Morphological Structure and Home Breeding of Yellow Mealworms
Yellow mealworms are naturally active, showing activity both during the day and night. Generally, they go through 3-4 generations with overlapping generations, and there is no hibernation phenomenon; they can still develop normally in winter. The suitable breeding temperature for yellow mealworms is between 20-30°C. At temperatures of 20-25°C, the egg stage lasts 7-8 days, the larval stage lasts 122 days, and the pupal stage lasts 8 days. It takes about 133 days from egg to adult. At temperatures of 28-30°C, the egg stage lasts 3-6 days, the larval stage lasts 100 days, and the pupal stage lasts 6 days. In this case, it only takes 110 days from egg to adult. Humidity also has a significant impact on their reproduction; relative humidity should ideally be between 60-70%. When humidity exceeds 90%, most larvae die after reaching the 2nd or 3rd instar. If the humidity drops below 50%, the number of eggs laid significantly decreases. The adult emergence rate reaches over 90%, with a gender ratio of 1:1. They prefer to live in groups and enjoy dim light, becoming more active after dusk. After emerging, they mate and lay eggs after three days. Eggs are laid at night on the feed surface, with each female laying around 200 eggs that often stick together in clusters covered with food debris. The eggshell is thin and soft. Female adults have lifespans ranging from 1 to 3 months, and after half a month, the egg-laying quantity decreases, allowing for culling. During the 7th or 8th month, the egg stage lasts about one week, while the larval stage has 1-10 instars, shedding skin every 4-6 days, taking 60-80 days in total. Larvae like to gather and begin feeding activities when the temperature rises above 13°C.
I. Morphological Structure of Yellow Mealworms:
The life cycle of yellow mealworms consists of four stages: adult, pupa, egg, and larva.
At 25°C, the eggs hatch within 3-5 days, but lower temperatures delay hatching. Once larvae turn into pupae, they need to be separated promptly because the pupae cannot move and may be bitten by other larvae. After separation, the pupae should be placed in a well-ventilated, dry environment with appropriate temperature. At temperatures above 20°C, they generally transform into black beetles after one week.
1. Adult Yellow Mealworms
After one week at temperatures above 25°C, the pupae molt into adults. Newly emerged adults are milky white with thin shells that turn yellowish-brown and then dark brown with a glossy finish after about ten hours. They take an elliptical shape, approximately 14 mm long and 6 mm wide, with the shell becoming thick and hard. At this point, they are fully matured and ready to reproduce the next generation. The adult body is divided into head, thorax, and abdomen. Adults have a pair of antennae not present in larvae, which are five times longer than those of larvae. There are three pairs of legs, one located on the prothorax and two on the abdomen, with the leg length being 8-10 times longer than those of larvae. Each foot has two hook claws with bristles on the toes. There are several vertical lines on the wings. Although adults have beautiful wings, they can only fly short distances. Wings protect the body and assist in crawling.
The process of adult emergence from the pupa takes 3-7 days, with the head, thorax, legs, and wings emerging first, followed by the abdomen and tail. The entire process is completed within a few days. Newly emerged adults are tender and less active. After about five days, their body color deepens, and the elytra harden. Adult males and females usually mate in the dark, with mating lasting a long time. Females lay eggs by inserting their tails into sieve holes. During this period, the tray should not be disturbed arbitrarily. When a layer of eggs is found attached to the bottom of the sieve tray, the tray can be changed. After sieving the eggs, place the adults in another tray with feed and remove dead insects. Change the egg trays every 5-7 days. Adults typically survive for around 50 days, and during the egg-laying period, they require substantial nutrients and water. Therefore, wheat bran and vegetables must be added in a timely manner. Fishmeal can also be added. If nutrition is insufficient, adult insects will cannibalize each other, causing losses.
2. Yellow Mealworm Pupae
After larvae grow for about 50 days, reaching lengths of 2-3 cm, they start to pupate. The pupae have large heads and small tails, resembling their basic adult form, with two thin wings tightly attached to the chest. The sides of the pupae are serrated and angular. Initially, the pupae are white and semi-transparent with relatively soft bodies, gradually turning brown and hardening.
