About 70 insects and five mites regularly or occasionally infest the cotton crop in subtropical Africa. The economic importance of these pests varies according to the climate and cropping pattern in the region. Cotton aphid, Aphis gossypii Glover and yellow tea mite, Polyphagotarsonemus latus (Banks) as foliage feeders and three bollworms, Pectinophora gossypiella Saunders, Diparopsis watersi Roths, and Heliothis armigera Hbn., during boll formation and development, are major pests. Pesticides have been used extensively to suppress the pest populations and infestation levels in the crop. Natural enemies of certain pests occur in the region, nevertheless, their effectiveness in pest control is not well-known or fully exploited. Research on yield loss evaluation, pest ecology, varietal resistance and cultural practices is underway in several countries. Therefore, a global pest management in cotton is discussed in the context of local conditions and perspectives are highlighted.

Field infestation of millet by Sitotroga cerealella (initial infestation) has been studied in two cropping systems and in three locations in Senegal. In all cases, ears were attacked since harvest, but the level of damage was 10 times higher on ears from fields close to dwelling houses than on those away from dwelling houses. In this way, the author discusses the problematic conservation of millet seeds in farm conditions, depending on that initial infestation in one hand and on the other hand on storage method of millet ears in traditional granaries.

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.

Studies were conducted on the biology of the recently described Goniozus sensorius Gordh (Hymenoptera: Bethylidae), a gregarious ectoparasitoid of Diaphania indica (Saunders) (Lepidoptera: Pyralidae). Eggs are laid after temporarily paralyzing the host. Mean development time from egg to adult is 11.96 days at 26.43 and 65.08% r.h. The female lays an average of 50.1 eggs during its life time and parasitizes 7.26 hosts on average. The sex ratio is 1:3.91, males:females. Mean adult longevity is almost similar for males (8.55 days) and females (9.81 days). Aphanogmus fijiensis (Ferriere) (Hymenoptera: Ceraphronidae) was recorded as a hyperparasitoid through G. sensorius.

Observations on the fauna that live in close association with mounds constructed by Cubitermes testaceus (Isoptera: Termitidae) were made in a grassland area of Uganda. Termite nests were systematically excavated and dissected and a careful record of the fauna associated with each was made.

Arthropods belonging to three different classes were recorded in mounds of C. testaceus and with varying degrees of occurrence. They included insects (93%), chilopods (5%) and diplopods (2%). Ants were found to be the commonest insects in the mounds followed by other termites (21%) Coleoptera (9%) and Dictyoptera (1%).

In view of the carnivorous nature of most of the ants recorded, and considering the feeding behaviour observed in the field, it is suggested that they can have considerable effect on C. testaceus populations in the grassland ecosystem at Kaazi.

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.

Biological control efforts on Parthenium hysterophorus L. (Asteraceae) in India have gained momentum after the limitations of other methods were realized. Native surveys revealed a large number of insects, but none of them was host specific. Although the introduced beetle Zygogramma bicolorata Pallister (Coleoptera: Chrysomelidae) has established at the sites of initial releases, its real impact on the weed and performance in different parts of the country need further evaluation. Fungal pathogens of the weed hold promise for classical as well as microherbicidal control. The use of parthenium phyllody MLO as a biocontrol agent requires establishment of host and vector specificity. Mycotoxins are a potential group of herbicides on which serious studies are yet to begin. Studies on control of the weed through interference and allelopathy by Cassia uniflora Mill. (= C. sericea Sw.) (Leguminosae) have produced promising results. Toxic leachates of C. uniflora and autotoxic principles of the weed deserve attention. Integrated biocontrol strategies envisaged for wastelands using introduced insects and pathogens, allelopathic plants, and agroecosystems using native pathogens, mycotoxins and autotoxic principles, will help combat this apparently invincible weed.

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 stable fly, Stomoxys calcitrans L., has two pairs of Malpighian tubules. Ultrastructurally, the tubules consist of three morphologically distinct zones: the distal, intermediate and proximal regions, which themselves are characterized by distinct cell types. The tubule cells have numerous mitochondria, microvilli and basal infoldings, which are associated with mitochondria. It is suggested that the distal and intermediate regions are secretory, while the proximal region is reabsorptive; and that the haemotophagous habit in S. calcitrans is probably correlated with the ultrastructure of its Malpighian tubules.

