Studies on the ecology of the yellow stem borer, Scirpophaga incertulas (Walker) (Pyralidae), in deepwater rice in Bangladesh uri icon

abstract

  • The yellow stem borer, Scirpophaga incertulas (Walker), emerged as the dominant pest of deepwater rice in an intensive 4-year ecological study in two farmers' fields in central Bangladesh. There were six annual broods. In brood 1 developing in transplanted dry season rice and brood 2 migrating to preflooded deepwater rice, the population density and level of stem damage were low. Borer populations built up in broods 3, 4 and 5 in flooded deepwater rice to reach densities of 16-52 immatures m-2, which damaged 33-80% of the stems. Borer populations declined in brood 6 at the end of the deepwater rice season, the larvae entering diapause in the field stubbles. The major factors regulating the populations were as follows: the incidence of weather extremes (temperatures > 34-degrees-C with relative humidity <70%) before flooding which are lethal to eggs and first instars; the presence of succulent, elongating stems which are favourable for larval penetration and development; the occurrence of rapid water rises (6-8 cm day-1) which drown the immature stages; the activity of natural enemies, particularly the complex of egg parasitoids, and spider and orthopteran predators; and the harvesting and threshing operations which kill many diapausing larvae in the stems. An early season population outbreak in 1977 was associated with exceptionally mild, wet weather; the highest population density and level of stem damage followed a late surge of flooding in 1980 that produced a second flush in elongating stems. The ecological studies revealed two occasions during the season when control measures might be feasible.

publication date

  • 1995
  • 1995