Four dispersal phases occur during larval development of Chilo partellus (Swinehoe) on young host plants, phase 1, ballooning of newly hatched larvae when moving from egg batch to plant whorl, phase 2, ballooning of first and second instars which leave the plant whorl in the week after egg eclosion, phase 3, walking prior to stem penetration, and phase 4, walking after stem penetration. In laboratory experiments larval dispersal was density dependent during dispersal phases 1, 3 and 4 and there were clear differences between maize and sorghum in the percentage of migrating lavae and time of migration. Maize plants accommodated many more pupae than sorghum plants which suggests that the distribution of older larvae in the field can be more clumped in maize than in sorghum. Pupal weight descreased with infestation level on sorghum but seemed less affected on maize. Resistance to starvation in four combinations of temperature and relative humidity increased with age. All hatchlings survived six hours′ starvation but with considerably reduced crawling capacity. Seven- and 15-day old larvae were descreasingly affected. Older larvae survived and maintained their mobility after 48 hours. Successful dispersal will depend on host-plant, egg load, and costs of migration; these costs will change with larval age.

A hand-applied ‘twist-ti’ pheromone formulation containing the combined pheromones of Pectinophora gossypiella (Saunders) (Gelechiidae), Earias vittella (Fabricius) and E. insulana (Boisduval) (Noctuidae) was used in trials conducted in Pakistan from 1986 to 1988. In plots of cotton ranging in area from 2.8 to 6.0 ha, season-long control of the bollworm complex was achieved using the pheromone formulation applied alone or together with one conventional insecticide treatment, with the conventional insecticide spray programme requring up to five applications of insecticide to achieve a similar level of control. No significant differences were found in yield estimates from plots treated with pheromones compared with plots receiving conventional insecticide treatments. Significantly higher levels of boll infestation and lower yield estimates occurred in control plots where neither pheromones nor insecticides were applied.

Insecticide resistant Myzus persicae (Sulzer) employ increased esterase activity to detoxify insecticides by hydrolysis and sequestration. The amount of esterase, and hence resistance, in individual aphids can be determined by measuring either overall naphthyl acetate hydrolysis in crude homogenates, or the specific enzyme responsible (E4 or FE4) after electrophoresis or immunological isolation. The ability of a total esterase assay, done in microplates, to discriminate between susceptible (S) aphids and resistant variants (R1, R2) with different amounts of E4/FE4, was compared with the resolving power of the more elaborate immunoassay technique. The immunoassay gave the better discrimination between variants, resolving them all with greater than 95% confidence, with particularly good separation of R1, from S. The microplate assay using crude homogenates, although a poorer discriminator, identified most of the very resistant (R2) aphids, and provided a robust and widely accessible method for broadly representing the resistance of field populations.

Chemical signals produced by leaves of stinging nettle (Urtica dioica), goat willow (Salix caprea) and tomato (Lycopersicon esculentum) attracted Anthocoris nemorum Linnaeus in a Y-tube plexiglass-walled olfactometer. A. nemorum reacted to odours of chloroform extracts of tomato foliage but not to water or methanol extracts. On the other hand, methanol or water extract of U. dioica attracted A. nemorum, but it was not attracted to chloroform soluble fractions of this plant. Adult A. nemorum could not distinguish between odour released by the aphids Myzus persicae (Sulzer) or Brevicoryne brassicae Linnaeus (Homoptera: Aphididae) and leaf odours emitted by Brussels sprout (Brassica oleracea). However, A. nemorum reacted to and distinguished between odours coming from either Tetranychus urticae Koch or T. cinnabarinus Boisduval (Acari: Tetranychidae) and from clean French bean (Phaseolus vulgaris) leaves.

A study was carried out to investigate the behavioural components of resistance in the Standlake strain of Musca domestica Linnaeus. The flies were collected from a poultry unit where azamethiphos spray-on-bait (Alfacron), had been regularly used to control the fly population. A no-choice laboratory cage test was used to observe the responses of the Standlake resistant strain to baits and compare it with two other strains namely, Sparsholt resistant and Cooper susceptible. The baits used were, Alfacron, sugar and analytical grade azamethiphos, sugar alone, and a blank target as control. Only female flies were used, each strain was exposed separately to each bait over a 50 minute period and the responses were recorded with a datalogger. The responses (per fly) recorded during each test period were: the number of visits to a bait; the time spent on a bait; the number of feeds and time spent feeding on the bait defined as the number of proboscis contacts and the length of time of proboscis contact with the bait. Knockdown of flies was recorded at the end of each test. All strains showed differences in their responses to baits. The Standlake strain showed the greatest difference to responses to Alfacron, with inhibition of proboscis extension when flies landed on the bait and a lower proboscis contact when extended, resulting in fewer flies being knocked down by Alfacron than by the sugar and azamethiphos bait. This suggested that inhibition of feeding on the Alfacron bait by the Standlake strain was caused by formulation components or contaminants and not the active insecticide ingredient, azamethiphos.

Six isofemale lines of the aphid parasitoid Aphelinus abdominalis (Dalman) were compared for life history traits related to parasitism of three cereal aphid species. The lines differed most in the number of hosts parasitized in 24 h and the developmental times of females and males. Cluster and discriminant analysis showed that these differences were pronounced between line I, line II and lines III-VI, but not between lines III, IV, V and VI. Cross-breeding experiments revealed reproductive barriers between the lines which proved to differ most in life history traits, indicating the possible existence of morphologically similar species. Given the variability in life history traits between lines of A. abdominalis recorded in this study, we suggest a careful selection of candidate strains for biological control will be rewarding.

