Ability of a generalist insect, Schistocerca gregaria, to overcome thioglucoside defense in desert plants: tolerance or adaptation?

Abstract

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.

Surviving the change to warning colouration: density-dependent polyphenism suggests a route for the evolution of aposematism

“…Previous research has shown that solitarious locusts avoid toxic compounds but that gregarious locusts mix chemically defended foods (Despland & Simpson 2005). Locusts appear to incur physiological costs when consuming toxic plants (Mainguet et al 2000). In the field, gregarious locusts exhibit greater dietary breadth than do their solitarious counterparts (El-Bashir 1996); this suggests that the phase differences we demonstrated here in response to hyoscyamine might also apply to a wide range of plant defensive compounds.…”

Purification and characterization of myrosinase from the cabbage aphid (Brevicoryne brassicae), a brassica herbivore

“…The insect myrosinase may give rise to hydrolysis products of lower toxicity. Myrosinase induction in a generalist insect, the desert locust ( Schistocerca gregaria ), was detected when they were fed on Brassicaceae and was suggested to be an adaptation for short‐term tolerance to plant allelochemicals [27]. If the aphid myrosinase is secreted in saliva it may play a role either in host recognition or detoxification [28].…”

Plant Cyanogenesis of Phaseolus lunatus and its Relevance for Herbivore–Plant Interaction: The Importance of Quantitative Data

“…S. gregaria is a polyphagous insect and an economic pest throughout many regions of Africa (Mainguet et al, 2000). Locusts were provided by the Biocenter Grindel and Zoological Museum (University of Hamburg) and were held under the same conditions as the plants.…”