Trichoplusia is not only damaging pest in crucifers, their favourite host, it can also be found in crops such as tomato, pepper, some cucurbits, soybean, sesame and cotton. One of the reasons why this plague can be serious is that the moth is able to disperse widely, reaching distances of up to 200 km.
Life cycle and appearance of Trichoplusia ni
Adults can deposit up to 300 eggs on the underside margins of the upper leaves of plants. The eggs have a spherical shape, with the flattened part attached to the leaf, and are a yellowish or greenish white colour. The Larvae hatch after 3 to 4 days. Since their legs are confined to the front and rear of the body, they move in a “looping” manner. They take 15 to 20 days to pass through 5 instars, changing colour from yellowish green to pale green with a white band on both sides of the body. Pupation takes place in webbed cocoons often on the underside of the host plants. The pupae have a green colour and then change to a coffee brown colour when close to adult emergence. Finally, the adult has a mottled grayish-brown colour with a silvery figure eight pattern on the forewings. Adults can survive 10 to 12 days.
The caterpillars feed mainly on the leaves causing irregular holes. The first three instars make small holes, while the following stages feed on the tissue between the veins, skeletonizing the leaves. They have a voracious appetite and can daily consume up to three times their body weight. Plants can be severely defoliated and stunted.