Semilooper in soybean, castor and cabbage: identify and control

Photo at the top: Adult moth of the soybean green semilooper (Chrysodeixis acuta). Look for the silver-white mark on the front wing. Photo: LiCheng Shih, CC BY 2.0

Quick answer

A semilooper is a green or brown caterpillar that walks by arching its back into a loop. It eats holes in the leaves of soybean, castor and cabbage, and a heavy attack strips plants bare. Check the crop weekly. Use hand-picking, neem and natural enemies first. At the threshold, spray an insecticide labelled for your crop and this pest.

How to identify a semilooper

In Telugu the semilooper is often called dasari purugu (దాసరి పురుగు). In Hindi the English word is widely used: सेमीलूपर (semilooper). Three different insects carry this name in India. Each one is a different moth, but they all have the same looping walk:

• Green semilooper of soybean (Chrysodeixis acuta). Soybean product labels name this species.
• Cabbage semilooper (Thysanoplusia orichalcea). The cabbage label we use names this species.
• Castor semilooper (Achaea janata). This is a bigger caterpillar found mainly on castor.

Most caterpillars have five pairs of fleshy legs under the body. A semilooper has only three pairs, all at the back end. So it walks by pulling its back end up to its front legs, which makes a loop, and then stretching forward again. If you see a caterpillar walking like this, it is a semilooper, not a tobacco caterpillar (Spodoptera) or a Helicoverpa pod borer.

Soybean green semilooper and cabbage semilooper

• Larva (caterpillar): light green, with thin white lines along the body. It is narrow at the head end and wider at the back.
• Egg: very small, round and pale. Eggs are laid one by one, mostly on the underside of leaves.
• Pupa: forms inside a thin silk cover, often under a leaf or in a fold of the leaf.
• Adult moth: active at night. The soybean moth is brown with shiny silver-white marks on each front wing. The cabbage moth has a large, shiny golden patch on each front wing.

Castor semilooper

The young castor semilooper is yellowish green. The grown larva is dull greyish brown and 6 to 7 cm long, as the NIPHM (National Institute of Plant Health Management) castor guide notes. TNAU (Tamil Nadu Agricultural University) adds a red spot on the back and red bumps near the tail end. The moth is grey-brown. Its hind wings are black, with a white band in the middle and three large white spots on the outer edge.

Damage signs

• Young larvae scrape the green surface of the leaf, so you see thin, see-through patches.
• Older larvae chew holes of different sizes in the leaves. In a bad attack only the veins are left.
• In soybean the damage hurts most at flowering and pod filling. That is when the plant most needs its leaves.
• In castor the larvae can strip a whole field, leaving only bare stems, leaf stalks and veins.
• In cabbage the larvae make holes in the outer and wrapper leaves, and their droppings lower the quality of the head.

Look-alikes and how to tell them apart

• Tobacco caterpillar (Spodoptera): young larvae feed in groups and scrape the leaf. Older larvae are dark, with black triangle-shaped spots, and they walk normally. They hide in the soil during the day.
• Helicoverpa: walks normally and bores into pods, buds and fruits. It does not only eat leaves.
• Diamondback moth (in cabbage): a much smaller larva, about 1 cm. It wriggles backwards when touched and drops down on a silk thread. See our guide to diamondback moth in cabbage and cauliflower.
• Girdle beetle (in soybean): not a leaf eater. It cuts two rings around the stem or leaf stalk, and the part above them dries. See how to spot and control girdle beetle in soybean.

Life cycle and when it attacks

The moths fly at night and lay eggs on the leaves. For the castor semilooper, NIPHM gives the numbers: eggs hatch in 2 to 5 days, the larva feeds for 12 to 13 days through five growth stages, and the pupa lasts 10 to 27 days. One generation takes about 28 to 45 days. So more than one generation can build up in a single crop season.

Semiloopers are mostly a kharif (rainy season) problem. NIPHM records the castor semilooper from July to September. In soybean the green semilooper builds up during the vegetative and flowering stages. In Telangana and Andhra Pradesh, soybean and castor are both kharif crops, so start checking for larvae from July. In cabbage, look for them when you check for diamondback moth.

Crops it attacks

Soybean: NIPHM lists green semiloopers among the major soybean pests across India. Larvae feed on the leaves from the vegetative stage. The loss is highest when they strip leaves at flowering and pod filling.

Castor: the castor semilooper is a serious pest wherever castor is grown in India, says NIPHM. Larvae can eat the leaves so heavily that only leaf stalks and branches are left.

Cabbage: the cabbage semilooper eats holes in the leaves and can foul the head with its droppings. It often comes along with diamondback moth and tobacco caterpillar.

