The build-up of resistance to phosphine and methyl bromide in the developmental stages of Tribolium castaneum (Herbst) after six selections in successive generations was investigated in the laboratory at 25 ± 1°C. Responses of the life stages of the fumigant-selected insects were compared with those of untreated controls with a 24 h exposure and mortality was assessed after 14 days. Phosphine induced the development of resistance irrespective of the life stage chosen for selection. The onset of phosphine resistance was noted after the first selection but the levels of resistance attained in the different stages varied depending on the stage tested, and in each case the degree of expression was different in the four stages of T. castaneum. After selection, phosphine resistance was highest in the pupae followed by eggs, adults and larvae. Resistance to methyl bromide in the methyl bromide treated insects increased only slightly (less than × 2.0). Adults derived from egg, larva, pupa and adult-selected methyl bromide lines showed cross-resistance to phosphine (× 1.8 to 11.5 at LD95), while cross-resistance of adults to methyl bromide was noted only in adult-selected phosphine-resistant insects (× 1.5 at LD95).

Eight steers of European breed, Bos taurus type which were shown to be negative for antibodies against Theileria parva, were divided into two groups of four animals each. Animals in one group were inoculated with 0.5 ml undiluted tick-derived T. p. parva Muguga strain and animals in the other group were inoculated with 1 ml undiluted tick-derived T. p. parva Kilae strain to infect them. The two infected groups of cattle were simultaneously infested with uninfected nymphal Rhipicephalus appendiculatus Neumann in separate cloth patches. Ticks were from five populations, i.e., four from different geographical zones in Kenya and one laboratory population, in separate cloth patches. After moulting, the adult ticks were fed on rabbits for three days and their salivary glands were examined by microscopy for infective stages of the parasite. This revealed significant differences in the five populations as regards to their susceptibility to Theileria parva parasites.

A significant relationship between pteridine content of the head, fly age and fly size, which was independent of temperature, was found for adult females of Simulium sirbanum Vajime & Dunbar using flies maintained at different constant temperatures after eclosion. Similar relationships for flies maintained at varying temperatures within the species' natural ranges were obtained in experiments with the Beffa form of S. soubrense Vajime & Dunbar (sensu Post, 1986), S. sanctipauli Vajime & Dunbar (= S. soubrense sensu Post, 1986), S. squamosum (Enderlein), S. yahense Vajime & Dunbar and S. damnosum sensu stricto. Common slopes for the effects of age and size could be fitted to all these species. Relations between pteridine concentration in the head, fly size and age, with the common slopes but with species-specific intercepts, were used to estimate the age structure of wild-caught populations of the Beffa form of S. soubrense, S. squamosum and S. yahense. A dry season sample of S. squamosum was estimated to be older than a wet season sample. The mean age of the S. soubrense population, sampled one week after its presumptive breeding sites were treated with larvicides, was estimated to be 13.5 days. The maximum was 30.9 days and a frequency distribution of the estimates had distinct peaks, at three day intervals between 8 and 21 days. The significance of the results is discussed in relation to fly longevity and gonotrophic cycle lengths.

A rapid visual field screening technique for resistance of cowpea (Vigna unguiculata) to the legume pod borer Maruca testulalis (Geyer) was developed. The methodology involved measurement of two damage parameters: field examination of flowers for signs of M. testulalis injury or larval presence (i.e. rapid visual technique - flowers) and/or a pod evaluation index, from the ratio of pod load to pod damage (i.e. rapid visual technique - pods). Highly significant (P <0.01) correlations were obtained between the rapid visual field screening technique and the existing field screening technique. The latter is recommended as a fast and precise method for initial screening large collections of genotypes while the former should be used for more detailed selection and other resistance studies. The technique described here uses fewer variables than the previous method and thereby reduces costs while improving efficiency and precision.

The osmolality and ion concentrations in the haemolymph and the body of lepidopterous larvae were studied under different experimental conditions. It was shown that the haemolymph osmolality of Aglais urticae (Linnaeus) larvae returned to normal three hours after the injection of 0.4 M sucrose or 0.4 M sodium chloride, despite the fact that in the latter case, the level of sodium was very high (to 53.1 mM vs 4.5 mM in control). The injection of 0.2 M or 0.4 M sodium chloride did not induce significant changes in the concentration of ions, other than sodium, in haemolymph. Treatment of Mamestra brassicae (Linnaeus) larvae with insecticides (DDVP, lindane, decis) led to a fast loss of body weight (up to 30%). This was due to dehydration, which was accompanied by a significant decrease of potassium content in body tissue, but not in the haemolymph. Study of the haemolymph parameters of Lepidoptera and insects taken from their natural environment indicates that the lowest values of variation coefficient related to osmolality and to the concentration of the dominant cation of the haemolymph (sodium, potassium or magnesium). These data suggest effective regulation of osmolality and ion concentration in the insect haemolymph.

