Isolation and efficacy of native Heterorhabditis bacteriophora against Aeolesthes sarta (Coleoptera: Cerambycidae) in North Kashmir apple orchards

Entomopathogenic nematodes (EPNs) of the genus Heterorhabditis are important biocontrol agents that form a lethal combination with their symbiotic bacteria Photorhabdus against a variety of insect pests. This study describes native strains of Heterorhabditis bacteriophora for the first time isolated from the Northern parts of Kashmir valley, India and its efficacy was tested under laboratory conditions against the city longhorn beetle, Aeolesthes sarta (Coleoptera: Cerambycidae), the serious pest of apple in Kashmir valley. Apple orchards surveyed at three districts in the Kashmir Valley isolated five H. bacteriophora strains (Rhabditida: Heterorhabditidae). The strains were characterized at morphological, morphometric, and molecular levels and using the rDNA ITS markers, their phylogenetic relationships were reconstructed. They showed a well-supported clade with the reference sequence of H. bacteriophora MK421460. Thus, the H. bacteriophora sequences were positioned in the ‘bacteriophora’ lineage together with H. georgiana and H. beicherriana . This assemblage formed a sister group to H. zealandica , H. downesi and H. atacamensis . Case studies of the five nematode strains were done for comparing their efficacy at different inoculum levels against 1st, 2nd and 3rd larval instars of A. sarta. The calculated median lethal concentration (LC 50 ) and median lethal time (LT 50 ) varied among nematode strains. The lowest number of infective juveniles and least time was required by H. bacteriophora PP549990 to kill 50% grub population of A. sarta followed by strains PP549987, PP549986, PP549988 and PP549989, respectively. The notable differences in LC 50 and LT 50 should contribute to the best EPN strain-host matching. The recorded merits of LC 50 and LT 50 herein are demonstrated to set the basis for developing novel, safe, and effective strategy for A. sarta management. Moreover, because in Photorhabdus - Heterorhabditis combinations, the bacteria play the major role on the biocontrol mechanisms to kill the host, the high level of virulence evidenced herein by the mutualistic bacterium in the strain PP549990 should be further investigated and exploited under field conditions.