Nyctinastic leaf folding mimic reduces herbivory by Chromacris trogon grasshoppers (Orthoptera:Romaleidae)

Abstract

Arachis pintoi (Fabaceae) is a common relative of the cultivated peanut, and folds its four leaflets up to look like one at night. The adaptive significance of this behavior (foliar nyctinasty) is unknown. To test the hypothesis that leaflet folding alone can deter herbivores, a leaf preference experiment was performed on Chromacris trogon grasshoppers. Small oval cutouts were made from leaves of the grasshoppers preferred food source, Iochroma arborescens (Solanaceae), and were combined with small pieces of tape and dry grass to construct artificial leaves resembling the day and night form of A. pintoi. In the experiment, groups of three grasshoppers were starved for 24 hours and then placed in petri dishes containing one closed and one open artificial leaf. After 30 six-hour trials, the average herbivory of open leaves was 12.3%, while closed leaves was 5.2% (p = 0.00145), indicating a significant preference for open leaves. This suggests that the folded configuration of A. pintoi leaves can be a defense against herbivory.