Feeding by adults of Neochetina eichhorniae Warner on water hyacinth, Eichhornia crassipes, significantly increased the hardness of the lamina of the youngest leaf and the petioles of the youngest three leaves, while the moisture content of the petioles and laminae was significantly reduced. However, variations in leaf hardness did not significantly affect feeding by the weevils, and leaf age was considered to have a greater effect. The results help explain field observations of the relative abundances of N. eichhorniae and the pyralid Sameodes albiguttalis (Warren), which also attacks water hyacinth.

Lucerne labelled with 131I or 125I was used to mark field colonies of the harvester termite Hodotermes mossambicus (Hagen) in South Africa. The foraging area was delineated by plotting the distribution range of radioactive workers collected on the soil surface over a period of up to 57 days. Foraging areas of single colonies varied between 0.5 and 3.1 ha. These areas were not necessarily the exclusive territory of a single colony. Inter-worker aggression assays confirmed these conclusions.

A key for the identification of males of all Afrotropical species of the subgenus Atherigona of Atherigona described to date is presented. Four new species, A. alaotrana sp. n. from Madagascar, A. bowdeni sp. n. from Uganda, A. dentifolia sp. n. from Kenya and A. palpalis sp. n. from Nigeria, are described.

Four groundnut genotypes were grown in a randomized block design across a drought-stress gradient to determine the influence of this factor on insect distribution in the 1985–86 post-rainly season near Hyderabad, in peninsular India. The leaf-miner Aproaerema modicella (Deventer) was most abundant on the most stressed plants. The cicadellid Empoasca kerri Pruthi had the reverse distribution. The thrips Frankliniella schultzei (Trybom) and Scirtothrips dorsalis Hood were at first densest where drought stress was least. Their distribution subsequently became reversed and, as the condition of their hosts worsened, they again became most abundant at the wetter end of the gradient. Bud necrosis disease caused most mortality where drought stress was highest. A subsidiary experiment indicated that the intensity of overhead irrigation did not influence the density of A. modicella. There were marked genotype effects: JL 24 carried the highest density of insects and was most susceptible to bud necrosis disease: NC Ac 343 had the lowest leaf-miner and cicadellid populations. M 13 and ICGS 11 had intermediate characteristics.

The impact of Phenacoccus manihoti Matile-Ferrero on growth and tuber yield of cassava, and the results of its biological control by the exotic parasitoid Epidinocarsis lopezi (De Santis) were investigated in a survey of 60 farmers' fields in Ghana and Ivory Coast over an area of 180 000 km2 of the savana and forest ecosystems. Twenty-nine variables associated with plant growth, agronomic and environmental factors, and insect populations were recorded. Densities of P. manihoti were closely correlated with stunting of the cassava shoot tips and, less so, with the rate of stunting early in the growing season. With increasing mealybug infestations, average harvest indices declined and populations of E. lopezi and of indigenous coccinellids increased, but parasitoids were found at lower host levels than were predators. The length of time E. lopezi had been present in an area was the most important factor influencing mealybug densities. Thus, P. manihoti populations were significantly lower where E. lopezi had been present for more than half the planting season than in areas where E. lopezi was lacking or had been only recently introduced. A significant proportion of the farmers in the savanna zone, where P. manihoti populations were much higher than in the forest zone, had observed this decline due to E. lopezi. Tuber yield losses due to P. manihoti in the absence of E. lopezi were tentatively estimated at 463 g/plant in the savanna zone. No significant effect was found in the forest region. When E. lopezi was present, average P. manihoti damage scores were reduced significantly, both in the savanna and forest regions. The increase in yields was 228g/plant or about 2.48 t/ha in the savanna region.

