Detailed Explanation of the New Technology for Raising Fly Larvae in Plastic Greenhouses

Raising flies in cage nets in ordinary civilian houses is a technology commonly adopted in the fly farms that have emerged in China in recent years. This technology requires heating facilities to be installed in the room; otherwise, when the indoor temperature in autumn, winter and spring cannot reach 27°C, the reproductive capacity of the flies drops severely. When the heating temperature in the room is on the low side, especially in the north, in winter one has no choice but to use the method of letting the flies pupate to preserve the insects through the winter, so fly farming has to be interrupted and economic returns decline sharply. Raising flies in plastic greenhouses successfully solves this problem; it allows flies to produce continuously all year round and increases farming returns several times over, making it a technology with great prospects.

Flies have the following requirements in terms of temperature, humidity and light: the most suitable temperature for flies is 27°C-30°C. At 8-12°C flies can move about, but they cannot mate, nor can they stand on food; they can only land on the ceiling and walls and do not like to move, and at minus 5°C they die within 3-5 days. Fly larvae require a higher temperature than adults; the most suitable temperature for their fastest development is 35°C, at minus 1-2°C they stop activity, at minus 5-6°C they die, and when the temperature is too high, 45-55°C, their rate of increase is reduced by half compared with the normal temperature. Fly larvae require the feed temperature to be suitably 30-35°C. In terms of humidity, adults require indoor humidity of 55%-60%; when humidity is too high, the flies' legs and bodies easily become wet, which hinders movement. The humidity needed during the larval growth period is 65%-70%. Flies like to be active in bright places; the greater the brightness, the greater their activity. For artificial fly farming, lighting equipment must be installed in the room, with more than 10 hours of light per day. Using plastic greenhouses to raise flies easily satisfies these characteristic requirements of flies during reproduction, and its advantages are as follows:

1. The rearing temperature is significantly higher. Without specially installing heating facilities, the temperature inside the greenhouse in spring, summer and autumn is easily maintained at 27-30°C. By rolling up and covering the straw curtains on the greenhouse roof, measures to raise and lower the temperature are simple and easy to carry out, and they hardly increase rearing costs. Even in cold winter, the temperature inside the greenhouse can still average around 20°C.

2. Humidity is stable and easy to maintain. When raising flies in ordinary civilian houses, maintaining a certain humidity requires constantly sprinkling water on the ground, whereas in plastic greenhouses, because of good airtightness, on ground not hardened with cement there is no need to sprinkle water and no need to specially regulate humidity.

3. Sufficient light. In plastic greenhouses, when the straw curtains on the roof are opened, sunlight filtered through the plastic film brightens the entire greenhouse, and maintaining light is simple and easy. The greenhouse area can be determined according to the scale of rearing. There are two methods for raising flies with plastic greenhouses: one is to set up three-dimensional gauze nets in the greenhouse and raise flies in the nets; the other is free-range rearing in the greenhouse, piling a certain amount of straw stalks and straw rope in the greenhouse and regarding each greenhouse as one cage. This method requires greater investment and floor space than the former method, and the rearing density is lower. In the method of setting up gauze nets in the greenhouse, a plastic greenhouse generally 20 m long, 4 m wide, with a low wall height of 2 m and a high wall height of 3 m is built, and 3 layers of gauze nets are installed.

Rearing method for adult flies: rearing cage: the cage frame size is 50 50 50 cm, on which gauze nets of the same size are attached; in the center of one end of one side of the gauze net is a cloth sleeve about 20 cm in diameter and 33 cm long, for taking out and putting in flies and changing feed. Rearing dish (7-9 cm in diameter), holding granulated sugar for adult flies to feed on, or with a piece of water-saturated foam plastic placed inside to provide a water source for adult flies, which can also be used to attract eggs. Each cage raises 8,000-10,000 adult flies. Whether they are newly collected adult fly breeding stock or adult flies after emergence, sugar and water must be supplied promptly to prevent death from starvation. An adult fly lays eggs 3-5 times in its lifetime, up to 10 times at most, with 100-150-300 eggs each time. Rearing method for larvae: first place the feed in the rearing box, with a thickness preferably not exceeding 4 cm, then slowly put the collected fly eggs (one-day-old larvae) onto the feed in the rearing box with a larvae-transferring shovel, and the young larvae will slowly disperse and burrow into the feed. When larvae eat the feed, they generally move from top to bottom. If the humidity and temperature in the box are high, or the feed is insufficient, or the population density is too high, the young larvae will crawl outward, and the rearer must check at any time and promptly take measures such as adding feed or lowering temperature and humidity.