Biology of Major Economically Important Insects, Biology tutorial


Insects are extremely abundant and have been named the most successful animal species in terms of numbers. In this chapter, we will be studying the different economic classes of insects with subgroups and illustrations in each category, the biology of a main economically significant insect, the honey bee. It is a beneficial insect as the honey derived from it is consumed through man and employed for other purposes like in medicine.

Economic Classification of Insects:

Insects are a much significant group of animals because of their advantageous and unfavorable effects on the life of man. They have form a tremendous impact on the environment, on human health and activities. Medical, economic and agricultural Entomology are significant branches of science.

Insects can be categorized as follows based on their economic significance.

1) Injurious Insects:

a) Pests of cultivated plants (crop pests): Each and every cultivated plant harbors lots of insect pests that feed on them and decrease the yield of the crop. Field and horticultural crops are attacked by most of the insect species. Example: cotton bollworm and Rice stem bores. 

b) Storage pests: These are the insects which feed on the stored products and cause financial loss. Example: Rice weevil and Pulse beetle. 

c) Pest attacking cattle and domestic animals: Cattle are influenced by pests such as Fleshfly, Horse fly, Fleas and Lice. They suck blood and at times eat the flesh.

2) Beneficial Insects:

a)  Productive insects:

  • Silk worm: The silk-worm filament secreted from the salivary gland of the larva assist in producing the silk. 
  • Honey bee: Gives us with honey and most of the other by-products such as bees wax and royal jelly. 
  • Lac insects: The secretion from the body of such scale insects is termed as lac. Helpful in making polishes and vanishes. 

 b) Insects helpful as drugs, food and ornaments:

  • As medicine example: Sting of honey bees - medication for arthritis and rheumatism; Eanthoridin extracted from the blister beetle - helpful as hair tonic. 
  • As food: For human beings and animals. 
  • For animals: Aquatic insects employed as fish food. 

c) Ornaments, entertainers

  • Artists and designers copy color of butterflies. 
  • Beetles worn as necklace. 
  • Insect collection is a hobby 

d) Scientific research:

Mosquitoes and Drosophila are helpful in genetic and toxicological studies correspondingly.

3) Helpful Insects:

a) Parasites: These kinds of insects are small insects that feed and live on harmful insects by finishing their life-cycle in a host and kill the host insect. Example: egg, larval and pupal parasitoids.

b) Predators: Such insects are the big insects that capture and devour harmful insects. Example: Coccimellids and Preying matritids.

c) Pollinators: Most of the cross-pollinated plants based on insects for pollination and fruit set. Example: Honey bees, help in pollination of the sunflower crop. 

d) Weed killers: Insects that feed on the weeds and kill them. Example: Parthenium beetle eats on parthenium.

e) Soil builders: Soil insects like beetles, ants, larva of cutworms, crickets and collembola make tunnels in soil and facilitate aeration in the soil. They become fine manure after death and enrich the soil. 

f) Scavengers: These are the insects which feed on dead and decaying matter is termed as scavengers. They are significant for maintaining the hygiene in the surroundings. Example: Carrion beetles and Rove beetles feed on the dead animals and plants.

4) Household and Disease Carrying Insects:

a) Pests that cause damage to possessions of human beings such as paper, furniture, wool and so on. Example: Furniture beetle, cockroaches, sliver fish and so on.

b) Pests that cause painful bite, inject venoms. Example: Wasps and bees sting us. Hairy caterpillar nettling hairs are poisonous. Mosquitoes and bugs bite and suck blood from us. 

c) Disease-causing: Mosquito causes Malaria; Filariasis causes Dengue fever; Housefly causes Typhoid, Anthrax and Cholera.

Biology of Major Economically Important Insects:

Characteristics of Insects:

1) Insects such as other mandibulates contain one pair of pre-oral antenniform appendages.

2) The insect body is generally categorized into three portions: head, thorax and abdomen.

3) The insect head comprises of six parts bearing a pair of antennae (segment 2), a pair of mandibles (segments 4), first maxillae (segment 5) and a pair of second maxillae (segment 6). Compound eyes are present.

4) The thorax includes of 3 segments and bears 3 pairs of walking legs ventrally and 2 pairs of wings dorsally.

5) The abdomen comprises of 11 segments generally and bears no ambulatory appendages.

6) Insects respire through trachea that opens through segmentally arranged spiracles.

7) Excretion in insects is through Malpighian tubules.

Biology of a Honey Bee (Apis):

There are an around 30,000 bee species globally. The vast mass of such species are solitary and don't produce honey or big nests with young, and thus don't show colony defense.

If one usually thinks of a bee, the species that in general comes to mind is the western honeybee, Apis mellifera. The genus Apis is composed of eight species. Apis mellifera is composed of 24 various races. The most general commercial production race is Apis mellifera ligustica, generally termed to as Italians. This race is acknowledged for its high rate of honey production and its gentle nature, making it a preferred in apiaries and in commercial bee production facilities. 

The majority of bees which one notices outside of a hive are workers (that is, sterile females). A characteristic honeybee colony comprises of 50,000 to 60,000 sterile workers, 500 to 1000 drones (that is, fertile males) and one queen, the mere fertile female in the colony and mother of the whole population of the hive.

Several people perplex bees with wasps. Bees tend to be vegetarians and are usually hairy, while wasps are likely to be carnivorous and hairless. 

Life cycle of a Honey Bee (Apis):

Honey bee life-cycle consists of four main different phases or stages: egg, larva, pupa and at last an adult. Honey bee colonies are usually perennial by the exceptions of bumble bee and paper wasp colonies. The colonies of bees comprise of three castes, Queen Bee, worker bee and drones (that is, males). Queen bees lay eggs, worker bees are non-egg producing bees and drones are inevitable for mating purposes.

Developmental time for honey bees:

The total growth or developmental time for a Queen bee is around 16 days, 21 days for worker bee and around 24 days for male or drone bee. Four different honey bee life cycle phases can be described in short as follows:

1) Egg stage:

Primary phase or stage of development in the life-cycle is egg stage. Eggs are much minute and have look of poppy seeds in shape. Each and every egg consists of an opening on the wider side which enables a sperm to penetrate in. Hatching of eggs generally takes place after three days of egg laying.

2) Larva stage:

This phase or stage usually lasts up to nine odd days. Throughout this phase, hatched larva is nearly microscopic in size devoid of legs and eyes. Larva is nourished on a diet termed as royal jelly for initial two days. As the third day steps forward larvae which are destined to build up into queen bees carry on to fed on royal jelly, whereas worker larvae feed on the honey, water and pollens. Larval phase for queen bee lasts for 5.5 days, 6 days for worker bees and 6.5 days for the drones.

3) Pupa stage:

Reformation of tissues massively occurs throughout the pupal phase. Worm-like body consists of now three different parts of the body. This phase generally lasts for 7.5 days for queen bee, 12 days for worker bee and 14.5 days for drone bee (that is, male bee).

4) Adult Stage:

All three kinds of bees are now completely grown and are totally ready to achieve their tasks. A characteristic colony of honey bee comprises of 50,000 to 60,000 worker bees, 600 to 1000 drone bees and just 1 queen bee.

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