Bio-efficacy of egg parasitoid, trichogramma chilonis (Ishii) against spotted stem borer, chilo partellus (swinhoe) in kharif maize

Maize stem borer, Chilo partellus, is a serious pest of maize in India. Insecticides are not the right choice as larvae feed internally. Moreover, the indiscriminate use of pesticides increases the cost and accounts for health and environmental hazards. Adopting non-chemical methods such as biological control is an important strategy for effective suppression of the pest population. Biological control agents such as egg parasitoids, Trichogramma spp. (Hymenoptera: Trichogrammatidae) substantially reduce the pest population and are widely used against lepidopteran insect-pests. We studied the efficacy of egg parasitoid, T. chilonis against C. partellus in Kharif maize and recorded maximum egg parasitism by T. chilonis when released twice at higher rates (i.e. 1,25,000 and 1,00,000 parasitized eggs ha-1). However, treatments with low release rates (one and two releases @ 75,000 parasitized eggs ha-1, one release @ 1,00,000 parasitized eggs ha-1) experienced significantly high plant damage and did not provide satisfactory monetary returns. In contrast, treatments with higher release rates (i.e. T. chilonis @ 1,25,000 parasitized eggs ha-1 at 7 and 14 DAG; T. chilonis @ 1,00,000 parasitized eggs ha-1 at 7 and 14 DAG) effectively suppressed plant infestation, dead heart formation and leaf injury by C. partellus. These treatments were statistically comparable with chemical control (dimethoate @ 660ml ha-1 at 7 DAG). It can be concluded that one release of T. chilonis is insufficient, and two releases are required for effective management of C. partellus. T. chilonis provides the best result when released twice @ 1,25,000 parasitized eggs ha-1 at 7 and 14 DAG (B:C ratio=1.42) which is at par with two releases @ 1,00,000 parasitized eggs ha-1 (B:C ratio=1.41). Although pesticide-treated plots (Dimethoate 30 EC @ 660 ml/ha at 7 DAG) provide a satisfactory monetary return, they are not environmentally compatible and ecologically viable for the long run.