Cabbage looper

The cabbage looper (Trichoplusia ni) is a medium-sized moth in the family Noctuidae, often called owlet moths. It gets its name from the plants it likes to eat, such as cabbage, bok choy, and broccoli, and from the way its baby stage, or larva, moves. When the larva crawls, it makes a looping motion by arching its back, which looks like it's making a loop.

Even though it prefers plants like cabbage, the cabbage looper can eat more than 160 different plants. The adult moth travels long distances and can be found all over North America and Eurasia, from places as far south as Florida to as far north as British Columbia. Because it moves around a lot and can live on many plants, it is seen in many areas.

The cabbage looper larva can be a small problem for gardens, especially for plants like cabbage, broccoli, and other cruciferous vegetables. While it does not usually cause big damage, it is becoming harder to control because it can resist many common insect-killing sprays. Scientists are studying many ways to manage and reduce the number of cabbage loopers.

Taxonomy

The cabbage looper larva is a type of cabbage worm, which is a general name for pests that mainly eat vegetables like cabbage and broccoli. These larvae look very similar—they are smooth and green—but they come from different families and are not closely related. The cabbage looper belongs to the family Noctuidae, one of the largest families in Lepidoptera. It is related to other pests that eat vegetables, such as the cutworm and armyworms.

Reproduction and life cycle

Cabbage loopers have interesting ways of mating and growing. When they are ready to mate, they show off by lifting their bodies and spreading their wings. Males also spread special hairs and open parts of their bodies to attract females. Mating usually happens at night, a few days after the moths emerge from their cocoons.

After mating, females look for plants to lay their eggs on. They prefer leaves that are bigger and higher up. The eggs are small, yellow-white, and hatch in about three days. The babies, called larvae, are green with a white stripe and move in a looping way, which is how they got their name. They eat a lot of leaves, sometimes three times their own weight each day.

Finally, the larvae turn into pupae and make a silky cocoon under leaves. This stage lasts from four to thirteen days. When they emerge as adult moths, they have gray-brown front wings and light brown back wings, and they are active at night. The whole process from egg to adult takes about twenty-four to thirty-three days.

Distribution and migration

The cabbage looper can be found across North America and Eurasia, as far south as Florida and as far north as British Columbia.

In North America, cabbage loopers move from Mexico to Canada with the seasons. They usually stay over winter in Mexico or southern California, where it stays warm enough. As northern areas get warmer, the cabbage looper moves northward, traveling only if the area is above 16 °C (61 °F). During summer, they are less common in very hot southern areas. Like the monarch butterfly, they likely travel in groups.

In Europe, the cabbage looper can be found from England to southeastern Europe.

Temperature

The cabbage looper's movement depends a lot on temperature, which affects its growth. If the temperature is around 10 °C (50 °F), the pupae might stop developing and can even come out looking strange if moved to warmer places. Very hot temperatures above 35 °C (95 °F) can also cause problems for adult moths, like bad wing development. Mating and flying are harder when it's too hot or too cold, which is why these moths move north when it gets warmer. Even though the embryos can grow in both very cold and very hot temperatures, they might not be able to hatch.

Host plants

The cabbage looper is an insect that can live and eat from over 160 different plants. It likes plants such as cabbage and broccoli because it grows faster on them. It can also live on tobacco plants, but these are not as good for it because some plants make sticky substances or have tiny hairs that can harm the young caterpillars. Older caterpillars are better at handling these plant defenses.

The number of caterpillars on a plant can change depending on how old the plant is. Plants that are just starting to grow big are more attractive to the caterpillars. The cabbage looper can find plants by smelling their odors. Female moths that have laid eggs are especially good at finding these smells because they need plants for both food and laying eggs. The cabbage looper is drawn to several plant smells, with a mix of different odors being even more attractive than just one smell.

Pheromones

Cabbage loopers, like many moths, use special smells called pheromones to find mates. Both females and males release these smells to attract each other. Females usually release pheromones from the tips of their abdomens, and males look for these smells to find a mate.

Males also produce pheromones from special parts on their bodies called hair pencils. These smells can help them compete with other males and attract females. When males are near plants that cabbage loopers like, their smells become even more attractive to females. This helps females find males that are close to food, making mating easier. The smells that males produce can also help both males and females find food when they are hungry.

Enemies

Spiders, ants, and lady beetles often eat cabbage looper eggs and young caterpillars. Lady beetles are especially good at finding and eating them.

The cabbage looper can also be affected by tiny flies called tachinid flies. These flies lay their eggs on the caterpillars, and the baby flies eat the caterpillar from the inside.

The moth can also get sick from a natural virus called nucleopolyhedrovirus. This virus is used by people to help control the moth population. Another natural enemy is a soil bacterium called Bacillus thuringiensis, which can slow down the growth of the caterpillars.

Genome

The cabbage looper's DNA, called its genome, is 368.2 million base pairs long. This is bigger than the genome of the common fruit fly but smaller than that of the silkworm. The genome includes genes that help the moth break down harmful substances, which might help it resist certain sprays used in gardening.

Scientists discovered a useful tool for changing genes called the PiggyBac Transposon in the cabbage looper, and it is now used in many different species.

Interactions with humans

The cabbage looper moth is a big problem for crops, especially vegetables like cabbage, broccoli, and bok choy. Its babies, called larvae, chew big holes in leaves and eat the parts where the vegetable grows bigger. They also leave sticky waste called frass, which makes the plants messy. Even though this moth can damage crops, young plants can usually survive. But when the plants start to grow big heads, the cabbage looper becomes harder to handle. This moth is tricky because it can live on many different plants and is becoming harder to control with common sprays.

Scientists are working on better ways to catch and control cabbage loopers. They have made special traps using a smell that the moths like, called a pheromone. These traps can catch some moths, but they are not enough to stop all the damage. Because these moths can grow resistant to sprays, scientists also study natural ways to control them, like using special viruses. One safe spray approved in the US works well on the moth’s eggs. Mixing different kinds of sprays seems to help slow down resistance, but some toxic chemicals are still needed. Researchers also use cabbage looper cells in labs to make important proteins, which helps in many scientific studies.