Phase Characteristics of the Desert Locust Schistocerca gregaria ...

Phase Characteristics of the Desert Locust Schistocerca
gregaria Swarming Populations During the 2004 Outbreak in
Tunisia and that of 2005 in Algeria
Mohamed Ammar, Institut National Agronomique de Tunisie, 1082 Tunis, Tunisia,
Amel Ben Hamouda Institut Supérieur Agronomique de Chott Mariem, 4042
Sousse, Tunisia, Sadreddine Kallel, Institut National Agronomique de Tunisie,
1082 Tunis, Tunisia, Khaled Moumène, Institut National de la Protection des
Végétaux, El-Harrach, BP 80 Alger, Alegria, and Mohamed Habib Ben Hamouda
Institut Supérieur Agronomique de Chott Mariem, 4042 Sousse, Tunisia
__________________________________________________________________________
ABSTRACT
Ammar, M., Ben Hamouda, A., Kallel, S., Moumène, K., and Ben Hamouda, M.H. 2009. Phase
characteristics of the desert locust Schistocerca gregaria swarming populations during the 2004
outbreak in Tunisia and that of 2005 in Algeria. Tunisian Journal of Plant Protection 4: 145-156.
Desert locust (Schistocerca gregaria) collected from the district of Tataouine South-East of Tunisia
during spring 2004 outbreak showed 4.6% of solitary form in swarming population. While desert
locusts collected during 2005 from the district of El Oued South-East Algeria showed almost no
solitaries form which is in concert with a higher control gregarization level reached during the second
year of outbreak. These locusts were coming directly from Sahelian countries which were unable to
organize anti-locusts programs, since as was mentioned the FAO that the aerial spraying operations
against locusts was insufficient. The discriminate analysis based on the overlap of these two
populations revealed that they are thoughtlessly conspicuous. Morphometric parameters related to
pronotum length and the head width have contributed the most in the discrimination between these
populations.
Keywords : Algeria, morphometrics, phase characteristics, plagues, Schistocerca gregaria, Tunisia
__________________________________________________________________________
During one century, the continuous the discovery of the gregarizing areas, the
ecological researches development led to understanding of the key factors of plague
the understanding of locust phase activation and finally the adjustment of a
polyphenism or polymorphism preventive control allowing the
phenomenon (a transition from the management of the natural risk performed
solitary phase to the gregarious phase), by the desert locust efficiently breeding
(16).
Corresponding Author: M. Ammar
ammar.med@inat.agrinet.tn
Four concepts are important in the
management of locust’s control:
gregarization interest, gregarigenious
areas, permanent outbreak and plague
Accepted for publication 27 May 2009
area. The gregarization hearths can exist
in the permanent area but only those
situated in the gregarigenious area risk to
Tunisian Journal of Plant Protection 145 Vol. 4, No. 2, 2009

