Butterfly Egg Mimicry

Abstract

For many years, the best known case of defensive animal mimicry by plants that was also tested experimentally was of butterfly egg mimicry. It has been proposed to reduce egg laying by Heliconius butterflies on Passiflora species, but to also operate for other plant and butterfly taxa (Benson et al. 1975; Gilbert 1980, 1982; Shapiro 1981a, b; Williams and Gilbert 1981). It was a development of the emerging understanding that butterflies can assess the presence of butterfly eggs on plants (e.g., Prokopy 1972; Rothschild and Schoonhoven 1977; Rausher 1979). Benson et al. (1975) studied interactions between Heliconiini butterflies and many plant species belonging to several genera of the Passifloraceae, showing several types of egg mimicry by tendril meristems, bulbous yellow petiolar glands, yellow deciduous flower buds, and yellow nectar glands on the abaxial leaf side (Fig. 55.1), and suggested that all these are aimed at defending from butterfly egg laying. Williams and Gilbert (1981) experimentally showed that Heliconius butterflies are less likely to oviposit on Passiflora cyanea and P. oerstedii host plants that have mimetic egglike structures. Shapiro (1981a) showed that egg mimics of Streptanthus breweri (Brassicaceae) in the shape of pigmented callosities on its upper leaves deter oviposition by Pieris sisymbrii. Removal of these egg mimics in the field significantly increased the probability of oviposition. Shapiro (1981b) showed that the same is true in another member of the genus S. glandulosus. Gilbert (1982) in his well-illustrated review of the issue in the genus Passiflora explained the multitudes of defense from Heliconius caterpillars, which include bodyguards in the shape of ants attracted by extrafloral nectar secration, changing leaf shape with time, mimicking non-host plants when the plants are juvenile, and having hooked trichomes that capture caterpillars. These tested cases of visual animal mimicry by plants as defense from herbivory provide a strong support for other phenomena of visual defensive animal mimicry by plants. I think that some plant taxa by colorful spots along leaf margins (Fig. 55.2) may mimic aposematic spines towards vertebrate herbivores and insect eggs towards arthropods. In this case, they may by this egg mimicry also attract predators and parasitoids.