Effect of agro-ecological zones on predacious mites (Acari: Phytoseiidae) and pest mite, Eutetranychus africanus (Acari: Tetranychidae) populations in citrus orchards of Kenya

Phytoseiidae mites' survival and reproduction depend on optimal environmental factors. A total of five different agro-ecological zones (AEZs) were surveyed twice each year from 2017 to 2019 in Kenya. In Eastern Kenya sample farms were small scale citrus orchards in the counties of Machakos [Low Midlands-Four (LM4)] and Makueni [Upper Midlands-Three (LM3)]. In the Coastal Lowlands-Four (CL4) similar small-scale citrus plots were sampled in Kwale, while in the highland Rift Valley region sample sites were ADC-Suam orchards of Kitale of the Lower Highlands-Two (LH2), where the large-scale farms were under citrus crop culture. The fifth site sampled was Baringo area of the Low Midlands-Five (LM5) where small plot citrus crop dominated the sample sites. Out of 68 fields of repeat surveys, 40% of citrus plots yielded varied diversity of phytoseiid mites. The major pest from the sites was citrus brown mite, Eutetranychus africanus. In this study, population fluctuation of phytoseiid mites was observed under different climatic conditions of temperature, relative humidity, dew-point and citrus plant age (in years). On the major pest E. africanus, three factors were evaluated for correlation and significance to infestation levels on the citrus crop. Of the three evaluated factors of temperature, citrus tree age and phytoseiid density in the orchards, temperature parameter did not significantly influence the pest mite (E. africanus) infestation levels for all combined AEZs factors. In the present case studies of specific AEZs, older trees led to higher pest mite density while low phytoseiid numbers correlated inversely to higher E. africanus infestation levels on the citrus trees. The information here could be used proactively to plan for management of E. africanus as the major pest in citrus orchards in specific agro-ecological zones.