SEASONAL ABNDANCE OF A PYRALID PEST AFFECTING DUCKWEED PRODUCTIVITY IN POND ECOSYSTEM

摘要

Severe infestation caused by a pyralid insect pest on duckweeds was recorded from July 2004 to February 2005 in some duckweed farms of Bangladesh. The larval and pupal case-making stages were identified as mechanical key factors for bringing the pyralid insect to its pest status. In Mirzapur station-1, larval abundance was in the peak in September and October. Larval abundance was diminished to zero state in January. Maximum number of pupa was recorded in September 2005. The pest population was virtually absent in December and January. Larval abundance in Mirzapur station reached to its peak in September and came to zero during the second half of December. The absence of larval case was found to continue up to the second half of January. The highestabundance of pupae was observed during September and October.