Natural occurrence of entomopathogenic nematode species (Rhabditida: Steinernematidae and Heterorhabditidae) in cotton fields of Tamil Nadu,India

A total of 200 soil samples collected from the cotton fields of 10 different districts of the state of Tamil Nadu in India were evaluated for the presence of entomopathogenic nematodes (EPN) belonging to Steinernematidae and Heterorhabditidae during 2008–2009. This survey detected the occurrence of EPN in arable lands through the use of a standard insect baiting bioassay technique. EPN were recovered from all 10 cotton growing districts with 27 positive sites (13.5%) ranging from irrigated to rain-fed cotton fields of varied soil types (sandy to clayey), soil pH (4.9–8.4), electrical conductivity (0.11–1.25 dS/m) and organic matter content (0.21–3.8%). Both morphological and molecular tools were used to identify the isolates. Among 27 positive samples, 20 samples yielded steinernematids (74%) and seven samples yielded heterorhabditids (26%). The Heterorhabditis isolates were identified as Heterorhabditis bacteriophora. The Steinernema included Steinernema carpocapsae, Steinernema siamkayai and Steinernema monticolum. Steinernema carpocapsae was the predominant species. The cropping patterns comprising cotton–vegetables had higher EPN prevalence (26%) than cotton–pulses (22%), cotton–banana (3.3%) and cotton–millets (2.8%). Steinernema carpocapsae was recovered from cotton–pulses, cotton–millets and cotton–vegetables cropping patterns, whereas H. bacteriophora was isolated from cotton–pulses, cotton–vegetables and cotton–banana cropping patterns. This study demonstrated that EPN are prevalent in the cotton fields of Tamil Nadu, India and could potentially be incorporated into biological control or integrated pest management programmes.