What defense doesSchouwia purpurea (Cruciferae) have against the desert locust?

Abstract

A field study of the food eaten by solitary desert locusts was carried out in a winter breeding area in Mauritania. The food eaten, determined by the plant epidermis found in fecal pellets, was compared to the plant's availability in the habitat.Schouwia purpurea, well represented in the diets, was dominant at the study site. Adults had a preference forTribulus terrester. Growth and feeding on these two plants were compared. The high water content ofS. purpurea leaves limited the dry matter eaten and slowed down growth. Glucosinolates were separated and quantified by gas chromatography. There are 132μmol/g dry matter in green leaves. In multiple choice tests, with paper disks, glucosinolate extracts were phagostimulant at a low concentration (21μmol/g dry matter) and repulsive at a higher one (214μmol/ g dry matter). Biting behavior onS. purpurea was recorded and analyzed on video. The importance ofSchouwia purpurea in desert locust habitats and its defenses is discussed.

Evaluation of Food Consumption, Haemolymph Protein Content and Survival of the Grasshopper Euprepocnemis plorans Fed on Clover, Lupine or Horsebean

“…This result agrees with those of several authors (El-Sayed, 1994; Barbosa et al, 1986;Ghaout et al, 1991 andGreenfield et al, 1989). This is probably because of the time and the energy required to degrade alkaloid or HCN, which compromises the digestion of the food, or the chronic toxicity of this allelochemical.…”

Watercress Allelochemical Defends High‐Nitrogen Foliage Against Consumption: Effects on Freshwater Invertebrate Herbivores

“…These stream shredders do rapidly utilize senescent tissues that contain reduced nitrogen levels and reduced defensive compounds. Utilization of senescent tissue in terrestrial systems seems poorly documented (but see Ghaout et al 1991 ). Stream invertebrates appear adapted to dealing with lower quality but lessdefended senescent tissue and terrestrial leaf litter (Webster andBenfield 1986, Newman 1991).…”

Density–dependent aposematism in the desert locust

“…The vegetation in the 3 km 2 region encompassing the centre of the basin is dominated by H. muticus (Culmsee 1997) and many parts of Lac d' Akjoujt are nearly a monoculture of this plant. Given that desert locust populations may eat plants in proportion to their availabilities in the habitat (Ghaout et al 1991), we would expect a large proportion of locusts at this locality to be toxic to vertebrate predators by virtue of their gut contents. This locality is just one example of many di¡erent habitats that constitute a patchwork of desert locust breeding areas throughout the plague recession area.…”

“…Schouwia, for example, contains at least four glucosinolates known to be toxic to vertebrates (Ghaout et al 1991). The extremely conservative palatability assay employed in this study investigated only single-trial learning following the consumption of a single locust.…”

“…All insects were fed on treatment diets for at least 24 h, a duration shown to be su¤cient to confer gut-content-mediated deterrence to predators in S. emarginata (Sword 1998(Sword , 1999. The plants used in this experiment are commonly consumed by preoutbreak, solitarious-phase S. gregaria in Mauritanian plague recession areas (Ghaout 1990;Ghaout et al 1991;Culmsee 1997;Louveaux et al 1998). Plant cuttings were ¢eld collected one day prior to use and refrigerated at 8 8C.…”