Impact of land use and cropping sytem on the distribution, occurrence and diversity of entomopathogenic nematodes in Embu and Taita district in Kenya
Entomopathogenic nematodes (EPNs) are considered as potential biological control agents against soil-borne insect pests in the world. The impact of land use and cropping system on their distribution in Kenya is still not investigated. This survey was done to determine the distribution, occurrence and diversity of these nematodes in Embu and Taita districts, Kenya. The study was conducted in different land use and cropping system. A total of 520 soil samples were randomly collected from the agro-ecosystems and EPNs were isolated using the baiting technique to determine their distribution and occurrence. Morphological identification revealed the presence of a single genus namely Steinernema of the nematodes from the two regions. Polymerase Chain ReactionRestriction Fragment Length Polymorphism (PCR-RFLP) of the ITS (internal transcribed spacer) region on the ribosomal(r) DNA of the isolates was amplified and then digested with Alu I restriction enzyme. The amplified and restricted fragments of the ITS were separated by agarose gel electrophoresis to indicate molecular differences. Based on the RFLP patterns, there was no molecular difference in the isolates from the planted forest and grassland while in the disturbed habitats, similar patterns were observed in the monoculture and intercropping farms. However, distinctive, differences were observed in the isolates from the natural forest, coffee farms and crop rotation farms. The EPNs occurrence and recovery frequency indicated that habitat type might influence their distribution as the intensity of agricultural management inversely affected their occurrence. The survey also showed that in the cropping system, plots that practiced monoculture recorded the least Occurrence of 27.5% followed by 52.5% crop rotation and the highest occurrence was in the intercropping farms with 55%. In the land uses, coffee farms had the highest number of EPNs (75 %) while 45% were found in the planted forest, 33.5% in the natural forest with the least occurrence of 30% in the grassland. Analysis of variance showed statistical difference between and within the cropping system and land use (P=0.004). These findings indicate that land use and cropping system should be taken into account if EPNs are to be used as effective biological control agents.