20.3.4 Sericulture
Application of Biology – Sericulture is the production of silk by the activity of worms known as silk worms. This process of rearing silk worms had been crude and laborious and often various diseases of silk worn wipe out all cocoons. Biological knowledge has enabled the farmers to overcome these and many other problems associated with sericulture.
Adult silk moth female lays eggs, which hatch in three to four days. Young larvae feed on buds and new shoots of mulberry. They grow in size and when fully-grown, silk worm larvae stop feeding and spin a continuous silk thread around it forming a cocoon. After few days cocoons are placed in hot water to kill the pupa. Workers then pick up one end of the thread and pass it over a reeling machine. These strands are then passed on machine to produce the fabric biologist have helped, making revolutionary progress in this field.
Japanese biologists have developed a wingless variety of silk moth which is easy to handle. Some varieties which complete 5-6 life cycles in a year have been raised.
20.3.5 Apiculture
Domesticating the honeybee for the honey production is known as apiculture. Honeybee is a social insect and lives in large colonies. Honeybees are trimorphic, consisting of queen, drones and workers. The queen bee is larger than the rest and is protected and fed by the workers. It is meant for egg laying. Workers collect nectar and pollen making honey, secrete wax, protect and feed the queen. Drones are male and their function is to fertilize the eggs and they no role in honey formation. Biological knowledge has led to a better understanding of usefulness of honeybees. Some varieties of domestic honeybees have been imported and their new breeds have been raised by the biologist in Pakistan.
20.3.6 Pests and their biological control
A large number of organisms damage useful plants and animals causing server damage to our economy and even to livestock and public health. Such destructive organisms (insects etc) are called pests. There are many methods to control the pests: e.g.
- Primary or cultural control: crop rotation should be used instead of mono cultures i.e. palting of only single-species crops again and again.
- Chemical control: chemicals like DDT are used as insecticide. Insects have developed DDT resistant strains. These insecticides also increase the toxicity and pollution, thus their use is now being discouraged.
- Biological control: biological control is the most promising pest control method. The method utilizes natural enemies like predators, parasites and pathogens of pests to control and destroy the pests (Fig 20.5).
Fig. 20. 5:biological controls of pests –here lady bugs are being used to control cottony cushion scale insect on citrus tree.
Advantages of biological control method
- They do not pollute the environment
- They do not disrupt and disturb the natural ecosystem.
- They usually provide permanent control of pest population, because pests rarely develop resistance to natural control.
Currently in some developed countries lace wings and lady beetles (predatory insects that feed on a variety of other pest insects) are raised commercially. Lace wings are much effective for controlling ball worm population in cotton fields. Recently certain pest pathogenic viruses have also been proved effective in controlling cotton ball worm and corn ear worm.
Pest pathogenic bacteria are also of great importance in this respect. Spores and toxins of the bacterium bacillus thuringiensis are sprayed on leaves, vegetables and flowers. They infect and kill the larvae of at least twenty species of butterflies and moths.