Leaf & Flower Thrips

• S. rubrocinctus: Adults are dark brown and about 1-2 mm long. Nymphs are pale yellowish and have a red band around the middle of their body. Eggs are laid singly into the lower epidermis and covered with excrement.
• R. cruentatus: Nymphs are white when they hatch, but pale red markings develop soon. The female thrips are 1.2 to 1.5 mm long, blackish-brown in colour, with the legs and antennal segments yellow and the fore wings pale with yellowish veins. Male thrips are similar to females in structure but their pronotum and abdomen is yellow in colour.
• S. dorsalis are pale or cream coloured. Adults are about 1.2 mm long with dark wings and dark spots forming incomplete stripes which appear dorsally on the abdomen.S. rubrocinctus S. dorsalis

Eggs are tiny, laid inside leaf tissues. Egg period lasts between 3-7 days depending on the temperature. Nymphs are wingless, vermiform, while adults are winged.

• In S. rubrocinctus, nymphs hatch in 12 days, move freely carrying a drop of excrement at the anal end. The nymphal, pre-pupal and pupal period lasts for 10, 1 and 2-3 days respectively.
• In R.  syriacus, adult is 1.3-1.5 mm long, dark red, the feather-like wings are pale brown. The nymphs are initially hyaline, later turning yellow-orange, and then red; length up to 1.5 mm.

Leaf thrips: August – November, flower thrips:  January – April

Many agricultural and horticultural crops.

1. S. rubrocinctus – arecanut (Areca catechu), avocado (Persea  americana), guava (Psidium guajava), pear (Pyrus sp.), mango (Mangiferra indica), cocoa (Theobroma cacao), rose (Rosa sp.) , Terminalia catapa.
2. R. cruentatus – Arecanut, cocoa (T. cacao), almond (P. dulcis), custard apple (Annona  squamosa), grapevine (Vitis vinifera), jamun (S. cumini), pomegranate (P. granatum), mango (M. indica), rose (Rosa sp.), castor (Ricinus communis), cardamom (Elettaria cardamomum), Jatropha (Jatropha curcas).
3. S. dorsalis ­– Ber (Ziziphus mauritiana), sapota (M. zapota), miracle fruit (Synsepalum dulcificum), Canistel (Pouteria campechiana), tea (Camellia sinensis), straw berry (Fragaria ananassa), citrus (Citrus sp.), chillies (Capsicum annum), grapevine (V. vinifera), cassava (Manihot esculenta), mango (M. indica), pomegranate (P. granatum), tamarind (T. indica), taro (Colocasia esculenta) and the common weed shrub in cashew plantations of west coast viz., Calycopteris floribunda.
4. R. syriacus – Custard apple (A. squamosa), grapevine (V. vinifera), pomegranate (P. granatum).

Leaf thrips

Leaf thrips mainly damage the tender cashew leaves. If they attack at nursery stage, even death of seedlings may occur.

• S. rubrocinctus is very serious in nursery and young cashew plantations. In seedlings, initially it attacks lower leaves and cause crinkling of leaves,pale brown spots, premature leaf fall, stunting and drying of seedling. In grown up plants, it damages young leaves, shoots and inflorescence and is more active during summer months. Honeydew excretory products from red-banded thrips give rise to black sooty mould.
• R. syriacus colonize the lower surface of young leaves and suck the sap, as a result leaves become silvery white initially, later turn into pale brown and crinkle with roughening of upper surface. In severe cases, shedding of leaves occur.

Selenothrips rubrocinctus nymphs (with red band) and adults (black and winged), its damage on cashew seedling showing distortion and discolouration

Flower thrips

They attack buds, flowers, immature apples and nuts. Thrips infestation causes shedding of flowers, immature fruit drop, formation of scabby as well as, malformed apples and nuts.

Up to 15-25 per cent fruit drop is noticed due to thrips damage.

                                  
Scirtothrips dorsalis and their damage on developing nuts

There are several predatory insects like various syrphids , coccinellids, lace wing bugs etc in cashew plants feeding on this pest.

Spraying of  lambda-cyhalothrin (0.6 ml/lit) or dimethoate (2 ml/lit) is effective for managing thrips.