Incidence of egg and larval parasitoids of Chilo partellus on Kharif maize

Abstract

The incidence of egg and larval parasitoids of Chilo partellus was monitored in insecticide free maize fields at the Indian Agricultural Research Institute, New Delhi, for three Kharif seasons of 2013 to 2015. The hymenopteran parasitoid, Trichogramma sp. was recorded to be the only egg parasitoid in this area, while a good number of larvae were parasitized by braconid, Cotesia flavipes. The egg parasitism was recorded on the freshly laid eggs of stem borer obtained by artificially releasing the adults of C. partellus on maize cultivars, HQPM1 and PMH1, at 12 days after germination. There was no egg parasitism recorded during Kharif 2013 and 2014, whereas 5.6 percent egg-mass parasitism by Trichogramma sp. was recorded during Kharif, 2015. The larval parasitoids were monitored by artifcially infesting the maize plants with neonates of laboratory reared C. partellus. The larvae were allowed to develop on maize plants under field conditions for 20 days. The plants showing stem borer damage were cut and brought to the laboratory. The larvae collected from infested maize plants were reared in the laboratory. The maggots of C. flavipes recovered from parasitized larvae ranged from 29-100, 41-50 and 20-80 percent during Kharif 2013, 2014 and 2015, respectively. The result of this study indicated that parasitism by Cotesia was influenced by age of plants damaged by C. partellus. The young maize plants seemed to be more attractive to the foraging of Cotesia and more stem borer larvae were parasitized on these plants as the maximum (58 percent) parasitism was observed at 40-day-old crop. The parasitoid was found to be active on maize from 40-60 days after germination and the incidence decreased thereafter. Insecticides should not be used during this period. The current studies also revealed that host densities had no significant effect on percentage parasitism by Cotesia.