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Nouakchott, Mauritania

Maeno K.,National Institute of Agro biological science at Ohwashi NIASO | Maeno K.,National Locust Control Center | Tanaka S.,National Institute of Agro biological science at Ohwashi NIASO
Physiological Entomology | Year: 2012

Crowding causes many organisms to express phenotypic plasticity in various traits. Phase polyphenism in desert locusts represents one extreme example in which a solitary form (solitarious phase) turns into a gregarious form (gregarious phase) in response to crowding. Conspicuous differences in body size and colour occur even in hatchlings. The phase-specific differences in hatchling characteristics are caused by the tactile stimuli perceived by the antennae of their mother. However, the nature of the tactile stimuli and the mechanism by which the perceived stimuli are processed as a gregarizing signal remain unknown. To explore this problem, the antennae of solitarious adult females of the desert locust Schistocerca gregaria are touched with the bodies of conspecific locusts at different physiological stages and those of other species. The results suggest that a cuticular chemical factor at a specific developmental stage of conspecific locusts causes the solitarious females to produce large eggs that give rise to black hatchlings characteristic of gregarious forms (progeny gregarization), and that this or a similar compound occurs in other acridids, crickets and cockroaches but not in beetles. The involvement of a chemical substance is also supported by hexane extracts of cuticular surfaces of locusts that induce the same effects. Interestingly, crowding induces such gregarizing effects only when the female receives the appropriate stimulus in the presence of light. Solitarious female S. gregaria with their head capsule coated with phosphorescent paint exhibit progeny gregarization in response to crowding and light pulses in darkness, whereas those treated in the same way without light pulses fail to do so. © 2011 The Authors. Physiological Entomology © 2011 The Royal Entomological Society.

Tanaka S.,Japan National Institute of Agrobiological Science | Maeno K.,Japan National Institute of Agrobiological Science | Ould Mohamed S.,National Locust Control Center | Ould Ely S.,National Locust Control Center | Babah Ebbe M.A.,National Locust Control Center
Applied Entomology and Zoology | Year: 2010

A short excursion was made to the western part of Mauritania to investigate increasing populations of the desert locust, Schistocerca gregaria, in October 2009. The size of locust populations observed ranged from <1 to >20 individuals per 25m2. Adults from low- and high-density populations were similar in morphometric ratios of F/C and E/F (F, hind femur length; C, maximum head width; E, fore wing length) and the ratios were similar to those reported for solitarious forms. However, locusts from high-density populations were mostly yellow, while those from low-density populations were brown or whitish. The former were observed ovipositing in groups. These observations, together with the fact that some of the females from high-density populations had ovarian eggs significantly larger than those found in females from low-density populations, suggested that gregarization might have occurred after adult emergence. Aggregations of nymphs were observed at many sites, and nymphs with black patterns typically observed in transient and gregarious populations were found together with those with solitarious body coloration, i.e. green or brown. A prompt action of locust control by National Locust Control Center was likely to have contributed to prevent further upsurges in the locust populations in the following seasons.

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