Desert locusts, Schistocerca gregaria (Forskål) (Orthoptera, Acrididae), are generalist herbivores that, in the Sahara desert, may at times feed only on Schouwia purpurea (Forskål) (Brassicaceae), that is 10 times richer in thioglucosides than currently observed in other crucifers (>100 μmoles/g d.w.). Thioglucosides, when ingested, release products that are usually toxic to generalist insects. We studied the short‐term (8 days) and long‐term (21–26 days) consequences of a Schouwia‐only diet on the digestion of these insects. The response was compared to the effects of a diet of Brassica oleracea, a crucifer well consumed in laboratory rearing conditions (7 μmoles/g glucosinolates d.w.). We found that the production of a myrosinase was induced in the midgut as early as 8 days following exposure to glucosinolates. No negative short‐term effects were observed on the growth of the insect, but the activity of β‐glucosidases decreased in the midgut. The long‐term exposure to the Schouwia diet affected activities of β‐glucosidases and β‐galactosidases, growth and assimilation efficiency. The limited adaptation of the desert locust to plant glucosides is compensated by an ability to tolerate high concentrations of allelochemicals for a short period.

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.

The present study describes the potential role of the insect Scapteriscus didactylus in egg mortality in nests of the leatherback sea turtle Dermochelys coriacea found in the Amana natural reserve in French Guiana. Out of the 3 mole cricket species (Scapteriscus didactylus [Latreille], S. borellii Giglio-Tos, Neocurtilla hexadactyla Perty) observed in the natural reserve, only S. didactylus was encountered on the sandy beaches where 4 species of marine turtles nest. Controlled experiments, in which S. didactylus individuals of various age classes and leatherbacks eggs were placed together, revealed that only the last instar nymphs of S. didactylus preyed on the eggs, making a characteristic round hole underneath the eggs in the sand. This same distinctive damage to eggs was seen in natural leatherback nests at Awala-Yalimapo beach in the Amana natural reserve. The predation affected on average 18% (range: 3.6 to 40.0%) of all yolked eggs in the nests. Juvenile S. didactylus were present on the beach throughout the nesting season of leatherback turtles, while adult S. didactylus were observed when the nest density on the beach reached its seasonal maximum at the end of July.

The glucosinolates of a Saharan crucifer Schouwia purpurea (Forskfil) (Brassicaceae) were determined by liquid chromatography. Two of these glucosinolates and sinigrin were tested for their deterrent effect on Schistocerca gregaria (Forskfil) (Orthoptera: Acrididae). Glucobrassicin, three indolyls and epigoitrin were synthesized for this purpose. Epiprogoitrin was extracted from Crambe seeds. Choice tests on artificial substrate compared feeding responses to glucosinolates and to related breakdown products released when the plant is eaten. Breakdown products were more efficient in deterring the generalist locust than were glucosinolates. Two patterns of dose responses were recorded: glucosidic compounds deterred or stimulated feeding, depending on the concentration tested; aglycones did not stimulate feeding at any concentration. Allyl isothiocyanate, a volatile compound, was a 100-fold higher deterrent than its substrate (sinigrin).