The influence of the black cocoa ant Dolichoderus thoracicus (Smith) on losses due to the mirid Helopeltis theivora Waterhouse, black pod disease (caused by Phytophthora palmivora (Peronosporales)) and mammalian pests (rats, squirrels and civet cats) was studied over a two-year period in two separate fields of cocoa. Both fields initially had high D. thoracicus activity. In each field, ant-scarce plots were created by treating these plots with insecticides; ant-abundant plots existed where the plots were left untreated. An abundance of D. thoracicus clearly had a negative effect on numbers of mirids, with respectively 380 and 2222% more nymphs and adults being recorded in the ant-scarce than in the ant-abundant plots over the two-year period. An abundance of D. thoracicus did not increase black pod incidence: on the contrary it reduced incidence of the disease in both fields. The number of rat-damaged pods in ant-scarce plots was significantly higher than in ant-abundant plots in one of the fields but no significant difference was detected in the other. Regarding number of pods lost to squirrels and civet cats, no significant difference between ant-scarce and ant-abundant plots was obtained for both fields; the losses to either of these mammalian pests were extremely low. The number of healthy ripe pods in ant-abundant plots was 40.4 and 32.1% higher than in ant-scarce plots in the two fields, these increases being ascribed to protection from H. theivora damage by D. thoracicus.

Mortality of Tabanus fuscicostatus Hine females, engorged to repletion on bullocks treated with lambda-cyhalothrin impregnated ear tags, or placed on treated bullocks for periods of 15, 30, 45 or 60 s but not allowed to feed, was equal to or greater than 96%, while from 0% to 8% mortality was observed for controls. Average feeding time was significantly lower in T. fuscicostatus fed on treated bullocks (33%) than in flies fed on control bullocks, but average engorged weight was not significantly different between treatments. Mortality of T. americanus Forster females, placed on the backs of treated bullocks but not allowed to feed for periods of 15, 30, 45 or 60 s, was 16%, 44%, 76% and 100%, respectively. Results of bioassays in which flies were exposed to treated filter paper (LC50) or were topically treated (LD50) are presented per fly and per weight for T. fuscicostatus and T. lineola complex.

Studies on the morphology and distribution, and the role of trichomes in damage to cowpea (Vigna unguiculata) by the legume pod borer Maruca testulalis (Geyer) showed that trichome cover on individual cultivars varied in trichome length and density, but not in trichome type from different plant parts. Trichome density on different parts decreased with increasing plant age. Significant (P <0.05) negative correlations were obtained between total trichome density on pods, pod infestation and damage severity. In contrast, correlations between length of non-glandular trichomes on pods, pod infestation and damage severity were not significant. Results suggest that trichome length may be less important than density in reducing pod damage by M. testulalis in cultivated cowpeas. It is, therefore, concluded that breeding for a higher level of trichomes in high yielding and agronomically desirable cowpea cultivars, will serve as an important component in the integrated management of M. testulalis.

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.

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.

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.

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.

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.

This paper presents the first report on the sublethal effect of an insect growth regulator (IGR), hexaflumuron, on the feeding behaviour of vector mosquitoes, Culex quinquefasciatus Say, Aedes aegypti (Linnaeus) and Anopheles stephensi Liston. Percentage engorgement and feeding behaviour of the adults of the three species emerged after sublethal exposures at the larval and pupal stages were markedly affected. Depression in blood feeding was significantly higher in Aedes aegypti with lower blood engorgement ratio. The proportion of females that failed to take a blood meal was higher in A. aegypti (30.2%) than in the other species when pupae had been exposed to 0.05 mg/1 hexaflumuron. Depression in blood feeding was probably due to abnormalities in the functioning of the mouth parts and feeding behaviour. No adverse effect on the feeding activity was noticed in the F1 generation of the treated species.

Population densities of male and female Musca vetustissima Walker were estimated from recapture rates of marked flies in baited fly traps. Marked flies of laboratory and field origin were equally trappable. Trap catches of field flies were also compared with net catches for which the human collector was the source of attraction, and relationships are presented for estimating population densities based on both sampling methods. Estimates of fly density from trap and net catches at fixed locations have similar precision, coefficients of variation being approximately 55% for both males and females of M. vetustissima. Comparison of estimated fly densities (flies/ha) and annoyance indices, estimated numbers of flies approaching a collector each minute at 29.5°C, in ‘good’ and ‘bad’ fly years suggests that M. vetustissima is a potential nuisance whenever population densities exceed 1000 flies/ha.

As the tsetse fly, Glossina morsitans morsitans Westwood extricates itself from the puparium and moves upward through the soil the ptilinum expands and contracts rhythmically and thus generates a stereotypic behavioural pattern that persists for up to 10 h if the tsetse fly remains confined. The response, which is easily recorded tensometrically from the movements of the ptilinum, can be exploited as a tool for evaluating the behavioral response of tsetse flies to various neurotoxic agents. The behavioural assay proves useful in providing precise information about the latency of the response and lethal time, and can suggest likely modes of action. For example, sublethal doses of pyrethroids reversibly suppressed the contraction cycles, a response consistent with the peripheral action of this insecticide. In contrast, chlorinated hydrocarbons greatly increased contraction frequency, a result consistent with the action of these agents on the central nervous system (CNS). Assays utilizing eight commercial insecticide preparations (Pybuthrin, K-othrin, Vaztak, Reldan, Safrotin, Acetellic, DDVP, Antrix) demonstrate the utility of this method for detecting subtle perturbations of the CNS and neuromuscular system.