The most important cotton pests in Egypt are the Egyptian cotton leafworm, Spodoptera littoralis, and the pink bollworm, Pectinophora gossypiella, together with localized infestations of spiny bollworm, Earias insulana.

Control of S. littoralis is achieved by the hand collection of egg-masses every 3 days during the early part of the cotton season by teams of children. Alternative control techniques currently being investigated include the use of microbial pesticides and insect growth regulators.

Large scale commercial applications of slow-release pheromone formulations are used to control P. gossypiella by the mating disruption technique as an alternative to four or five sprays of conventional pesticides. Similar pheromone formulations are being developed for control of E. insulana, which occurs towards the end of the cotton season.

As a result of using such a combination of selective control methods, beneficial insect populations have remained at high levels throughout the season and acceptable levels of infestation have been achieved associated with relatively few applications of conventional pesticides.

In a series of field experiments conducted since 1977, various cultural pest management techniques have been tested to reduce damage by the sweetpotato weevil, Cylas formicarius formicarius F. Planting rice after harvest of the weevil-infested crop does not reduce weevil damage in the ensuing sweetpotato crop if the source of weevil is present in the vicinity. Rice rotation initiated away from the weevil source, coupled with removal of the common wild-host Ipomoea sp., can reduce weevil infestation and maximize the effectiveness of carbofuran transplant dip treatment. In order to reduce the weevil source from the weevil-infested sweetpotato of the previous season, a 2-week flooding of the field soon after harvest practically eliminated the number of volunteer sweetpotato plants and the weevil. Covering the planted area with rice straw or plastic mulch reduced weevil infestation.

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.

Sweetpotato weevil, Cylas formicarius formicarius F is the most destructive pest of sweetpotato, Ipomoea batatas in tropical and subtropical regions. The larvae and adults feed on sweetpotato roots and crowns. For the past 12 years we have been screening sweetpotato germplasm for resistance to this pest in order to breed an agronomic cultivar with weevil resistance. Resistance screening is conducted at AVRDC and Penghu island in autumn and summer, respectively. Germplasm is planted between heavily infested source rows maintained in a weevil nursery. Roots are harvested, sliced into thin pieces, and the number of insects (larvae + pupae + adults) per unit weight, as well as the weight of damaged and healthy root slices, are recorded. The resistance rating is based mainly on the number of insects found in the root. Considerable differences in resistance rating are observed from location to location and season to season. Even at one location, tremendous differences are observed in weevil infestation of a particular entry among the replicates. Although over 1000 sweetpotato accessions have been screened, we have not found any that is consistently less damaged over several seasons at either location. Our recent screening of a population of I. trifida × I. batatas crosses show certain hybrids with high yield and low weevil infestation. These hybrids need to be evaluated further to confirm their resistance.

The sweetpotato weevil (SPW), Cylas formicarius elegantulus (Summer), is the most destructive insect pest of sweetpotatoes throughout the world. Losses due to direct damage, cost of control and regulatory action conservatively exceed $7 m annually in the USA. First reported in New Orleans in 1875, SPW has infested 11 states over time. Studies in Louisiana indicate SPW control by leaving postharvest residue on the soil surface, by applying a protectant to roots going into storage, spraying plant beds, and by using cut plants. SPW quarantine has effectively reduced detections in Alabama. In North Carolina (NC), a restriction on potato growing in a small infested area isolated from commercial production has proven effective. The NC Extension Service initiated a multimedia programme on SPW. A resource notebook containing a slide set/script, coloured flyer, photograph, plastic embedded SPW stages, insect note and suggested news releases was shared during a 1-day-workshop. Television, an exhibit, oral presentations and newsletters were used to disseminate information. Promising SPW control tactics and management strategies were shared via a workshop and proceedings. Interest is high and traditional and innovative extension and regulatory activities have intensified, and the SPW remains in abeyance.

The Africa-wide Biological Control Programme of cassava mealybug, Phenacoccus manihoti, and cassava green mite, Mononychellus tanajoa, (ABCP) was started by the International Institute of Tropical Agriculture (IITA) in Ibadan in early 1980 following the request of several African countries for help in solving this disastrous pest problem.

The Africa-wide Biological Control Programme (ABCP) gratefully acknowledges the financial support of the following: International Fund for Agricultural Development, Rome; Directorate for Technical and Humanitarian Aid, Switzerland; Deutsche Gesellschaft für Technische Zusammenarbeit, West Germany; Austrian Government Development Aid Division, Austria; International Development Research Centre, Canada; since 1984/85 the Food and Agriculture Organization of the United Nations, Rome; Danish International Development Agency, Denmark; International Cooperation, The Netherlands; and the Department for Development Cooperation, Italy; and since 1986 the Norwegian Ministry of Development Co-operation.

