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.

Surveys were conducted to determine the species composition of stemborers and their natural enemies in maize and sorghum in 1999 and 2000 in eastern, northern, southern and western Ethiopia. The six species of stemborers found attacking maize and sorghum were Chilo partellus (Swinhoe) (Lepidoptera: Crambidae), Busseola fusca Fuller, Sesamia calamistis Hampson (Lepidoptera: Noctuidae), S. nonagrioides botanephaga Tarns & Bowden (Lepidoptera: Noctuidae), Rhynchaenus niger (Horn) (Coleoptera: Rhynchophoridae) and Pissodes dubious (Ström) (Coleoptera: Rhynchophoridae). Twenty species of primary parasitoids of eggs, larvae and pupae of Ch. partellus, B. fusca and S. calamistis were recorded. Other natural enemies, including predators, fungi and nematodes, were also found. Cotesia flavipes Cameron (Hymenoptera: Braconidae) was the dominant and the most widely distributed parasitoid of stemborers in Ethiopia, and was reared from field-collected Ch. partellus, B. fusca and S. calamistis.

A survey among 240 resource-poor farmers at the Kenya coast indicated that insect pests were considered to be the main production constraint. Over 70% of respondents mentioned stemborers to be the most important insect pest. Unlike the eggs and adults, stemborer larvae and pupae were frequently seen by farmers. Alternative gramineous host plants for pests were common near maize fields and were often not destroyed until after the first rains. Nearly all farmers left dry stems and stubble in the field after harvest. Farmers knew of many methods for controlling stemborers, but only 32 and 56% of farmers in Kilifi and Kwale Districts, respectively, used any of the methods. Chemical control was the most popular control method, being applied regularly by 19 and 38% of farmers in Kilifi and Kwale Districts, respectively. Traditional methods and cultural control methods were seldom used. Approximately 50% of farmers had heard of beneficial insects, with farmers collectively mentioning 17 predators of stemborers. Cocoons of the parasitoids Cotesia flavipes, released in a biological control programme in the study area in 1993, and the indigenous Cotesia sesamiae had been seen by 33% of respondents, but none knew what these were. The results of the present study stress the need to educate farmers about the biology and ecology of stemborers and the role of natural enemies. Also, after effective control methods suitable for resource-poor farmers have been identified, both groups should be trained in pest management methods, for example through the Farmers Field School approach.

Prospects for the biological control of locusts and grasshoppers have become much brighter during the last ten years thanks to a number of international research projects. This paper examines a number of options, including one that is ready for immediate implementation: the mycoinsecticide, Green Muscle®, based on the fungus Metarhizium anisopliae (flavoviride) var. acridum. It has been registered in South Africa and other African countries are likely to follow during 1999. Trial results on grasshoppers and several locust species have been very encouraging, and preliminary tests on red locusts show potential as well. Recent research on pheromones also points to some interesting possibilities, both when used alone and in combination with a mycoinsecticide. Finally, microsporidian protozoans and rhabditid nematodes show some promise for long-term suppression of red locust populations, but more research and development is needed to demonstrate their potential.

Life table statistics on the age-specific fecundity and survival of female Spilosoma obliqua Walker reared on sunflower showed a net reproductive rate of 513.6 eggs per female, with approximate generation time of 48.2 days. Its intrinsic rate of increase (rm) was 0.1295, meaning that its population could double in 5.35 days. Spilosoma obliqua on sunflower was parasitised by Apanteles obliquae, Glyptapanteles creatonoti and Carcelia sp.

Surveys for natural enemies of Mexican stemborers and the major biocontrol attempts using indigenous and exotic parasites in Mexico are reviewed. Although biological control of stemborers in Mexico was initiated in the 1920s, parasite explorations were intensified during the 1980s and have continued to date in response to the invasion of Diatraea grandiosella Dyar, D. lineolata (Walker) and Eoreuma loftini (Dyar) into the United States from Mexico. Recent surveys for stemborer parasites in Mexico has led to the discovery and laboratory culturing of the braconids Allorhogas pyralophagus Marsh, Digonogastra solitaria Wharton & Quicke and Macrocentrus prolificus Wharton; the ichneumonid Mallochia pyralidis Wharton and the tachinid Lydella jalisco Woodley. The Asian braconid Cotesia flavipes Cameron was introduced and established in the states of Tamaulipas and Sinaloa against Diatraea spp. Unsuccessful attempts to establish other exotic parasites are also discussed. Stemborer predators and diseases have been poorly studied in Mexico, and their potential as biocontrol agents is unknown. The current biological control programmes of stemborers in Mexico and the potential of indigenous and exotic parasites as biocontrol agents are discussed. National and international collaboration is stressed for optimisation of resources and efficient exchange of natural enemies and their mass rearing technology.

