Insect Pests of Vegetable, Ornamental and Spice Crops (2+1)

Stem weevil and Leaf caterpillar

1. Amaranthus stem weevil, Hypolixus truncatulus (Curculionidae: Coleoptera)

• Distribution: India and neighboring countries
• Host range: Amaranthus (both wild and cultivated)

Damage:

• Newly emerged grubs tunnels the stem
• The affected stems become weak and often split longitudinally due to excessive transpiration and evaporation
• The plants desiccate and ultimately dry up completely
• Adults feed on tender leaves and stems but the loss caused by them is negligible.

Identification

• Eggs are smooth, oval, about 1 mm, pale yellow
• Grubs are stout, curved, legless, white and about 13-17 mm long
• Pupae are yellowish brown in colour
• Adult weevils are ash-grey, 10-15 mm long

Life cycle

• Eggs hatch in about 2-4 days during summer and 10-12 days during winter
• Grub stage lasts for about 12 days during summer and 20-24 days during winter
• Pupate inside the stem
• Adults on emergence remain inside the stem for 5-6 days
• Adult longevity varies from 12-66 days.

Salient features

• Each female lays about 30 eggs singly inside the plant stem
• Grubs feed inside the stem by making tunnels
• 17-18 grubs/stem have been reported
• Full fed grubs cut a small round hole in the stem, leaving thin semi transparent apidermal tissue
• Pupate in the stem
• Adults after 5-6 days cut epidermal membrane and emerge out

Management

• Destroy all wild amaranthus plants in the vicinity
• As soon as infestation is observed, remove and destroy promptly all the affected plants with grubs inside.
• Spraying with malathion @ 0.05% or dichlorvos @ 0.05% is also effective.
• After spraying the crop with insecticides observe a waiting period of 7-10 days.

2. Amaranthus leaf caterpillar, Hymenia recurvalis

• Distribution: Tropical and sub-tropical regions of Africa, Asia, Australia and Hawali Islands.
• Host range: Grasslands and pastures, beans, Coleus, Luffa spp, melons, spinach, amaranthus, etc.

Damage:

• Young caterpillars feed on epidermis and palisade tissues of leaves.
• Older ones web the leaves together and feed with in.
• Webbed leaves become completely devoid of chlorophyll and dry up.

Identification

• Eggs are spherical in shape and snow white in colour.
• Caterpillars are greenish in colour with white lines.
• Full grown larva measures 17-20 mm in length.
• Pupae are 10-14 mm long and brownish in colour.
• Adults are black coloured.
• Both pairs of wings are dark fuscous in colour, outer margins are fringed with short hairs.
• Wing expanse is 15-20 mm.

Life cycle:

• Eggs hatch in about 3-4 days
• Larval period is 12-16 days
• Pupal period lasts for 8-12 days
• Total life cycle is completed in 3-4 weeks.

Salient features

• Each female lays 50-80 eggs singly or in batches of 2-5 usually on grooves of leaf veins
• Larvae feed on leaves
• Pupate in soil

Control:

• Spray with malathion @ 0.05%