Progress in the adoption of biological control in the 100 years since the introduction of the vedalia beetle into California is reviewed briefly as a background to examining current trends, especially in tropical countries. Recent successful classical biological control programmes have increased interest in applying biological control to other major pest problems as has increasing public appreciation of the dangers of over-reliance on chemical pesticides. Consequently, there is an unprecedented opportunity for greater use of biological control. However, the opportunities for classical biological control are limited and greater attention to other biological control techniques is necessary, especially the development of pathogens as biopesticides and techniques to increase the impact of native natural enemies. Biological control is not a panacea and can seldom be effective on its own. It must, therefore, be integrated with other pest control techniques in integrated management programmes. International collaboration is required to increase awareness of these opportunities, facilitate the procurement of biotic agents and generally to promote the adoption of biologically sound sustainable pest and vector management procedures. Support for biological control should include training of personnel who will be involved in decision-making and in implementing control. Practitioners must be prepared to promote the use of biological control by farmers, and also address legitimate public concerns about the safety of biological control so as to ensure continuing public support and appropriate regulatory procedures.

Interest in the study of parasitic Hymenoptera has been revitalized consequent to recent emphasis on biological control and the role that the parasitoids play in effective biological control methods. However, our knowledge of the species of parasitic Hymenoptera, and their host associations is rather imperfect, and the family Ichneumonidae is no exception. The potential that parasitic Hymenoptera offer in the control of unwanted pests, and thereby increase agricultural output, cannot be utilized unless basic taxonomic and biological studies on them are fully supported and funded.

The known species of Ichneumonidae at the present moment are approximately 19,000, which is only about 10% of the estimated number of species occurring in the world. Most species occurring in the tropical countries are unknown. The described number of species from various regions are approximately 7000 in Eurasia, 4500 in Indo-Australian area, 3500 in North America, 2000 in South America, and about 2000 in tropical Africa.

The African ichneumonid fauna is rich and diverse, but very few areas have been intensively and extensively explored. Certain countries like Malagasy Republic and Zaire have been more extensively explored than the others, but recent studies indicate that species diversity is much greater than what we know today. Catches made in limited areas by using Malaise traps in places like Kampala, Uganda during 1964–1965 and in Freetown, Sierra Leone during 1969–1970 increased the number of species 300–400 per cent.

Successful attempts made for biological control of sugar-cane pests by introduction, redistribution, conservation and augmentation are discussed.

In Pakistan, Apanteles flavipes (Cameron) became established on Chilo partellus (Swinhoe), following its introduction from Japan, but it seldom attacked sugar-cane borers. Sugarcane-adapted strains were introduced which became established in Punjab and NWFP, but were not recovered after winter in Sind. A hybrid between sugar-cane-adapted strain and strain found locally on maize borer, was released. This resulted in its establishment.

In Sumatra (Indonesia), a local strain of A. flavipes was being encapsulated in Chilo auricilius Dudgeon. Following introduction of its strain from Thailand, it is giving very high parasitism of C. auricilius and C. sacchariphagus (Bojer).

A parasitoid, Epiricania melanoleuca (Fletcher) is giving excellent control of sugar-cane Pyrilla pe pusilla (Walker) in NWFP following its redistribution from the Punjab and in Sind after redistribution from the Punjab and NWFP. In Sind it is also being controlled by conserving its egg parasitoid Parachrysocharis javensis (Grault) by keeping some trash unburnt near the fields.

In Sind, infestation of Chilo infuscatellus Snellen was reduced to sub-economic level by augmentative releases of Trichogramma chilonis Ishii in March as soon as the pest started laying eggs.

The coffee berry borer, Hypothenemus hampei, which originates from Africa, is one of the most serious pests of commercial coffee and is now present in most of the major coffee growing parts of the world. Quite recently, this beetle spread into Mexico and Ecuador and is now causing serious economic losses in these two countries. In 1985, a classical biological control programme was started to control the pest using the bethylid, Prorops nasuta and other hymenopterous natural enemies from Africa. During the programme, various studies were conducted in Kenya on P. nasuta and H. hampei including their field distribution and life history. A technique of rearing and screening P. nasuta against plant diseases was developed and several shipments have now been made to Ecuador and Mexico. In 1988 a continuous laboratory culture of P. nasuta had been established in Ecuador and the wasp was also reported to be reproducing in sleeves cages in the field.

