Earias insulana

Scientific Name Earias insulana (Boisduval, 1833)
Common Names English: Spiny bollworm, cotton spotted bollworm; German: Ägyptischer Baumwollkapselwurm; Spanish: Barrenador del tallo; French: Chenille epineuse du cotonnier
Description The fully-grown larva is 13-18 mm (0.51-0.7 inch) long. The adult moth has an overall wingspan of about 20-22 mm (0.78-0.86 inch). It is covered with a soft, dense coating of scales and has a variable, mostly green or yellow-brown color.

Biology

Damage

Initially, the caterpillars will tunnel into buds: by destroying vessels and growing points, they cause adjacent blooms, young leaves and eventually whole shoots to turn blackish-brown and die off. This can result in bunched growth of young plants. Examination of the affected plant parts reveals a number of small holes either on, or near to, leaf or flower buds. On cotton, the damaged flower buds sometimes spread their bracteoles prematurely („flared squares“).

When fruiting starts, the larvae will turn towards the bolls, which then become brown and fall off as a result. Older bolls may stay on the plant, but are often so damaged that they cannot be harvested. Secondary invasion by fungi and bacteria sometimes occurs. The entrance holes in bolls are neatly rounded, about 1 mm (0.039 inch) in diameter, and mostly filled with frass. On okra, the symptoms are very similar: severely-affected flower buds will be shed, and the pods are tunneled into in the same way as the cotton bolls, and are sometimes also hollowed out.

Lifecycle

The 3-7 day-old female lays up to 200 eggs, preferably on young bolls, shoot tips and buds. Some days later, the larvae emerge, and after wandering about on the plant, they bore into the soft terminal shoots. Older larvae feed on flower buds („squares“) and green, unripe bolls. Towards the end of their development, they often move from boll to boll, thus increasing the amount of damage. The five instars of the larval stage normally last 8-25 days. For pupation, the larvae spin felt-like cocoons, which they attach to dry leaves on the food plant or to plant debris on the ground. The pupal stage normally lasts about 9-15 days, but it may extend to up to two months if development is delayed by low temperatures. There is no true diapause. In some areas, the insects move between crops with different growing seasons (e.g. okra and cotton), so there is no interruption to their food supply, and populations can build up over a long period.

Occurrence

Additional Crop Information

Mainly okra, cotton and hibiscus, but also rice, sugarcane and occasionally corn.

Agricultural Importance

Earias insulana is found in most of Africa, southern Europe, the Near and Middle East, in Japan, Taiwan, the Philippines and in Australia.
The adults show seasonal polymorphism, depending on the temperature. In some parts of the distribution area, two distinct forms can be discerned - the bright green summer moth, and the brownish-yellow autumn moth. Earias insulana can make cultivation of some crops nearly impossible in some years, for example in India, where it is one of the most important pests of cotton.

Control

Integrated Crop Management

After harvest, cotton plants (which can sprout from the stump) should be uprooted and destroyed in order to eliminate the food source for Earias spp. - and thereby to interrupt population build-up.

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