An odour-baited electric net placed in thick bush caught more Glossina pallidipes Austen when sited at ground level (0.2–1.2 m) than when sited in the top of the bush (1.4–2.4 m) or just above it (2.6–3.6 m). However, a similar net running concurrently 4 m away in a game trail through the bush caught far more flies. When electric nets were placed in the centre of two adjacent game trails in this bush and then one of the trails was barricaded with branches from nearby bushes, the catch declined in that trail and increased proportionately in the other. It is inferred that tsetse flies navigate up host odour plumes by finding gaps in thick vegetation rather than by flying over the top or through it, and that game trails are important forms of such gaps. The implications for siting traps and targets are noted.

The effects of ambient temperature on all component life cycle stages of the sheep blowfly Lucilia sericata Meigen were examined under controlled conditions. The critical base temperatures and the number of day-degrees required for completion of each stage were determined. Using these data a simple simulation model was developed to evaluate temperature effects on the seasonal pattern of L. sericata abundance. The number of flies estimated by the model to be available for capture, together with the temperature over each capture period determining adult activity levels, were able to account for 77% of the variance in L. sericata abundance observed over a season.

The oviposition, larval arrest and establishment by the stem borer Chilo partellus (Swinhoe) were measured on different maize genotypes during anthesis. The maize genotypes tested were: Inbred A (Susceptible), Mp 704, MBR-8637, MBR-8650, MBR-8668, Poza Rica 7832, ER-29 SVR, Katumani Composite B, MMV 400, Bulk CG 4141, and ICZ2-CM. The moths oviposited on the middle leaves of the plant and the neonate larvae moved to leaf sheaths and ear husks to feed (arrest). As they grew older, the larvae invaded the stem, ear shanks and tassel to complete feeding (establishment) and to pupate. The response of the stem borer differed with resistant and susceptible maize genotypes at anthesis. More eggs were laid and larval arrest was higher on the susceptible than on resistant genotypes. Genotypes also differed in the resistance of feeding sites to larval establishment; the genotype Poza Rica 7832 showed resistance to larval establishment in the stems and ears, but the shank was heavily infested. By contrast, MBR 8637 showed greater resistance to larval establishment in the shank than the other genotypes. These resistance sources could be utilized effectively in a maize breeding programme to develop varieties with moderate to high levels of resistance at all potential feeding sites.

A model has been developed which estimates the egg and nymphal development periods of the desert locust Schistocerca gregaria (Forskål). The model uses long-term monthly mean temperatures from a number of weather stations in the desert locust area. The computer program calculates the daily mean temperature and the daily related amount of development. It then accumulates the percentage of development estimated on successive days until the total reaches or exceeds 100. The model can be started on any day of the year at any given development stage and it can calculate development backwards in time as well as forwards. The model should be a useful aid in forecasting desert locust population developments and for the planning of surveys.

Trypanosome infections were monitored in three species of tsetse fly (Glossina pallidipes Austen, G. morsitans centralis Machado, and G. brevipalpis News-tead) at four locations in the Kagera River region of Rwanda from May 1989 to September 1990. Two of the four areas (Mpanga Ranch and Bukora Ranch) were subjected to tsetse fly suppression operations with odour-baited traps. Proboscis infections of the Trypanosoma congolense and T. vivax types accounted for roughly equal numbers of the 207 mature infections detected (3.8%). Variation in infection rates was area-specific rather than tsetse species-specific. Order of magnitude differences in tsetse fly densities among areas were not correlated with differences in infection rates at the start of tsetse fly suppression operations. Similarly, declines in population density on both control and experimental areas were not associated with significant changes in infection rates. The prevalence of trypanosomiasis in cattle at Bukora Ranch was not affected by a roughly 90% reduction in Glossina densities. T. congolense accounted for 79% of the infections at an overall prevalence rate of 5.5%. Trypanosomiasis in cattle persisted at extremely low densities of about 0.1 fly/trap/day. Treatment of cattle with diminazene aceturate (BereniR) suggested that many T. congolense parasites were drug resistant, and hence, were cycling among cattle due to the few Glossina present.

