Integration of fertilizers, predacious mites and acaricides in the management of cassava green mite mononychellus species (acari: tetranychidae) in Kenya

Abstract

The cassava mite complex of the genus Mononychellus is among the major arthropod pests of the cassava crop in Kenya. The present investigations addressed the integrated pest management (IPM) method as it applies to the protection of field cassava crops from losses due to phytophagous mites. The work employed use of IPM components, namely, predacious mites, soil fertility and acaricides to ensure effective protection. A survey was conducted to determine the taxonomy of the individual species in the complex of the phytophagous and predacious mites of the genus Mononychellus, major arthropod pests of cassava crops in Kenya. Standard sampling methods developed by previous workers were employed and yielded both phytophagous and predacious mite specimens for identification. Both morphological and molecular analyses methods were used to sort out the taxonomy of the mites identification based on morphological features and confirmation made by comparison with previously identified specimens by mite taxonomic experts. Confirmation of the species was made by molecular analyses of a fragment of ribosomal DNA (ITS 1& 2) and mitochondrial cytochrome oxidase sub-unit I (COI). The techniques revealed that Mononychellus progresivus Doreste as major pest on cassava. Out of the 29 species from all the surveyed agro-ecological zones, two were most abundant, namely, Euseius fustis Prichard & Baker and Typhlodromalus aripo De Leon. The ecology of M. progresivus density growth on different cassava varieties was carefully examined in a screen house study as a baseline for the respective agroecological zones. Increased cyanide content of >10<30mg / kg cyanogen glycoside content on the varieties attracted the highest density of M. progresivus. Mite economic threshold density for control of M. progresivus on cassava was deduced to be ≥27 mites /leaf. Further, in an experiment to determine the most effective mite predator for use as a biological control agent in the IPM study against the phytophagous mite M. progresivus was carried out in the laboratory. Of the two mite predators, namely, T. aripo (predominant from survey sites) and another newly acquired species from South America, Phytoseiulus longipes Evans, the former was chosen on the basis of prey consumption and fast development rate on CGM. Field evaluations were conducted using the selected IPM components stated above. The zones included the eastern dry lowmidlands of LM4 at Katumani and LM5 at Kiboko, the cool upper midlands of UM3 at Embu and the warm coastal lowlands of CL3 at Mtwapa. The results revealed that the phytoseiid mite T. aripo effectively suppressed population densities of M. progresivus in the warm-humid coastal zone. The acaricide (abamectin) spray in the manure integrated treatment gave the best control option for complete suppression of CGM densities at all sites. Soil fertility input led to higher yield in the sandy soils of coastal and eastern lowlands in the T. aripo introduced plots. The performance results by the integrated components give choice of implementation of integration of biological (predacious mites), chemical (acaricide) and soil fertilizer inputs on management of the M. progresivus on cassava in the different agro-ecological zones of Kenya.