Phase Theory
By Alan
Phase theory was proposed by B.P. Uvarov in1921. Phase theory explain the
finding that two previously distinct species of locusts, Locusta migratoria and L. danica,
were actually different forms - gregarious and solitary - of the same species (Anonim,
2007; Chapman, 1990).
When locust present at low densities, the individuals are solitarious, as locust
increase, they cluster into dense group and they become gregarious. There is transition
between solitarious phase to gregarious (vice versa) an it is called as transient phase
(Symmons and Cressman, 2001).The gregarious phase was the well known locust, while
solitary phase was the form in which locust survived during non-swarming periods.
The difference between gregarious and solitary locust are in their morphology,
physiology and behaviour. This phase of locust depend largely on the physical and social
environment experienced by individual insect during its lifespan (Chapman, 1976)
Locust phase is belongs to of density-dependent phenotypic that interpreted as an
adaption to heterogeneous environmental conditions brought on by high population
density (Song, 2005)
Characteristic of phases
Nymph
Pronotum
Solitary
Uniform coloration, most
often green or straw
coloured depending on the
humidity and the colour of
their background
Presence high crest
Size
Bigger than gregarious one
Instar (in Nomadacris)
Seven or eight instar
Ration of head with and Greater than gregarious
hind femur length (F/C)
Hatchling First instar
Not heavy as gregarious
Agregation
Active
Number of egg laid
Gregarious
Present striking pattern of
black marking on a
background of yellow
Sadle-shaped and without a
marked crest
Smaller than solitary
Six instar
Less than solitary
Dark in colour and heavy,
have higher water content
and more fat, haemolymph
amino acid and ascorbic
acid
Having no tendency to Aggregate strongly even in
aggregate
a uniform environment
Less active
Much more active
Laid more eggs per pod Laid fewer pod than
than crowded female
isolated females
Reference
Anonym. 2007. aab news. Newsletter of the association of applied biologist. Issue 63
http://qs.aqvs.co.uk/aab/images/Indesign%2063%20Final.pdf
Chapman, K.F.1976. A Biology of Locust. Edward Arnold Publisher. London
Chapman, Reginald Frederick, Anthony Joern.1990. Biology of Grasshoppers.WileyIEEE.563p
Song, Hojun. 2005. Phylogenetic perspective on the evolution of locust phase
polyphenism. Journal of Orthoptera research. 14(2):235-245.
Symmons,
P.M.; K.Cressman.2001. Desert Locust Guidlines, Biology and
Behaviour.Food and Agriculture Organization of the United Nations.Rome.
Phase Theory
By Arya
Phase theory was proposed by Uvarov in 1921. This theory explains that locust can suffer
a very surprising reversible transformation (Buj Buj 1995). The idea of the phase theory
shows that locusts of certain grasshoppers may change their way of life.; when the
condition is crowded, they live as swarming locust (gregarious phase) and at the other
times they live as solitary grasshoppers (solitarious phase) (ALRC 1966). Between the
solitarious phase and gregarious phase, there are two intermediate phase or transient
form, called congregation phase if the change is moving from solitairiuos to gregarious
and segregating phase if moving in reverse direction (ALRC 1966).
The phases are different in behavior, appearance (shape and color) and Physiology. The
character of appearance of the phases are considered as morphometrical character and
may be used to differentiate the phases. This character include the shape of the
pronotum, the ratio of the length of the wingcase (elytron) to the hind femur, and color
(Baron 1972, ALRC 1966). In locust, solitarious phase is green and gregarious phases is
orange and black. The ratio of the length of elytron to the hind femur for adult solitarious
phase is 2.05 and for the gregarious phase is 2.65 (ALRC 1966). Unfortunately,
morphometric characteristic may be influenced by the environmental condition during the
life. Because of that a note of warning should be given (ALRC 1966).
Besides morphometrical character, solitarious phase and gregarious phase may be
different in their physiological and behavioral character. In locust, gregarious phase
produce hatchling first instar nymph which is dark in color and heavier than the
solitarious one. Gragarious nymph also aggregate strongly and much more active than the
solitarious nymph (Chapman 1976).
There are three processed involved in the phase transformation. These processed are
concentration, multiplication , and gregarization, the transformation of a solitariuos locust
to the gregarious one (Symmons and Cressman 2001, Chapman 1967). Concentration is
the process of bringing together of locust by environmental factor (Chapman 1976). Once
the process of concentration has started, it will be reinforced by the insect learning to
aggregate. After concentration, locusts will enter the multiplication process to produce
more individuals. If numbers of individuals is low, they will not develop full gregarious
behavior of coloration, but they will continue the process in the next generation
(Chapman 1967).
