No Indication of Background Color Matching in a Population of the Brown-Green Polymorphic Admirable Grasshopper ( Syrbula admirabilis )

In color polymorphic insects, individuals may track available habitats and select those that better match their color phenotype. This so-called habitat choice mechanism can balance the chances of survival between morphs, equalizing fitness, which can contribute to the long-term maintenance of color polymorphism in a population. We used a population of the brown-green polymorphic admirable grasshopper ( Syrbula admirabilis ) to test whether color morphs differ in their preferences when exposed individually to two contrasting background colors (brown vs. green) in an experimental arena. We obtained data on how the locations (background choices) and frass (number of pellets, as a proxy for the relative use of each color area) of each grasshopper were distributed between the brown and green sections to estimate their background color preferences. We did not detect differences in background color preferences between color morphs in either (molting or non-molting) nymphs or (unmanipulated or color-manipulated) imagoes, rejecting the occurrence of habitat-choice mechanisms. We attribute this lack of habitat selectivity to the widespread presence of a disruptive body pattern on the back of nymphs and imagoes that blurs individuals’ shape and may provide similar crypsis on any background environment. As an alternative hypothesis, we suggest that color polymorphism might be maintained because it impairs prey detection by predators that form search images when hunting, which would reduce overall predation rates in admirable grasshopper populations.