Cabbage moth

The cabbage moth (Mamestra brassicae) is a spread pest. It is a polyphage. The insect consumes plants of more than 70 species from 22 families amidst them vegetable, industrial, flower-ornamental crops and some wild plants.

Biology. Life cycle

The wingspread of the moth is 40–50 mm. The fore-wings are dark-brown with dark transversal strips. The kidney-shaped spot is surrounded with a white area. The line under an edge is yellow-white with 2 scallops in the form of the letter «M». The hind-wings are grey. They are darker at the edges. The life span of females takes 2–3 weeks. An average fertility is 600 eggs. The maximal is 2700. The eggs are yellow-white. The oviposition (egg-laying) has the form of an unequal polygon. It is fulfilled on a leaf underside and includes 20–159 eggs. The duration of egg development is 4–12 days. The caterpillars vary from a grey-green to dark-brown almost black coloration. There is a figure in the form of a fur-tree on the back. The figure consists of dark spots. There are yellowish and light strips at the sides. The caterpillars of the 1st age sceletonize leaves from below leaving intact the epidermis of a leaf upside. The 2–3^rd age caterpillars gnaw out through holes. The caterpillars of elder ages lead the night mode of life hiding at the bases of plants in daytime. They often eat the leaves almost entirely leaving the thick veins only. Besides, they enter a cabbage head, make gangways and contaminate it with excrements which provoke its rotting. The caterpillars develop during 24–50 days in dependence on temperature, air and ground humidity reaching a length of 35–40 mm in the last 6^th age. The pupa is reddish-dark-brown. The pupa stage of summer generations lasts 8–15 days. Having entered diapausa the pupa overwinters in the ground in a depth of 5–10 cm.

Mode of life

Under favorable conditions the moth is able to reproduce 3 generations. The emergence of overwintered moths occurs in different terms and depends on climatic zone. Usually it happens in May-June. The first summer generation emerges in July-September. A sum of effective temperatures for pupa development of the summer generation is 230–260°C (at the lowest threshold of 10°C and at the optimal temperature of 19–21°C). For egg development this level is 60°C (at the lowest threshold of 10°C and at the optimal temperature of 16–25°C). For caterpillar development it is about 400°C (at the lowest threshold of 9°C and at the optimum of 16–30°C). The cabbage moth is a moisture-loving species therefore it more often occurs in regions with high humidity, especially in the bottom lands of rivers. To lay the eggs the imago needs in additional nutrition on blooming plants. That is why a limiting factor for species spreading is low air humidity and the absence of nectariferous blooming. Wintering pupae are able to bear long flooding.

Symptoms of injuries

At first the caterpillars keep in colonies on the undersides of leaves scrapping their flesh off. Then they begin to bite into plant tissues contaminating a plant with excrements. As a result of pest life activity merchantable production loses its original qualities. The pest causes the injuries of leaf apparatus, flower buds, flowers and shoots.