Pigmentation Measurements

Frozen insects were photographed using Panasonic DMC-FZ5 digital camera. Using ImageJ software (U.S. National Institutes of Health, Bethesda, Maryland), we quantified the total surface area of each individual’s carapace by outlining the dorsal surface, excluding the soft wings. We measured the amount of black pigmentation on each carapace by summing the surface area of all black regions (Fig. 1) and used these values to calculate the ratio of black to yellow pigmentation. This ratio served as a quantitative measure of cuticle melanization independent of size. Although the non-black pigmentation of adult harlequin bugs can range from a yellow to red hue, a visual examination of our colony showed that adults displayed a consistent yellow color, and thus, we did not quantify total reflectance. Although we acknowledge that this is a possible source of pigmentation variation that we did not account for, we believe that hue variation in this colony was negligible relative to the variation in overall albedo. Nymphs that did not survive to adulthood and adults with malformations were excluded from our analysis.

Variation in melanization observed in adult M. histrionica. (a) Newly molted adults lack a fully melanized carapace, though the pattern that will develop is discernible. The full black pigmentation will develop within the first few hours post-molt (Supplementary Material). (b) An individual with a relatively high degree of melanization (black:yellow = 3.55), and (c) an individual with a relatively low degree of melanization (black:yellow = 0.613). Outlines in (b) and (c) indicate regions of the hard carapace pattern that contributed to measurements of ‘black’ pigmentation.