Abstract
In 2001, populations of the leaf folder (LF) (Cnaphalocrocis medinalis Guenee) reached 19–30 larvae/hill in Rabi rice (variety Lalat) fields at Choudwar, Baranga, Alani and Tangi, Orissa, India infesting 61–98% of the plants. Three bacteria viz. Pseudomonas aeruginosa (Pa1 and Pa2) and P. fluorescens (Pf) infected 62–98% of the larvae in different fields. No correlation was found among populations of the Pseudomonas spp. on the rice phyllosphere and larvae harboring the bacteria at different fields. The median lethal concentrations (LC50s; ×103 bacteria/mL) of Pa1, Pa2 and Pf were 4–4.2, 4.8–4.9 and 5.7–5.9, respectively, for the leaf piece assay and 4.8–4.9, 5–5.1 and 6.3–6.7, respectively, for the potted plant assay against second to fifth instar larvae. The median lethal times (LT50s) were 2.1–2.4, 3.2–3.5 and 5.3–6 days for the leaf piece assay, and 4–4.7, 4.7–4.9 and 6.1–6.8 days for the potted plant assay with Pa1, Pa2 and Pf, respectively. The Pa1 and Pa2 were compatible, exhibited synergistic effect and co-inoculation reduced the LC50 and LT50 as compared to inoculation with individual organisms. The Pf had no synergism with Pa1 or Pa2, and therefore, the lethal values for Pf alone or with the other bacteria were similar. Fulfillment of Koch's postulates confirmed that Pa1, Pa2 and Pf were pathogens of C. medinalis.
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