Phase theory give a new approach of control strategy. In order to prevent the attack of the
locust, it should be stopped in its non-swarming stage, that is, in its outbreak area. This
means that We have to be able to found its outbreak area first (Baron, 1972).
References
Anti Locust Research Center (ALRC). 1966. The locust handbook. Anti Locust Research
Center, London.
Baron, S. 1972. The Desert locust. Eyre Methuen, London.
Buj Buj, A. International experimentation and control of the locust plague African in the
first half of the 20th century. 1995. Yvon Chatelin y Christophe Bonneuil (eds): Nature et
environnement. Vol. 3, Les sciences hors d'Occident au XXe siècle, París, ORSTOM Éd.,
1995, pp. 93-105.
Chapman, R.F. 1967. A biology of locust. Edward Arnold, London.
Symmons, P.N. and K. Cressman. 2001. Desert locust guidelines, biology and behavior.
Food and Agricultural Organization, Rome.
PHASE THEORY
By Boy
Phase Theory is a theory proposed by Sir Baron Uvarov (1921) in order to explain
the fact that sometimes there were swarms of locusts and sometimes there were not (The
Anti-Locust Research Centre, 1966). In this theory, Dr. Uvarov concluded that the lives
of all locusts, extremely can be divided into two phases; Solitarious Phase and Gregarious
Phase (Baron, 1972). The intermediate stages may be referred to as transient forms, and
they may be divided into a congregating phase; if the change is moving from solitarious
to gregarious; and a segregating phase if moving in the reverse direction (The AntiLocust Research Centre, 1966).
The phases are different in behavior and in appearances (overall sizes, the relative
sizes of different parts of the body such as the wings and hind femora, color), for
example, in Locusta, solitarious hoppers are green and gregarious hoppers are orange
and black. In the adult, the shape of pronotum and the relative length of the hind femur
are very different (Chapman, 1976; The Anti-Locust Research Centre, 1966).
The differences in behavior can be clearly seen in the desert locust. In solitarious
phase, these species never form groups (or form only small temporary groups), they do
not move more than a few yards per day and adults fly by day only when disturbed, their
life-time are longer (for adults), their development generally slower, and also the number
of eggs per pod is commonly 120 and time interval between laying of egg pods generally
longer (The Anti-Locust Research Centre, 1966). While in Gregarious phase, these
species form dense groups of hoppers and swarms of adults, they move as much as one
mile per day and adults fly spontaneously (mainly by day), their life-time are shorter (for
adults), their development generally quicker, and also the number of eggs per pod is
commonly 60 and time interval between laying of eggs pods generally shorter (The AntiLocust Research Centre, 1966). Comparing between the two characteristics showed us
that locusts in gregarious phase are designed by Allah to prepared them to survive in
migrating from one area to another area in a long distances.
The phase of locust depends largely on the physical and social environment
experienced by the individual insect during its life span. For instance, it is clearly shown
by the fact that solitarious and gregarious insects can be reared from a single egg-pod
simply by keeping them in isolation or in a crowd (Chapman, 1976). Egg which is kept in
isolated condition will produce solitarious locust while egg kept in a crowded condition
will produce gregarious locust. Another factor that also influence the phase of locust is
the treatment of the parents (Chapman, 1976). For example, the offspring of locust
which is kept in isolation for several generations show a reduced tendency to march, even
when crowded, than do the offspring of crowded parents (Chapman, 1976).
The development of a fully swarming population from a solitarious population to
gregarious will depend on three interrelated processes: multiplication, concentration, and
gregarisation, and all of this processes are also depend on the environmental condition
(Chapman, 1976). At the first time, locusts will increase the number of individuals of the
population. The next step is concentration process where the solitarious locusts will
concentrate themselves into one area and make a group on it. There are many
environmental factors to make this step happens, one of them is temperature condition.
When temperature become high, the locusts will move to another area that can become a
shelter from the sun, By this condition, the process of concentration has been started
where the locusts start to make a contact among them in a group. This condition influence
locust to learn about aggregation; the coming together of locusts due to their gregarious
tendencies. Having once been forced into a group, the locusts will tend to aggregate
spontaneously (Chapman, 1976). And finally, if the numbers are high, they will develop
full gregarious behavior or coloration while if the numbers are low, the will not enter to
gregarisation step but the process will be continued in the next generation (Chapman,
1976).
REFERENCES:
Baron, S. 1972. The Desert Locust. Eyre Methuen: London. □
Chapman, R.F. 1976. A Biology of Locusts. Edward Arnold Publisher.□
The Anti-Locust Research Centre. 1966. The Locust Handbook. The Anti-Locust
Research Centre Publication: London.
