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Reasons for the dominance of insects over other animals
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BENEFICIAL AND HARMFUL EFFECTS OF INSECTS
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Learn Introductory Entomology with Rahul
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Families of economic importance

a. Cicadellidae: (Jassidae): Jassids or leaf hoppers

  • Slender, usually tapering, posteriorly, wedge-shaped insects usually rest in a position ready for jumping.
  • When disturbed they leap often several feet.
  • Antennae minute, bristle-like, 3-segmented
  • One or two rows of small spines are present on the hind tibia which is the most important feature.
  • Both young ones and adults have the characteristic habit of running sideward or diagonally.
  • These are very important vectors of viral diseases.
  • The ovipositor is well developed and adopted for lacerating plant tissues for egg laying.
  • Many excrete honeydew through the anus.
  • Forewings are somewhat thickened and often brightly colored
  • Anal veins 1A and 2A do not unite to form a ‘Y’ shaped vein. Eg: Cotton leafhopper –Amrasca biguttula biguttula Paddy leafhopper –Nephotettix virescens – Mango hoppers – Amritodes atkinsoni, Ideoscopus clypealis

 

 

b. Delphacide Plant hoppers

  • This is the largest family among the plant hoppers
  • Most of the species are small with reduced wings
  • The characteristic feature of this family is the presence of a large mobile apical spur on the hind tibiae.
  • Costal cells are absent in the winged forms
  • Alary polymorphism is very common winged, wingless, and brachypterous
  • Forms occur in some species. Eg Brown plant hopper of paddy (BPH)-Nilaparvata lugens
  • White-backed plant hopper on rice (WBPH) –Sogatella furcifera

 

 

c. Aphididae : Aphids or plant lice

  • This family constitutes a large group of small soft-bodied, pear-shaped, fragile phytophagous insects that are frequently found in large numbers sucking the sap from various parts of plants.
  • Antennae fairly long
  • Rostrumis  usually long and well-developed
  • The characteristic feature of aphids is the presence of a pair of cornicles on the dorsal surface of 5th or 6th abdominal segments (It is believed that they produce waxy substances)
  • Winged / Wingless. Alary polymorphism is prevalent. When winged, hind wings are much smaller with fewer veins. At rest, the wings are generally held vertically above the body.
  • Tarsus – 3 segmented with a pair of claws
  • Nine pairs of lateral spiracles present
  • Excrete honeydew through the anus (honeydew consists of excess sap, excess sugars, and waste materials) to which ants are attracted,
  • Associated phenomena in reproduction are parthenogenesis, oviparity, and viviparity.
  • Occurrence of alternation of generations. The sexes are unequally developed, males often being rare. Eg: Myzus persicae – Tobacco aphid, Aphis gossypi – Cotton aphid, Aphis craccivora – Groundnut aphid

 

 

d. Pseudococcidae Mealy bugs

  • Females are wingless, elongated oval with distinct segmentation.
  • Body covered with powdery wax or filamentous waxy secretions.
  • Legs well developed. No instar is sessile. All the insect stages can move because of legs.
  • Eggs are placed in a loose cottony waxy material.
  • Eg: Brinjal mealy bug – Planococcus insolitus Citrus mealybug –Planococcus citri Sugarcane mealy bug –Saccharicoccus saccharin

 

e. Coccidae Scale insects (Soft scales):

  • The females in this group are flattened, elongated oval insects with obscure segmentation and hard smooth exoskeletons or covered with wax or tough scales.
  • They are wingless, legs present or absent and the antennae absent or much reduced.
  • Males are active, 1st pair of wings well developed, 2nd pair reduced to halters.
  • Tarsus if present 1 – segmented with a single claw.
  • Metamorphosis complex. 1st instar nymph has legs & antennae anis d active known as the crawler after 1st molt, becomes sessile a waxy or scale-like covering is secreted.
  • In males, the last instar preceding adult is quiescent and called a pupa. Females have one less instar than males.
  • Oviparous, ovoviviparous
  • Excrete honeydew-like aphids Eg: Pulvinaria side – Guava scale, Icerya purchase – cottony cushion scale

 

f.  Aleurodidae E.g. White flies

  • E.g.: Sugarcane whitefly – Aleurolobus barodensis Cotton whitefly –Bemisia tabaci Castor whitefly –Trialeurodes.
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