Investigations were conducted on dried fish samples purchased from Faku and Sabo markets (in the Kainji Lake Area) and stored for 6 months. The most abundant insect pest was Dermestes maculatus particularly the larvae. At 3 months of storage, weight losses were 13% for S. galilaeus, 17% for T. niloticus and 19% for Alestes sp. respectively, with the products reduced to powder mixed with insect exuviae and dead larvae. An analysis of the salt content of the samples showed no significant difference between salt composition at the beginning and end of the experiment. A relationship between salt content and the degree of infestation by insect pest could not be established, possibly because of the low percentage salt composition observed on all samples. A suggestion is made as to the possible areas of research to combat the menace of insect pest infestation of dried fish.

A large and varied group of insects attack crops of the tropical farmer, and carry various disease-causing organisms to him and his animals. The control of these agricultural pests, and vectors of human and animal diseases relies mostly on chemical pesticides. However, investigations show that alternative methods such as biological control and resistant crop varieties are available, which may be used in the reduction of pest infestation, resulting in an Increase in food production by the African farmer.

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.

The study of the population dynamics of Helicoverpa armigera (Hübner) in Cicer arietinum (chickpea), Lycopersicon esculentum (tomato), Abelmeschus esculentus (okra) and Zea mays (maize) crops revealed that the insect passed through five overlapping generations in a year. The growth of the population of H. armigera and its generation survival were maximum in second generation followed by fourth, third, fifth and first generations. Parasitoids, predators, fungal and viral diseases and abiotic factors were among the various observed mortality factors, although the role of predation was not specifically investigated. The key mortality factor within generation was an unidentified pupal parasitoid. The key mortality factor operating between generations was the variation in natality (log of ratio of maximum potential natality and actual eggs). In spite of the biotic mortality factors operating on H. armigera populations, the number of eggs laid is the most important factor that governs the trend of the population growth in all generations. Therefore, a powerful control measure is necessary by either trapping the adult moths or by cultivating trap crop to distract egg laying for those crops to be protected.

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.

Cytogenetic studies in indoor resting An. gambiae s.l. complex in five selected localities from east, south, and southwestern parts of Ethiopia were conducted. An. arabiensis was the only cyto-species found. Close examination of the inversion polymorphisms revealed the existence of two more polymorphisms in the 2Ra and 2Rd inversions, in addition to those previously reported viz. 2Rb and 3Ra, by Mekuria et al. (1982) and White (1974). The study covered wide ecological and altitudinal ranges and the karyotype frequencies were in agreement with the Hardy-Weinberg expectations. However, it was not possible to correlate the relationship between the 2Rb inversion and altitude as has previously been reported by Mekuria et al. (1982). The adaptive value of the 2Rb to increase in altitude (Mekuria et al., 1982), in view of diverse ecological and climatic conditions in An. arabiensis in Ethiopia is open to question.

The paper acknowledges the need for pesticide usage to boost agricultural production and for disease control in Uganda and elsewhere in Africa. But drawing from some instances of pesticide pollution so far reported in Africa, the paper highlights the need for cautious use of the chemicals in order to avoid further pollution.

The need for using pesticides within the framework of integrated pest management (IPM) is presented, but also presented are results of a survey which indicates that quantities of pesticides used continue to increase, and that the attitudes of farmers and extension workers are still heavily weighted in favour of pesticide application alone.

A number of options that could be taken to inculcate IPM ideals and concepts among the people are presented, emphasizing education and training, not only for farmers and extension workers, but also for the youths most of whom are destined to become the future farmers.

The various agricultural ecosystems in The Gambia are described in brief, and the richness of flora and fauna discussed. Indiscriminate cutting of trees without replanting, bush fires and mechanization of commercial crops have so far been much more destructive to the environment than has chemical control.

In the future one may expect more chemical control to be used in commercial crops, but probably not in subsistence cultures. With more commercial enterprises and less government participation, risks for the environment will probably increase.

The CILSS Integrated Pest Management Project (1983–1987) showed that it is possible to reduce yield losses without endangering the environment. IPM approaches can improve the methods of cultural and traditional control in subsistence cultures, and keep chemical control at a low level in commercial crops. Introduction of varieties which are tolerant or resistant to the most important pests, and biological control agents can be used for a number of crops. The system of surveillance, which was introduced for a number of pests by the CILSS project, should serve as a permanent basis for all control activities.

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.