Incubation of eggs of the African migratory locust, Locusta migratoria migratorioides (Reiche & Fairmaire), was examined in the Orange Free State (OFS) highveld of South Africa where the locust is a recurring pest of cereal crops. A minimum incubation time of 16±SE 0.97 d was recorded in summer and this progressively increased through autumn as temperatures declined. Eggs laid in autumn overwintered for 140±2.63 d until spring, when rising temperatures initiated hatching. Controlled laboratory studies established that the threshold for egg development was in the region of 15.6°C and that eggs required 5268 degree-hours to complete their development. Analysis of hourly soil temperature records, measured at egg pod depth in the field, showed that temperatures first dropped below this critical temperature threshold during mid-April, after which eggs became quiescent and overwintered until spring. There was no evidence of diapause in the field and overwintering eggs exhibited a wide range of embryonic development. Quiescence during winter on the OFS highveld was therefore a simple temperature-induced response. This is the first record of prolonged overwintering in the egg stage of the migratory locust in Africa.

Four Old World blow flies (Diptera: Calliphoridae), Chrysomya albiceps (Wiedemann), C. putoria Wiedemann, C. megacephala (Fabricius), and C. rufifacies (Macquart), have recently invaded the New World. The interaction of Chrysomya rufifacies (Macquart) with native carrion flies in Texas, USA, was investigated by reducing oviposition by the invader on rabbit carcasses outdoors. These carcasses produced significantly more Cochliomyia macellaria (Fabricius) adults compared to carcasses on which the invader was not reduced. The results suggest that C. macellaria populations will decline where the two species co-occur. They also support the hypothesis that the carrion community is saturated with species, and provide a mechanism for the possible elimination of Lucilia caesar (Linnaeus) in Madeira and the reduction of C. macellaria in South America by Chrysomya albiceps (Wiedemann).

A range of techniques was used to quantify the nocturnal flight behaviour of Helicoverpa armigera (Hübner) in pigeon pea (Cajanus cajan) crops near Hyderabad, in central India. These included visual observations in the field, the use of field cages and a vehicle-mounted net, optical and video imaging in the infra-red, and radar. Moth emergence from the soil was observed to start at dusk and recruitment continued steadily throughout the first half of the night. Little activity was observed in moths on the night of emergence, except for weak flying or crawling to daytime refuges. Flight activity of one-day old moths started about 20 min after sunset, peaked 15 min later and within about an hour of sunset had declined to a low level which persisted for the rest of the night. Flight of reproductively mature moths was most frequent about 1 h after sunset and at this time mainly comprised females searching for oviposition sites and nectar sources. By about 2 h after sunset, flight had decreased markedly, but there was a slight increase in activity in the second half of the night caused by males undertaking mate-finding flights. Under the conditions studied, the majority of H. armigera dispersed below 10 m, and there were no mass ascents to higher altitudes like those observed at outbreak sites of the African armyworm, Spodoptera exempta (Walker) (Lepidoptera: Noctuidae). The contrasting migratory strategies of H. armigera and S. exempta are briefly discussed.

Shin Etsu twist-tie ropes containing the spiny bollworm (Earias insulana(Boisduval)) pheromone were tested for mating disruption in a cotton field in Israel during 1991. Two applications of the Shin Etsu rope formulation (1000 ropes/ha), containing 50 mg pheromone per rope, effectively disrupted mating of E. insulana, reduced damage to cotton bolls, and minimized the number of chemical treatments needed. The success of the mating disruption, which lasted for more than 3.5 months, was indicated by the following: 1. Reduction of trap catches in the pheromone-treated plot as compared with the control plot (commercially treated with insecticides). 2. Lower infestation of cotton bolls in the pheromone-treated as compared with the control plot. 3. Over 90% reduction in mating success in the pheromone-treated plot, as indicated by the number of mating pairs collected at night in the two plots. 4. Reduced number of insecticidal treatments applied in the pheromone-treated plot. The release rate of the pheromones was monitored by periodical gas chromatography analyses of the remaining pheromone in ropes. The half lives of the E. insulana and Pectinophora gossypiella (Saunders) (Lepidoptera: Gelechiidae) formulations were similar, with t1/2=45-60 days. In Israel, E. insulana and P. gossypiella infest cotton fields almost simultaneously and are controlled by the same insecticides. Therefore, the control of E. insulana with pheromones is essential in order to give reasonable meaning to the commercial application of pheromones for the control of P. gossypiella, as is practised today in many cotton fields. The present study indicates that control of E. insulana by the mating disruption technique is viable.

