The development of resistance to insecticides in insect pests is an important and increasing problem. As insecticide use increases in tropical areas, the numbers of resistant insect strains will increase.

The adverse effects of insecticide resistance include crop losses, increased production costs, increased environmental hazards, and socio-economic problems. The increasing difficulties and costs of discovering and developing new insecticides together with the widespread occurrence of resistant strains of insect pests means that insecticides are a limited resource that must be conserved. Methods of conserving insecticides include sensible management of their use and the implementation of IPM programmes.

The problems of insecticide resistance and strategies for minimizing and managing resistance in tropical areas are discussed using examples of insect pests of stored products, cotton, rice and bananas.

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.

Since it was first reported in Tanzania in 1981 the Larger Grain Borer (LGB) has spread from a small area in the northwest of the country to 17 of the 20 regions. Only in the extreme south, along the Mozambique border, has the pest not been found. It has also become established in Kenya, Burundi, Togo and Benin.

LGB can cause very high weight loss in farm stored maize and dried cassava, commodities on which it is able to breed. After 5 months storage during the dry season in western Tanzania, mean losses of 9% were found, a much higher level than losses of less than 1% which would be expected in LGB-free areas in East/Central Africa.

Application of 0.5% permethrin dust at 2.8 ppm provides excellent protection against LGB when applied to loose maize grain for 1 year. However, the storage of shelled maize predisposes towards the development of Sitophilus species which can result in high losses being sustained. A “cocktail” of permethrin and pirimiphos-methyl, applied at 3.3 and 17.7 ppm respectively, successfully controls all storage pests and is currently being used in an extensive control campaign in Tanzania.

A multi-donor funded control and containment campaign, co-ordinated by FAO, has been in operation in Tanzania since 1984. The programme is comprised of a training element for agricultural staff and several field extension campaigns which assist with insecticide distribution and with dissemination of information to farmers. The primary objectives of the programme are to reduce farm storage losses and to contain LGB within the areas it is now found. In some regions, where LGB is relatively isolated, attempts are being made to eradicate it.

Local West African strains of Sitophilus oryzae (L.) and Tribolium castaneum (Herbst) were placed in 200 g of wheat samples, one species after the other, during 6 weeks. The rate of infestation for S. oryzae was 6, 12, 24 or 48 pairs of adults, while it was fixed to 20 for T. castaneum. The generation of S. oryzae was killed by fumigation before T. castaneum infestation of the grain samples. The loss in dry weight and the frass production were recorded at the end of each rearing period of time for each species.

The dry matter loss caused by S. oryzae was highly correlated with the rate of adult infestation and measured as high as 600 mg per infesting pair of weevils. The frass production for both S. oryzae and T. castaneum was highly correlated with the rate of infestation by weevils only. For S. oryzae, the average frass production was about 60 mg per adult pair, while for T. castaneum it was variable from 27 to 44 mg per pair of the primary infestation level by the weevils.

The importance of these results is discussed in relation to standard loss assessment methods when there are several infesting species and particularly when there is a preponderance of secondary species over primary species.

The importance of rice in West Africa and the problem posed by pests were highlighted. Stem-borers are regarded as major insect pests of rice and available information on yield losses attributable to insect pests in general and stem-borers in particular, was reviewed. Damage caused by stem-borers usually results in “dead hearts” and “white heads” though other effects including a synergistic interaction between stem-borers and rice blast have been recorded. Survey methods and sampling of rice stem-borers were discussed and brief descriptions on distribution, behaviour and biology of the major rice stem-borers namely, Chilo spp., Maliarpha separatella, Scirpophaga spp., Sesamia spp. and Diopsis spp. were given. Current control tactics under investigation in West Africa include chemical, cultural and biological methods.

Despite considerable efforts in developing sweetpotato cultivare resistant to two species of sweetpotato weevils, Cylas formicarius and C. puncticollis, no cultivar has yet been bred, utilizing previously identified sources of resistance, and cultivated in any appreciable area for weevil control. Escape, nonpreference, tolerance, and antibiosis, and the possible mechanisms involved do not seem to exist in the sweetpotato plant or cannot be utilized because of the peculiarities of ecology and host plant relationship of the weevils. Since weevil infestation of roots does not adversely affect the growth and reproduction of sweetpotato plants, it is possible that weevil resistance to root infestation does not exist in this crop.

