Cnaphalocrocis medinalis

Scientific Name Cnaphalocrocis medinalis (Guenée, 1854)
Common Names English: Rice leaffolder; Spanish: Doblador de hojas; French: Pyrale des herbes; Japanese: Kobu-nomeiga
Description The adult moths are golden-brown and have a wingspan of about 13-18 mm (0.5-0.7 inch). The larvae are yellowish-green and up to 25 mm (0.97 inch) in length.

Biology

Damage

The larvae of C. medinalis feed on the mesophyll of rice leaves, thereby causing a reduction in the leaf area available for photosynthesis. They leave the vascular bundle, including the sheath and sclerenchyma, intact.

After hatching, the young larvae move towards the basal regions of young leaves, their first feeding sites. Later (mostly around the early second instar stage), they disperse again and each individual starts to build a feeding chamber by folding a leaf lengthwise and connecting its edges with silk. The caterpillar lives and feeds inside this tubular structure.
The affected leaf blades will then show longitudinal white, transparent streaks. Heavily infested fields may have 'scorched'-looking patches.

Lifecycle

Each female C. medinalis will lay about 300 disc-shaped eggs one-at-a-time, usually near the tip of a leaf. The larvae emerge after 4-6 days. There are normally 5 larval instars, but on older plants, 6-7 instars have been observed. Together, these stages will last 3-4 weeks, followed by 6-10 days for the pupal stage.
C. medinalis is found at all rice growth stages, but more frequently during the boot leaf stage. It prefers high humidity and, while infestations will occur throughout the year in the tropics, they are more severe during the rainy seasons.
The adults avoid exposure to direct sunlight: they are mainly active at night, and hide in shady places during the day. The rice leaf roller is found wherever rice is grown in Asia, on the Pacific islands and in Australia. It has been reported in Madagascar, too, but not yet on the African mainland.
In some regions, especially those with seasonal climates, it regularly migrates over long distances.

Occurrence

Additional Crop Information

Mainly rice, but also found on corn, wheat and sorghum.

Agricultural Importance

Modern rice varieties are largely able to compensate for the damage to their leaf surface. Heavy feeding damage on the flag leaves during the plant's grain-filling stage may lead to yield loss; however, infestation of younger plants normally causes only moderate injury.

Control

Integrated Crop Management

Avoid excessive use of nitrogen fertilizer, as this increases the susceptibility of plants to infestation.
Over-use of chemical control can disrupt natural control mechanisms and thereby lead to increased development of secondary pests, e.g. the brown planthopper (Nilaparvata lugens). Therefore pesticides should be chosen and applied judiciously.

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