lead an activation of a widespread plague
(8).
The breeding of the desert locust,
Schistocerca gregaria (Orthoptera,
Acrididae), can assume a sporadic
character with alternation of remission
and plagues (16). In the remission
periods, solitary locusts are located in
areas that occupy reduced spaces
compared with the plague period. These
are the gregarigenious areas whose
geographical boundaries are known
relatively inside the area of the locust
permanent habitat.
Lecoq (16) noticed that during the
summer 2003, unusual heavy rainfall in
the Sahel, have improved rapidly
generalizing swarm in the most of Sahara
areas, southwards Mauritania until Sudan.
Swarms and hopper bands have begin to
move southwards Morocco and Algeria
during autumn 2003 and have invaded the
whole the North Africa countries in
spring 2004. Ammar and Ben Hamouda
(2) showed by a morphometrical analysis
of the locusts taken at the time of this
plague in Douiret area of Tataouine, that
South Tunisia risks to constitute a
permanent habitat of S. gregaria.
The comparison of these locusts
with those captured in Snad region
(Gafsa) at the time of 1988 and 1989
plagues revealed that South Tunisia show
in fact some indications in favor of the
probable creation of such a permanent
habitat of the desert locust (3). Permanent
habitats of S. gregaria have already been
revealed in 1976 by Sitouh (17) in the
South Algeria then have been confirmed
in 2005 by Gendouz-Benrima (14) for the
period 1994-2005. Abbassi et al. (1)
showed the quasi permanent presence of
solitary populations of S. gregaria during
the plague 2003-2005 in Morocco.
An extend curative control measures
(terrestrial and aerial) have been
undertaken in the spring of 2004 against
the desert locust but it did not prevent a
return into the Sahelian countries where a
massive plague during the summer
breeding the same year has been preceded
(5, 16).
In this region, the control was
insufficient and the whole North African
country was again invaded in the autumn
2004. A second intensive control
campaign was made during the autumnal
cold weather effect. These conditions
have decreased plagues in the beginning
of 2005 (16). However, in spring 2005,
the winter breeding of S. gregaria has led
to a small infestation by first stage larvae
in some sites in the North-East of the
Algerian Sahara in El Oued area near to
the Tunisian border.
In the present paper, we report the
results of the comparison between the
Algerian and the Tunisian population’s
locust collected in Douiret at the time of
2004 plague in order to provide some
explanations concerning the possibility of
an establishment of a permanent habitat
in Tunisia or in the boundary side
regions.
MATERIALS AND METHODS
Locust collecting and breeding.
First instars larvae (nearly one thousand)
and egg pods (twenty) were collected in
April 2005 in El Oued region, 80 km
North of the village Taleb Elarbi in
Algeria. The locusts were reared in the
laboratory under crowded (gregarious)
conditions according to Ammar et al. (4)
(100 insects/cage, size: 40 x 40 x 40 cm,
12/12 h photoperiod, 28-30°C). Few days
after fledging, locust morphometrics of
both sexes were measured and band eyes
were counted separately (115 females and
128 males in the case of “L1” population,
collected at the stage of first instar larvae;
44 females and 45 males in the case of
“W” population, collected at the stage of
egg pods). These two forms of locusts
Tunisian Journal of Plant Protection 146 Vol. 4, No. 2, 2009

having the same parent descents,
constitute the 2005 population.
Adults (nearly five hundred) were
collected early in the morning in April
2004 from a swarm that was spread out
on cultivated area in “Djessr” facing the
former village of Douiret in the
mountainous region of Tataouine South-
East Tunisia. The majority of locusts was
mature and was reared in the same
gregarious conditions according to
Ammar et al. (4) (252 females and 145
males were measured). These locusts
constitute the 2004 population.
Morphometric measurements.
Digital calipers were used to measure the
following classical morphometric phase
characteristics for adults to determine
E/F, F/C, M/C, H/C, P/C, H/P and LF/LM
ratios (E = Length of fore wing, F =
Length of hind femur, C = Maximum
head width, M = Minimal width of
pronotum, H = Maximum height of
pronotum, P = Maximum length of
pronotum and L = Total length of adult:
LF for female and LM for male). F/C and
E/F ratios were reported on morphometric
chart according to Rungs In Duranton and
Lecoq (9). LF/LM ratio indicates the sex
dimorphism state. It is more pronounced
in gregarious phase to solitarious one (8).
Number of eye stripes. The locust
head are observed under loupe for
counting their eye stripes. Solitary adults
were characterized by 7 eye stripes and
gregarious by 6.
Statistical analyses. Data analysis
was undertaken using the Principal
Component Analysis (PCA) and
Discriminated Analysis (DA) in
STATISTICA® (7, 15).
RESULTS
The carry out of males
morphometrical ratios of the three
populations via Principal Compound
Analysis (PCA) explain 84.92% of the
total variability and excerpt three factorial
axes. The first axis explains 38.82%, the
second one 25.77% and the third one
represents only 20.33% of the total
distribution. Overall, most ratios
contribute highly to PCA with the
exception of M/C and E/F that
participates only by a small fraction of
their variability (Table 1).
With females, PCA explain 88.50%
of variability. It extracts also three
factorial axes which explain 46.65, 25.13
and 16.72% of the total distribution,
respectively.
Like with the male proportion, most
female ratios participates highly at the
total variability with the exception of
M/C and E/F that contributes a little bit to
this variability (Table 1).
Table 1. Representation of male and female morphometrical ratios subjected to PCA
Morphometrical ratio Female R 2 multiple Male R 2 multiple
P/C 0.995408 0.991915
H/C 0.995653 0.990575
M/C 0.399415 0.161373
F/C 0.728884 0.674526
E/F 0.467182 0.596539
H/P 0.995455 0.991913
Tunisian Journal of Plant Protection 147 Vol. 4, No. 2, 2009