In Cameroon, the demand for hive products is growing. Honey and pollen yields are low in this country, partly because of the poor knowledge of the apicultural value of the flora. To determine the apicultural value of Combretum nigricans Lepr. ex Guill. & Perr., Erythrina sigmoidea Hua, Lannea kerstingii Engl. & K. Krause and Vernonia amygdalina Delile, Apis mellifera adansonii Latreille activity was observed on the flowers of these plants in Ngaoundéré from December 2001 to May 2002 and from December 2002 to May 2003. The flowers of each plant species were prospected for at least 4 days per month, between 07.00 and 18.00 h, for recording the nectar and/or pollen foraging behaviour of A. m. adansonii workers. Results show that A. m. adansonii harvested the nectar of each plant species. In addition, L. kerstingii and V. amygdalina were visited for pollen. The greatest number of workers foraging simultaneously on a plant varied from 26 (E. sigmoidea) to 4200 (V. amygdalina). Apis mellifera adansonii workers that visited flowers of a given plant species once generally remained with these nectar and/or pollen sources throughout the observation period. Thus C. nigricans, E. sigmoidea, L. kerstingii and V. amygdalina could be cultivated and protected to increase honey production; L. kerstingii and V. amygdalina could enable beekeepers to increase their pollen production as a hive product. During foraging, A. m. adansonii workers increased the pollination possibilities of each plant species.

Insect pest problems on cowpeas can be reduced by use of strategies which involve ecological manipulations. These include crop diversification (mixed cropping, etc.), alteration of planting dates, crop rotation, trap-cropping and weed control. The merits of these cultural methods of pest control are discussed.

The status of biological control of cowpea pests is still low but promising. The crop is an annual and therefore offers very limited possibilities for the application of the classical biological control techniques. However, a large number of parasitic Hymenoptera, Diptera and predatory Hemiptera, notably Reduviids have been identified in the cowpea ecosystem. Ecological studies of some of these have been carried out and levels of parasitism determined in a few cases, but their significance in the dynamics of cowpea pest populations have not been fully established.

It is however known that conservation of parasites and predators in their wild environment is one of the traditional biological control methods. Therefore, a rationalized pesticide programme for the control of cowpea pests should aim at preventing hazards to their natural enemies so as to increase their biocontrol efficiency.

From August 1988 to January 1997, natural enemies were reared from 335 colonies of Plnnococcus citri Risso (Homoptera: Pseudococcidae) sampled for 87 months from 225 randomly selected cocoa farms in the six cocoa-growing regions in Ghana. A total of 20,408 P. citri individuals was recorded, comprising adult females, third instar nymphs and mummified individuals harbouring parasitoids. Observed predators were larvae of Coccodiplosis coffeae Barnes (Diptera: Cecidomyiidae), nymphs and adults of Hyperaspis egregia Mader and Scymnus (Pullus) sp. (Coleoptera: Coccinellidae), as well as an unidentified lepidopteran. Twelve parasitic Hymenoptera were also reared, including Aenasius abengouroui (Risbec), Leptomastix dactylopii Howard, Anagyrus beneficions Compere, Tropidophryne melvillei Compere, Anagyrus amoenus Compere and Chryptochetum (Lestophonus) spp. Also recorded were a hyperparasitoid, Cheiloneurus carinatus Compere, parasitising Coc. coffeae, Xyplugaster pseudococci Risbec and six rare, undetermined parasitoids. Coccodiplosis coffeae was the commonest parasitoid, occurring throughout the year and infesting 72.8% of the P. citri colonies. Parasitism levels were generally low, the highest mean being 4.6 ± 2.6% for Aen. abengouroui. Simultaneous parasitism by more than one species was common and this gave rise to mean monthly parasitism levels ranging from 0.8 to 4.5%. Aenasius abengouroui, Ana. amoenus and H. egregia are being reported for the first time in P. citri on cocoa in Ghana, and the recovery of L. dactylopii suggests its establishment in the country, where it was introduced in 1949.

