A tomato that looks beautiful and red from the outside, with a round hole the size of a lentil on its side near the calyx. You open it and find a cavity full of droppings and a fat larva eating quietly. This is the signature of the American bollworm (Helicoverpa armigera), a nocturnal moth with many names depending on the crop: the cotton bollworm in cotton, the tomato fruitworm in vegetables, the corn earworm in corn, and the chickpea pod borer in chickpeas.
Its problem is not its numbers but its location: a single larva inside the fruit is completely protected from any spray, and may move between several fruits and spoil them all. So the grower who waits until he sees perforated fruit has already lost the first round, and the real question is: how do you hit the larva in the few days between leaving the egg and entering the fruit?
Pest: The American bollworm punctures tomato, cotton and corn fruit and feeds inside them, spoiling the fruit from within.
Sign: A small round hole in the fruit with droppings inside it and rapid decay after fungi enter.
Difficulty: It spends most of its life inside the fruit, so late spraying does not reach it and you must act before it enters.
Common mistake: Spraying after the holes appear. The right timing is when eggs or small larvae show up, and that is the key.
Rule: Pheromone traps for monitoring, regular fruit inspection and destroying infested fruit, together with rotation of pesticides, reduce losses.
American Bollworm Overview
It occurs in Africa, southern Europe, Asia and Australia, and reached South America around 2013, causing major losses there. What makes it one of the most dangerous pests in the world:
- Migration: The moths can migrate long distances.
- Resistance: A long record of resistance to pyrethroids, carbamates and organophosphates in many regions, and to some Bt toxins in some regions.
- Pupal dormancy: The pupa can go dormant in the soil, so that infestation starts from your own field in the next season.
It has been recorded on nearly two hundred plant species, cultivated and wild, and it always heads for the valuable parts: flowers, buds, fruit, ears and pods. Its most important hosts:
- Vegetables: Tomatoes, peppers, eggplants, okra, beans, peas and lettuce.
- Field crops: Cotton, field corn and sorghum, chickpeas, soybeans, sunflower and tobacco.
- Others: Some fruit such as strawberries, ornamental plants and weeds.
Damage Symptoms: What to Look For
The damage starts light on the leaves and buds and then moves quickly to the fruit, and its form differs from crop to crop. Knowing the early signs gives you time before the larva disappears inside the fruit.
By Larval Age
- Newly hatched larva: Feeds for a day or two on tender leaves, buds or flowers, leaving small holes and light scraping, then heads to the fruit. This is the golden window for control.
- Medium and large larvae: They bore into fruit, ears, bolls and pods, and move between more than one fruit. Large larvae are cannibalistic, so you rarely find more than one large larva in a single corn ear, but a single larva is enough to spoil it.
By Crop
- Tomatoes: Round holes with clean edges in green and colored fruit, usually near the calyx, which become an entry point for rots and flies, so the fruit rots or drops. If the leaves have tunnels and the fruit has multiple small holes, the problem may be the Tuta absoluta pest.
- Cotton: Feeding on squares, flowers and small bolls, which then drop, and holes in large bolls. Fallen squares under the plant are a sign worth checking.
- Corn: It enters from the tip of the ear through the silk and eats the top kernels, leaving wet droppings and an entry point for fungi.
- Chickpeas and legumes: Perforated pods and eaten seeds. The plant may look healthy from a distance while the pods are empty.
- Peppers, okra and eggplants: Holes in the fruit and internal rot, with droppings near the entry hole.
During scouting, always look for these signs:
- Single eggs: On the tips and flowers.
- Round holes: In the fruit.
- Droppings: At the fruit openings.
- Dropping: Fallen squares and small fruit.
Life Cycle and Appearance
In hot weather the cycle is completed in about 4 to 6 weeks, with several generations a year (possibly more than five generations in warm regions), and the pupae go dormant in the soil when conditions worsen.
Egg
- Shape: Very small, about 0.5 mm in diameter, round with a raised top and fine lengthwise ribs.
- Distinguishing mark: Laid singly, one egg here and another there, on young upper leaves, buds, flowers and corn silk, unlike Spodoptera, which lays its eggs in masses.
- Color: Shiny white when laid, then it turns yellow and becomes brown with a dark ring just before hatching.
- Number: The female may lay hundreds of eggs, and may exceed a thousand during her life.
- Hatching: The eggs hatch within about 2 to 4 days in warm weather.
The change in egg color helps you in practice: many white eggs mean hatching is coming within days, so get the spray ready; dark brown eggs mean hatching is imminent and spraying now is at the most suitable moment; and empty shells mean the larvae have emerged and are looking for a fruit.
Larva
- Duration: It usually passes through six larval instars in about two to three weeks.
- Newly hatched: About 1.5 mm long, cream colored with a dark brown head and distinct hairs.
- Full grown: Reaches about 3.5 to 4 cm in length.
- Distinguishing marks: Its color is highly variable (green, brown, pink, yellowish, almost black), so do not rely on it. Rely on the light lateral stripes along the body, the distinct hairs coming from small dark bumps, and its fruit-boring behavior.
Pupa
- Pupation site: The full-grown larva drops to the soil and pupates at a depth of about 2 to 10 cm inside an earthen cell.
- Appearance: The pupa is shiny reddish-brown, about 1.5 to 2 cm long.
- Duration: It lasts about 10 to 14 days in summer, and may go into dormancy lasting weeks or months in cold or extreme heat.
