No honesty in warning signals across life stages in an aposematic bug

Theory predicts that warning signals should exhibit low variation to increase learning efficiency in predators. Many species, however, exhibit variation in warning colours within species and even within populations. An understudied example of within species variation is that between life stages, where animals change warning colouration throughout ontogeny. Understanding how warning signals change throughout life can help us identify the different ecological pressures that affect the evolution of warning signals. We used the Australasian cotton harlequin bug (Tectocoris diophthalmus) to explore how adults and nymphs differ in their defensive secretions and colouration. We performed spectrophotometric colour measurements and toxicity bioassays. Our results show, overall, no consistent association between colour and toxicity within species. There was no clear pattern for females and nymphs. Adult males, however, present the highest contrast against backgrounds, highest internal contrast, and highest toxicity. There was no association between colour and toxicity within males, nymphs or females. Our results suggest weak signal honesty in warning signals across life stages and sexes, and demonstrate that variation in colour within species is not necessarily linked to changes in toxicity.