Some aspects of flight behaviour in the triatomine bug Triatoma sordida were investigated. A strong link between flight initiation and nutritional status as expressed by weight: length ratio was shown. Flight activity was strongly nocturnal and unimodal, commencing with the onset of darkness. A capacity to lay eggs after flight initiation was noted.

A new 6a-hydroxylated pterocarpan, named hildecarpin, has been isolated from the healthy roots of Tephrosia hildebrandtii. It has been assigned the structure (−)-3, 6a-dihydroxy-2-methoxy-8, 9-methylenedioxypterocarpan on the basis of its spectroscopie data, optical rotation and chemical transformations. Hildecarpin has exhibited insect antifeedant activity against the legume pod-borer Maruca testulalis, an important pest of the cowpea (Vigna unguiculata), and antifungal activity against Cladosporium cucumerinum. This finding suggests that the pterocarpan phytoalexins formed as a result of microbial infection of the cowpea plant may constitute a basis for induced resistance in the plant against M. testulalis.

Data on the populations of larval and pupal stages of Aedes africanus, an important sylvan vector of arboviruses, were collected from tree-holes which are its natural breeding sites in forests. Comparable data were also simultaneously collected from bamboo pots stationed in the Zika Forest to simulate the natural breeding sites. Survivorship curves and time-specific life-tables were constructed. It was observed that the immature stages of A. africanus in both tree-holes and bamboo pots suffered very high mortality rates (an average of 91% in tree-holes and 83.2% in bamboo pots). It was further observed that mortality rates varied monthly. The survivorship curves constructed for the immature stages collected on a daily basis tended to show that a large proportion of the mortality rate was confined to the early instar stages, but the survivorship curves based on the combined data for the 2 years indicated constant mortality rates for all the stages. The high mortality rates of the immature stages of A. africanus appear to be attributed to predation by larvae of Toxorhynchites brevipalpis, with which it shares the same breeding places.

Field surveys along the Lake Basin and the Coastal regions of Kenya were carried out to assess the natural incidence of pathogenic microorganisms associated with the legume pod-borer, Maruca testulalis Geyer on the cowpea crop. A regular sampling regime was maintained on plots planted with four varieties of cowpea: T VX 66–2H, Vita 3 (TVU 1190), Ex-Luanda and Nyar-Milambo. Larvae of M. testulalis were recovered from the flowers and pods of the crop, and subjected to routine laboratory disease diagnosis including: tissue examination, culture incubation, microscopy and pathogen identification. The main groups of pathogenic microorganisms found to act as natural mortality factors to M. testulalis larvae include: protozoa, bacteria, fungi and a virus. A higher level of disease incidence and diversity on M. testulalis larvae occurred in the lake basin region of Kenya than the coastal part.

The larvae of Mussidia nigrivenella Ragonot, attack various fruits; it is the main maize cob borer in Ivory Coast. The development of attack during the cultivation, the behaviour of larvae in the field, the spatial distribution of eggs and larvae, the mortality of pre-imaginal instars and the annual fluctuations of populations are considered in this paper. This insect may represent an economical problem for seed producers in the south of the savannah area of Ivory Coast where its density exceeded 14 insects per cob, at harvest in 1984, whereas the risk of cob damaging by Mussidia nigrivenella appears to be very weak in the north and west of this region.

The legume pod-borer, Maruca testulalis was reared in the laboratory for 10 successive generations using a semi-synthetic diet. The diet was composed of locally available soybean flour and cowpea flower powder as basal ingredients. The artificial medium was as suitable as the cowpea host plant for M, testulalis in supporting larval growth and development. Fecundity increased with advancing generations on the artificial medium. Field collected pupae were heavier than diet-reared pupae. However, the fecundity, fertility, adult life span, and sex ratio did not differ between the two rearing regimes. The laboratory-reared insects were of acceptable uniform quality and predictable performance even after 10 successive generations of laboratory rearing. Adult emergence ranged between 70–90%. One litre of diet produced on average 400 pupae or adults with a mean fecundity of 200 eggs per female. One person working 8 hr/day can produce a minimum of 1000 healthy pupae or adults daily. The laboratory rearing management protocol is described.