Mating competitiveness and sexual or total competitiveness of males of the house fly, Musca domestica Linnaeus, treated with 1.0% hexamethyl phosphoramide (hempa) were measured quantitatively from direct observations and ratio test methods, respectively. From direct observations, treated males of Cooper and Boxted strains of M. domestica were found to obtain more first matings than untreated males (P <0.01 and P <0.05, respectively) when competing for untreated females, whilst by using the ratio test method under laboratory conditions, total competitiveness values (C) of treated males of the two strains were estimated to be 0.72–0.89 and 0.75–0.97, respectively, at three different ratios from 1:1:1 to 3:1:1.

Heifers were treated with the recommended doses of ivermectin: 0.2 mg/ kg bw by subcutaneous injection or 0.5 mg/kg bw by pour-on. An analytic procedure is described and used for the detection of ivermectin residues excreted in dung. A large amount of the higher pour-on dose was excreted during the first five days after dosing due to a more rapid distribution to intestinal contents. Later faecal concentrations after the pour-on treatment were lower than those found after subcutaneous injection. No degradation of ivermectin was detected in pats exposed in the field for up to 45 days. Ivermectin excreted in dung voided 1–2 days after both treatments significantly reduced the number of dung inhabiting larvae of Aphodius spp. (Coleoptera: Scarabaeidae), but no effect was seen in dung deposited 13–14 days after treatments. Development of cyclorrhaphan larvae was inhibited in dung deposited up to 28–29 days after subcutaneous injection treatment, but only inhibited in dung deposited up to 13–14 days after pour-on treatment. The numbers of Nematocera larvae were not affected. In a laboratory bioassay the Diptera Musca autumnalis DeGeer and Haematobia irritans (Linnaeus) suffered higher mortality in dung from heifers treated by the subcutaneous injection 13–14 days earlier than in dung from heifers treated by pour-on at the same time. After subcutaneous injection, a significant reduction in the rate of decomposition was found in dung from heifers treated 1–2 days earlier, whereas pour-on led to a delayed decomposition in dung collected up to 13–14 days after treatment.

A key is provided for the recognition of previously described Encarsia species which are known to attack the tobacco whitefly, Bemisia tabaci (Genna-dius). 28 nominal species are included, of which type material has been examined for 22. Eight new synonymies are proposed: Encarsia aleyrodis (Mercet) and E. partenopea Masi are both synonymized with E. inaron (Walker); E. bemi-siae (Ishii) is synonymized with E. transvena (Timberlake); E. citri (Ishii) is synonymized with E. strenua (Silvestri), E. angelica Howard and E. deserti Rivnay & Gerling are both synonymized with E. luteola Howard; E. perspicuipennis (Girault) is synonymized with E. quaintancei (Howard); E. tabacivora Viggiani is synonymized with E. pergandiella Howard. E. hispida De Santis is removed from synonymy with E. meritoria Gahan. A lectotype is designated for E. porteri (Mercet). The known distributions and alternative hosts of Encarsia species attacking B. tabaci are provided as well as references to biology and notes on their use in biological control.

Deposits of deltamethrin suspension concentrate (s.c.) on Terylene net and cotton cloth were bioassayed in Zimbabwe by exposing them to fed, female Glossina pallidipes Austen, using a 45 s contact with cloth and a brief collision with net. On textured yarn net, the effective life of deposits produced from immersion in 0.1% deltamethrin was longer than on flat yarn net, apparently because the textured net held more insecticide and the insecticide was lost more slowly. The addition of an absorber for ultra-violet light (0.1% 2-hydroxy-4-methoxybenzophenone-5-sulphonic acid) did not significantly extend the effective life of deltamethrin deposits on cloth or net. Applying deltamethrin s.c. as a 0.6% suspension to cotton cloth produced mortalities of <90% for 300 days. Applications of 0.8% deltamethrin on cotton cloth and textured net produced mortalities of <70% for 12–16 months and 9 months, respectively, compared to 4–10 months and 5–7 months, respectively for applications of 0.1% deltamethrin. Chemical analyses indicated that the longer effective life of the 0.6–0.8% was due to a higher initial amount of insecticide and a lower rate of loss. It is suggested that for controlling tsetse in southern Africa, all-cloth targets sprayed with 0.6% deltamethrin s.c. will have an effective life of ca. one year.