Crop Prot 111 Module 3 Lesson 1 The Nature of Insects PDF

Page 1 of 4 MODULE 3 Lesson 1 The Nature of Insects Introduction Welcome to the wonderful world of insects! Insects are the most numerous, diverse group of animals on our planet earth. This module shall discuss the nature o...

Page 1 of 4 MODULE 3 Lesson 1 The Nature of Insects Introduction Welcome to the wonderful world of insects! Insects are the most numerous, diverse group of animals on our planet earth. This module shall discuss the nature of insects, their distinguishing characteristics and their effects on us and on our environment. Learning Outcomes After completing this lesson, you are expected to be able to:  Distinguish insects from other animals; and  Understand the benefits and harm that insects can do to our resources and environment. Duration: Three Hours ABSTRACTION What are insects? INSECTS are distinguished from their relatives by the presence of three body divisions – head, thorax and abdomen. The thorax bears three pairs of legs (although immature mites also have three pairs of legs) and usually two pairs of wings in the adult stage. Some insects, like flies and mosquitoes, have one pair of functional wings while others are wingless, such as bedbugs and fleas. The exoskeleton of arthropods contains a horny substance called chitin which makes it impervious to water and resistant to chemicals. The appendages such as the legs and antennae and palpi consist of definite joints or segments. The structural features of these appendages relate to the insects’ habit and mode of life and rate of value in identifying them. Arthropods comprise about 80% of all animal species described and insects constitute 90% of the identified arthropod species. Insects, therefore, constitute over 70% of all known species of animals. They are the most predominant in both total number and kind. Among the CROP PROT 111 – PRINCIPLES OF CROP PROTECTION  Page 2 of 4 MODULE 3 Lesson 1 insects, the most numerous are the beetles, butterflies, moths, ants, bees, flies, termites and mosquitoes. How do insects affect man? A. Beneficial effects 1. Some insects (like honey bees and wasps) are good pollinators of many economic crops especially those plants whose male flowers are located on different plants. Yields of some crops can be increased when honeybees are present in the farm. For example, cucurbits (cucumber, squash, & patola) yield could increase 100% with pollinators. 2. As source of useful products Some insects manufacture useful products that are traded internationally such as silk, honey, bees wax, pollen, royal jelly, shellac and varnish. Silk is produced by silkworm larva when it is about to pupate by wrapping around itself silk thread at the rate of 1.5cm a minute for 2 to 3 days. Honey is produced by the worker bee from the nectar collected from plants and converting it to honey and storing it in the honeycomb. It takes a single worker bee about 100,000 to 200,000 trips to flowers, or a trip roughly equivalent to five times around the earth, to gather a kilo of honey. Bees wax is produced by worker bees in order to build combs while pollen is gathered and stored in the honeycomb as source of protein. The royal jelly is produced by the young bees in order to feed the queen bee throughout its life and the immature larvae during the first three days of their existence. Shellac and varnishes are products derived from the secretion of female insects grown on some tropical trees. 3. As natural enemies of insect and weed pests Many insects serve as predator, parasitoid, parasite, antagonist and competitor of insect and weed pests. They are sometimes referred to as biological control agents. 4. As food for humans A number of insect species are utilized as food and are considered as delicacies, e.g. “adobong suhong”, fried crickets, fried June beetle, honey bee larvae and locust. Most insects contain about 70% protein and can be a potential source of food nutrient for people in the future. In some countries, canned insects are occasionally considered delicacies and are expensive. 5. As food for animals that are valuable to humans Insects constitute a sizeable proportion of the food of fishes, frogs, snakes, lizards, birds, and mammals. Animals that feed on insects are called insectivorous or entomophagous. Many of these animals serve as food for people or assist them as companions, guides, protectors or source of amusement. Mudfish, catfish or “tilapia” grown in fishponds and rice fields could be commercially grown using insect light traps to attract insect pests for food. This, at the same time, regulate pest population to a non- damaging level. CROP PROT 111 – PRINCIPLES OF CROP PROTECTION  Page 3 of 4 MODULE 3 Lesson 1 6. Other uses Some burrowing insects can improve the physical condition of the soil and the deposition of metabolic by-products and dead bodies can increase soil fertility. As scavengers, they rid the earth’s surface of decaying organic matter and help reduce pollution in our environment. Insects are convenient materials for genetic and biological studies. They can be mass produced cheaply in the laboratory at a very short time. They can also be used as indicator for pollution. Sanitary biologists use some insects to determine presence of contaminants in drinking water. B. Harmful effects 1. As source of annoyance or injury Common household insects such as bed bugs, head lice, fleas and mosquitoes cause discomfort by biting. Skin disorder can result from scratching the affected skin. Insect bites can cause skin infection among people who have very sensitive skin. A number of pathological conditions are directly attributed to insects. Bees and wasps’ stings are painful and these may cause fever, nausea, vomiting, paralysis and even death to some sensitive people. For instance, a pregnant woman had an abortion after a bee sting. Some fly larvae may invade eyes, ears, nostrils, digestive tract, urinary tract or skin. The netting hairs of some caterpillars can cause inflammatory reaction of the skin. The bodies of some insects when inhaled by some sensitive persons produce an allergic reaction similar to hay fever and asthma. 2. As transmitter of diseases of humans and animals Insects may serve either as mechanical carriers or as biological vectors of human and animal diseases. Some flies can carry causative agents of cholera, dysentery and typhoid fever through their mouth parts, legs, body hairs and feces. Plague Bacilli and malarial parasite can multiply in the digestive tract of fleas and mosquitoes, respectively, before they are transmitted to animals and humans. The importance of insects to public health is recognized by the international community. Four of the six internationally quarantinable diseases are transmitted by insects. These are plague, relapsing fever, typhus and yellow fever. Mosquitoes can transmit to people malaria, filarial and viral diseases such as dengue, Japanese B encephalitis and the hemorrhagic fevers of Southeast Asia. Among the various nervous disorders of humans is an aversion to the sight of and contact with insects. 3. As economic pests Insects cause losses to economic animals, crops and forest tree production worth billions of pesos annually. They can reduce the quality of stored food products and various articles of commerce by feeding and by contaminating these products with their excreta and body parts. Insects can transmit a number of plant pathogens such as viruses, bacteria and fungi, causing high damage to animals, crops and forest products. Some insects such as termites, book lice and some beetles are pests in construction CROP PROT 111 – PRINCIPLES OF CROP PROTECTION  Page 4 of 4 MODULE 3 Lesson 1 materials, books and furniture. The price of and efforts in controlling insects are relatively small compared to the losses incurred in terms of time, money and manpower. Closure Having learned the nature of insects, we will explore in the next lesson the biology and ecology of insects and the factors affecting their abundance and distribution. This will guide crop protectionists in the proper identification of crop insect pest/s and in the manipulation of their population to a non-damaging level. REFERENCES BALTAZAR, C.R. and N. SALAZAR. (1982). Philippine insects. UP Press, Quezon City. p. 138 PEDIGO, L.P. and M.E. RICE. (2009). Entomology and Pest Management. 6th Ed. Waveland Press, Inc. p. 769. QUISADO, C. C. (2018). Lecture Guide in Crop Protection. USeP-Mabini. CROP PROT 111 – PRINCIPLES OF CROP PROTECTION