Tryporyza incertulas, The Yellow Stem borer

(Lepidoptera: Pyralidae)

Host: This is primarily a pest of rice but also has been recorded to feed on maize and some wild grasses.

Damage: The larva feeds inside the stem and makes gallery causing dead heart in younger plants. The flowering plants show white head, i.e. panicles dry up and become whitish in colour. One larva can damage several tillers before maturing.

Life cycle: Adults show sexual dimorphism. Females are yellowish brown to orange yellow in colour, with wing span of 3.0 cm, one black spot in the middle of fore wing and tip of abdomen bearing yellowish to buff coloured anal tuft of hairs. Males are slightly smaller in size; have yellowish forewings containing 6-7 small blackish spots. Eggs are oval, flattened and whitish in colour. Incubation period of eggs is 5-8 days.

Larvae are pale yellow in colour with a brownish head, 20 mm long and bore into the stem near the node. They usually feed on the lower part of the stem and migrate from one plant to another to mature. There are 6 larval instars and larval development takes 20-27 days. Pupation takes place inside a whitish silken cocoon within the rice stem, near the root-stem joint. Before pupation larva cuts an exit hole on the stem, above the surface of water and covers it with a silken web as an exit for emerge. Pupal period is 9-10 days or longer in cold weather. Total life cycle takes about 45 days and 4-5 generations can be completed from April to October.

Distribution: The pest is found all over the Indian subcontinent, SE Asia, China and southern Japan.

Control: Collection and destruction of egg masses and plants showing dead hearts helps to reduce pest population, particularly in nurseries. Burning of stubbles or ploughing the field after harvesting is a good cultural practice. Early or late planting is recommended in areas of heavy infestation.

Spraying of the following insecticides: fenthion 0.05%, endosulfan 0.035%, endrin 0.025%, parathion 0.04% @ about 400 litres per hectare 2-3 weeks after transplanting and then every 20 days. Application of granules in the root zone of the following insecticides: Lindane 10%, diazinon 5%, carbofuran 5%, quinalphos 5% @ 2-2.5 kg a.i./ha at 20 days interval gives satisfactory control of this pest.

The following natural enemies keep the pest population under check and must be conserved: Egg Parasites: Tetrastichus schoenobii, Telenomus beneficiens, Trichogramma sp. Larval parasites: Amauromorpha accepta schoenobii; Isotima javensis. Larval-pupal parasite: Trichomma sp.