The Africa-wide Biological Control Programme of Cassava Pests (ABCP) was established in 1980, following requests for assistance by an increasing number of African countries. Its objectives in the short term are to: (1) achieve permanent, ecologically safe and economically sustainable control of the cassava mealybug (CM), Phenacoccus manihoti, and cassava green mite (CGM), Mononychellus tanajoa, throughout the African cassava belt, (2) provide specialized training in biological control techniques and (3) initiate National Biological Control Programmes (NBCPs). In the long term, the objective is to establish full-fledged NBCPs in countries requesting assistance by using the ABCP as a model. ABCP research thus far includes: exploration for natural enemies in South America, bionomic studies of the pests and their natural enemies, field ecology, modelling plant growth, and experimental ground releases and large-scale aerial releases of CM and CGM natural enemies. Epidinocarsis lopezi, a CM parasitoid, has been established in 13 countries within 2 years of its release. CM populations are being maintained mostly below the injury level in all areas of establishment where detailed surveys have been made.

Taxonomy is the starting point of any basic or applied biological research. In biological control work, the pest species, its probable area of origin, and, consequently, the location where promising natural enemies may be found, are identified. The close co-operation of taxonomists during pre- and post-release surveys of natural enemies in target areas helps to indicate the indigenous fauna present and the progress of a biological control programme. Biological control programmes should budget for appropriate taxonomie studies in areas where the local fauna is poorly known. Instructing local researchers on the correct collection, preservation, and identification of relevant indigenous and exotic species should be emphasized.

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.

Detailed age-specific life table studies were carried out under controlled conditions to measure the effect of temperature, leaf quality ( = age), variety and plant drought stress on net production rate (R0), intrinsic rate of increase (rm) and generation time (G) of Phenacoccus manihoti Mat.-Ferr. in order to explain changes in population densities observed in the field. The developmental threshold calculated from our data and results published by various authors was 14.7°C. At 35°C all mealybugs died before reaching the adult stage. Mealybugs reared on leaves of different ages showed little differences in rm, and the higher occurrence of P. manihoti on plant tips and oldest leaves could not be explained with better nutritive value of these plant parts alone. Cassava varieties have a strong influence on the intrinsic rate of increase, which could explain differences in results published by other authors. Plant drought stress had little influence on the life table statistics, but rainfall is assumed to be a determinant factor in the dynamics of the mealybug.

Epidinocarsis lopezi proved to be an efficient biological control agent of the cassava mealybug (CM), Phenacoccus manihoti, despite apparently low parasitization rates. Laboratory experiments indicated that its killing power at higher temperatures was two to three times higher than the per cent mummy formation suggested. Following an attack by an E. lopezi female some CM hosts were killed through host feeding and some through successful development of the parasitoid larva, processes which both benefit the parasitoid. If the host was found unsuitable, no egg was laid, and the CM survived the attack. Other CM died from the wasp attack without forming a mummy. This mortality is attributed to mutilation and unsuccessful larval development of E. lopezi. Most ovipositions induced a defence reaction by the host that lead to melanization. This process involved mainly wound tissue, sometimes partial encapsulation of the tail end of the parasitoid larva, and infrequently complete and fatal encapsulation of the parasitoid larva.

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.

Cassava green mite (CGM), Mononychellus tanajoa s.l., originating from South America, has become a serious pest in Africa, where it often occurs in mixed infestations with indigenous spider mites like Tetranychus lombardinii. The neotropical phytoseiid Neoseiulus idaeus is a candidate predator for classical biological control of CGM. Its prey preference and reproductive success on CGM and T. lombardinii were studied in the laboratory. Foraging individually on leaf discs, N. idaeus consumed CGM and T. lombardinii adult females equally in single-species populations but showed a distinct preference for CGM when both species were presented together at the same density. The predators developed and reproduced equally well on CGM and T. lombardinii.

A programme to control the cassava green mite (CGM), Mononychellus tanajoa, using classical biological control was initiated in 1983 as part of the Africa-wide Biological Control Programme (ABCP). Basic studies on the field ecology and biotic potential of CGM, and surveys of CGM and associated indigenous natural enemies found on cassava throughout Africa are being used to develop ecologically sound release and follow-up strategies. Applied work includes colony maintenance of exotic phytoseiids, development of methodologies for mass producing, transporting and releasing natural enemies, plus experimental releases and post-release surveys. Important parts of the work are being done in collaboration with several institutes and agencies, including foreign exploration and preliminary screening of exotic natural enemies, international quarantine services, regional release and follow-up surveys, taxonomy of CGM and phytoseiids, simulation modelling of CGM in the cassava ecosystem, artificial diets for transporting CGM natural enemies, survey of entomopathogens of CGM and predatory behaviour studies of exotic phytoseiids.

