Red locusts frequently cause crop damage in Madagascar. This problem has worsened in recent years, likely due to the intensive deforestation that is under way. Little is known about this locust In Madagascar, contrary to continental Africa. Several studies have been carried out in southwestern Madagascar, where locust damage is regularly reported, with the aim of determining the cause of recent outbreaks and improving control strategies-they included surveys of rural inhabitants and an analysis of over 25 years of archival data at the Centre national antiacridien (Malagasy locust control centre). The results revealed several zones between which the red locust-a single-generation species that undergoes imaginal diapause in the dry season-seasonally migrates on a northeast to southwest track, and vice versa, depending on rainfall and wind patterns. The migration dynamics and interannual variations associated with rainfall irregularity certainly partially account for the recurrence of red locust outbreaks in Madagascar.Résumé. Ecologie et migrations du criquet nomade, Nomadacris septemfasciata (Serville) (Orthoptera : Acrididae) dans sa phase solitaire dans le sud-ouest de Madagascar. Le Criquet nomade est un problème récurent de protection des cultures à Madagascar. Il s'est aggravé récemment, très certainement en partie sous l'influence d'une déforestation intensive. Contrairement au continent africain, cette espèce est peu connue dans la Grande Ile. Afin d'établir les causes des récentes pullulations et d'améliorer la stratégie de lutte, plusieurs études ont été entreprises dans le sud-ouest du pays où des dégâts sont régulièrement rapportés : en particulier des enquêtes en milieu rural et l'analyse de 25 années de données d'archives du Centre national antiacridien. On ainsi a pu mettre en évidence plusieurs zones entre lesquelles le Criquet nomade, espèce monovoltine à diapause imaginale de saison sèche, effectue des migrations saisonnières, du nord-est vers le sud-ouest et inversement, en fonction des pluies et de l'alternance des vents. La dynamique de ces déplacements et leurs particularités interannuelles liées à l'irrégularité des pluies sont certainement une cause importante des pullulations de cette espèce à Madagascar.

Little is known about phase polymorphism in the red locust, Nomadacris septemfasciata (Serville) in Madagascar, despite its economic importance. Only solitary and transiens forms have been reported from the island earlier, but not the gregarious form. Important recent outbreaks have allowed for the studying of the phase polymorphism under experimental and field conditions. Morphometric differences (pronotum size and shape, and F/C and E/F ratios) were noted among hoppers and adults caged for several generations and at various densities, in a field laboratory. These criteria were later used to study adults collected in different areas between 1996 and 2002, from populations with various densities (, 1000 to . 25,000 imagos/ha). Morphometric measurements revealed that gregarious red locust populations have existed naturally in Madagascar and that these were erroneously classified as transiens forms. The upper threshold density for the solitary phase was estimated at 5000 adults/ha; beyond this limit, locusts develop either into transiens or into highly gregarious forms. The southern part of the island, known as a red locust outbreak area, has harboured gregarious phases despite previous reports that prevailing ecological conditions are not suitable for its complete phase transformation. Deforestation in the northern part of the island has probably led to new favourable biotopes for serious outbreaks and gregarious populations development.phase grégaire existe à Madagascar et que tous les individus grégaires ont été depais longtemps considérés abusivement comme des transiens. Le seuil maximal des populations solitaires a été estimé à 5000 imagos/ha, au-delà duquel commence la transformation phasaire. Le sud de l'île a abrité depuis longtemps des populations grégaires quoique, les conditions écologiques dans cette zone Acrididae étaient traditionnellement considérées comme impropres à favoriser la grégarisation et les pullulations du criquet. Dans le Nord, des pullulations sont aussi récemment survenues probablement suite à la déforestation qui a permis l'apparition de nouveaux biotopes très favorables à la grégarisation.

Pigmentation of the Red locust hopper, Nomadacris septemfasciata Serv., was studied in natural conditions in Madagascar in relation to population density. More than one thousand hoppers were collected and described according to a semiquantitative method. A typology is proposed, strictly reflecting the increase in population densities. This correctly translated the progressive evolution of a solitary state into a gregarious state, while passing through several intermediate transiens stages. According to their density, hopper populations consist of a mixture, in various proportions, of several pigment types. The gregarization threshold is estimated at 100,000 hoppers/ha. A slight black spot on the hind femur is the first sign of gregarization. These results should improve the reliability of the information collected by the Malagasy National locust centre when surveying this major pest. They question the rapidity of the gregarization process in natural conditions as well as the stimuli involved.

Red locusts, Nomadacris septemfasciata (Serville, 1838), frequently damage crops in Madagascar, and this problem has worsened in recent years, likely because of intensive deforestation. Little is known about this pest in Madagascar, contrary to southern Africa. We studied the reproductive maturation in relation to climate and vegetation in northwestern Madagascar. Our results show that adults overwinter, with females undergoing a 6- to 7-mo-long reproductive diapause, followed by a variable quiescent period of 2-4 wk, depending on ecological conditions, during which vitellogenesis is delayed,. Food availability in response to good rains at the end of spring seems to be the key factor for triggering the end of quiescence and the beginning of rapid vitellogenesis (=reproductive maturation). Hind wing color in adults changes throughout the year and was correlated with age and reproductive state in females and seasonal climate change.

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