Table 2 shows that P/C and F/C
ratios in males are linked and positively
related to the first factorial axis. The
second axis is positively connected to H/P
ratio.
Table 2. The coordinates of males’ morphometrical ratios measured in the plane defined by the different
factors kept by the PCA
Morphometrical ratio Factorial axis 1 Factorial axis 2 Factorial axis 3
P/C 0.763785 -0.441458 0.292053
H/C 0.588058 0.550983 0.516047
M/C 0.490157 -0.210313 0.499424
F/C 0.841349 0.229365 -0.358365
E/F -0.635450 -0.208890 0.676438
H/P -0.219916 0.952451 0.181772
On the other hand, the first factor
extracted by PCA for females was
correlated negatively with P/C, H/C, M/C
and F/C ratios. The second was
negatively associated to H/P ratio as in
the case of males and the third factor was
positively correlated with E/F (Table 3).
The Discriminative Analysis (DA)
executed on P/C, F/C, E/F and H/P ratios
of males explain 100% of the total
variability.
The first discriminating axis
explains the most of the total dispersion
(91.41%). It is explained positively by
H/P and negatively by P/C. It shows a
beginning of separation between 2005 L1
and 2004 populations. The 2005 W
population remains intermediate between
the two others (Fig. 1). The second
discriminating axis explains 8.59% of the
total dispersion. It is positively connected
to F/C ratio.
Table 3. The coordinates of females’ morphometrical ratios measured in the plan defined by the different
factors kept by the PCA
Morphometrical ratios Factorial axis 1 Factorial axis 2 Factorial axis 3
P/C -0.758906 0.448310 0.380057
H/C -0.747789 -0.537274 0.308061
M/C -0.766790 0.091520 0.142372
F/C -0.904421 -0.065588 -0.228003
E/F 0.508106 -0.113662 0.829185
H/P -0.007092 -0.996370 -0.061617
Tunisian Journal of Plant Protection 148 Vol. 4, No. 2, 2009

Axe discriminant 2 (8.59%)
8
7
6
5
4
3
2
1
0
-1
-2
-3
-4
-5
-6
-4 -3 -2 -1 0 1 2 3 4 5 6 7
Axe discriminant 1 (91.41%)
2005 L1
2005 w
Tunisian Journal of Plant Protection 149 Vol. 4, No. 2, 2009
2004
Fig. 1. Distribution of principal variables measured on the three populations of males
harvested in the factorial plan defined by the discriminative analysis.
It seems that P/C and H/P ratios are
the best morphometrical criteria which
distinguish between the three populations.
P/C separates the 2005 L1 population
from the other locusts and H/P
distinguishes the 2004 population from
the others. Discriminating Analysis
(DA) carried out on all morphometrical
ratios of females explains as in males,
100% of the total variability.
Axe discriminant 2 (11.77%)
8
7
6
5
4
3
2
1
0
-1
-2
-3
Axe discriminant 1 (88.23%)
The first discriminative axis
explains the most total dispersion
(88.23%). It is positively linked to H/P
ratio. It shows as in the case of males, a
beginning of discrimination between
2005 L1 and 2004 populations. The 2005
W population remains also intermediary
(Fig. 2). H/P separates the 2004
population from the others.
2005 L1
2005 w
2004
-4
-5 -4 -3 -2 -1 0 1 2 3 4
Fig. 2. Distribution of principal variables measured on the three populations of females
harvested in the factorial plan defined by the discriminative analysis.