Patterns of stemborer life history and the foraging patterns exhibited by a taxonomically diverse array of stemborer parasites are described. Foraging strategies provide functional descriptions of natural parasite groupings and include elements of the guild concept plus ecological, behavioural, and morphological adaptations that enable a parasite to locate and exploit a particular host effectively. Elements of the foraging strategy include: host stage attacked, microhabitat of the host, cues employed to locate and identify the host, and method of host attack. Possible constraints presented by the crop plants to the success of different foraging strategies exhibited by groups of parasites are explored.

Stemborers in Africa are attacked by a complex of about 120 species of hymenopteran parasitoids, including about 15 species which are either facultative or obligatory hyperparasitoids. Several dipteran parasitoids also attack stemborers. An overview of hymenopteran stemborer parasitoids is here presented by superfamily and family, giving numbers of genera and species involved, their biologies (where known) and distributions.

The noctuids Busseola fusca and Sesamia calamistis and the pyraloids Chilo partellus, Chilo orichalcociliellus and Eldana saccharina are the most important stemborers of maize in East Africa. A wide range of egg, larval and pupal parasitoids of stemborers have been identified, but information on predators, nematodes and microbial pathogens is less extensive. The most abundant and widespread parasitoids in the East African region are the egg parasitoids Telenomus spp. and Trichogramma spp., the larval parasitoids Cotesia sesamiae and Sturmiopsis parasitica and the pupal parasitoids Pediobius furvus and Dentichasmias busseolae. Predators, such as ants, spiders and earwigs can cause high mortality of eggs and young larvae in some areas. Nematodes and microbial pathogens have been reported to infect all life stages, but their impact is low under natural conditions. The abundance of natural enemies can vary considerably between locations and seasons. In general, indigenous natural enemies are not able to keep stemborer populations below economic injury levels. This paper summarises what is currently known of the natural enemies of cereal stemborers in East Africa.

Several species of stemborers attack sorghum and pearl millet in Africa and Asia. The commonest species on sorghum are Chilo partellus (Swinhoe) and Busseola fusca (Fuller) and on pearl millet, Contesta ignefusalis (Hampson). This paper discusses control options and the extent to which farmer perceptions of stemborers and associated crop losses have been considered. Examples of research aimed at developing IPM strategies are presented in the context of their impact or lack of it, on the farming community. Research efforts have traditionally focused on the development of resistant cultivare and only recently are they being targeted towards a combination with cultural and biological tactics. Conventional breeding procedures have not produced adequate levels of resistance to stemborers and natural enemies are not effective in regulating borer populations. The prospects of applied biological control and improved intercropping configurations are discussed. Reference is also made to progress in the role of semiochemicals in parasitoid activity on Ch. partellus and sex pheromones in the control of Con. ignefusalis. Unless resistance levels to stemborers are increased through biotechnological approaches, optimisation of the yield potential in existing cultivars requires that IPM research should focus on the improvement of cultural and biological components and should incorporate farmers' perceptions and an assessment of traditional pest management practices.

Pesticides provide an important component of integrated pest management, but the timing, accuracy of dosage, and method of applying the pesticides need careful consideration to permit harmonisation with other control tactics. Concern about pesticide spray drift has led to categorising the spray quality of nozzles, which is defined by comparing the droplet spectra of selected reference nozzles measured with a laser light diffraction analyser. However, there is a conflict between a need for small droplets for increased biological efficacy and large droplets to reduce downwind drift. Registration authorities tend to favour a coarser spray with large droplets, and an untreated barrier area that can be left around a treated crop to protect sensitive crops downwind that can provide a refuge for natural enemies. In some circumstances, drift can be reduced with small droplets by electrostatically charging a spray. The charged spray needs to be released close to the crop to avoid the upward dispersion of droplets within a spray cloud due to mutual repulsion exacerbated by convective air movement. Increased deposition of charged sprays on the crop foliage is associated with less soil contamination which allows greater survival of ground-dwelling predators. This feature needs to be exploited by growing relatively narrow strips of a range of crops so that if one crop needs a pesticide treatment, natural enemies can be conserved in adjacent untreated crops. By careful selection of insecticides and dosage rates, these predators should be able to recolonise the treated area and thus integrate chemical with biological control. Application of more selective mycopesticides may require special formulations as well as particular droplet spectra. Pesticides can also be applied mixed with attractants such as pheromones, as a ‘lure and kill’ technique.

