False meter. It is a very polyphagous plague. It can cause considerable reductions in yields due to the damage it causes when feeding on the foliage. Attacks crops like: tomato, cotton, celery, sweet potato, broccoli, pumpkin, cabbage, cauliflower, chrysanthemum, spinach, beans, peas, lettuce, melon, mustard, turnip, potato, cucumber, pepper, radish, beet, watermelon and tobacco, among others
Plusia ni, Autographa brassicae.
Other common names
Worm fake meter, caterpillar geometer.
Morphology and biology
Performs holometabola metamorphosis. The eggs are rounded and flattened at their base, approximately 0.6 mm in diameter. They are pearly or greenish white and are placed in isolation or in small groups, usually on the underside of the leaves.
False meter larva (Trichoplusia ni)
The larva normally has five stages, although they can vary between four and seven. The first one is almost transparent white and with the capsule of the black head. The successive stages are of pale green coloration, with a distinguishable thin white line on each side of the body, just above the spiracles, in addition to two other white lines near the middle part of the back.
In mature larvae these lines may be missing and therefore be totally green. Its body is narrower in the anterior part and wider in the posterior, reaching to measure 3 to 4 cm long. It has three pairs of thin legs near the head and three pairs of false legs on the back of the body. When it moves it arches the middle section of the body. This way of walking is its main feature and consists of making a waving with the body giving the impression of being measuring, hence its vulgar name.
During its last larval stage, it weaves, on the underside of the leaves or in the vegetable residues, a fragile cocoon of white threads that will protect the chrysalis. This is a yellowish green color that turns brown when it ages. It measures approximately 2 cm long.
The adult is 2.5 to 3 cm long, marbled in color or chestnut gray. The extension of the wings or wingspan is 3.5 to 4 cm. The front ones have two small silver spots near the middle part, one round and the other U-shaped. The rear wings are light brown at the base and darker at the end. A tuft of hairs is lifted from the back of the thorax. The males have brown tufts, like hairs near the end of the abdomen, some with black tips. They are of seminocturnal habits since they are more active at night, although they can be seen in activity also in the hours preceding nightfall and on very cloudy days.
The eggs hatch in 2 or 3 days at 29 oC, the larvae develop between 15 and 20 days, the pupa takes 4 to 7 days. The total cycle lasts from 21 to 30 days. The adult comes to live for 10 to 12 days, a period in which females lay 300 to 1,500 eggs.
Symptoms and damages
The larvae of this insect feed mainly on the foliage, producing irregular holes of considerable size and reducing the leaf area.
The first 3 stages feed normally respecting the upper epidermis, unlike the last two that usually feed without affecting the edge of the leaves. They are very voracious when they reach their maximum development and their presence can also be detected when accumulating, in the feeding sites, large amounts of wet and sticky fecal material.