Learn about the pests that damage sesame and its control.
1. Til Leaf and Pod Caterpillar, Antigastra Catalaunalis (Duponchel) (Lepidoptera: Pyralidae):
The sesame leaf and pod caterpillar is a serious and regular pest of til (Sesamum orientale and S. indicum) and is also distributed throughout India. This species has also been reported from Europe, Africa, Cyprus, Malta, Indonesia and South-east Africa.
The caterpillars damage apical shoots and young pods. They are pale yellow, when young, but gradually become green and develop black dots all over the body. The full-grown larva measures 14-17 mm. The moth is a small insect with a wing span of about 2 cm having dark brown markings on the wing-tips.
Life-Cycle:
In northern India, the moths appear in August. Females lay up to 140 eggs singly on the tender portions of plants at night. The eggs are shiny, pale-green and they hatch in 2-7 days, depending upon the season. On emerging, the young larva, which measures about 2 mm in length, feeds for a little while on the leaf epidermis or within the leaf tissue.
Soon after, it binds together the tender leaves of the growing shoot with the help of silken threads and continues to feed in the webbed mass. The size of this rolled mass increases gradually as the caterpillar grows older. It becomes full-grown in about 10 days in summer, but the period may be prolonged to 33 days in winter.
The grown-up larvae creep to the ground and pupate in silken cocoons in soil. Sometimes, pupation also takes place in the plant itself. Pupal development is completed in 4-20 days, depending upon the season. In summer, a generation is completed in about 23 days but in the winter it takes about 67 days.
The moths start laying eggs 4-5 days after emergence. They are active in the cool hours of the day and live for about 3 weeks. All stages of the insect are seen in autumn and sometimes up to December. During January and February, the insect hibernates as a larva inside pods, stubble or the harvested stalks. There are nearly 14 generations in a year.
The braconids, Bracon hebetor Say, B. kitcheneri D and G (Braconidae) and Ichneumonids, Cremastus flavoortictalis Cam. and Temelucha biguttula Matsumura (Ichneumonidae) are known to parasitize its larvae.
Damage:
Young caterpillars feed on leaves. They also bore into the shoots, flowers, buds and pods. An early attack kills the whole plant, but infestation of the shoots at a later stage hampers further growth and flowering. One larva can destroy 2-3 young plants. The maximum infestation occurs in May and again in September-October. The pest is also capable of sustaining itself on some wild species of Sesamum.
Control:
(i) Collect and destroy the webbed leaves and infested pods, and
(ii) Spray the crop twice (first at pest appearance and then at flowering stage) with 250 ml of fenvalerate 20EC or 375 ml of deltamethrin 2.8EC or thrice with 500 ml of cypermethrin 10EC at pest appearance, flowering and pod formation in 250 litres of water per ha.
2. Til Hawk Moth, Acherontia Styx (Westwood) (Lepidoptera: Sphingidae):
This pest of sesamum is common in India and is also distributed in Indonesia, Sri Lanka, the Philippines and Myanmar. Besides sesamum, it has been reported on potato, brinjal, lablab and ornamental plants such as balsam. The moth is also harmful because it sucks honey from honey combs in apiaries, although at times it is stung to death by the bees.
This insect is variously known as hawk moth, sphinx-moth or death’s head moth based on its structural and behavioural characteristics. The adult is a large reddish brown, robust thick-set moth with a wing span of about 10 cm. The forewings are decorated with a mixture of dark-brown and grey patterns with dark or black wavy markings and a prominent yellow spot on each wing. There is a prominent Death’s head mark on the thorax. The moths are swift fliers and often make hawk like darts to a source of light at dusk.
The full-grown caterpillar, which measures about 5 cm in length and 1 cm width, often retracts some of its anterior body segments and looks like a sphinx. The horn-like projections on the hind end of the abdomen are conspicuous. The body of the larva is plump and is decorated with a pleasant mixture of soft colours.
Life-Cycle:
The moths lay globular eggs singly on the underside of leaves of food plants. The eggs are conspicuous since they are fairly large. They are greenish white when freshly laid but turn yellow later on. The pale-yellow larvae emerge in 2-5 days and start feeding on leaves. The larval period is usually long and may last two months or more.
The pupal stage lasts 2-3 weeks in summer and about 7 months in winter. The changes in coloration of the larvae and adults aid them in protective mimicry. The impression of ferociousness created by the larva as well as by the moth is probably a protection against predators. There are 3 generations in a year. The winter is passed in the pupal stage in soil.
The eggs are parasitized by Agiommatus acherontiae Ferr (Pteromalidae) while Apanteles acherontiae Cam. (Braconidae) has been reported from the larvae.
Damage:
The larvae feed voraciously on leaves and defoliate the plants. The insect is capable of inflicting heavy damage at times, but generally it is not a very serious pest in India. However, it draws our attention because of its peculiar characteristics.
Control:
(i) Hand-pick the larvae in the initial stages of attack and destroy by keeping in kerosene oil.
(ii) Plough the field during winter to expose the hibernating larvae.
3. Sesame Gall Fly, Asphondylia Sesame Felt (Diptera: Cecidomyiidae):
The sesame gall-fly, also known as the sesamum gall-midge, occurs all over India and sometimes assumes serious proportions, particularly in southern India. It has been recorded in Tamil Nadu, Andhra Pradesh, Kerala, Madhya Pradesh, Gujarat and Maharashtra. It has also been reported as a serious pest in Rajasthan.
Life-Cycle:
The adult is mosquito-like and small. The female lays eggs singly in buds, flowers and developing capsules. The eggs hatch in 2-4 days. The young maggots feed on floral parts and cause malfomation of the buds which fail to develop into seeds. The larvae complete their development in 14-21 days and pupate inside the galls. The moths emerge from the galls in 7-12 days. The life-cycle is completed in 23-37 days. There are several generations in a year.
Eurytoma dentipectus Gohan and E. nesiotes (Eurytomidae) parasitize its maggots.
Damage:
As a result of feeding by maggots, the buds develop into galls and produce no fruits and seeds. When infestation is severe, the crop may be a total failure. However, some varieties are comparatively resistant to its attack.
Control:
(i) Clip the galls and pick and burn the shed buds, and
(ii) Spray 2.5 kg of carbaryl 50WP in 625 litres of water per ha.