromedarii Koch, H. impeltatum Schulze & Schlottke and H. impressum Koch were collected in the steppeland areas. H. nitidum Schulze was collected for the first time in Mali. This comparatively more hydrophilic species was prevalent in the North Guinean forest and Sudano-Guinean vegetation zones. Of eight Rhipicephalus species from livestock, seven were collected from cattle: R. cuspidatus Neumann, R. evertsi evertsi Neumann, R. guilhoni Morel & Vassiliades, R. muhsamae Morel & Vassiliades, R. sanguineus (Latreille), R. senegalensis Koch and R. lunulatus Neumann. R. sulcatus Neumann was obtained only from sheep. The distribution and phytoclimatic associations of these species are discussed.