Entomopathogenic Nematodes (EPN): Diversity in Indian Tropical Sugarcane Ecosystem and Its Biocontrol Potential Against White Grub Holotrichia serrata F. on Sugarcane

Abstract

The root-feeding larvae of white grub Holotrichia serrata F. (Coleoptera: Scarabaeidae) causes serious damage in sugarcane fields in India. Generally, the damage caused by white grubs is in patches, but during severe outbreaks the entire crop in a field may be dried up. Entomopathogenic nematodes (EPN) have proven to be the safest and most effective way of controlling white grubs as both organisms spends a large portion of their life cycle in the soil. To ascertain the diversity of EPN, a survey was conducted in the white grub endemic areas of sugarcane ecosystem in the tropical India. Isolation, molecular identification of EPN and laboratory bioassays was conducted at Nematology Laboratory, ICAR-Sugarcane Breeding Institute, Coimbatore, India. Twenty-four EPN were isolated out of 243 samples, and frequency of occurrence of EPN was 9.87%. Among the 24 positive samples, eight EPN (three Heterorhabditis and five Steinernema) were isolated from dead larvae of naturally infested third instar white grub H. serrata. Out of 24 positive samples, 14 (58.3%) were heterorhabditis and 10 were (41.6%) sterinernematids. Sequencing and characterisation of the internal transcribed spacer region was used to identify all nematode isolates to species level. Out of 14 Heterorhabditis isolates, eight have grouped with H. indica in the indica-group and remaining six were unknown species. Out of 10 Steinernema isolates, two were grouped with Steinernema siamkayai and two isolates grouped close to S. backanense, while the remaining six unknown isolates clustered closely with S. affine, but these isolates form a separate cluster which is genetically different from other group of Steinernema spp. Bioassay studies were conducted under laboratory conditions against first, second and third instar larvae of white grub H. serrata. Among the five H. indica isolates, H. indica (DSM78) recorded maximum mortality of the grubs and low median lethal dose (LD50) value for all the three instars of white grub. Two field trials were conducted during June 2011 to evaluate the efficacy of H. indica (DSM78) against naturally infested white grub H. serrata sugarcane fields. In both the trials, reduction in number of grubs observed in the EPN treated plots compared to the control. The reduction in grub population due to EPN treatment ranged between 43.5 and 77% at field trial I and 30–78% at field trial II. The results of the present study clearly indicated that EPN, H. indica isolate DSM78 was found to be effective and a potential EPN isolate against all the three instars of white grub larvae under laboratory bioassays as well as in the field conditions.