In order to specify our knowledge on this diapause (induction, elimination, survival capacities of the eggs) we carried out an experiment in semi-natural conditions.
Egg-pods, collected at the end of the rainy season, from mid-August to the end of
September (period for diapause induction), were placed in incubation and humidified on various dates from November to August of the following year.
Design and production: CIRAD - March 2009
Egg survival strategies of the Senegalese
grasshopper during the dry season in the
African Sahel.
French Agricultural Research Centre for International Development CIRADT
he Senegalese grasshopper
is an important pest for the
Sahelian crops in Africa.
It develops 3 generations per
year and undergoes an
embryonic diapause during the long dry
season that can last up to 7-8 months.
Maiga I.H. 1, Lecoq M. 2, Morand S. 3
1 Direction de la Protection
des Végétaux, Niamey, Niger
2 CIRAD Acridologie,
F-34398 Montpellier, France
3 CNRS Institut des Sciences
de l'Evolution,
F-34095 Montpellier, France
Results show that the survival strategy
of the Senegalese grasshopper during the
dry season is more complex than previously supposed and does not rely merely on a
simple embryonic diapause. The strategy combines several components :
✔
The embryonic diapause during the dry season allows a global adaptation to the regular seasonal variation in rainfall.The other components constitute the adaptations of the species to the various risks related to different irregularities in rainfall pattern especially in the Sahel.
✔
The high number of hatchlings within a short period of time at the end of the rainy season, for egg-pods laid before the end of August and without diapause, allowed an adaptation to the frequently abrupt end of rainfall.✔
The possibility of embryonic quiescence can allow the eggs to survive for up to one year without diapause and constitutes an adaptation to a reduced rainy season (end before diapause induction).✔
Lastly, the staggering of hatchlings for diapausing eggs over a lengthy period at the beginning of the rainy season, constitutes an adaptation to the progressive set in of the rains and tofrequent long interspersed periods of drought following the first rains that trigger hatchlings.
Method
Results
Acknowledgements
– This work was carried out
within the framework of a collaborative program between the Plant Protection
Direction in Niger, the Regional centre
AGRHYMET of the CILSS (Permanent Interstate Committee for Drought Control in the Sahel), the Biological Control Centre for Africa of the
International Institute for Tropical Agriculture (IITA), and the Danish National Environmental Research
Institute (DNERI) through the regional program for IPM control of grasshoppers into the
Sahel (PRéLISS) funded by the Danish Cooperation
(DANIDA). Niger
© J. Mestre,1988
(top: dry season ;
bottom : rainy season)
Adult of Oedaleus senegalensis Krauss, 1877
Hatchlings of eggs laid in August (without diapause)
and humificated during the dry season between 1st
November and 1st March.
Hatchlings of eggs laid late September (with
diapause) and humificated during the dry season
between 1st November and 1st August of the
following year. Typical environment
of the Senegalese
grasshopper in Niger (Zinder area)
The Senegalese grasshopper (1, female; 2, male).
N o vemb er 0 10 20 30 40 50 60 70 80 90 1 61 121 181 241 301 361 421
Days after h u m id ificatio n
0 10 20 30 40 50 60 70 80 90 Decemb er 0 5 10 15 20 25 30 35 1 61 121 181 241 301 361 421
D ays after h u mid ificatio n
0 10 20 30 40 50 60 70 80 90 Jan u ar y 0 2 4 6 8 10 12 14 16 18 20 1 61 121 181 241 301 361
D ays after h umid ificatio n
0 10 20 30 40 50 60 70 Feb ru ary 0 5 10 15 20 25 1 61 121 181 241 301 361
D ays after h u mid ificatio n
0 10 20 30 40 50 60 70 M arch 0 5 10 15 20 25 1 61 121 181 241 301
D ays after h u mid ificatio n
0 10 20 30 40 50 60 70 80 Number of hat chlings Number of hat chlings Number of hat chlings Number of hat chlings Number of hat chlings C umulativ e number C umulativ e number C umulativ e number C umulativ e number C umulativ e number November December January February March N o vem b er 0 2 4 6 8 10 12 14 16 18 1 61 121 181 241 301 361 421 Days after h u m id ificatio n
0 20 40 60 80 100 120 D ecemb er 0 1 2 3 4 5 6 7 8 9 1 61 121 181 241 301 361 421 D ays after h u mid ificatio n
0 10 20 30 40 50 60 70 80 90 100 Jan u ary 0 2 4 6 8 10 12 14 16 18 1 61 121 181 241 301 361 D ays after h u mid ificatio n
0 10 20 30 40 50 60 70 80 90 Feb ru ar y 0 2 4 6 8 10 12 1 61 121 181 241 301 361
D ays after h umid ification
0 20 40 60 80 100 120 140 160 M arch 0 5 10 15 20 25 30 1 61 121 181 241 301
D ays after h u mid ificatio n
0 20 40 60 80 100 120 140 160 Apr il 0 2 4 6 8 10 12 1 61 121 181 241 301 D ays after h u mid ificatio n
0 10 20 30 40 50 60 70 M ay 0 2 4 6 8 10 12 14 16 18 20 1 61 121 181 241
Days after h u mid ificatio n
0 20 40 60 80 100 120 Ju ne 0 10 20 30 40 50 60 1 61 121 181 241
D ays after h u mid ificatio n
0 20 40 60 80 100 120 140 160 180 Ju ly 0 20 40 60 80 100 120 140 1 31 61 91 121 151 181 211
D ays after h u mid ificatio n
0 50 100 150 200 250 Au g u st 0 10 20 30 40 50 60 70 80 1 31 61 91 121 151 181
D ays after h u m id ificatio n
0 50 100 150 200 250 Number of hat chlings Number of hat chlings Number of hat chlings Number of hat chlings Number of hat chlings Number of hat chlings Number of hat chlings Number of hat chlings Number of hat chlings Number of hat chlings C umulativ e number C umulativ e number C umulativ e number C umulativ e number C umulativ e number C umulativ e number C umulativ e number C umulativ e number C umulativ e number C umulativ e number November December January February March April May June July August © Maiga Idrissa, DPV , Niger
© Maiga Idrissa, DPV, Niger
Finaly, the Senegalese grasshopper developed a bet-hedging strategy which does not seem besides to be too much
“expensive” because nonassociated with a reduction in the
hatchling rate. Such a strategy fits particularly well to the sahelian environment and makes it possible to maximize the chances of
