Thrips are polyphagous and cause significant economic losses in tomato crops. They destroy seedlings by piercing and sucking the leaves and plant parts. Thrips also spread the tomato spotted wilt virus(TSWV). Thrips infestation is high in hot and dry climatic areas. A loss of up to 90-100 % is caused by thrips.
Identification of thrips
Eggs- The eggs laid by adults are minute in size. Thrip eggs vary in their shape from elongate to kidney-shaped. They are laid underside of leaves in random fashion near the veins. The saw like ovipositor of the female makes an incision in the parenchyma tissue of leaves and inserts the eggs into it. The eggs hatch after 3 to 4 days.
Nymph- the nymph of the adults feed for 2 to 3 weeks. The nymphs are transparent when they are early instars but slowly they turn yellowish and possess dark colored legs, head and antennae.
Pupa- Thrips do not possess a true pupal stage. Pupae of thrips are found in leaf litter or crevices within plants.
Adult- the adults measure nearly 1.5-2mm in size and slender in shape. They are yellow to light brown in color. The life cycle varies from 15 to 45 days. The adults possess dark colored, fringed wings for flight. Thrips sometimes have red eyes. Males are smaller and slender than females. Thrips reproduce parthenogenetically. The adult females lay kidney-shaped eggs.
Host plants- Thrips feed on a variety of crops including many vegetables, flowering plants and weed plants.
Damage caused by thrips.
Eggs- the females lay eggs by making an incision on the leaves. This damages the leaves when the eggs emerge out of them and also when they are inserted.
Nymph- the nymphs feed on soft parts of the plant and new leaves by sucking the plant sap.
Adult- thrips feed through their piercing and sucking mouthparts on various parts of the plant such as on the fruits, flowers, leaves and shoots. Due to the sucking of sap from the plants, the leaves are damaged, develop spots and wilt. White spots can be seen on the leaves as a result of damage. Damage to the leaves also occurs due to oviposition by the females. Eventually, the leaves dry and drop prematurely. Due to this, the plant also shows stunted growth. In case of heavy infestation, flowers are not produced. The damage of thrips can be identified by the presence of small black colored faecal deposits.
Adults also act as vectors for tomato spotted wilt virus(TSWV). This virus is transmitted to the plants while feeding on them. Thus, thrips cause dual damage to plants directly and indirectly.
Management and control of thrips
- Various insecticides can be applied to control thrip infestation in tomato crops. Example- Azadirachtin, abamectin etc.
- Chemical insecticides such as methyl demeton or dimethoate 30 EC can be sprayed @ 1 litre per hectare. Monocrotophos @ 40ml can also be sprayed.
- Use of natural enemies like Lacewings, Chrysoperla, predatory mites and parasitic wasps.
- Ensure proper weed control to eliminate thrips.
- Install yellow or blue sticky traps to attract the adults @ 15-16 per hectare and kill them.
- Kaolin clay acts as a repellent for thrips and can be applied on leaves.
- Avoid excessive application of nitrogen fertilizers. Excess fertilizers increase chances of thrip infestation.
- Pruning and destroying infested plant parts is essential to avoid increasing the damage. Pruning is mostly carried out in winter.