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.

The various pests of the cassava plant, Manihot esculenta Crantz, were reviewed with particular reference to the two exotic pests viz: cassava mealybug,Phenacoccus manihoti, Mat-Ferr, and cassava green mite, Mononychellus tanajoa Bondar which were accidentally introduced into Africa without their natural enemies in the early seventies.

Classical biological control programme for these two pests initiated and championed by the International Institute of Tropical Agriculture (IITA), Ibadan, Nigeria was also reviewed and both successes and limitations of the programme highlighted. Suggestions on how to improve the efficiency of the programme are made.

Lepidopteran stem borers account for heavy losses in cereals in areas where they are prevalent throughout Africa. Microsporidia, especially Nosema sp. may be developed for use in the management of this group of insect pests. Studies carried out so far show that the application of Nosema spores may increase yield up to 34% in sorghum when the plants are infested with Chilo partellus eggs and sprayed with the pathogen, and up to 80% in sorghum infested with borer larvae.

The procedure for spore production is simple, and may easily be adapted for small scale industrial production by local or regional communities and organizations. In trials aimed at the mass production of Nosema sp. for the management of C. partellus, a yield of 109 spores/larva has been attained. If this production level can be maintained, then a system that produces only 6000 larvae/day would yield enough cadavers for preparation of 6000 1 daily. At the rate in which the pathogen suspension is applied as foliar sprays in the field, this would be sufficient to treat 5373 ha. If widely adopted, use of microsporidia would revolutionize cereal stem borer management in the tropics.

A range of materials were collected from a number of ecological and environmental zones within Kenya as being likely sources of entomopathogenic bacteria. These were soils, insect frass and dead insect material. Using an isolation protocol involving use of a selective medium, over 150 Bacillus thuringiensis (B. t.) strains were recovered from the sample material. Their identity as B. t. strains was confirmed by their growth characteristics, morphology and presence of a parasporal delta-endotoxin crystal.

All strains were screened for activity against two Lepidopteran pest species, the spotted stem borer, Chilo partellus and the African army worm, Spodoptera exempta. Isolates causing over 80% mortality in the screening assays were retained for further evaluation. The selected isolates were subjected to bioassay against C. partellus and S. littoralis. Following bioassay, the most toxic isolates were selected for screenhouse trials against C. partellus and field trials against a natural outbreak of S. exempta.

In the screenhouse trials all of the B. t. treated plants showed reduced levels of damage and yields were 5 to 7 times higher than the yield obtained from the untreated, infested control plots. Three isolates, A-3, A-C-2 (isolated from insect material) and M-44–2 (isolated from soil) seemed to offer superior levels of protection. Two new B. t. isolates, K-26–21 and MF-4B-2, both isolated from soils, showed high levels of toxicity to S. littoralis and S. exempta in the laboratory. When isolate K-26–21 was applied to maize seedlings in the field, almost total control of the larval population was achieved within 48 hr at each of the concentration levels tested.

The first report on the entomopathogenic fungi in the tropics dates back to 1853. Despite their variety, little attention has been focused on their incidence on agricultural pests. Studies over the last 20 years in the tropics have revealed that entomogenous fungi (Deuteromycetes and Entomophthorales) may play an important role in natural control of arthropod populations. Therefore, the use of insect pathogenic fungi as pest control agents is promising.

An important consideration in developing an entomopathogenic fungus as a mycoinsecticide is the selection of the correct and well-adapted strain. New techniques in biotechnology will help in developing methodology for mass production and formulations. Other factors which can be considered, and which may be determinants on the potential of insect pathogenic fungi include the environmental conditions and cultural techniques (e.g. intercropping, planting density, irrigation). The cultural techniques can result in change of the environment favourable to the disease.

