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 varied agroecological zones (AEZs) were surveyed twice each year from 2017 to 2019 during dry and rainy seasons in Kenya. In eastern Kenya, sample farms were small-scale citrus orchards in counties of Machakos Low Midlands-Four (LM4) and Makueni of Upper Midlands-Three (UM3). In the Coastal Lowlands-Four (CL4) similar small-scale citrus plots were sampled in Kwale, while in the highland Rift Valley region visited sample sites were ADC- Suam orchards of Kitale of the Lower Highlands-Two (LH2), where the large scale farmers grew citrus crop. The fifth region site 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 Phytoseiidae mites. The major pest scored from the sites was citrus brown mite, Eutetranychus africanus among other minor pests. In the study, Phytoseiidae mite population density growth was observed under different climatic factors of temperature, relative humidity, dew-point and citrus plant age (in years). It was only in the warm-humid coastal region of CL4 where the four factors of temperature, relative humidity, dew-point, and citrus plant age appeared to positively correlate to higher Phytoseiidae population density. In other warmer agro-ecological zones older trees positively correlated to higher Phytoseiidae density. 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 Phytoseiidae density in the orchards temperature parameter did not significantly appear to 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 Phytoseiidae numbers correlated inversely to higher E. africanus infestation levels on the citrus trees. The information here could be used proactively to plan for the management of E. africanus pest in citrus orchards in specific agro-ecological zones.