Mass rearing, larval behaviour and effects of plant age on the rice caseworm, Nymphula depunctalis (Guenée) (Lepidoptera: Pyralidae) uri icon

abstract

  • The mass-rearing method for efficient production of rice caseworm Nymphula depunctalis (Guenee) was improved. Moths oviposit most in ventilated cages on the undersides of floating cut rice leaves aged 4-8 weeks after transplanting (WT). There was no effect of leaf width on oviposition. Greatest egg production occurs with a 12 h scotophase. Moths are highly tolerant of crowding in oviposition cages, as up to 40 females averaged 86-115 eggs per female in 0.14 m3 cages. Honey as a carbohydrate energy source increases the rate of oviposition but not total oviposition. Larvae require standing water to fill their cases as respiration occurs with tracheal gills. Larval survival was equal when reared in distilled water, pesticide-free ricefield water, or chlorinated tap water, whether aerated or not. Larvae survive better, grow larger, mature more rapidly, and become more fecund adults when reared on plants 2-6 WT. Pupae are non-aquatic. The caseworm's inability to develop satisfactorily on post-vegetative rice may be attributed to poor nutrition and less favourable oviposition substrates. Females prefer to oviposit on drooping leaves floating on the water surface. As the crop matures, fewer leaves touch or float on the water surface. Eggs desiccate if laid on aerial portions of plants and are more exposed to natural enemies.

publication date

  • 1994
  • 1994
  • 1994