Three aromatic juvenoids were evaluated for morphogenetic activity on Schistocerca americana. Fenoxycarb, the most active insect growth regulator examined, was found to induce a significant mortality in developing fifth stage nymphs and caused severe morphogenetic damage during ecdysis to the adult. Juvenoid treatments were also observed to increase the duration of the last nymphal stage and to induce chromotropic colour changes similar to that observed in the solitary phase of the desert locust, Schistocerca gregaria Forskal.

Vegetable oil and palm oil were tested for their ability to suppress the populations of Rhyzopertha dominica Fabr. and Dinoderus distinctus Lesne on maize, sorghum and wheat grains using three dosages of 1 ml/kg, 5 ml/kg and 10 ml/kg. A dosage of 5 ml/kg of each oil, completely protected the three grains from D. distinctus and R. dominica on maize grain. Vegetable oil at 10 ml/kg dosage controlled R. dominica on sorghum and wheat. Palm oil had a similar effect, but did not control R. dominica on wheat even at 10 ml/kg dosage. The populations of R. dominica when treated with 1 ml/kg dosage were not significantly lower at 5% level than the control, with the exception of maize. Percentage weight losses of all grains at 5 ml/kg and 10 ml/kg dosage were significantly lower at 5% level than the control. Oil treatment did not significantly affect the germination of grains and protected the grains from the two pests for only 3 months. The highest population of R. dominica after 2 months of reinfestation was 67 and the highest mean population of D. distinctus was 1.4. The use of vegetable oils in the management of insect pests in storage is discussed.

Bruchid beetles cause high losses of stored legumes in the tropics. Chemical control is inappropriate for the small scale farmer and the use of alternative measures should be encouraged. Different biological methods of control such as cultural, physical, varietal, biological, biorational and genetic control are reviewed. Cultural control techniques such as timely and frequent harvesting, legumes planted away from granaries, crop hygiene and storage in pods, are within the technical and financial means of the small scale farmer. The use of inert substances, vegetable oils and repellent plants may be cheap and effective if properly managed. The use of controlled atmosphere, vacuum, heating, cooling and sterilizing, requires relatively advanced techniques. Growth regulators and pheromones are currently not available for control. Varieties resistant to bruchids have been identified, but incorporation of resistance into suitable varieties has proven to be difficult. Biological control of bruchids should receive more attention in particular research on the introduction and conservation of natural enemies. To effectively implement control measures at farmer's level socio-economic and cultural aspects should be taken into account. Proven appropriate techniques should be combined in an overall integrated pest management strategy.

Neem oil (NO), and different formulations of neem oil in a solution of Tetrapleura tetraptera as emulsifier, including neem oil emulsifiable concentrate (NOEC), neem oil slurry emulsifiable concentrate (NOSEC) and 5% NOEC obtained from the seeds of the neem plant, were tested for their efficacy in the control of Maruca testulalis Geyer, under laboratory conditions using flowers of Ife Brown, cowpea variety.

The different concentrations of NOEC (5, 10 and 20%) exhibited a high degree of insecticidal activity on M. testulalis larvae. All the treated flowers were protected from larval damage 2 days after treatment as compared to the 100% damage recorded on untreated flowers and on the flowers treated with T. tetraptera solution alone.

The NOSEC and the 5% NOEC prepared using different volumes of the emulsifier also exhibited some insecticidal activity which decreased with a decrease in concentration. NO/NOEC were superior to NOSEC and the 5% NOEC prepared in different volumes of the emulsifier.

The insecticide application techniques on cotton were compared in a series of trials. The new techniques compared well with knapsack sprayers and can play an important role in the control of Heliothis and other insect pests of cotton in Zambia. The ‘Electrodyn’ knapsack and ULV sprayers gave similar yields and pest control with cypermethrin at 30 g a.i./ha. A new pyrethroid lambda cyhalothrin (12 g a.i./ha) gave similar yields to cypermethrin (30 g a.i./ha) irrespective of the spraying techniques (Electrodyn, knapsack and ULV). The new application techniques have more potential for small-scale cotton farmers in developing countries as they receive limited training on the dilution of insecticides with water and calibration of knapsack sprayers.