Morphologically, the 2005 L1
population is heterogeneous including
99.18% of 6 striped eye locusts and
0.82% of 7 striped eye locusts exclusively
in females (Table 4).
Table 4. Proportions of locusts with 6 and 7 striped eyes in 2005 L1 population
Individuals 6 striped eyes 7 striped eyes Total
Global number 241 2 243
Percentage (%) 99.18 0.82 100
Females number 113 2 115
Percentage % 98.3 1.7 100
Males number 128 0 128
Percentage % 100 0 100
The abacus of Fig. 3 shows that
82.2% of 2005 L1 locusts are transiens
F / C
2,5
2,6
2,7
2,8
2,9
3
3,1
3,2
3,3
3,4
3,5
3,6
3,7
3,8
3,9
4
4,1
4,2
4,3
4,4
Female M ale
TRANSIENS
SOLITARIOUS
congregans with a minority gregarious
shape.
Fig. 3. E/F and F/C scatter plot (abacus) of locusts of 2005 L1 population
The 2005 W population is also
heterogeneous, composed by 97.6% of 6
striped eye locusts and 2.4% of 7 striped
L1 (2005)
GREGARIOUS
4,5
4,6
4,7
E/ F
1,4 1,5 1,6 1,7 1,8 1,9 2 2,1 2,2 2,3 2,4 2,5 2,6 2,7 2,8 2,9
eyes (Table 5). As in the case of 2005 L1
population, the proportion of 7 striped eye
males was nil.
Tunisian Journal of Plant Protection 150 Vol. 4, No. 2, 2009

Table 5. Proportion of locusts with 6 and 7 striped eyes in 2005 W population
Individuals 6 striped eyes 7 striped eyes Total
Global number 87 2 89
Percentage (%) 97.6 2.4 100
Females number 42 2 44
Percentage % 95.5 4.5 100
Males number 45 0 45
Percentage % 100 0 100
The abacus of Fig. 4 shows that
77.5% of 2005 W locusts are transiens
congregans with a minority gregarious
shape.
The gregarization is more
accentuated in population collected at the
first instar larvae (2005 L1) than the one
collected at the egg stage (2005 W)
showing a gregarizing effect of density of
the first instar larvae. Morphologically,
the 2004 population contains 4.63% of 7
striped eye locusts (Table 6). This
w (2005)
F/C
2,5
2,6
2,7
2,8
2,9
3
3,1
3,2
3,3
Female Male
GREGARIOUS
3,4
3,5
3,6
3,7
3,8
3,9
4
4,1
4,2
4,3
TRANSIENS
4,4
4,5
4,6
4,7
SOLITARIOUS
1,4 1,5 1,6 1,7 1,8 1,9 2
E/F
2,1 2,2 2,3 2,4 2,5 2,6 2,7 2,8 2,9
proportion is higher than those from the
two populations of 2005 which are
composed of 2.4% of W population
(Table 5) and 0.82% of L1 population
(Table 4).
Contrary to males of the two
populations of 2005 which are all with 6
striped eyes (Tables 4, 5), 2.76% of those
of 2004 population are with 7 striped eyes
(Table 6). This rate increases to 5.4% in
the case of females.
Fig. 4. E/F and F/C scatter plots (abacus) of locusts of 2005 W population
Tunisian Journal of Plant Protection 151 Vol. 4, No. 2, 2009

