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In field studies during 2000-2005, seasonal dynamics of sugarcane shoot borer Chilo infuscatellus Snellen (Lepidoptera: Crambidae) and its parasitoid Sturmiopsis inferens Tns. (Diptera: Tachinidae) were examined and augmentative releases of the parasitoid against the borer were evaluated at Coimbatore, India. The borer was active throughout the study period with the overall range of 0.3 -28.6% fortnightly deadheart incidence. With considerable yearto-year variation, the borer peaked during July-August in high incidence years but showed indistinct peak activity periods in low attack years. Sturmiopsis inferens was found in all the study years with zero activity in some fortnights and overall maximum parasitism rates of 23.3 and 21.0% in 2000 and 2001, respectively; parasitoid activity dropped drastically in 2002 and the decline continued thereafter. The high parasitism years witnessed distinct peak activity in March and somewhat higher activity in July-August. Simple and multiple correlation analyses showed inconsistent influence of weather parameters on borer and parasitoid activity. Shoot borer activity was weakly related to St. inferens activity either in individual years or in the entire five-year period. Augmentative releases of St. inferens gravid females at dosages of 25-95 females/ha enhanced parasitism rates and reduced borer incidence in some trials but produced variable effects in some other trials. Dosage of parasitoid was not related to post-release parasitism rates in release plots. The results of the field trials and their implications are discussed.

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