Culture and mass production of exotic phytoseiid predators is one component of a classical biological control programme directed toward the cassava green mite (CGM), Mononychellus tanajoa, in Africa. Five species of phytoseiid predators are currently maintained at the International Institute of Tropical Agriculture, Euseius concordis, Galendromus annectens, Neoseiulus anonymus, N. idaeus and Typhlodromalus limonicus. CGM from cassava and two-spotted spider mites, Tetranychus urticae, reared on mucuna, peanut and cowpea plants, are harvested as phytoseiid food using a mite brushing machine or a water based mite separator unit. Stock maintenance cultures are initiated at regular intervals, have a definite productive period and are used as a source for mass-rearing phytoseiids for release in Africa. Mass-rearing techniques utilizing artificial substrates, detached leaves and entire plants, in the insectary and field, are being developed.

Systems of different technological levels have been developed for the mass-rearing of cassava mealybugs, Phenacoccus manihoti, cassava green mites, Mononychellus tanajoa and their natural enemies. Prototypes have been built and are being evaluated for host plant growth, host insect and mite production and output of natural enemies. One of the prototypes uses a paternoster system in which trays each holding 66 cassava plants rotate around a light source. After each rotation the trays receive and empty a given amount of nutrient solution. The other uses a perforated vertical cylinder holding up to 250 cassava cuttings. The plants are irrigated through a pump or gravity system. Six to eight weeks are required to complete the cycle from planting to harvest of the natural enemies in either system. These systems reduce significantly the labour input required for conventional rearing systems and at the same time improve the reliability and quality of the end product.

An automatic insect release system (AIRS) has been developed by the International Institute of Tropical Agriculture in collaboration with Firma Dieringer of Austria and Ciba-Pilatus (now Zimex Aviation) of Switzerland for the aerial distribution of natural enemies of two cassava pests—cassava mealybug (Phenacoccus manihoti) and cassava green mite (Mononychellus tanajoa). The AIRS, installed in a twin turbo-prop aircraft, has undergone a series of tests to evaluate suitable packaging substrates, pre- and post-release mortality, biological performance and ground distribution of natural enemies.

Preliminary results show 25% of the mealybug parasitoid, Epidinocarsis lopezi died from packaging to release, maximum 25% died during the release and minimum 50% survived. The mortality of predatory mites released in small packages was negligible. Further work on post-release survival and dispersal is needed.

Epidinocarsis lopezi an exotic parasitoid to Africa, was first released to control the cassava mealybug (CM), Phenacoccus manihoti, at IITA (Ibadan) in November 1981, and a year later at Abeokuta, both in southwestern Nigeria. Population dynamics study of CM and its natural enemies was conducted for 4 years. CM population peaks usually occurred during the second half of the dry season (January–April). E. lopezi was the only natural enemy that was found during the whole year and in high densities. Parasitization rates of E. lopezi alternated with CM densities, thus suggesting a regulatory effect on CM populations by this parasitoid. CM populations were drastically reduced in release fields when compared with control fields. Subsequently CM populations have been maintained below injury levels for 4 years. E. lopezi is considered an efficient parasitoid of the CM.

Over 130 species of insects were found in association with the cassava mealybug (CM), Phenacoccus manihoti, and its newly introduced parasitoid Epidinocarsis lopezi in Africa. As the CM in SW Nigeria declined under the influence of E. lopezi, this introduced wasp maintained densities of 2.8–3 per CM-infested tip early in the dry season and 1.3–1.6 per infested tip late in the dry season, but declined overall from 1.3 to 0.2 per randomly collected tip within 1 year. The decline of CM led to a sharp reduction in numbers of indigenous coccinellids, particularly of Hyperaspis spp. and to a lesser extent of Exochomus sp., due to competition with E. lopezi for the common food source. Numerous species of other polyphagous predators and parasitoids of coccinellids were found in low numbers. Indigenous primary parasitoids, Anagyrus spp., were rare, but their 10 spp. of hyperparasitoids were often reared from E. lopezi, with Prochiloneurus spp. and Chartocerus spp. being the most common. Hyperparasitism declined from 41.3% in March 1983 to 16.9% in Dec 1984 and proved to be positively density-dependent. The effects of hyperparasitoids on this biological control programme are discussed.