Among the important constraints to vegetable production in Africa are the lepidopteran pests, in particular Helicoverpa armigera (Hb.) and Plutella xylostella (L.) which cause direct yield loss as well as cosmetic damage. Egg parasitoids, especially Trichogramma spp., shown promise as biocontrol agents against both species in previous studies. In Africa, surveys have so far recorded 18 species of Trichogramma, eight of Trichogrammatoidea and seven of Telenomus besides one species each of Baryscopus and Oencyrtus. For effective utilisation of egg parasitoids in vegetable ecosystems in Africa, the experience gained elsewhere should be suitably utilised, and complementary research undertaken. This paper examines the scope for use of egg parasitoids in Africa, focusing on five research areas. Firstly, surveys should be undertaken to collect, characterise, and catalogue the different species and strains of egg parasitoids occurring in the region. Secondly, the pest status of target Lepidoptera and the potential demand for use of egg parasitoids in the major ecologies should be assessed. Thirdly, the local and/or exotic species/strains with good potential to control H. armigera and P. xylostella need to be identified, and fourthly, analyses aimed at selecting appropriate mass production and delivery systems for Trichogramma use in major vegetable crops should be undertaken. Finally, optimisation of inundative release strategies should be researched on. The scope for research collaboration within Africa and internationally is discussed.

The number of eggs and mobiles (immatures and adults) of Amblyseius manihoti on entire plants was determined during a 10-month period in a cassava field located in the Bahia region of Brazil. Observed percentages of eggs, immatures and adults were compared to theoretical stable age distributions (58 % for eggs, 24 % for immatures and 18 % for adults). These comparisons served as a basis to discuss the influence of fecundity, mortality and migration on the age structure of populations.

The effect of gamma irradiation on the time-course mortality and radiosensitivity indices in 1- and 10-day-old adult Tribolium anaphe, T. brevicornis, T. castaneum, T destructor and T. freemani, was studied. Longevity was always adversely affected by irradiation, and it was linearly dependent on the dose rate. Except for 10-day-old adults, all the insects died within 12 weeks of γ-irradiation at 4 and 5 krad. In addition, T. destructor was markedly more radioresistant at all dose levels, and lived longer than the other species. The mean survival times of adults were generally shorter in females than in males for all species. The radiosensitivity indices did not vary widely among the species, but decreased as the dose increased in all the species, indicating that the resistance of the species was dose-dependent.

A 1994 field survey of Sahelian grasshoppers and locust populations in natural vegetation, millet and rice fields in The Gambia determined the period between mid-August and early September to be the optimal time for applying oil-formulated conidia of the entomopathogenic fungus Metarhizium anisopliae var acridum to control the acridids. Locust and grasshopper cadavers were also examined for fungus infection. Metarhizium anisopliae was absent from cadavers of natural grasshopper populations, while the entomopathogenic fungus Entomophaga sp. was recovered on Hieroglyphus daganensis cadavers and the nematode Hexamermis sp. from Kraussaria angulifera, The predatory cattle egret fed on swarming adult desert locusts.

Insecticidal δ-endotoxins of Bacillus thuringiensis, Cry IA (a, b and c) were prepared from over-expressing cells of Escherichia coli and bioassayed against the third instars (6-day-old) of the spotted bollworm, Earias vittella Fabricius (Lepidoptera: Noctuidae), using artificial diet. The median lethal concentration (LC50) values were calculated for 6 days of exposure to δ-endotoxins. Cry IA(a) was found to be the most toxic (LC50 141.2 ng/cm2) followed by Cry IA(a) and Cry IA(b) with LC50 values of 224.5 and 300.5 ng/cm2 respectively. A highly significant reduction in larval weight took place in the surviving larvae treated with sub-lethal doses of the insecticidal crystal proteins.

l-menthol isolated from the essential oil of Mentha arvensis and seven of its acyl derivatives were tested for contact and vapour toxicity, and ovicidal and repellent activity against the storage pests Callosobruchus maculatus F., Rhyzopertha dominica F., Sitophilus oryzae L. and Tribolium castaneum Herbst. Menthyl propionate and l-menthol were highly toxic in contact assays and vapour toxicity assays respectively. l-menthol was also found to be strongly repellent (82–100% at 0.353 μg/cm2 dose) against all the insects, while menthyl acetate was highly ovicidal against T. castaneum.

