The role played by the lepidopteran yellow stem borer, Scirpophaga incertulas (Walker) in the life cycle of deepwater rice (Oryza sativa) is controversial. The major question is whether or not larval feeding in the elongated stems is damaging and if so, although no visible symptoms can be observed, leads to loss of yield. Drawing on evidence from entomological and agronomic studies, especially in Bangladesh and Thailand, I have tried to show:

• That there is little or no correlation between early- or mid-season borer infestation and yield
• That stem density always declines from a pre-flood maximum, irrespective of borer infestation
• How late-season infestations can lead to serious crop loss
• How a promising concept for strategic timing of insecticide application was developed and tested.

Introduction

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