Mermithid parasitism of shoot borer (Conogethes punctiferalis) infesting ginger and turmeric and its biocontrol potential

A mermithid nematode parasitic to larvae of Conogethes punctiferalis, a serious pest of ginger and turmeric was recorded under field conditions during 2015 at Peruvannamuzhi (Kerala, India). The infection reached epizootic levels during July to September 2015 exceeding 50% mortality in host insect populations and the parasitism ranged from 18.2 to 80.6% and 17.9 to 66.7% in C. punctiferalis collected from ginger and turmeric, respectively. The level of host parasitism by the mermithid was positively correlated with rainfall and negatively influenced by maximum temperature. Molecular analysis of the partial 185 small ribosomal subunit gene region and phylogenetic analysis with other mermithid sequences available in the GenBank indicated that the present nematode clustered with other nematodes belonging to different genera and hence could not be attributed to a specific genus. The pairwise Kimura 2-parameter (K2P) distance revealed that the closest taxon to the study nematode was an undescribed mermithid species reported to infect slugs with a K2P distance of 0.009. The epizootics caused by this mermithid nematode in the natural populations of C. punctiferatis suggest its potential as a biocontrol agent against a polyphagous pest of international importance. The results of our studies provide a basis for using this nematode as a biocontrol agent for developing integrated pest management strategies against C. punctiferaiis.