Cowpea, Vigna unguiculata (Walp) and beans, Phaseolus vulgaris are attacked by several insect pests worldwide. The pests include economically important borers, the control of which often requires the use of more than one tactic. In Africa, the major borer species of cowpea is Manica vitrata Fab. (syn. M. testulalis [Geyer]); in Southeast Asia and eastern Africa the beanfly or bean stem maggot complex, Ophiomyia spp., is important on beans. The bean borer, Etiella zinckenella (Treitschke), is also of considerable importance in Asia. In South America Epinotia apotema (Wals) and Cydia fabivora (Meyrick) are the most important borers on beans, while Helicoverpa armigera (Hïbner) and M. vitrata to a lesser degree are important on beans in some parts of Africa. Presently, only chemical control provides complete protection against crop borers, but despite its usually favourable cost-to-benefit ratio, insecticide use is not a sustainable option. Other tactics such as cultural control, host plant resistance and the use of beneficial organisms are more dependable in the long-term. They form the core of the new vision for environmentally friendly pest management, or bio-intensive pest management, which minimises the use of synthetic insecticides. In recent times, research efforts directed at these measures have been intensified. This paper discusses the various interventions and presents different IPM models on how they can be combined to optimise the control of borers. Suggestions are made on the future outlook of IPM on cowpea and beans.

Cowpea, Vigna unguiculata (L.) Walp., is susceptible to a wide spectrum of insect pests from seedling to harvest as well as in storage. Insecticide use has been the most commonly adopted method for the control of cowpea pests. However, due to the deleterious effects of insecticides on man, livestock and the environment, research over the years has been focused mainly on developing resistant/tolerant cultivars as a vital component in the integrated management of cowpea pests. This approach has, however, recorded varying degrees of success, due in part to the multiple and often overlapping pest complex attacking at different phenological growth stages of the crop.

In spite of the progress in the utilisation of insect-resistant cowpea varieties, the use of resistance as a control tactic has by no means been fully realised. There are many important cowpea insect pests for which resistant varieties are not yet available for commercial cultivation. Where resistant varieties are available for a given insect, these varieties may not be widely planted because of their unsuitability to local conditions.

In this paper, the status of host plant resistance research in cowpea is reviewed and some novel approaches aimed at solving its seemingly intractable pest problem are proposed, based on the state-of-the-art scientific and crop biotechnological development. The proposed framework for orientation of cowpea resistance research should ensure yield stability and sustainability for the resource-poor, smallscale farmers in Africa.

The oviposition behaviour of the cowpea weevils, Callosobruchus rhodesianus (Pic.) and Callosobruchus maculatus (F.) on clean and egg-laden adzuki beans was examined in choice and no-choice experiments. The oviposition rate of C. maculatus was greater than C. rhodesianus in both experiments. Both weevil species were able to distinguish between clean and egg-laden beans. Discrimination by both species was greater against seeds with 12 eggs than with 6, regardless of which species had previously laid eggs. There was a weak indication that the presence of C. maculatus eggs at high densities might reduce the oviposition rate of C. rhodesianus.

Populations of larvae and pupae of the African rice gall midge, Orseolia oryzivora Harris & Gagne (Diptera: Cecidomyiidae), and two parasitoids, Platygaster diplosisae Risbec and Aprostocetus procerae (Risbec)[= Tetrastichus pachy diplosisae Risbec], were recorded in replicated experiments on farmers' fields at Karfiguéla, Burkina Faso in the 1992 wet season and the 1993 dry season. In each season, four plantings were made at 14-day intervals and samples taken at weekly intervals for 10 weeks. Gall midge populations in the wet season developed through three distinct phases: an initial slow increase, followed by a period of rapid increase coinciding with maximum tillering, and then a final decline. On average, the highest midge populations and highest levels of parasitism developed in the later plantings. During the dry season midge infestations were low and no parasites were detected.

The host plant range of two ricefield caseworms, Parapoynx fluctuosalis (Zeller) and P. diminutalis Snellen (Lepidoptera: Pyralidae), was determined from screening rice and 61 weeds in the Philippines. Both species developed best on the aquatic weed Hydrilla verticillata (L.f.) Royle (Hydrocharitaceae). Parapoynx fluctuosalis also completed a full generation from egg to egg on Cyperus brevifolius (Rottb.) Hassk. (Cyperaceae), Commelina diffusa Burm. f. (Commelinaceae), Leptochloa chinensis (L.) Nees, and Paspalum conjugatum Berg (Poaceae). Parapoynx diminutalis completed a generation on Chara vulgaris L. (Characeae), Ottelia alismoides (L.) Vahl and Blyxa auberti Rich. (Hydrocharitaceae), and Cyperus rotundus L. (Cyperaceae).