When to spray: semilooper threshold

The economic threshold is the pest level at which a spray starts to pay for itself. For the green semilooper in soybean, the NIPHM soybean IPM package gives it as 2 larvae per metre of row at the flowering stage. To count, walk across the field and check one metre of row at several places. Shake the plants over a cloth or paper laid between the rows, and count the green looping larvae that fall.

For castor and cabbage we could not confirm a threshold from a recognised public source, so we do not give one here. Check the crop each week. Start the non-chemical steps as soon as you see young larvae.

Semilooper control without chemicals

• Hand-picking: the larvae are large and easy to see. Pick and destroy older larvae when numbers are low, as NIPHM advises for castor.
• Light trap and bonfire: moths fly to light at night. NIPHM advises one light trap per acre in castor, run from 6 pm to 10 pm. It also advises a bonfire at 7 to 8 pm.
• Pheromone traps: in castor, NIPHM advises 4 to 5 traps per acre, if lures are available, to watch moth numbers. Change the lure every 2 to 3 weeks.
• Bird perches: set up T-shaped sticks in the field. Birds such as the black drongo (king crow) and mynah sit on them and eat the larvae.
• Intercropping in castor: NIPHM says growing castor with cluster bean, cowpea, black gram or groundnut (1 row of castor to 2 rows of the other crop) lowers the attack and builds up natural enemies.
• Soybean in semilooper-prone areas: NIPHM advises against intercropping soybean with maize or sorghum in areas where girdle beetle and semilooper are common.
• Tolerant soybean varieties: NIPHM lists varieties such as JS 97-52, NRC 37 and JS 93-05 as tolerant to the green semilooper. Ask your KVK (Krishi Vigyan Kendra) which tolerant varieties suit your area.
• Neem: spray neem seed kernel extract (NSKE) 5% on the eggs and young larvae.
• Bt sprays: NIPHM advises Bacillus thuringiensis var. kurstaki (Bt), a natural bacterium that kills caterpillars, for the soybean semilooper. It works on young larvae, and NIPHM advises it when air humidity is above 75%. Use a registered Bt product and follow its label.
• Protect natural enemies: small wasps such as Trichogramma attack the eggs. Spiders, ladybird beetles, lacewings and predatory bugs also eat the larvae. Avoid sprays you do not need, so these helpers survive. If larvae look dead and are covered in white fungus, wait a few days before spraying. The fungus may be doing the work for you.

Chemical control: semilooper insecticide by crop

Only the products below have that crop and this pest on their official label (one, Ajanta, from the company's product booklet). Doses are per acre, as printed or converted from the label's per-hectare dose. Use one product at a time. Do not mix products in one tank. Spray the whole plant well, including the lower leaves.

Soybean

Product	Contains	Label dose per acre	Water per acre	Wait before harvest
Coragen Insecticide	Chlorantraniliprole 18.5% SC	61 ml	200–300 L	29 days
Aston Insecticide	Chlorantraniliprole 18.5% SC	61 ml	200–300 L	22 days
Mokin Insecticide	Chlorantraniliprole 18.5% SC	61 ml	200–300 L	22 days
OMG Insecticide	Chlorantraniliprole 18.5% SC	61 ml	200–300 L	22 days
Shenzi SC Insecticide	Chlorantraniliprole 18.5% SC	61 ml	200–300 L	29 days
Exponus Insecticide	Broflanilide 300 g/L SC	17–25 ml	200 L	37 days
Simodis Insecticide	Isocycloseram 9.2% w/w DC	243 ml	200 L	35 days
Pirate Insecticide	Chlorfenapyr 240 g/L SC	132–172 ml	200 L	21 days
Ampligo Insecticide	Chlorantraniliprole 9.3% + Lambda-cyhalothrin 4.6% ZC	81 ml	200 L	41 days
Alika Insecticide	Thiamethoxam 12.6% + Lambda-cyhalothrin 9.5% ZC	51 ml	200 L	48 days
Sperto Insecticide	Acetamiprid 25% + Bifenthrin 25% WG	101 g	200 L	28 days
Ajanta Insecticide	Profenofos 50% EC	400 ml	Not given in our record	Not given in our record

Notes from the labels:

• Coragen and OMG: spray at ETL (economic threshold level), preferably in the vegetative stage or at the start of flowering. The Coragen label allows no more than two sprays.
• Aston, Mokin and Shenzi: spray at ETL with a knapsack sprayer.
• Exponus: spray when the pest appears, in the morning or evening. Do not spray within 2 hours of rain or when bees are foraging. No more than two sprays.
• Simodis: first spray at ETL. Repeat once after 10 to 15 days if needed. No more than two sprays in a season.
• Pirate: spray as soon as the pest reaches ETL. Up to two sprays.
• Ampligo: first spray when the pest starts, at ETL. Repeat once after 10 to 15 days, depending on the pest level.
• Alika: first spray at ETL, then one or two more sprays depending on pest level.
• Sperto: spray in the vegetative stage soon after the pest appears, in the morning or evening, with a hollow cone nozzle. Two or three sprays, depending on pest pressure.
• Ajanta: our record comes from the company's product booklet. It gives only the dose per acre, with no water volume, timing or waiting period. Check the pack label before use.
• Coragen, Aston, Mokin, OMG and Shenzi all contain the same active ingredient, chlorantraniliprole. Treat them as one choice, not five.
• Ampligo, Alika and Sperto each have two active ingredients. They are ready-mixed products approved on the label. They are not tank mixes.