Published information was used to compile a summary of natural enemies (parasitoids, predators and diseases) reported attacking Spodoptera litura (F) under field conditions. Species (71) of insect parasitoids in seven families of Hymenoptera and two families of Diptera were listed as parasitoids of different stages of S. litura. Predatory insects (36) belonging to 14 families and 12 species of spiders from six families have been reported to feed on this species. Four protozoan, four fungal, seven bacterial, four each of viral and nematode species were also reported to be the pathogens of this species. Published information suggested that periodic releases of large number of egg parasites could help in suppressing populations of this pest. There is a considerable scope for increased attention to the role of natural enemies as component of integrated pest management programmes of S. litura.

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.

Studies at ICIPE's Mbita Point Field Station (site 1) and a farmer's field in Lambwe Valley (site 2) in Western Kenya, revealed the presence of at least seven parasitoids, two predators, one nematode and several microorganic pathogens attacking Maruca testulalis on cowpea crop. Some parasitoids and pathogens were also recovered from M. testulalis cadavers collected on wild host plants of the pest. A pupal endoparasitoid, Antrocephalus sp. was the most predominant, while the pathogens Nosema sp. and Bacillus sp. caused the highest natural mortality on M. testulalis in this region.

Parasitoids and pathogens contributed 40.65 and 35.6% to the total generation mortality (K) at sites 1 and 2 respectively. Observed parasitism only contributed 3.25% at site 1 and 3.8% at site 2 of the generation mortality. Mortality due to disappearance which included predation accounted for 59.35 and 64.8% of K at the respective sites. Life table data and survival curves for the pest revealed high generation mortality (ca. 98%), most of which occurred in the early life stages of the pest. The results suggest a high potential for utilizing biocontrol agents in IPM of the pest.

A taxonomie inventory is under way in South America to identify the major natural enemies of the cassava green mites, Mononychellus tanajoa. Special emphasis is being given to the Phytoseiidae, important predators of phytophagous mites feeding on cassava. Several insect predators and more than 40 species of Phytoseiidae have been identified in Colombia; Typhlodromalus limonicus and Neoseiulus anonymus are the most frequently found species. Selected aspects of the bionomic studies on T. limonicus and N. anonymus are presented, and methods of rearing numerous phytoseiid species are discussed. Five species are being reared at the Centro Internacional de Agricultura Tropical (CIAT) and have been sent to the International Institute of Tropical Agriculture (IITA) in Nigeria. Surveys for natural enemies will include most cassava-growing areas of Central and South America. Selection of exploration sites and timing of explorations will be guided by matching agrometeorological zones in the country of origin with those in the proposed country of introduction. Duration of dry periods, rainfall patterns and temperature are particularly important considerations in the matching.

In Africa, cassava green mite (CGM) is an exotic tetranychid, recently introduced from the Neotropics. In the absence of effective natural enemies, seasonal changes in the weather, either directly through several climatic factors or indirectly through the host plant, dominate the phenology and limit the growth rates of CGM populations. The intrinsically high rate of increase of CGM results in large populations when enhanced by high temperatures and suitable host plants during periods when evaporation exceeds precipitation. Mite numbers decline as precipitation increases and when suitable host plants are not available. The suitability of a host plant, as measured by CGM's intrinsic rate of increase, varies with drought stress, plant age, leaf age and cultivar. The introduction of effective natural enemies from CGM's area of origin is expected to dampen the seasonal abundance of this mite without changing its general phenology.

Breeding biology of oil palm weevil, Temnoschoita quadrimaculata Gly., was studied. Females lay small, whitish and cylindrical eggs singly in cut wounds made on the fronds and trunk of oil palm, Elaeis guineensis Jacq. The larvae were found to feed voraciously in the fresh and dead tissues of the palm fronds and trunk. The weevil has six overlapping generations. Unmated females were observed to have longer pre-oviposition period, laid fewer eggs and lived longer than the mated ones. Durations of the immature stages of the weevil are studied. Natural enemies and alternate host plants of the pest are given.