Pesticide spray thresholds, as a component of Integrated Pest Management, must be integrated with the world of smallscale farmers if they are to be useful to them. The capacity and desire to spray have specific features of significance for threshold control. Threshold use may be encouraged by maximising the divisibility of pesticide technology. Farmers' perception of thresholds, often subjective and personal, may be enhanced by information learned from outsiders, as complementing, rather than supplanting, their existing knowledge and experience.

This paper justifies the need for a single taxonomic work providing a key to the common mealybugs of tropical Africa, and provides such a key for identification of some adult mealybugs of Central Africa. If users find that their specimens do not fit into the key, then the specimens are probably other species and should be sent to an expert for identification.

Survival and development of Chilo partellus were studied on five sorghum cultivars (IS-18363, IS-18520, ICS-1, ICS-2 and IS-4660) in the laboratory at Mbita Point Field Station, Kenya, at 26 ± 2°C and 65 ± 5% RH. Larval developmental period differed significantly on different cultivars. Number of instars was numerically greater for the females than for the males on all cultivars. Average pupal weight varied with sex; females were twice as heavy as males. The pupal period was longer for males than for females on all cultivars, with the exception of ICS-1, where the pupal period of males was equal to that of females. Ovipositional period was significantly longer on IS-18520 (5.18 ± 0.30 days) than on other cultivars. The shortest ovipositional period (3.70 ± 0.27 days) was recorded on IS-4660. There were no statistically significant differences in adult longevity. Sex ratio of the moths also did not affect the adult longevity of C. partellus reared on the five sorghum cultivars. The variations found in the development of C. partellus on different cultivars were attributed to the nutritional value of the food source.

A chromatographically enriched fraction designated Fraction B from dry fruits of the plant Melia volkensii (family Meliaceae) was evaluated with the objective of determining its toxic and growth inhibiting effects on the larvae and adults of Culex quinquefasciatus mosquitoes. The fraction was purified from a crude methanolic extract by cold precipitation and elution of the precipitate dissolved in a hexane-ethyl acetate solvent system through a silica gel column. Larval treatments involved rearing the larval stages in water containing the fraction at concentrations of between 5 and 200 ppm. The LC50 for this fraction was found to be 34.72 μg/ml in 48 h. Second instar larvae were found to be more susceptible to fraction B when compared to fourth instar larvae. All fourth instar larvae that survived the treatment moulted into larval-pupal intermediates that were short-lived. The extract was also found to be an oviposition deterrent at a concentration of 20 ppm and above. It is concluded that M. volkensii extract has potential in the control of Culex quinquefasciatus.

Crop protection problems of smallholders farming maize in the Chokwe Irrigation Scheme in southern Mozambique were investigated in a long-term field study programme during 1984–1990. Downy mildew, Peronosclerospora sorghi (Weston & Uppal) C.G. Shaw, maize streak virus, stemborers (mainly Chilo partellus Swinhoe) and the multimammate rat (Praomys natalensis Smith) were the most important, with the first three showing highest incidence in the warm rainy season (October-March). Average percentage infestation of maize at 30 days after emergence in four successive rainy seasons were 11% for maize streak virus, 16% for downy mildew and 26% for stemborers. The multimammate rat was most abundant at the beginning of the cool, dry season (April-May). Maize streak virus attacks were aggravated when there was rainfall in the preceding cool, dry season. High rainfall in the early part of the warm season increased the likelihood of outbreaks of the multimammate rat in the subsequent cool season. Early sowing decreased the intensity of downy mildew and stemborers, but not of maize streak virus. In on-farm trials involving varieties with combined tolerance to maize streak virus and downy mildew, ESR-DMR-W from IITA (Nigeria) produced 32% more grain while CW-1, a locally bred improved variety, produced 31% more than the local unimproved variety.

The effects of temperature on the life history of Spilostethus pandurus (Scopoli) were examined by determining the different developmental and reproductive parameters with respect to days of hatching, oviposition, and adult emergence of insects reared in field cages at Giza, Egypt. Hatching, oviposition, and adult emergence continued all year round; the average daily temperature in the coldest month (January) seemed to be above developmental thresholds for different stages. This lygaeid completed six overlapping generations in 1 year. The basic population parameters, i.e. net reproductive rate (R0), gross reproductive rate (GRR), instantaneous rate of natural increase (r), finite rate of natural increase (λ), and mean generation time (T) exhibited a more or less cyclic pattern in successive generations. The highest value of r (rmax) was considered as the intrinsic rate of natural increase of this species.

Random amplified polymorphic DNA (RAPD) amplified by the polymerase chain reaction (PCR) was used to estimate the relatedness of three biotypes of brown planthopper, Nilaparvata lugens (Stål), from the Philippines. Each individual brown planthopper had a unique set of RAPD bands, but no bands were diagnostic for any one biotype. Brown planthopper types 1, 2 and 3 were genetically homogeneous. This supports results of other studies which conclude that brown planthopper biotypes are not sub-specific categories, but merely represent individual variation for virulence to rice cultivars.