Tropical environments provide optimum conditions for insect growth and multiplication in the ideal medium of food stored by humans. Some insects begin infestation in the field and continue attack in storage. Other species diapause and remain in cracks and crevices in granaries or feed on grain residues while awaiting the new harvest. Since most of the tropical produce is for subsistence, the losses resulting from severe insect attack contribute to malnutrition and famine. In central stores and warehouses commodity management is poor and large amounts are lost to insects. In countries where heavy insecticide and fumigant pressure is maintained to preserve food stocks, insects rapidly build up resistance. The solutions for the future are to reduce dependence on pesticides and utilize in an integrated way the cultural, biological and physical techniques developed in recent years for safer storage and the successful preservation of strategic reserves for food security.

The paper presents a way of estimating average daily mortality rates of female tsetse from ovarian age distributions. This technique was applied to monthly biconical trap samples of G. palpalis taken during and after insecticidal campaigns in the Bouaflé region of Ivory Coast. A clear inverse relationship is demonstrated between the annual mean number of females per trap per sample at 10 separate sites, and the mean annual mortality rates calculated for them. Local variation in the impact of insecticides is explained in terms of the grouping of the sites either side of a level of natural mortality above which tsetse populations cannot be sustained through reproduction alone.

A theoretical model for density dependent population growth is presented and applied to a particular control situation, that of the sterile insect release method. The model demonstrates that the effectiveness of any particular level of induced sterility (or mortality) is crucially determined by the natural resilience of the target population.

In olfactometer assays, the predatory mite Amblyseius ciicumeris (Oudemans) recorded a significantly higher response to volatiles from chrysanthemum, Denranthemct morifolium plants infested with western flower thrips (WFT), Frankliniella occidentalis (Pergande) than to volatiles from healthy plants. This increased attraction was attributed to the presence of higher amounts of Germacrene-D in WFT-infested plants. In choice experiments using synthetic volatiles, the predator remained longer in the olfactometer treated with 50 ng Germacrene-D and made many entries at 500 mg.

Preferential attraction of WFT to healthy chrysanthemum flower buds was observed, and attributed to the significantly higher amounts of (E)-β-farnesene found in the buds compared to leaves and open flowers. This attraction peaked at 100 ng/μl (E)-β-famesene. In greenhouse experiments, blue sticky traps with 500 ng (E)-β-farnesene or 1000 mg p-anisaldehyde attracted 32.3% and 27.5% more WFT than the untreated controls, respectively.

The prospects of using Germacrene-D in improving the attraction of A.cucumeris to whole chrysanthemum plants and (E)-β-farnesene in monitoring WFT, are discussed.

Trials for cold storage of the mummies of Aphis craccivora Koch parasitized by Trioxys indicus Subba Rao & Sharma were made. Newly formed mummies having fourth instar larvae of the parasitoid were put either at 20–25°C or at 12–15°C, 10 hr photoperiod for 24–72 hr before storage inside the refrigerators (4–8°C) for 10–40 days. A higher proportion of adult emergence was usually associated with the group of mummies passed at 12–15°C before storage and practically good emergence was recorded even if the mummies were stored for a month at 4°C if kept at 12–15°C for 72 hr prior to storage.

Six foliar insecticides were evaluated for efficacy in the control of different stages of Clavigralla tomentosicollis, the most important cowpea coreid in Nigeria.

Monocrotophos was highly effective in controlling adults for up to 16 DAT and was statistically better than cypermethrin + dimethoate (Sherpa Plus(R)), deltamethrin, endosulfan and deltamethrin + endosulfan 8 days after treatment. Comparative overall results were obtained between monocrotophos and the mixture of cypermethrin + chlorpyrifos. The best control of nymphs was obtained with monocrotophos, cypermethrin + dimethoate and endosulfan, while the mixtures of cypermethrin + dimethoate and cypermethrin + chlorpyrifos completely inhibited egg hatch. More than 78% egg hatch was obtained from monocrotophos and deltamethrin, while the water-treated control had 96% hatch.

These findings are discussed in the light of product toxicity, residual action and overall reduction of the pod bug populations.