Table 6. Proportion of locusts with 6 and 7 striped eyes in 2004 population
Individuals 6 striped eye 7 striped eye Total
Global number 474 23 497
Percentage (%) 95.37 4.63 100
Females number 333 19 352
Percentage % 94.6 5.4 100
Males number 141 4 145
Percentage % 97.24 2.76 100
E/F and F/C scatter plot of locusts of
population 2004 show that 73% of locusts
are transiens congregans with a minority
gregarious shape (Fig. 5). Locusts
F/C
2,5
2,6
2,7
2,8
2,9
3
3,1
3,2
3,3
3,4
3,5
3,6
3,7
3,8
3,9
4
4,1
4,2
4,3
4,4
4,5
4,6
4,7
Female Male
TRANSIENS
SOLITARIOUS
collected in Douiret at the time of 2004
plague are less gregarious than those
collected at the time of 2005 plague in El
Oued.
Tunisian Journal of Plant Protection 152 Vol. 4, No. 2, 2009
2004
GREGARIOUS
1,4 1,5 1,6 1,7 1,8 1,9 2 2,1 2,2 2,3 2,4 2,5 2,6 2,7 2,8 2,9
Fig. 5. E/F and F/C scatter plots (abacus) of adults of 2004 population
E/F

The mean of total length of males
and females of 2004 population is more
important than those of the two
Fig. 7 shows that LF/LM ratio is
different at the three populations. The
LF/LM
Length (mm)
Fig. 6 . Mean of total length of locusts of the three populations
1,15
1,14
1,13
1,12
1,11
1,1
1,09
1,08
1,07
76
74
72
70
68
66
64
62
60
58
Female Male
2005 L1 2005 w 2004
Population
2005 L1 2005 w 2004
Population
Fig. 7. LF/LM ratios of the three populations of locusts
populations of 2005 that are similar (Fig.
6).
2005 L1 population has the most elevated
ratio.
Tunisian Journal of Plant Protection 153 Vol. 4, No. 2, 2009

DISCUSSION
The statistical analysis of the
morphological characters of the three
analyzed desert locust populations shows
that H/P is the best morphometrical
criteria which distinguish the phase state
of females and P/C and H/P are the best
for males.
The density of the hatchlings has a
gregarizing effect. At the time of the
collect, they were grouped by thousands
safe from the plant tufts, whereas rearing
conditions shift them toward a solitary
phase. The W population had hatched in
the laboratory. Hatchlings were kept by
hundred per cage (40 x 40 x 40 cm) in
crowd rearing. In these conditions, the
gregarization was declined in relation to
L1 population to which the crowding of
hatchling was stronger in their natural
habitat and the effect of density has
reinforced the gregarious instinct (6). The
percentage of 7 striped eye solitarious
larvae was only 0.82% in crowding
conditions. If these larvae have been let
rage in their natural habitat, these
proportions would have been nil.
Locusts of the two populations of
2005 outbreak show more physiological
and morphometrical gregarious characters
than those of the population of 2004 up
search. Indeed, the 2005 outbreak that did
not reach practically Tunisia (13) does
not come from the same gregarizing areas
like the 2004 plague (16). This latter
crossed Mauritania, Morocco, Algeria
and Tunisia (12) while the first went by
the circuit of the Sahel countries, and
Algerian Sahara, Algerian South-East
(near the Tunisian border) (11).
At the time of the first circuit,
locusts were exhibited at several
treatments carried out by invaded
countries. The recessions and
miscellanies with the autochthonous
populations took place probably in these
countries in favor of an increase of the
proportions of solitary locusts in swarms.
However, during the second circuit,
Sahelian countries have not financed
enough the locust control and let rage the
proliferations of the gregarious locust
swarms (16). In the Southeast of Algeria,
the solitary locust proportions in 2005
outbreak were quasi nil with regard to a
stronger gregarization.
The control undertook in the North
Africa countries at the 2004 spring did
not prevent a massive plague of the Sahel
during the summer. In this region, control
organized via the belated helps of the
donors was insufficient and the North
Africa countries were invaded again in
the autumn 2004. A new control
campaign was driven in 2005. According
to Lecoq (16), it will have been necessary
to spend more than 100 million dollars,
whereas donors hesitated beginning 2003
to invest 4 million dollars for a program
of preventive control on 4 years. It was
necessary to be organized better in the
future to prevent similar mistakes.
__________________________________________________________________________
RESUME
Ammar M., Ben Hamouda A., Kallel S., Moumène K. et Ben Hamouda M.H. 2009.
Caractéristiques phasaires des populations du criquet pèlerin Schistocerca gregaria au cours de
l’invasion de 2004 en Tunisie et celle de 2005 en Algérie. Tunisian Journal of Plant Protection 4 :
145-156.
Les criquets prélevés en 2004 dans la région de Tataouine au Sud-Est de la Tunisie présentent 4 à 5%
de solitaires dans les essaims. Par contre, les criquets prélevés en 2005 de la région d’El Oued du Sud-
Est de l’Algérie montrent des proportions quasi-nulles de solitaires en faveur d’une grégarisation plus
Tunisian Journal of Plant Protection 154 Vol. 4, No. 2, 2009