The already known benzoquinone, embelin (mixed with rapanone), and two new benzoquinones, myrsinone and myrsinaquinone, were isolated from the Myrsinaceae plant, Rapanea melanphloes (L), Mez. All the three compounds showed antifeedant activity when bioassayed on nymphs of the desert locust, Schistocerca gregaria (Forsk). They also inhibited growth of second-instar larvae of mosquito Aedes aegypti at low doses, and had acute lethal effects at higher doses.

The phenotypic stability of resistance to the stemborer, Chilo partellus and grain yield in 10 newly developed sorghum hybrids namely HYD-1, HYD-2, HYD-3, HYD-4, HYD-5, HYD-6, HYD-7, HYD-8, HYD-9 and HYD-10, and two local checks, Serena (tolerant) and IS-1044 (resistant), were evaluated for seven seasons at the International Centre of Insect Physiology and Ecology (ICIPE) Mbita Point Field Station and Ungoye Field Site in western Kenya. Two stability parameters were determined: (1) The linear regression (b1) of an entry mean on an environmental index, and (2) the deviation from regression (S2d). The significance found for the linear component of environment implies that the variation over the different environments is adequate to test for cultivar stability. Hybrids HYD-1, HYD-5, HYD-8 and HYD-10 were identified as the most suitable genotypes for future commercial production.

Studies on losses in yield of rapeseed, Brassica campestris cv. Brown Sarson, caused by the mustard aphid, Lipaphis erysimi (Kalt.) were conducted under natural and artificial conditions. Based on the experiments on the influence of aphid exposure to the crop on aphid number and seed yield and the effect of varied aphid population at flowering/pod initiation stage and artificial release of aphids at 10-day intervals starting from 40 days of sowing on the plant height, number of siliquae per plant, number of primary branches, seed yield per plant and 1000-grain weight, a positive correlation between length of aphid exposure to the crop and aphid population was found. A negative relationship between aphid population, length of aphid exposure and seed yield was observed. An inverse and significant relationship existed between parameters contributing to yield loss and losses in seed yield. However, this relationship was not significant in siliquae per plant and 1000-grain weight. A similar relationship was observed in artificial infestation.

Azadirachtin, the principal active ingredient of neem seed and aqueous neem seed extracts (ANSE) reduced food intake and utilisation efficiency in the penultimate instar level of the African armyworm (Spodoptera exempta) when applied either topically or mixed with the diet of the insect. These observations reflect interference of neem with centres in the insect that regulate feeding and metabolism. The decreased food utilisation efficiency in treated insects indicated higher metabolic costs as they had to direct some energy into dealing with neem deposits in their bodies rather than biomass production.

Differences in population growth among four variation types of the ladybird beetle, Harmonia axyridis Pallas, namely succinea, conspicua, spectabilis and aulica, were investigated using various growth parameters. The variation types showed three growth patterns from the intrinsic growth rates (rm), with rates of 0.093–0.099 (for conspicua and aulica), 0.073 (for succinea) and 0.040 (for spectabilis). The growth rates of these patterns were realised in different ways. Spectabilis differed from the other three types in the age and per cent distribution of the specific period to the rm values.

The effect of maternal crowding on the offspring sex ratio of a cereal aphid parasitoid Lysiphlebus delhiensis (Subba Rao & Sharma) (Hymenoptera: Braconidae) was examined. Increasing the number of mothers per host-patch always increased the proportion of males in the population (p). The extent of variations in p at different levels of maternal crowding was compared with the prediction of the Hamiltonian LMC model, i.e. p = (n-1)/2n, where n = number of mothers/host-patch. The perception of trace odours of conspecific females induced haploid oviposition. Differential mortality of the larvae by sex in superparasitised hosts, shifting the p towards sons has been discussed. The inversely parasitoid-density-dependent p indicates that for obtaining maximum number of female progeny, the ratio of female parasitoid to the host in mass breeding should not be less than 1:100 at a time.

The effect of protein fractions isolated from cereal grains on the development and survival of the bean weevil, Callosobruchus maculatus, was investigated using wheat, rice and maize. These cereals were fractionated into albumins, globulins, prolamins, glutelins and a residue. The fractions were incorporated in artificial seeds which were infested by C. maculatus. Survival (as indicated by LD50) and development (as indicated by WD50) of 20-day-larvae of the bruchid were negatively affected by most of the fractions. Rice globulins were the most detrimental and affected both the survival and development of the larvae, while wheat albumins and globulins had a stronger effect on larval development than on survival. A previously isolated maize α-amylase/trypsin inhibitor showed an LD50 of 1.5% to Callosobruchus maculatus.