AppearanceThis small moth is colored gray and brown. It can potentially identified by a cream-colored band that may be present in the shape of a diamond on its back. 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-colored 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.
BehaviorThe moth has a short life cycle, is highly fecund, and is capable of migrating long distances. Diamondback moths are considered pests as they feed on the leaves of cruciferous crops and plants that produce glucosinolates. However, not all of these plants are equally useful as hosts to the moth. Because of this, studies have suggested using wintercress as a trap crop around agricultural fields because diamondback moths are highly attracted to that plant but their larvae fail to survive when eggs are laid on it.
ReproductionThe eggs are oval and flattened, measuring 0.44 mm long and 0.26 mm wide. They are yellow or pale green at first, but darken later. They are laid singly or in groups of two to eight eggs in depressions on the surface of leaves. Females may deposit up to 300 eggs in total, but average production is probably half that amount. 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 colorless in the first instar, but pale or emerald green with black heads in later instars. Of the five pairs of prolegs, one protrudes from the posterior end, forming a distinctive "V". The larvae are quite active, and when disturbed, may wriggle violently, move backward, and spin a strand of silk from which to dangle.
The feeding habit of the first instar is leaf mining, although they are so small, the mines are difficult to detect. The larvae emerge from these mines to moult and subsequently feed on the lower surface of the leaf. Their chewing results in irregular patches of damage, though the upper leaf epidermis is often left intact. These irregular patches are called window panes.When female diamondback moths lay their eggs, some of their sex pheromones are left behind on the leaves. Diamondback larvae are attracted to the major component of this species-specific pheromone, which is 11-hexadecenal. For larvae, the sex pheromone is a foraging indicator, rather than a mating attractant so they use it to find a healthy source of food and avoid competition for food from other species on the host plant. After the fourth instar, larvae are no longer attracted to the sex pheromone for food sources.
PredatorsThe agriculture industry has been trying to find biological and natural ways to eliminate the diamondback moth especially since the moths have become resistant to pesticides. Common enemies of the moth include the parasitoids ''Trichogramma chilonis'' and ''Cotesia plutella'' and the predator ''Chrysoperla carnea'', or lacewings. Lacewings feed on eggs and young larvae, while the parasitoids only feed on the eggs. These organisms can recognize diamondback sex pheromones, larval frass odors, and green leaf volatiles emitted from cabbage. Cabbage odors in combination with the sex pheromone are particularly capable of attracting the predators and parasitoids, which will then consume the diamondback larvae and eggs.
CulturalFirstly, inter-cropping is good for reducing pests. Because of the biological diversity, two or more crops can be planted in one field, which can reduce fertilization or pesticide use, making planting the most profitable, and producing higher quality cabbage or increasing yield. High and low growing trifolium pratense was used to inter-plant cabbage and compared with cabbage alone. It was concluded that only inter-cropping with the high-growing red clover could reduce the number of eggs produced by the diamondback moth.
Secondly, planting time can be considered. This is because pest populations are affected by seasonal factors. For example, during wet periods, the infection rate of the diamondback moth is very low. As a result, growing cruciferous plants during wet seasons can effectively reduce pesticide use. Thirdly, crop rotation could be used. To avoid continuous rotation of cruciferous vegetables, cruciferous vegetables can be rotated with melons, fruits, Onions and garlic, and several different vegetables can damage the food chain of the diamondback moth. In addition, maintaining clean cabbage field hygiene is a simple but important pest control and prevention measure. A clean growing environment can greatly reduce the likelihood of infection. Before farming, for example, the land is usually turned over and exposed to the sun for at least a week. This helped to clear the diamondback moth and strengthen the quality of the soil.
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