1. Onion thrips or cotton thrips, Thrips tabaci (Thripidae: Thysanoptera)
- Distribution: This pest is widely distributed throughout India.
- Host range: Onion, garlic, cotton, cabbage, cauliflower, potato, tobacco, tomato, cucumber, peas, pine apple etc.
Damage:
- Adults and nymphs lacerate the epidermis of the leaf and lap the exuding sap
- The affected leaves show silvery white blotches which later become brownish
- Retardation of growth
- Bulbs remain undersized and get distorted
- Also transmit viruses.
Identification
- Eggs are tiny, kidney shaped and white in colour
- Nymphs and adults are slender, fragile and yellowish in colour
- Adults have fringed wings heavily with fine hairs.
- Males are 0.8-1.0 mm long while the females are 1.0-1.2 mm long
Life cycle
- Adult longevity is 2-4 weeks
- Eggs hatch in 4-9 days
- Nymphs become full grown in 4-6 days
- Pass thought four stages
- Pupate in soil
- Prepupal and pupal periods are 1-2 & 2-4 days
- Several overlapping generation in a year.
Salient features
- The pest is active throughout the year
- Breeds on different hosts during different seasons
- Eggs are laid singly in slits made in leaf tissue
- On onion and garlic they are usually congregated at the base of the leaf or in the flower
- Full grown nymphs fall on to the ground and pupate at a depth of about 2.5 cm
Other thrips species
- Ground nut thrips, Caliothrips indicus (Thripidae : Thysanoptera)
- Blossom thrips, Aeolothrips collaris (Thripidae : Thysanoptera)
Management:
- Grow resistant verities of onion like White Persia, Grano, Sweet Spanish, Crystal Wax etc:
- The pest can also be controlled by spraying the crop with any of the insecticides like malathion @0.05% and dimethoate @ 0.03%
- After the application of insecticides observe a waiting period of 7 days
2. Onion maggot or onion fly, Delia antiqua (Anthomyiidae: Diptera)
- Distribution: France, Germany, Canada, USA, Japan, erstwhile USSR, England, India etc.
- Host plants: Onion & garlic
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
- Larger bulbs are attacked by many maggots at a time
- Partially attacked bulbs get rottened
- Attach in storage also
Identification
- Eggs are elongate in shape and white in colour
- Maggots are also white in colour and 18 mm in length when full grown
- Adult flies are slender about 6 mm in length and greyist in colour having large wings.
Life cycle
- Eggs hatch in 2-7 days
- Maggots become full fed in 2-3 weeks
- Pupal period is 2-3 weeks
- Three generation
Salient features
- Eggs are laid near the base of the plant in cracks in the soil
- Newly emerged maggots crawl up to the plant and enter the leaf sheath and reach the bulb.
- Large bulb can be attacked by many maggots, each carving out a small cavity
- In third generation, pest attacks the crop near harvest which is responsible for rotting of bulbs in storage.
Management:
- Treat soil with phorate 10 G followed by irrigation
- Spray the crop with malathion @ 0.05% at 15 day interval is also effective.
3. Leaf eating caterpillars:
- Cutworms, Agrotis spp
- See insect pests of cole crops
- Tobacco caterpillar, Spodoptera litura
- See insect pests of cole crops
- Fruit borer, Helicoverpa armigera
- See insect pests of tomato
4. Ground nut earwig, Euborellia annulipes (Labiduridae: Dermaptera)
- Cause damage by boring into onion bulbs. Incubation period is 7-11 days, larval period in 106-252 days.
- Control: drenching with chlorpyriphos @ 0.04 %.
5. Pea leaf miner
6. Other storage pests:
- Anthrenus jordanicus (Dermastidae: Coleoptera)
- A ocenicus (Dermastidae: Coleoptera)
- Alphitobius laevigatus, (Tenebrionidae: Coleoptera)
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