Decision making for food choice by grasshoppers (Orthoptera: Acrididae): Comparison between a specialist species on a shrubby legume and three graminivorous species
2003
Picaud, F. | Bonnet, E. | Gloaguen, V. | Petit, D.
Dwarf gorse bush (Ulex minor) heathlands in Limousin, France, are ecological islands often separated by tens of kilometers of grasslands and hedges, where several species of grasshoppers belonging to the genus Chorthippus (Acrididae: Gomphocerinae) coexist. Chorthippus binotatus (Charpentier) feeds only on Ulex minor; nymphs feed exclusively on leaves whereas adults become florivorous at the end of the season. The other species studied (C. biguttulus (L.), C. albomarginatus (De Geer), and C. parallelus (Zetterstedt)) are all graminivorous. The importance of sugars, nitrogen content, sparteine (a quinolizidine alkaloid), and plant architecture in food selection was investigated. Chorthippus binotatus is sensitive to sucrose and fructose, consistent with the high sugar content of Ulex minor flowers. Experiments with grass coated with sparteine showed that this molecule associated with sucrose is a phagostimulant for this grasshopper. Different behavioral responses of graminivorous species are observed with sparteine alone, but never phagostimulation. We compared the response times corresponding to decision-making between the different species toward several components involved in food selection. The food choice toward host plant and sugars is as quick for C. binotatus as for the two graminivorous species (C. parallelus and C. albomarginatus), whereas C. biguttulus is slower and exhibits atypical reactions. Chorthippus binotatus can feed on Poaceae, but with more time spent, leading to an increasing predation risk. This situation is a limitation toward dispersal between different heathlands (patchy habitats).
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