REASONS OF DOMINANCE

I. Structural characters:-

1. Exoskeleton:

• The insect body has an outer exoskeleton or body wall made up of cuticular protein called as chitin.
• Prevent from physical or mechanical injuries and to maintain shape and size of the body, providing area for muscle attachment.

2. Small size:

• Most species are of insects are between 2 and 200 mm (0.1 -1.0 inch) in length.
• Some may be smaller while some may be bigger like Goliath beetle of Africa ( 4 inch ) and walkingstick of Malaysia (13 inch)
• Minimal resources are needed for survival and reproduction.
• Ideal for avoiding predation.

3. Flight:

• Highly effective mode of escape from predators.
• Efficient means of transportation, allows populations to expand to new habitats and resources.
• Monarch butterfly can fly 600 km at time.

4. Hexapod locomotion:

• Because of the presence of six legs on the three thoracic segments, the insect will have equilibrium during all the phases of its locomotion.

5. Compound eyes:

• Most of the adult insects and nymphs consists of compound eyes as visual organs which possess number of hexagonal units known as ommatidia.
• Because of presence of number of ommatidia , even if some or few ommatidia get damaged, the insect does not lose the power of vision.
• Compound eye comprised of few to as many as 28,000 (in dragonflies) ommatidia.

6. Scattered sense organs:

• The sense organs viz., visual organs, gustatory organs (senses of taste) , smell (olfaction), organs of touch etc. are distributed on different parts of the body.
• Like antennae, eyes, mouth parts in the head, legs with claws on thorax, tympanum (auditory membrane), cerci ( sensory appendages) at the posterior of the abdomen etc.

II. Developmental characters:-

1. High Fecundity:

• It helps to increase the population at faster rate. e.g. Queen Honey bee can produce 4000 eggs per day.

2. Method of reproduction:

• Many species of insects (aphids, scales, thrips, and midges) can reproduce without males- parthenogenesis.

3. Controlled reproduction:

• Though insects possess high fecundity, there is also high degree of control over reproduction by reducing the number of females that can lay eggs.
• Eg: honey bees and termites.

4. Short life cycle:

• Most of insects have very short life cycle i.e. 2 to 4 weeks.
• Dorsophila melanogaster has shortest development time (egg to adult) i.e. 7 days, is achieved at 28 °C.
• Similarly, a flesh fly has a life cycle of 3 days.
• The adult mayflies are short-lived, from a few minutes to a few days normally say one day, depending on the species.

5. Feeds on variety of foods and Specificity of food:

III. Protective adaptations and devices:-

1. Morphological adaptations (mimicry):

• The body color and shape of some insects make them look like part of the plant e.g.: stick insects and leaf insects.

2. Physiological adaptations:

• Some insects produce or release poisonous or unpleasant odors from their body or possess warning coloration by imitating certain distasteful insects.
• g.: Stink bugs have specialized exocrine glands located in the thorax or abdomen that produce foul smelling hydrocarbons.
• Some blister beetles (Meloidae) produce cantharidin, a strong irritant and blistering agent.

3. Behavioral adaptations:

• It is a defense strategy adopted by some insects through feigning death or imitating the voice of dangerous insects or mimicry.
• Colarado potato beetles when disturbed, draw their legs beneath and drop to the ground and pretend as if dead.

4. Construction of protective structures:

• Some insects construct shelter with the available plant material for protecting themselves from adverse conditions, natural enemies and to store food material for use during the period of scarcity.
• Eg: Cases / Bags in case of case worms/bag worms, Termatoria in case of termites, Honey comb in case of honey bees.