Experiments were conducted to investigate the role of pubescence in the resistance of two wild cowpea varieties, TVNu 72 and TVNu 73, to feeding and damage caused by two cowpea pests, Maruca testulalis (Geyer) and Clavigralla tomentosicollis Stål. The fine structure of the trichomes was also studied by electron microscopy in order to try to determine the role played by trichomes in the resistance of these varieties to both pests. Feeding and development were deterred in both insects on pods of TVNu 72 and TVNu 73 with or without trichomes compared to the susceptible variety, IT84E-124. In M. testulalis, the same effect was observed on seeds and flowers. However, M. testulalis larvae fed and developed better, as indicated by the higher growth index values, when trichomes were removed. Growth index estimates showed a 13-fold decrease when trichomes were left intact on both TVNu 72 and TVNu 73 compared to the cultivated susceptible control. It was concluded that resistance to M. testulalis was based on trichomes in the first instance (as a first line of defence) and phytochemicals. Survival of C. tomentosicollis nymphs was not affected by trichome removal even though adult feeding damage was slightly increased. This is explained in line with previous reports which indicate that phytochemicals may be the principal factor in the resistance of TVNu 72 and TVNu 73 to this species. Glandular and non-glandular trichomes were found to be present on both the cultivated and wild cowpea. Trichomes in the two types of cowpea differ significantly only in trichome number (susceptible cultivated cowpeas have more) and non-glandular trichome length (those on wild cowpea are ca 20 times longer). Trichome length and angle to pod surface seemed to be more important than density per se.

The importance of Toxoptera species as agricultural pests is briefly discussed, along with the recent discovery in Africa of T. odinae (van der Goot). Banana is recorded as an unusual new host-plant record, and a table of other hosts is presented. The genus Toxoptera is defined and a key to species given.

Insecticidal aerosols dispersed from aircraft are used in control measures against Glossina spp., and the interpretation of spray monitoring data in terms of the likely effect on the flies requires some knowledge of variation of the collection efficiency of the flies under a range of appropriate conditions. A low speed wind tunnel was used to measure the collection efficiencies of the various component parts of an adult of G. morsitans Westwood when at rest on cylinders simulating the branches and twigs of the natural habitat. The wind speed range was from 0·25 to 1·5 m/s and monodisperse droplets 10, 15, 20 and 25 μm in diameter were used. Although certain body zones exhibited very high apparent collection efficiencies (primarily due to interception), the average overall efficiencies varied from as low as 0·8% for 10-μm droplets at 0·25 m/s up to 22% for 25-μm droplets at 1·5 m/s.

The human helminth parasite burdens on cyclorrhaphan flies was studied in an aboriginal settlement in Malaysia in 1987–88. Chrysomya megacephala (F.), which formed 79.5% of total fly population trapped in this settlement, had eggs of the roundworm Ascaris lumbricoides, the pinworm Trichuris trichiura and hookworm (Necator americanus and/or Ancylostoma duodenale) on the external body surface and gut lumen. There was a close correlation between monthly rainfall and the mean numbers of C. megacephala caught per two trap-hours. Eggs (but no larvae) of the parasites were found on flies when the monthly rainfall and the C. megacephala population were relatively high, in April-June 1987, October-November 1987 and March 1988. Human helminth eggs were also isolated from C. rufifacies (Macquart) and Hemipyrellia tagaliana (Bigot), being recorded from the latter in Malaysia for the first time.

Field observations on the foraging behaviour of Hodotermes mossambicus (Hagen) showed that workers did not exhibit any marked preference for a particular grass species in a degraded savanna area in the north-western Orange Free State, South Africa. Two commercial baits, with carbaryl and sodium fluosilicate as their active ingredients, are used for H. mossambicus control; these baits were shorter, heavier and wider than the natural plant material collected by the workers. Thus, they are probably not transported as readily into the nest as the natural food. Minor workers were observed to be mainly responsible for transporting plant material, while the major workers were primarily responsible for cutting it. Observations on laboratory colonies indicated that workers collected litter first and thereafter harvested a tussock of grass from the top downwards. Foraging stopped once the tussock had been trimmed to a height of approximately 3 cm.

Cormiococcus gen. n. is described for C. dieramae sp. n., a mealybug collected in South Africa on the corms of Dierama sp., imported to the Royal Botanic Gardens, Edinburgh, UK. Another mealybug species, Chorizococcus lachenaliae sp. n., is described from the bulbs of Lachenaliae sp., imported from South Africa to the Royal Botanic Gardens, Kew. Chorizococcus bardus (De Lotto) comb. n., originally described from South Africa on bulbs of Narcissus capensis, is transferred from Maconellicoccus Ezzat.

