Mites of cassava (Manihot esculenta Crantz) habitats in Southern Africa
Résumé
This paper presents the first of a series of studies to evaluate the safety of a classical biological control programme of the cassava green mite Mononychellus tanajoa (Bondar) (Acari: Tetranychidae) in Mozambique and Malawi involving the introduction of Typhlodromalus aripo DeLeon, a predatory mite of the family Phytoseiidae. The objective of this study was to determine the mite fauna of cassava and other common plant species in or around cassava fields in those countries. Twenty-one phytoseiid species were recorded in Mozambique and 32 in Malawi. On cassava, the dominant phytoseiids were Euseius baetae (Meyer and Rodrigues), Euseius bwende (Pritchard and Baker) and Typhlodromalus saltus (Denmark and Muma) in Mozambique, and Euseius fustis (Pritchard and Baker), Iphiseius degenerans (Berlese) and T. saltus in Malawi. On other plants, the dominant phytoseiids were E. baetae, Amblyseius sundi Pritchard and Baker and Paraphytoseius horrifer (Pritchard and Baker) in Mozambique, and L. degenerans, Euseius magucii (Meyer and Rodrigues) and Euseius orygmus (Ueckermann and Loots) in Malawi. Several of the most common plants associated with cassava were observed to harbour phytoseiid species that also were found on the latter. Those plants may be important as reservoirs of such predators when conditions are not suitable for them to live on cassava. This seemed to be particularly true for 6 phytoseiids in Mozambique (A. sundi, E. magucii, P. horrifer, Typhlodromalus spinosus (Meyer and Rodrigues), Typhlodromips shi (Pritchard and Baker) and Neoseiulus teke (Pritchard and Baker)), and 6 phytoseiids in Malawi (E. orygmus, Phytoseius amba Pritchard and Baker, T. shi, Typhlodromus (Anthoseius) kikuyuensis Swirski and Ragusa, Typhlodromus (Anthoseius) malawiensis Zannou, Moraes and Hanna and N. teke), that were found on cassava at the end of the rainy season, but only on other plants in the dry season. Mononychellus tanajoa was the dominant mite species on cassava in both countries in addition to the phytoseiids; few other species were found on that plant in either country. A larger diversity of mites in addition to phytoseiids was found on other plants, but always at low numbers. Phytoseiid diversity and abundance varied between savannah and forest zones. These variations are likely due to differences in biotic and abiotic factors between the two zones