Insect Pests of Vegetable, Tuber and Spice Crops

Exercise: Insect Pests of Onion & Garlic
1. Onion thrips, Thrips tabaci (Thripidae: Thysanoptera)

• Damage: Damage is the caused by the adults as well as nymphs by lacerating the epidermis of the leaf and lapping the exuding sap. The affected leaves show silvery white blotches which later become brownish and get distorted form tip down ward, wilt and ultimately dry up. Heavy infestation at seedling stage results in retardation of growth and severe scarring of leaves which out rightly kill the seedlings. In case of heavy infestation at later stage the bulbs remain undersized and get distorted in shape. Attacked plants do not form bulbs and the flowers do not set seed. In Hawaii T. tabaci is known to act as a vector of the streak virus disease of peas and yellow spot disease of pine apple.
• Eggs: Eggs are tiny, kidney shaped and white in colour.
• Nymphs: Nymphs and adults are slender, fragile and yellowish in colour.
• Adults: Adults have four narrow and long wings fringed heavily with fine hairs. Males are 0.8-1.0 mm long while the females are 1.0-1.2 mm long.

2. Onion maggot or onion fly, Delia antiqua (Anthomyiidae: Diptera)

• Damage: The maggots bore into the bulbs causing the plants to become flabby and yellowish. They mine thought the small bulbs completely, leaving only the outer sheath and thus causing a thin stand of the crop in the field. Larger bulbs are attacked by many maggots at a time by making cavities. The larger bulbs may not be destroyed by the attack but are subsequently rotten in the storage. It has been observed that onion maggots cause the initial damage which leads to the development of soft rot of onion caused by Bacillus carotovorus.
• Eggs: Eggs are elongate is shape and white in colour.
• Larvae: Maggots are also white in colour and 18 mm in length when full grown.
• Adults: Adult flies are slender about 6 mm in length and grayest in colour having large wings.

3. Leaf eating caterpillars: The common caterpillar pests reported

• Cutworms, Agrotis spp
• For details please see insect pests of cole crops
• Tobacco caterpillar, Spodoptera spp
• For details please see insect pests of cole crops
• Fruit borer, Helicoverpa armigera
• For details please see insect pests of tomato

4. Leaf miner

5. Storage pests:

• Anthrenus jordanicus (Dermastidae: Coleoptera)
• A. ocenicus (Dermastidae: Coleoptera)
• These are small hemi spherical beetles clothed with hairs. Grubs feed on dried and stored products including onion in storage.
• Alphitobius laevigatus, (Tenebrionidae: Coleoptera) is another minor pest of onion which feed on bulbs in storage.