Castor

None of the products in our store has the castor semilooper on its label, so we do not suggest one here. Use the non-chemical steps above, and ask your local agriculture officer or KVK for a product labelled for castor.

Cabbage

Product	Contains	Label dose per acre	Water per acre	Wait before harvest
Gracia Insecticide	Fluxametamide 10% EC	162 ml	200 L	5 days

Gracia: spray when the pest reaches ETL. Two or three sprays, 7 to 14 days apart, depending on the attack. The same label also lists diamondback moth and tobacco caterpillar on cabbage.

Rotate to avoid resistance

If you spray the same insecticide group again and again, the pest slowly stops dying from it. Insecticides are grouped by how they work, using the IRAC group number (IRAC is the international Insecticide Resistance Action Committee). Change the group from one spray to the next.

IRAC group	Active ingredient	Products in this article
28 (diamides)	Chlorantraniliprole	Coragen, Aston, Mokin, OMG, Shenzi; one part of Ampligo
30	Broflanilide, isocycloseram, fluxametamide	Exponus, Simodis, Gracia
13	Chlorfenapyr	Pirate
3A (pyrethroids)	Lambda-cyhalothrin, bifenthrin	One part of Ampligo, Alika and Sperto
4A (neonicotinoids)	Thiamethoxam, acetamiprid	One part of Alika and Sperto
1B (organophosphates)	Profenofos	Ajanta

For example, in soybean, if your first spray is Coragen (group 28), do not follow it with Aston, Mokin, OMG, Shenzi or Ampligo. Choose a product from another group, such as Exponus or Simodis (group 30), or Pirate (group 13). Keep to the number of sprays each label allows.

Safety and waiting period

• The waiting period before harvest (PHI, pre-harvest interval) for each product and crop is in the tables above. Count the days from the last spray. For Ajanta our record gives no waiting period, so check the pack label before use.
• Wear gloves, a mask, full-sleeve clothes and boots while mixing and spraying. Do not eat, drink or smoke while you work. Wash well afterwards.
• Spray in the morning or evening, not in strong wind or hot afternoon sun.
• Bees: pyrethroids (group 3A), neonicotinoids (group 4A) and organophosphates are toxic to bees. The Exponus label also says to avoid bee foraging time. Do not spray on open flowers when bees are working, and tell beekeepers nearby before you spray.
• Silkworms: the Coragen label warns that chlorantraniliprole is toxic to silkworms. Keep spray drift away from mulberry gardens.
• Fish: keep sprays and washings away from ponds, canals and wells.
• Read the label and leaflet before use.

Frequently asked questions

Why is it called a semilooper?

Because it walks in half loops. It has fewer legs in the middle of its body than most caterpillars, so it arches its back to move forward.

How many semilooper larvae in soybean before I spray?

The NIPHM soybean IPM package gives the threshold as 2 larvae per metre of row at the flowering stage. Below that, use Bt, neem and natural enemies, and keep checking every week.

Which insecticide is labelled for semilooper in soybean?

On our store these are Coragen, Aston, Mokin, OMG, Shenzi, Exponus, Simodis, Pirate, Ampligo, Alika, Sperto and Ajanta. The doses are in the soybean table above. Change the IRAC group from one spray to the next.

Is the castor semilooper the same insect as the soybean semilooper?

No. The castor semilooper (Achaea janata) is a different, bigger moth. Its control is also different, and none of our products lists it on castor. Ask your agriculture officer or KVK for a product labelled for castor.

Related reading

• Spodoptera litura (tobacco caterpillar): identification and control
• Helicoverpa armigera: fruit borer, pod borer and bollworm control
• Diamondback moth in cabbage and cauliflower
• Girdle beetle in soybean
• Stem fly in soybean
• All insecticides

Sources

• National Institute of Plant Health Management (NIPHM), Government of India: Integrated pest management package for soybean
• National Institute of Plant Health Management (NIPHM), Government of India: AESA based IPM package for castor
• Tamil Nadu Agricultural University, TNAU Agritech Portal: Insect pests of castor
• Insecticide Resistance Action Committee (IRAC): Mode of action classification
• Product labels and leaflets of the insecticides listed above.