Adult Moth
- Size: Body length about 1.5 to 2 cm, and wingspan about 3 to 4 cm.
- Forewing: Yellowish brown or reddish brown (the female tends toward orange-brown and the male toward greenish gray), with a dark kidney-shaped spot.
- Distinguishing mark: The hind wing is light yellowish with a wide dark band near the outer edge that contains a light spot.
- /strong> Active at dusk and at night, feeds on flower nectar, and lives about one to two weeks or more.
Monitoring and Biological Control First
Pheromone traps for Helicoverpa armigera are widely used for monitoring and mass trapping. Their major importance is that they tell you when to start intensive scouting for eggs:
- Early hanging: Hang the traps before flowering.
- Intensive inspection: When moth numbers in them rise, inspect the tips and flowers with a hand lens twice a week, and count eggs and young larvae.
- Timing of intervention: Set it at the start of hatching.
Biological control plays a big role here, because single eggs and young larvae are exposed before they enter the fruit:
- Egg parasitoids Trichogramma: Single eggs exposed on the plant tips are an excellent target for them, and they are released commercially in tomato and cotton programs.
- Bacillus thuringiensis bacteria and the bollworm nuclear polyhedrosis virus (HaNPV): They work well on young larvae before they enter the fruit, and they preserve natural enemies.
- Predators: Lacewings, predatory bugs, ladybugs and spiders, which feed on the eggs and young larvae.
Chemical Control: Spray Before It Enters
The core idea: the pesticide works before the larva enters the fruit, not after. Therefore:
- Timing: Spray when hatching begins (brown eggs and newly hatched larvae), preferably in the evening or early morning.
- Coverage: Cover the flowers, small fruit and tips well, because these are the places the larva will head for.
- Do not waste pesticide: Spraying perforated fruit with large larvae inside is mostly a waste of pesticide. Collect the infested fruit and destroy it, and focus on protecting the new fruit set.
As for rotation, the bollworm's history with pyrethroids is a well-known lesson: in many regions they were used so heavily that the insect became almost unaffected by them.
Use one effective group for roughly one generation, then move to another. Effective groups include: 28 (diamides), 5 (spinosyns), 18 (methoxyfenozide), 6 (emamectin), 22A (indoxacarb), and 11A (Bt bacteria). And do not exceed the number of applications allowed per group per season.
Suitable Products From Our Store
At Orkida Agri we choose products for the bollworm that hit the larva in its early instars, and from different groups so you can rotate between them safely:
- Coragen 20 SC: Chlorantraniliprole (Group 28). It paralyzes the larva's muscles so it stops feeding within hours, and it is one of our strongest options against the American bollworm. Its effectiveness is highest on the early instars before they enter the fruit, so we spray it at hatching, not after the holes appear.
- Runner 24 SC: Methoxyfenozide (Group 18), a growth regulator that pushes the larva into a premature, fatal molt, and we use it against the bollworm in beans, cucumbers and zucchini. It stops feeding quickly and suits the second rotation window.
- Radient 120 SC: Spinetoram (Group 5) for worms, a strong option for rotation with Groups 28 and 18.
- Exirel 10 SE: Cyantraniliprole (Group 28) works on worms with the same mode of action as Coragen, and we use it on tomatoes, peppers, eggplants and cucurbits. Use it as an alternative to Coragen in the same window, not right after it.
Our advice: follow the dose and pre-harvest interval written on the label, especially in vegetables that are harvested frequently.
Prevention and Farming Practices
A large part of next season's infestation starts from pupae that remained in your field's soil or in the weeds around it, so prevention focuses on cutting this chain:
- Turning the soil after harvest: Shallow plowing exposes the pupae and destroys their emergence tunnels, which reduces the numbers that start the next season.
- Disposing of crop residues: And of fallen infested fruit.
- Trap crops: In some programs, rows of African marigold are planted around tomatoes to attract egg laying, then treated or removed.
- Removing host weeds: Around the field.
- Avoiding overlapping plantings: Consecutive plantings of host crops side by side.
- Hand picking: In small areas, of perforated fruit and of tips carrying eggs.
- Screening on greenhouse openings: To prevent moths from entering.
Frequently Asked Questions
Is the American bollworm the same as the tomato fruitworm?
Yes, the two names usually refer to the same insect, Helicoverpa armigera, and the common name changes with the crop.
Why doesn't spraying kill the worm inside the fruit?
Because the larva is protected inside the fruit and the pesticide does not reach it by contact, and it does not feed on the sprayed parts. So spraying must be done at hatching and before entry.
How do I tell bollworm damage from Tuta absoluta damage in tomatoes?
The bollworm makes a relatively large, clean hole with a fat larva inside the fruit. Tuta absoluta makes tunnels inside the leaves and multiple small holes in the fruit, and its larva is small and slender.
Are pyrethroid pesticides effective against the bollworm?
In many regions the insect has recorded high resistance to them, so do not rely on them alone, and use newer groups in rotation.
When does the bollworm appear during the season?
It increases at the start of flowering and fruit set, and in warm weather its generations may overlap throughout the season. Pheromone traps are the best indicator of the start of activity in your field.
Is removing infested fruit useful?
Yes, collecting perforated fruit and destroying it reduces the larvae that would complete their cycle and pupate in the soil, and it limits the spread of rots.