SILKWORM PESTS

Among the insects that attack silkworms, the most important ones are the parasites Tricholyga bombycis Beck., Tricholyga sorbillans Wiedman, and Sturmia sericariae Cornelia ,(Cross ocosmia sericariae) which are commonly known as "Usi” or "Uji” flies.

Uzi fly (Tricholyga bombycis) : Trioholyga bombycial a diptersn fly of the family Taohinidae, commonly known as Uzi or Uji fly, is a serious peat of silkworm larvae and pupae. This fly can cause considerable damage to silkworm rearing and as a result the seri­oulture industry frequently suffers in the cocoon crop production.

Life cycle, habit and nature of damage: T.bombycis is a large fly with prominent black and grey stripes and dark ebony in color. Each female fly lays about 300 eggs. The egg hatches within one to three days of oviposition and the young maggot bores its way into the body of the silkworm larvae. A black spot or scar appears on the body of the silkworm at the point of entry after penetration of the maggot. The maggot lives on the tissues of the silkworm especially the fat bodies, for about a week and gets its air supply from the aperture through which it entered. The maggot lives in the body cavity of the silkworm for about a week and having finished feeding, the fully grown maggot wriggles its way out killing its host. If the infestation takes place in the late fifth instars of the silkworm, the larva may be able to spin its cocoon, but the cocoons cannot be used as seed cocoons and are also unreel able since the fully grown maggot makes its way out of the silkworm pupa and cocoon for pupation in the soil, by killing its host and cutting the cocoon layer. In any case the damage is serious because either the silkworm larva itself is killed or the spun cocoons are rendered useless for reeling or for seed purposes.

Prevention and control: The most effective method of control is to prevent the entry of the fly into the rearing rooms by providing suitable wire mesh (fly‑proof nets) for doors, windows and ventilators, wherever rearing is done in separate rearing houses or rooms. Pest‑trapping rooms may also be provided at the entrance, bat this may not be financially feasible for poor rearers. The maggot infected larvae and cocoons must be destroyed by burning or by treating with chloropicrin. All crevices on the floor must be closed up to prevent the maggots from creeping under the floor to pupate.

Uji fly (Tricholyga sorbillans) : The Uji fly is found in China, Korea and south‑east Asian countries. It produces seven to eight generations a year in tropical zones and is quite hazardous. It is hardly considered a pest of silkworms in Japan and yields only five to six generations a year.

Life cycle, habit, nature of damage and control measures are generally similar to that of Tricholyga bombycis.

Ants: This insect pest attacks silkworms in the rearing trays and this can be prevented by placing the legs of the rearing stands in ant wells.

Nematode: Nematodes belong the phylum, Nemathelminthes and class Nematode. The nematode Hexamermis microamphidis is mostly found in silkworms of late‑autumn rearing. This orpanism attacks the young‑stage larvae and penetrates into their bodies. The head of this affected silkworm becomes transparent and the body milky white.

Lizards: These commonly frequent the rearing houses and often pick up the young‑age worms and eat them, thus causing considerable damage.

Rats and squirrels: These mammalian predators eat the silkworms avoiding only the silk glands and the pupa after biting open the cocoons. Their entry into the rearing house can be prevented by providing suitable wire mesh (fly‑proof nets) for doors, windows and ventilators. Traps and poisonous baits can also be used.

Birds: Birds such as crows and sparrows pick up the silkworms when the montages are kept out‑of‑doors at the time of spinning. Damage by these predators can be avoided by keeping the montages indoors at the time of spinning.