Influence of plant ontogeny on rice susceptibility to Lepidopteran stem borers

The susceptibility of plants to herbivores differs at different ontogenic stages, and previous studies show varietal differences in rice against stem borers. In this study, we investigated the susceptibility of rice at different growth stags to infestation by stem borers Diatraea saccharalis and Eoreuma loftini. To evaluate ovipositional preference of D. saccharalis on rice, we conducted a greenhouse choice experiment with two rice varieties, Cheniere and PVL03 and four plant stages, mid tillering, panicle differentiation, 1-5 cm panicle and early booting. Total number of eggs/plant and oviposition events/plant were counted 5 days after introduction of adults into cages. Our results indicated that oviposition varied significantly across varieties and growth stages. Oviposition was approximately 2.5-fold greater at 1-5 cm panicle stage than late tillering stage regardless of the variety. Across all stages, PVL03 recorded 1.35-fold more oviposition events than Cheniere. The lowest oviposition occurred on Cheniere at the late tillering stage while PVL03 consistently received more eggs indicating higher susceptibility in terms of oviposition. To evaluate effectiveness of foliar application of insecticides at different growth stages, we conducted a field experiment in which we used one variety ‘PVL03’ and foliar applications of lambda-cyhalothrin was applied at following growth stages: late tillering, panicle differentiation, 2-5 mm panicle, 1-5 cm panicle. Results showed that spraying at later reproductive stages provided better control of stem borer infestation. Thus, both greenhouse and field experiments show that rice at reproductive stages is more susceptible to stem borer infestation.