Honours / Discipline Specific Elective (DSE)
BIOLOGY OF INSECT
►Unit 1: Insect Taxonomy
Basis of insect classification; Classification of insects up to orders (Ruppert and Barnes, 1994)
Q.Mention the salient features of orders Dictyoptera and Orthoptera with examples.
(i)Antennae long and many segmented
(ii)Thoracic wings two pairs.
(iii)Mouth parts biting and chewing type.
(iv)Anterior pair, tegmina hard translucent and opaque and posterior pair delicate and transparent.
(v)Cerci many segmented.
Example— Periplaneta americana
(ii)The anterior part of thoracic wings narrow and leathery.
(iii)The forewings, or tegmina, are narrower than the hindwings and hardened at the base, while the hindwing is membranous, with straight veins and numerous cross-veins. At rest, the hindwings are held folded fan-like under the forewings.
(iv)Mouth parts biting and chewing type.
►Unit 2: General Morphology of Insects
External Features; Head – Eyes, Types of antennae, Mouth parts with respect to feeding habits Thorax: Wings and wing articulation, Types of Legs adapted to diverse habitat Abdominal appendages and genitalia
Q.What is Johnston’s organ?
Johnston's organ is a collection of sensory cells found in the pedicel (the second segment) of the antennae in the class Insecta. Johnston's organ detects motion in the flagellum (third and typically final antennal segment). It consists of scolopidia (A scolopidium is the fundamental unit of a mechanoreceptor organ in insects. It is a composition of three cells: a scolopale cap cell which caps the scolopale cell, and a bipolar sensory nerve cell) arrayed in a bowl shape, each of which contains a mechanosensory chordotonal neuron. The Johnston's Organ is located in the second segment of an insect's antenna. Sound waves vibrate the antenna of the insect and these vibrations are detected by the Johnston's organ. The Johnston's organ is commonly used to find a mate as an insect can detect the sound of wing beats of a mate.
It is the presence of the Johnston's organ that separates insects from the non-insect hexapods.
► Unit 3: Physiology of Insects
Structure and physiology of Insect body systems - Digestive, respiratory, endocrine and nervous system Photoreceptors: Types, Structure and Function Metamorphosis: Types and Neuroendocrine control of metamorphosis
Q.What are the disadvantages and advantages of compound eye?
i)The compound eye is not very good for distance vision compared to the large eyes of birds and mammals. The world within about 20 cm is much more important to most arthropods, however and compound eyes are effective within this range.
ii)Images formed by compound eyes are not sharp, they are crude at best, for the small size of the eye limits the number of photoreceptor units (ommatidia).
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i)Compound eyes are especially good at detecting motion. As an object moves across the visual field, it stimulates a succession of ommatidia, which the brain interprets as motion.
ii)A little shift in a point of light caused by a movement results in a corresponding shift in the ommatidia being stimulated.
ii)The total corneal surface of a compound eye can be strongly convex, resulting in a wide visual field. This is particularly true of stalked compound eyes, in which the cornea may cover an arc of more than 180⁰.
►Unit 4: Insect Society
Social insects with special reference to termites Trophallaxis in social insects such as ants, termites and bees
Q. State 3 characteristics of eusocial societies.
(i)Members of the society cooperate in caring for the juveniles. There is a reproductive division of labour, with sterile individuals performing the physical labour of the society while reproduction is left to fertile individuals. There is an overlap of at least two generations so parents can be assisted by their progeny.
(ii)No individual can exist independent of the colony nor it can be a member of any other colony but the one in which it developed.
(iii)All eusocial insects exhibit some degree of polymorphism and the different types of individuals in a colony are termed castes. The principal castes are reproductive male (or "king").
►Unit 5: Insect Plant Interaction
Theory of co-evolution, role of allelochemicals in host plant mediation Host-plant selection by phytophagous insects, Major insect pests in paddy
Q. What are allelochemicals?
Communication chemicals (semiochemicals) may function between individuals of the same species (pheromones) or between different species (allelochemicals). Allelochemicals are mostly so-called ‘secondary metabolites’ produced by organisms such as plants, animals, or microorganisms, and which are not needed for basic (primary) metabolism. Rather, they have ecological functions to counterbalance abiotic and biotic stressors. Allelochemicals affect other organisms, either in their physiology, growth, and behavior or life history. Effects range from stimulation to regulation and inhibition. Some allelochemicals are released by one organism and taken up or recognized by another organism. Other allelochemicals are located within the producing organism (i.e., a plant or algae) and affect grazers, herbivores, or pathogens upon damage.
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►Unit 6: Insects as Vectors
Insects as mechanical and biological vectors, Brief discussion on houseflies and mosquitoes as important vectors
Q.Define biological and mechanical vector.
The pathogens (parasites or arboviruses- Arbovirus is a term used to describe a group of viral infections transmitted to humans from a group of insects known as arthropods. There are many strains of arbovirus. The viruses range in severity from no symptoms to mild flu-like symptoms to very severe symptoms) in the infested host, are ingested by the vector where they undergo change and multiplication in order to mature to an infective stage. This usually takes several days before they are capable of being transmitted to a new host (e.g. human malaria parasite).
Mechanical vectors transmit diseases by transporting the causative agent from contaminated material (e.g. faeces) on their feet or mouth parts and then spreading the pathogens or parasites on to human food, drink, faces or eyes. An example of a mechanical vector is a housefly, which lands on cow dung, contaminating its appendages with bacteria from the feces and then lands on food. The pathogen never enters the body of the fly.