Some facts about insects:
- Insects are the most prevalent features of our environment.
- Everybody has to deal with insects. Some find then fascinating while others may see them as a hindrance
- It is the abundance (large number) of these insects which make them important and attract our attention
- The abundance of insects depend upon their inherited traits and environmental factors. Since both these factors are dynamic, insect number is also dynamic
Beneficial effects:
- Industrial importance
- Pollination
- Entomophagous insects
- Nutrient cycling
- Human food
- Aesthetic value
- Study tools
- Insect collection can be adopted as a hobby
- Scavengers
Insects of industrial importance:
- Honeybees: Honey, beeswax, bee venom, royal jelly, propolis and pollination
- Silk worm: Silk
- Lac insect: Shellac
Pollination: Transfer of pollens from anthers to stigma
- Self pollination
- Cross pollination
Reasons for cross pollination:
- Male and female parts at different flowers at same plant or different plants
- Maturity of male and female parts do not coincide
- Structure of flower
Insect Pollinators:
- Honey bees (75-80%), butterflies, flies, beetles, thrips, etc.
Entomophagous insects:
Predators:
- Coccinellids (Coleoptera): e.g. Coccinella septempunctata, Hippodamia variegata, cheilomenes sexmacula, etc.
- Syrphids (Diptera): e.g. Episyrphus balteatus, Metasyrphus corrollae, Scaeva pyrastri, Ischiodon scutalaris, Metasyrphus conferator, etc.
- Chrysopids (Neuroptera): e.g. Chrysoperla zastrowi sillemi, Mallada sp
- Predatory bugs (Heteroptera): e.g. Anthocoris minki, Orius spp, Blaptostethes pallescens
- Preying mantids (Dictyoptera): e.g. Statilia maculata
- Predatory wasps (Hymenoptera): e.g. Vespa spp
Parasitoids:
- Egg parasitoid: e.g. Trichogramma spp.
- Larval parasitoid: e.g. Apanteles spp. Cotesia spp., Bracon sp.
- Egg-larval parasitoid: e.g. Chelonus blackburni,
- Larval-pupal parasitoid: e.g. Ceromosia auricaudata (Diptera: Tachinidae)
- Pupal parasitoid
- Adult parasitoid:
- Nutrient cycling:
- Detritus and dung feeders e.g. Termites, dung beetles etc.
- Human food:
- Over 500 spp. like crickets, grasshoppers, beetles, caterpillars, termites are used as food by human beings in different parts of the world.
Aesthetic value:
- Brightly coloured butterflies and beetles are used for various decorations
Harmful effects
- Greater importance of insects lies in their harmful effects than their beneficial effects.
- Only a few species (0.01%) are harmful and attain the status of pest.
- Higher the status of species as pest more important the species is.
- Crop losses by the insect pests vary from 10-40 per cent depending upon the crop and environment.
- Annual monetary losses of Rs. 60,000 crores despite using more than 4,800 m tons of technical grade pesticides.
Different pesticides used:
- Insecticides – 60%
- Fungicides – 19%
- Herbicides – 16%
- Bio pesticides- 2%
- Others – 3%
Harmful effects caused:
- Destruction and spoilage of food (Both fresh and in storage) including forests
- Cutworms (reduce the no of plants in the field)
- Fruit borer, fruit flies and other direct pests
- Leaf eaters
- Sap suckers
- Stem borers
- Chlorophyll eaters
- Root feeders
- Gall formers
- Damage to goods: leather, paper, textile, timber etc. (beetles cockroaches, silverfishes, termites, timber borers, etc)
- Vectors for impossible to control viral diseases in plants e.g. some aphids, whiteflies, thrips etc.
- Cause diseases in human beings and live stock (malaria, dengue etc.)
- Venoms, allergies, rustication etc. (ants, wasps, bees, hairy caterpillars, etc.)
- Nuisance : Bush flies and ants
- Phobias: such as hairy caterpillars
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