Phase variation in

Locust

PRESENTED BY

Mariama Mili-117474Ariful Islam-117475

Hasan-Al-Razi-117476

WHO ARE LOCUSTS? Locusts are  any of a group of insects belongs

to the family Acrididae of order Orthoptera. Locust are commonly known as short-horned

grasshoppers They Often increase greatly in numbers and

migrate long distances in destructive swarms. They are distributed worldwide.

SOME COMMON LOCUSTS ARE:1. American locust: Schistocerca

americana2. Bombay locust: Nomadacris succincta3. Brown locust: Locustana pardalina4. Desert locust: Schistocerca gregaria5. Italian locust: Calliptamus italicus6. Migratory locust: Locusta migratoria7. Red locust: Nomadacris septemfasciata8. Tree locusts: Anacridium spp. etc.

LOCUSTS

Locusta migratoria (Migratory Locust)

Schistocerca gregaria (Desert Locust)

PHASE VARIATION Phase refers to the different forms of the insects. Uvarov (1921) proposed the “Phase Theory of

Locusts”. According to Uvarov and Zolotaresvsky(1929),

species of Locusts are phase polyphenic, existing in a series of forms.

Sharing the same genotype, individuals may display different phenotypes that incorporate variations in morphology, coloration, reproductive features and significantly in behavior.

Of these two extreme forms or phases are distinct.

These phases are:

1. Solitarious Phase (or phasis solitaria)

2. Gregarious or Migratory phase (or phasis gregaria)

They are often strikingly so distinct that they were earlier regarded as separate species by taxonomists.

Solitarious Phase (or phasis solitaria)

Major Characteristics of Solitary phase are:

Habit: They used to solitarious in habit. Solitarious individuals are repelled from

other locusts.Walk slowly with creeping.Diet restricted.Active mostly at night.

Coloration: Nymphs extremely variable in color-

green, grey, brown etc. Colors usually similar to their normal

environment.

Pronotum: Pronotum of adult is extremely large

and with a mid-longitudinal crest or carina.

There is no constriction.

Wings: Normal

Femur: Hind femur is relatively longer. Tactile hairs are present in large numbers.

Maturity: Attain sexual maturity without a diapause or migratory flight.

Diapause: Eggs develop without a diapause (suspended growth).

Behaviour: Solitary Locust behave like a large grasshopper does little damage.

SOLITARY PHASE

Locusta migratoria Schistocerca gregaria

GREGARIOUS OR MIGRATORY PHASE

Major Characteristics of gregarious phase are:

Habit:Nymphs and adults are definitely

gregarious. They are attracted to conspecifics. Walk rapidly with upright gait. Diet broad. Active mostly at day.

Coloration: Nymphs have a bold coloration.Mainly of black, yellow or orange

irrespective to environment.

Pronotum: Pronotum of adult is shorter, and

saddle-shaped. It is laterally constricted and dorsally

concave. There is no carina.

Wings: Wings conspicuous and proportionately large.

Femur: Hind femur is relatively shorter. Tactile hairs relatively less in femur.

Maturity: Do not attain sexual maturity without a migratory flight.

Diapause: Eggs required a diapause at low temperature for their development.

Behaviour: Gregarious locusts are very active in

swarming.They are destructive to green foliage.

GREGARIOUS PHASE

Locusta migratoria Schistocerca gregaria

Two distinct phases togethershowing the femoral length

PHASIS TRANSIENSA third phase also occurs during transition

of the population from one extreme phase to another.

It is called “Phasis transiens”.

It has no definite form but is represented by a continuous series of transitional or intermediate forms.

When phase transitions occur from solitary to gregarious phase, these forms are termed phasis congrigens.

And when phase transitions occur from gregarious to solitarious these forms are termed as phasis dissocians.

Transitions occur from a solitarious state to a gregarious one & vice versa.

These phase transitions are called solitarization and gregarization.

FACTORS GOVERNING PHASE PRODUCTIONUnder specific conditions in their natural breeding places, the solitary locusts increase in numbers and leading to gregarization.This conditions or factors may be:Environmental:

Meteorological: Temperature Physical: Water

Physiological: Food, fat, protein, hormone

Gregarization dominates when large numbers of locusts gather at the same site.

In tropical regions increase in number of locusts may be provided by dryness or lack of water and in temperate by a high temperature.

When food is scare, the solitary locusts become congregated in restricted areas where water is available to keep vegetation green.

In overcrowded conditions a juvenile is secreted in large quantities by a gland in the head of solitary locusts.

This hormone speeds up reproduction leading to characteristics of gregarious phase.

Locust gregarization may be induced by visual, olfactory, or tactile cues.

In Schistocerca gregaria, the most potent stimulus is tactile like- repetitive stroking of the femora of hind legs, functions as a crowding indicator.

Gregarious locusts sometimes migrate a very long distance in vast swarms which is known as invasion or plague, under the influence of winds.

In sparse surroundings, with the influence of different conditions number of their generations reduce.

When the area affected by swarms become smaller, the locust plague ends and the locusts enter upon the solitary phase.

Cessation of physical contact leads to solitarization.

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