Larvae of the southern African geometrid moth Comostolopsis germana Prout feed on the shoot apices and axillary buds of Chrysanthemoides monilifera, a serious alien weed of native vegetation in Australia. The insect was found in low abundance throughout the distribution of its hosts, C. incana and C. monilifera, in southern Africa. Larvae were present throughout the year in subtropical Natal, but were absent in winter in the cooler, Mediterranean type climate of Cape Province. In host-specificity tests using 65 plant species from 26 families, Comostolopsis germana completed development only on Chrysanthemoides monilifera monilifera and C. monilifera rotundata. Insignificant, exploratory feeding occurred on Olearia axillaris (Compositae) and pea, Pisum sativum (Leguminosae). In multiple-choice oviposition tests eggs were laid on 41 species, but a strong preference was shown for the foliage and stems of C. monilifera. Larvae grazing the flower buds, pedicels and peduncles of C. monilifera may reduce the reproductive capacity of their host and contribute to its control. Comostolopsis germana has been approved for release as a biological control agent of Chrysanthemoides monilifera in Australia.

Temephos resistance in savanna cytospecies of Simulium damnosum Theobald s.l. and the forest cytospecies S. sanctipauli Vajime & Dunbar, from West Africa is correlated with an increase in general esterase activity. Metabolism studies indicated that esterase products were the major metabolities in both forest and savanna resistant strains of S. damnosum s.l. compared to the susceptibles. In the presence of an esterase synergist, a large amount of the oxon analogue of temephos was produced by the resistant forest cytospecies S. sanctipauli. This strain is also resistant to chlorphoxim, and it is likely that the increase in oxidative activity observed is connected with the chlorphoxim rather than the temephos resistance. There was no evidence of glutathione transferase-, oxidase- or acetylcholinesterase-based temephos resistance machanisms in the savanna species of S. damnosum s.l.

Rastrococcus invadens Williams was first noticed in Togo in 1981 and has since become a serious pest on many plants, especially mango and citrus. In June 1986, a programme for its biological control was begun, resulting in the introduction into Togo in October 1987 of an encyrtid parasitoid, Gyranusoidea tebygi Noyes. The parasitoid was reared under a simple system and releases were made from November 1987. The parasitoid established readily under a range of ecological conditions and produced significant control within the first year up to 100 km from each release point.

DDT metabolism in Phlebotomus papatasi (Scopoli) was investigated and compared to that in DDT-resistant and susceptible strains of Culex quinquefasciatus Say and Anopheles gambiae Giles with the objective of establishing baselines for sandfly studies. P. papatasi produced eight metabolites of DDT, with DDE predominating, as in the two mosquito species. Both oxidases and glutathione transferases were found to be involved in DDT metabolism in insecticide-susceptible adults of P. papatasi. The activity level of glutathione transferases and the reduced and oxidized difference spectra of cytochrome P-450 were measured spectrophotometrically. The level of glutathione transferase activity in P. papatasi was lower than that in susceptible C. quinquefasciatus adults when expressed in terms of the activity per milligram of soluble protein but, in contrast, the cytochrome P-450 was slightly higher in both the reduced and oxidized states.

A cheap power pack that could be run off a 12-V car battery was constructed using a 12–250–V DC-DC converter. The power pack is small and light and can be used to run a Helena cellulose acetate electrophoresis system away from a mains electricity supply. The system was used sucessfully to identify adults of the Simulium damnosum Theobald complex in a field laboratory in northern Sierra Leone.

An airborne radar system able to measure insect density profiles and the orientation of individual insect targets was developed using standard components. Using the system, typical moth targets, with a radar cross-section of 1 cm2, can be detected to a range of about 1 km. Signals from 48 separate height bands, each 15 m deep, are recorded on three analogue data channels. Analogue outputs related to aerial population per hectare can be viewed in real-time. Signals recorded during recent field work show an inclined layer over a track length of 30 km, with target orientation profiles at two positions along the layer. The strongest orientation occurred in regions of wind shear. Airborne entomological radar powerfully complements existing techniques by virtue of its mobility, providing unique opportunities to study the spatial organization of migration, to track features as they develop and to survey large areas.