The charged and partially discharged Electrodyn was evaluated at various swath rows of cotton. The results of field trials suggest that under a low pest pressure, a wider swath up to two or even more rows is possible, with the current version of Electrodyn sprayer, without any significant effect on the yield of seed cotton. Similar yields of seed cotton were also obtained with both charged and partially discharged Electrodyn.

Increasing costs of tick control have necessitated a complete re-assessment of its economic impact. There are two main approaches to studies on production economics. Some researchers advocate a “systems approach” in which all production traits and their interactions are monitored simultaneously, whilst others claim that studies must produce specific data on selectively identified components in the system which can then be used in process/simulation type models.

Studies were carried out in Zambia using a farming systems approach to quantify the effects of tick control on traditionally managed Sanga cattle. It seems that this decision was justified, because it is evident from the results that the determinants of the effects of tick control are extremely complex.

Overall herd productivity, i.e. outputs of milk and weaner calf per livestock unit carrying capacity, was about 25% higher in a tick-free herd. However, the annual cost of control in 1988 at ZK286.26 per livestock unit was greater than the increase in value of the products at ZK175.48 per livestock unit carrying capacity.

From this study, the intensive tick control in this system is not justified in the absence of serious tickborne disease. However, the analysis of various interactions indicate that limited seasonal tick control of adults from November to April would be economically viable. Calves should not be treated until they are 3 months of age.

Genetic analyses were carried out to determine inheritance of resistance, heterotic effects and reciprocal effects for resistance to the spotted stem borer, Chilo partellus in three maize crosses. Resistance was found dominant over susceptibility. Highly significant heterosis was detected for percentage dead hearts. Both additive and nonadditive gene effects were important in the inheritance of resistance to C. partellus in all crosses. Additive gene effects were highly significant for all the three resistance parameters: leaf-feeding, dead hearts and stem tunnelling. However, a high magnitude of nonadditive (dominance and epistatic) gene effects were detected for dead hearts. No cytoplasmic effects were detected in reciprocal crosses between resistant and susceptible maize lines, suggesting that the resistance to C. partellus is conferred only by nuclear genes. Recurrent selection methods should be used to accumulate alleles for resistance. Resistant F1 hybrids could be developed between resistant and susceptible lines in reciprocal combinations.

Correlations were established between an endemic infestation of the coffee margorodid, Icerya pattersoni Newst and the characteristics of the veins of the leaves it infested in four coffee species in Kenya. The attack was variable between species although there was an affinity for it to be confined to midribs of definite length and thickness and laminal veins of quantifiable dimensions.

The susceptibility of maize germplasm from CIMMYT — Mexico, Malawi and Zimbabwe — to attack by the maize weevil, Sitophilus zeamais (Motsch.) was investigated under controlled temperature (28°C) and r.h. (70–75%). An index of susceptibility (I), derived from the numbers of F1 progeny and the mean development period was used as the basis for measurement of the susceptibility. The indices of susceptibility of the CIMMYT germplasm ranged from 9.25 for Rattray Arnold (I) 8149 to 14.48 for Poza Rica 7737. Of the 17 collections of Malawi local maize evaluated MLM#20 was the least susceptible (I = 10.72), while MLM#24 was the most susceptible (I = 13.25). The least susceptible of the Zimbabwean germplasm was a local collection of an indigenous maize, Variety 8 (I = 10.61), while the most susceptible was a hybrid PNR 6334 (I = 14.74). Further, the nine Mexican materials and a local hybrid SR 52 were evaluated under field conditions in small farmers' granaries. Rattray Arnold (I) 8149 and Population 68 were the least damaged and produced the lowest numbers of weevils. Maize classified as susceptible in laboratory tests also suffered high damage levels in on-farm storage trials.