Plutella xylostella Linnaeus, 1758
Common names: Diamondback moth, Cabbage moth [En], Teigne des crucifères, Teigne des choux [Fr], Koolmot [Nl], Kohlschabe, Kohlmotte [De], Tignola delle crucifere [It], Polilla de la col [Es]
Tubize, BRABANT ● Belgium
Description: The diamondback moth has a wingspan of about 15 mm and a body length of 6 mm. The forewings are narrow, brownish-gray and lighter along the anterior margin, with fine, dark speckles. A creamy-coloured stripe with a wavy edge on the posterior margin is sometimes constricted to form one or more light-colored diamond shapes, which is the basis for the common name of this moth. The hindwings are narrow, pointed toward the apex, and light gray, with a wide fringe. The tips of the wings can be seen to turn upward slightly when viewed from the side. The antennae are pronounced.
Biology: The diamondback moth lays its eggs only on plants in the family Brassicaceae. Nearly all cruciferous vegetable crops are attacked, but some are favoured over others. These include broccoli, Brussels sprouts, cabbage, Chinese cabbage, cauliflower, collard, kale, kohlrabi, mustard, radish, turnip, and watercress. Several wild species in the family also act as hosts, especially early in the season when cultivated crops are unavailable. The egg-laying females have been reported to recognize certain chemicals in the host plants, glucosinolates and isothiocyanates, that are characteristic of the Brassicaceae family (but also occur in some related families). These chemicals were found to stimulate oviposition, even when applied to a piece of paper. One plant species that contains the egg-laying cues is wintercress, Barbarea vulgaris. Indeed, diamondback moth females lay eggs on this plant species, but the newly hatched larvae die due to the effects of additional natural plant chemicals called saponins.
The moth has a short lifecycle (14 days at 25 °C), is highly fecund, and is capable of migrating long distances. It is one of the most important pests of cruciferous crops in the world.
The lifespan averages three to four weeks for females, but rather less for males. These moths are weak fliers, seldom rising more than 2 m above the ground and not flying long distances. They are, however, passive migrants, being easily transferred by wind over long distances. Diamondback moths overwinter as adults among field debris of cruciferous crops, and active adults may be seen during warm periods at any time during the winter in temperate areas. They do not survive cold winters and reinvade colder areas each spring, being carried there by the wind. Moths are active usually at twilight and at night, feeding on flowers of cruciferous plants, but they also fly in the afternoon during mass outbreaks.
The eggs are laid singly or in groups of two to eight eggs in depressions on the surface of leaves. The larvae emerge from the eggs in about six to seven days.
The larvae have four instars, each with an average development time of about four days. The larval body form tapers at both ends. The larvae have a few short black hairs and are colourless in the first instar, but pale or emerald green with black heads in later instars. The larvae are quite active, and when disturbed, may wriggle violently, move backward, and spin a strand of silk from which to dangle. The larvae feed on the lower surface of the leaf.
The yellowish pupae are about 8 mm long and are wrapped in a loose silk cocoon. They are usually found on the lower or outer leaves of the food plant.
Larvae damage leaves, buds, flowers, and seed-buds of cultivated cruciferous plants. Although the larvae are small, they can be very numerous and cause complete removal of foliar tissue except for the leaf veins.
Distribution: The diamondback moth has a global distribution and is found in Europe, Asia, Africa, the Americas, Australia, New Zealand, and the Hawaiian Islands. It probably originated in Europe and was first observed in North America in 1854, in Illinois.
Wikipedia, Diamondback moth