Phase theory
By Haris
The phase theory was put forward in 1921 by Uvarov in order to account for the fact
that some times there were swarms of locust and sometimes there were not. The idea was
this, Locust are certain kinds of grasshopper which can change their way of life, some
time they life in crowds as swarming locust and at other times they lives as solitary
grasshopper. There are other kinds of grasshopper which when crowded do not change
into locust (Anti Locust research center, 1966).
Generally the phase theory give the explanation that during the life time, locust have
phase which each other different. Generally Locust have four phase, gregarious,
segregating, solitaries , and transient. But the other adding with some phase.
Solitarious is Phase when individuals live mostly separate from each other or ntn
crowded . Gregarious is Phase when large numbers of individuals gather together or
crowded. Transiens is Intermediate phase when locusts are grouping and starting to act as
a single mass and are either changing from solitarious to gregarious (gregarization) or
from gregarious to solitarious (dissociation). Congregans is Part of the transiens phase
during which locusts are congregating and are in transition from the solitarious to the
gregarious phase. Often used for nymphs. Dissocians is Part of the transiens phase during
which locusts are in transition from the gregarious to the solitarious phase. Often used for
nymphs. Solitaricolour is Showing types of colour associated with solitarious behaviour.
Gregaricolour is Showing types of colour associated with gregarious behavior
(FAO,2008; Barras, anon).
In general the solitarious nymphs of all the locust species are characterized by uniform
coloration, most often green or straw coloured depending on the humidity and the colour
of the background on which they were reared. Gregarious nymphs on the other hand are
distinguished by striking pattern of black marking on a background of the yellow, in the
case of Schistocera and Nomadacris , or orange on the case of Locusta. In the adults the
sharp distinction in colour between solitarious and gregarious forms is lost, although
solitarious adult Locusta do tend to remain green ( Chapman, 1976). In the end, the
differences in Locust not only in the behavior but in color and even, although to a less
certain extent, in the locust’s morphometrics – the measurements of its physical form
(Baron, 1872).
References :
- Horn , David J.1976. Biology of insect. W.B. Saunders Company. Philadelphia,
USA.
-
Elzinga, Richard J. 1978. Fundamentals of Entomology. Prentice Hall Inc. New
Jersey.
-
Romoser, Wiliam S. 1981.Science of Entomology, second ed. Macmillan
Publishing Co.Inc. New York
-
Gullan, P.J and Cranston, P.S.1995. The insect : an outline of entomology.
Chapman and Hall. London
-
Schowalter, Timothy D.2006. Insect ecology. Academic press. London.
May, Robert M and Mc Lean, Angela R.2007. Theoretical ecology principles and
applications. Oxford University Press New York.
Anon.http://en.wikipedia.org/w/index.php?title=Island_biogeography&actio
n=edit
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-
-
□Baron, Stanley. 1972. The Locust. Eyre Mathuen, Great Britain.
□Chapman, R. F. 1976. A Biology of Locust. Edward Arnold Publ.
□Barras, Robert.1974. The locust. Barry Shurlock press
□The anti locust research centre. 1966. The locust handbook. Anti locust research
centre, London.
-
.FAO.
2008. FAO Desert Locust Guidelines – latest
http://www.fao.org/ag/locusts/en/publicat/gl/gl/index.html
edition
(2001-2003).
Phase theory for locust
By Koko
A phase theory has been developed to account for the sporadic appearance and
disappearance of locust swarms. According to the theory a plague species has two phases:
one solitary and the other gregarious. The phases can be distinguished by differences in
coloration, form, physiology, and behavior. A solitary phase nymph, for example, adjusts
its coloration to match that of its surroundings. A gregarious phase nymph, on the other
hand, has black and yellow or orange coloration in a fixed pattern, gathers in large
groups, has high metabolic and oxygen intake rates, and is active and nervous.
The solitary phase is the normal state of the species, with the gregarious phase
being a physiological response to violent fluctuations in the environment. A gregarious
phase locust is restless and irritable, and it flies spontaneously on warm, dry days when
its body temperature is high. The muscular activity of flight further raises its temperature.
A swarm ceases flying only when environmental conditions change.
The important biological differences between solitaries and gregarious locust are
in their physiology and behavior and also an important different between solitaries and
gregarious adults in the number of eggs they lay (Chapman, 1976). Barrass, 1980, say
that crowding of the hoppers affect the color, structure and behavior and the ensuing
adults. In nature, locusts are much active when crowded together than when they are
alone and they reach maturity more quickly.

reference
Barrass., R. 1980. The Locust A Laboratory Guide. Heinemann Educational
Books. London.

Chapman., R.F. 1976. Biology of Locust. The Institute of Biology. London.
http://www.britannica.com/EBchecked/topic/345932/locust