forte. Ces criquets provenaient directement des pays du Sahel qui, selon les rapports FAO, ont été
démunis de moyens financiers pour organiser des programmes de lutte anti-acridienne. L’analyse
discriminante prouve, par le chevauchement de ces populations, qu’elles se distinguent légèrement. Les
rapports morphométriques afférents au pronotum et à la largeur de la tête, ont le plus contribué à
distinguer entre ces populations.
Mots clés : Algérie, caractéristiques phasaires, invasions, morphométrie, Schistocerca gregaria,
Tunisie
__________________________________________________________________________
ﻣ
ﻊﻣ راأ ﺎﺧ . 2009 . ةدﺣ ﺑ ﻟا ﻣو ﻣﻣ ﻟﺎﺧو لﻼﻗ ﻳﻟا رﺻو ةدﺣ ﺑ لﺎﻣأو ﻣ ،رﺎﻋ
.2005 ﺳ اﻟاو 2004 ﺳ ﻧﻟ
ﺣﺎﺟا
ءﺎﺛأ Schistocerca gregaria يواﻟا داﻟا باﺳأ
Tunisian Journal of Plant Protection 4: 145-156.
% 4.6 ﻧ 2004 ﻊﺑر ﻲﻓ ﻧﺗ ﻲﻗﺷ بﺟ ﻲﻓ ﻳوﺎﺗ
ﻣ حﺎﺟا يﻟا يواﻟا داﻟا ﻣ تﺎﻋ تﻬأ
اﻟا ﻲﻗﺷ بﺟ يداﻟا ﻣ حﺎﺟا يﻟا داﻟا ﻣ تﺎﻋ تﻬأ ﺣ ﻲﻓ بﻟا ﻊﻣ ﻲﻓ ﻳداﻧا تﻻﺎﺣ
مَِﻗ ﻟ . حﺎﺟﻻا ﻣ ﻧﺎﻟا ﻟا ﻲﻓ ﻰﻋأ ﻊﺗ ىﻣ ﻊﻣ ﻟذ ﻓاﻳو . ﻳداﻧا تﻻﺎﻟ اﺟ ًﺎﻧ 2005 ﺳ
ﻣ ﺗ ﻬأ . داﻟ وﺎﻟا ﻣاﻟا ﺗ ﻰﻋ ةردﺎﻗ ﺗ ﻟ ﻲﻟا ةﺷﺎﻣ ﻲﻳﻓا ﺣﺎﻟا ناﺑ ﻣ داﻟا اه
لﺑ ﺗﻟا ﻳﻣﻓرﻟا
ﻳﺎﻌﻟا ﻬﺳأو ،ﻳﻣ ﻏ ﺎﻬﻧأ
ﻰﻋ داﻟا ﻣ ﻌﻟا ﻳه ﺧاﺗ ﻰﻋ
. ﻌﻟا ﺑ ﻳﻟا ﻲﻓ آأ سأﻟا ضﻋو مﺗﻧوﻟا
Schistocerca gregaria ،ﻳﻣﻓرﻣ تﺎﺳﺎﻗ ،راﻷا ﺎﺧ ،ﻧﺗ ،ﺑوأ ،اﻟا : ﺣﺎﻣ تﺎآ
__________________________________________________________________________
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