Surveys of the cereal stemborers and their natural enemies in Zambia were initiated in 1997. The surveys verified the presence of three stemborer species on maize, sorghum and pearl millet. These were the maize stalk borer, Busseola fusca Fuller (Lepidoptera: Noctuidae), the spotted stemborer, Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) and the African pink borer, Sesamia calamistis Hampson (Lepidoptera: Noctuidae). Occasionally, the sugarcane borer, Eldana saccharina Walker (Lepidoptera: Pyralidae) was also recovered especially around areas near the sugarcane plantation at Mazabuka, Southern province. Chilo partellus was the predominant stemborer in region I (areas with less than 600 mm of rainfall per annum). Three ‘hot spot’ areas, namely Luangwa, Buleya Malima and Kalobolelwa, were identified based on the abundance of Ch. partellus. The exotic parasitoid, Cotesia flavipes Cameron (Hymenoptera: Braconidae) was released in the three areas for the control of Ch. partellus. However, post-release surveys in these areas have not revealed any recoveries of Co. flavipes. Three indigenous natural enemies, namely Cotesia sp., Dentichasmias sp. and Dolichogenidea sp. emerged from the field-collected larvae.

This paper addresses the competitive interaction between Cotesia sesamiae, a gregarious larval endoparasitoid that is native to Africa, and Cotesia flavipes, an introduced parasitoid from southern Pakistan which has recently been established in East Africa for biological control of the exotic stemborer, Chilo partellus. The two parasitoids are morphologically similar, and they both attack medium-sized to large larval stages of gramineous lepidopteran stemborers. Based on previous work which suggested that Cotesia flavipes was competitively superior to Co. sesamiae, we speculated that Co. sesamiae may be locally extirpated in some areas of Africa. However, evidence from the field does not support this prediction. Recent field surveys in areas where both parasitoids occur, revealed that Co. sesamiae was still present, and densities were not declining. The interaction of the two parasitoids, as well as the influence of this interaction on host regulation, are discussed.

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.

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.