Sqaska

The serpentine leaf miner is the larva of a small fly (Liriomyza brassicae) that eats out slender, winding, whitish or greenish burrows in the leaves of cabbage and related plants, cultivated and wild. In addition to cabbage, it is considered a serious pest on broccoli, cauliflower and Chinese broccoli.
The fly is the most cosmopolitan species known in the leaf miner fly family, Agromyzidae. It is not found in Britain and parts of northern Europe, but it is widely distributed in the Pacific, including Australia and Hawaii, and parts of Asia and Africa. In North America it can be found locally in Canada and is abundant in California, as well as Florida and other southern states.
Larvae feed as leaf miners on the mesophyll, or middle tissue layer, of the leaf. Thread-like black frass occasionally extends from the mines. Individual mines are of little significance, but entire leaves may be weakened when larval populations are large. Injury to mature cabbage plants is usually confined to the outer leaves and does not affect plant growth. However, seedlings may be killed or severely weakened by high larval densities.
The average life cycle of the fly is 21 days but can be as short as 15 days, varying with host and temperature. Eggs are laid singly in punctures in the leaf epidermis, either upper or lower. The freshly laid eggs are creamy white and shaped like an elongated oval. The eggs are small, one hundredth of an inch in length, and hatch in 2 to 4 days. The legless, wedge-shaped maggots may be whitish or bright yellow to yellow green, 1/6- to 1/8-inch long and 1/50-inch broad. There are three larval stages of 2 to 3 days each. Pupae are light brown, oval and ringed with ridges. Adult flies are 1/8-inch long, with yellow and black thorax and a black head. They fly quickly for short distances when disturbed.