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Desert locusts, Schistocerca gregaria (Forskal) (Orthoptera, Acrididae), are generalist herbivores that, in the Sahara desert, may at times feed only on Schouwia purpurea (Forskal) (Brassicaceae), that is 10 times richer in thioglucosides than currently observed in other crucifers (> 100 mu moles/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 mu moles/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 beta-glucosidases decreased in the midgut. The long-term exposure to the Schouwia diet affected activities of beta-glucosidases and beta-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.