Lec. no. 2

7/21/2019 Lec. no. 2

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Lecture No. 2

Insect dominance-structural, morphological and physiological factors

responsible for dominance

Animal kingdom is found to be the biggest kingdom in the world. In which 2/3(75%) of animal kingdom is insects onl.

Measures of dominance

!ore number of s"ecies.

Insect e#istence was recorded $& million ears ago.

'ccu"ing 2/3 of animal "o"ulation.

arge number of indiiduals in a single s"ecies* e.g. ocust swarm com"rising

of +&,

number of indiiduals- occu"ing large area.

reat ariet of habitats.

ong geological histor.

Reasons for dominance (11 points

here are seeral structural- mor"hological and "hsiological factors

res"onsible for insect dominance. he are*

1. !apacity for flight

Insects "ossess two "airs of wings which enable to coloni0e on new source of

food and facilitates ra"id esca"e from unfaourable conditions their enemies. ocusts

and some milk weed butterflies migrated between the countries. 1ling ca"acit of

some of the insects are-

onebee , km/h

oer fl 4 +2 km/h

awk moth 4 +7 km/h

ragonfl 4 36 km/h

utterfl 4 ,& km/h

2. More adaptability or uni"ersality

Insects are found to e#ist in all known enironments from the e8uator to the

"oles. he found to feed on ariet of food materials.

#g. Insects lie on egetation 4 9hto"hagous insects

iing on dead and decaing organic matter 4 :a"ro"hagous insects

1eeding on animals 4 ;arniorous

ie in "etroleum well 4 Psilopa petroli

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ie in great salt lake 4 Ephydra fl

ie in snow 4 :now flea (;ollembola)

ie in desert 4 esert locust

Insects of social nature (lie in colonies) 4 ermites and ants

$. %maller si&e!a<orit of insects are small in their si0e conferring "hsiological and

ecological adantages. he si0e ranges from &.2 mm (small "arasitic was"- =orth

American beetle Nanosella fungi) to 36 cm (stick insect- ra0ilian moth Erebus

agripinna- giant silk moth- atlas moth and goliath beetle). :mall si0e enables the

"resence of higher number of insects in a unit area.

>g. !ore than +&& a"hids can be seen on lab lab "od.

'. resence of e)os*eleton

Insect bod is coered with an outer cuticle called e#oskeleton which is made

u" of a cuticular "rotein called !hitin. his is light in weight and gies strength-

rigidit and fle#ibilit to the insect bod. >#oskeleton also "reents water loss from

the bod (desiccation) and "rotects the internal organs from an "hsical and

mechanical damage (click beetles and <ewel beetles cannot be killed easil).

+. Resistance to desiccation

Insects minimise the water loss from their bod surface through "reention of

water loss (wa# laer of e"icuticle- closable s"iracles- egg shell)- conseration of

water (ca"able of utili0ing metabolic water- resor"tion of water from fecal matter b

rectum- use less 8uantit of water to remoe the nitrogenous waste).

. racheal system of respiration

Air tubes or tracheal sstem ensures direct transfer of ade8uate o#gen to

eer cell of the bod. :"iracles through their closing mechanism admit air and

restrict water loss.

. Reproducti"e beha"iour

a. ?e"roductie "otential of insect is high.

#g. >gg laing ca"acit (fecundit) of 8ueen termite is 6&&& 7&&&

eggs "er da for +5 long ears and 8ueen bee las 2&&&3&&& eggs "er da.

b. :hort deelo"ment "eriod.

#g. ;orn a"hid "roduces +6 nm"hs "er female which reaches the

adulthood within +6 das.

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;otton cushion scale Icerya purchasi has fecundit of 5&&+$&& eggs

"er female and there will be 3$ broods "er ear.

c. 9resence of s"ecial t"es of re"roduction other than oi"arit and ii"arit

like 9olembron (deelo"ment of man indiiduals from a single egg. >g.

9arasitic was")- 9arthenogenesis (re"roduction without fertili0ation. >g.

a"hids) and 9aedogenesis (re"roduction b immature stages. >g. ;ertain flies).

/. resence of complete metamorphosis

!ore than 2 "er cent of insects undergo com"lete metamor"hosis

(holometabolous insects) with four stages (egg- lara- "u"a and adult). As the laral

and adult food sources are different- com"etition for food is less.

0. resence of defence mechanisms

different defense mechanisms- insects esca"e from the enemies to increase

their surial rate.

a. eha"ioural mechanism 4 some insects if touched will act as the are dead

called feign to death mechanism or thanatosis. >g. ?ed flour beetle.

b. structural mechanism 4 "resence of hardened forewing (eltra). >g.

eetles.

c. !olorational mechanism 4 some insects attain same colour of

enironment. >g. :tick insect.

d. chemical mechanism 4 some insects hae "oisonous stings and in<ect

enom. >g. ees and was"s.

1. 3igher mobility and stability

9resence of three "airs of legs and two "airs of wings are er much useful for

mobilit of insects. Insects uses 3 legs at a time during locomotion- while the

remaining 3 legs are static- which gies greater stabilit.

11. !ommunication

;ommunication behaiour is much deelo"ed in insects. 9heromones are used

for se#ual attraction- alarm- aggregation- caste determination etc. ees

communication during foraging (bee dance) is uni8ue. Allelochemicals "roide

information about host "lant- "re- natural enemies and oi"osition site etc.

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@>:I'=:

+. Bhich is the dominant grou" of organism in animal kingdomC

2. Bhich is the biggest insect b lengthC

3. Bhich is the smallest insect b lengthC

$. Brite on the reasons of insect dominance.

5.

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Lec. no. 2