Mealworm larvae pupate on the surface of the feed. Before pupation, larvae crawl to the surface of the feed and remain stationary as their bodies slowly contract, completing the final molting process to become pupae. This transformation occurs within a few seconds. Newly formed pupae are white-yellow, slightly elongated, with abdominal segments moving until the body shortens and turns dark yellow.
There are individual differences among yellow mealworm larvae, shown in the timing of pupation and individual strength. Newly formed pupae mixed with larvae in a wooden tray are prone to being bitten on the thorax and abdomen by larvae, leading to internal organs being eaten and forming empty shells. Some pupae may be infected by viruses during pupation, resulting in dead pupae. Regular checks are necessary. If such cases are found, a solution of bleaching powder at 0.3x10^-6 concentration can be sprayed to disinfect and sterilize the space. Dead pupae should be promptly removed and disposed of.
3. Yellow Mealworm Eggs
Eggs are milky white, very small, about 1-2 mm long, with a diameter of 0.5 mm, and oval-shaped. The outer shell is relatively thin and serves a protective function. The egg fluid is a white milky sticky liquid. The egg consists of the shell, nucleus, yolk, and protoplasm.
Adult yellow mealworms lay eggs in wooden trays containing feed. Placing the trays with eggs on a rack allows natural hatching of larvae. Careful observation is necessary to avoid disturbing the eggs or harming hatching larvae. When larval skins appear on the feed surface, the first-instar larvae have been born.
4. Yellow Mealworm Larvae
Larvae are yellow and shiny, about 35 mm long and 3 mm wide, with a cylindrical shape. They have thirteen segments connected by brownish rings. The underside is pale yellow, hence the name "yellow mealworm." The proportion of the head and thorax in the insect's body is relatively short, approximately 1/5 of the body. The body is straight, with firm skin and a thicker middle section. The last segment of the abdomen is smaller. The head seam is U-shaped, with a flat mouthpart. The tail spike is pointed and curves upward.
Wheat bran is the main feed for yellow mealworm larvae and also their habitat. Therefore, the feed should be kept at a natural temperature. Normally, when the temperature is high, larvae tend to stay on the feed surface, while they burrow deeper when the temperature is low. The thickness of the feed in the tray should be within 5 cm. As the feed gradually decreases, use a sieve to remove insect feces and add new feed. For 1st and 2nd instar larvae, a 60-mesh sieve should be used to prevent larvae from falling through the sieve holes. A new wooden tray with fresh feed should be prepared, and the sieved clean larvae should be placed on the tray and racked.
For larvae growth, they need to break through the outer skin (molt), growing larger with each molt. Larvae undergo seven molts during the larval stage, growing one instar per molt. On average, they molt every nine days. During molting, the skin splits along the thoracic back seam, followed by the head, thorax, legs, abdomen, and tail gradually shedding. Molting generally occurs on the feed surface, and after molting, larvae retreat into the feed. Newly molted larvae are milky white with delicate skin.
IV. Home Breeding of Yellow Mealworms
The entire life cycle of yellow mealworms is about four months.
Breeding yellow mealworms is relatively simple: Clean smooth-walled enamel or ceramic basins (plastic or iron-made ones are also acceptable), grab a handful of wheat bran, break a steamed bun into pieces, and drop them into the shallow basin. Mealworms will burrow into the bun to eat.
1. During the larval stage, change the feed and sift out feces after each molt, adding fresh feed. In the adult stage, the presence of eggs and feces at the bottom of the feed can easily cause mold, so the tray needs to be changed promptly.
2. When feeding vegetable leaves, ensure the leaves are dry before feeding to prevent moisture.
3. Ensure the feed is fresh, the bran does not deteriorate, and the vegetables do not rot.
4. Breeders should check the condition of the mealworms daily. Any sick or dead insects should be promptly removed to prevent bacterial infections.