The effects of increasing population densities of the cowpea pod-sucking bugs (PSB) Riptortus dentipes, Mirperus jaculus, Anoplocnemis curvipes and Nezara viridula were studied in caged potted cowpea (Vigna unguiculata) plants with infestation levels from 0 (control) to 12 adult bugs per cage. Generally, there was an increase in damage to cowpea (measured as damage to pods and seeds) with increasing in insect density. There was also a highly significant correlation between the number of infesting adult bugs and damage to pods and seeds, and a significant negative correlation between bug numbers and cowpea yield. The results suggest that control measures should be initiated at: 4 bugs (fourth instar and above) per 10 plants for R. dentipes and M. jaculus; 2 bugs per 10 plants for A. curvipes and 6 bugs per 10 plants for N. viridula at podding stage.

A field survey on maize stemborers, stemborer damage, maize plant physical conditions, and maize yield was conducted in eastern Kenya under natural conditions. Chilo partellus was the dominant stemborer accounting for 89.5 % of all borers. Stemborer damage greatly reduced maize yield, with tunnel lengths greater than 20 cm causing a 40 % reduction of potential yield. A 33 % yield loss was found in plants with more than one stemborer exit hole. Each stemborer (at harvest time) was correlated with a 8–10 % yield loss. Good plant physical characteristics significantly increased grain yield. Principle component analysis showed that stemborer damage, plant height and stem diameter were key factors affecting maize grain yield. Regression analysis indicated that one centimetre of stemborer tunnel reduced yield by 3 g/plant. Multiple regression analysis implied a 13.3 ± 1.5 g yield loss (8–10 % of potential yield) due to the damage of a single stemborer. Comparison with average yields in the study area suggested that our results were representative of losses on farmers' fields.

—Organophosphorus-derived pesticides are commonly used to control Culex quinquefasciatus, the principal vector of filariasis in India. This paper reports on the susceptibility of C. quinquefasciatus from Madurai city, Tamil Nadu and its environs, to the organophosphate Malathion. It was observed that both larval and adult mosquitoes had low levels of resistance to the pesticide, with resistance ratios at LC50, LC90, and LC95 varying from 0.94 to 3.07 in larvae, and 0.93 to 34.68 in adults. This observation indicates the possibility of higher resistance developing in C. quinquefasciatus populations, the limitation of organophosphorus compounds as larvicides in mosquito breeding sites as a measure to control filariasis, and the importance of research into alternative measures for managing C. quinquefasciatus.

Farmers in the groundnut belts of Mali, Burkina Faso, Niger, Nigeria and Benin in West Africa were interviewed for their ability to identify economically importanct soil pests infesting their groundnut (Arachis hypogaea L.) crops, and to obtain information on farm histories and cultural practices which may influence soil pest infestation and spread in a field. Termites, whitegrubs and millipedes were recognised by the farmers as being the most important soil pests, with termites being the most damaging group. A negative correlation (P < 0.05) was found between the number of years a farm was cultivated and the frequency of termite occurrence in it. Information on cultural practices obtained from interviews and field visits indicated that practices such as late harvesting and the leaving behind of residues of previous sorghum, millet and maize crops increased termite infestation. The cutting down and burning of the vegetation in a farm before planting significantly (P < 0.05) reduced the percentage of plants attacked by termites. The cultivation of short-duration (< 100 days) varieties to escape drought at the end of the cropping season did not significantly reduce termite damage, due to late harvest. Other farmers' practices which are likely to have contributed to soil pest damage are also discussed.