Wing pattern polyphenism in two behavioural forms of Ochrogaster lunifer (Lepidoptera: Notodontidae)

Polyphenisms are common among butterflies (most pronounced in females) but less well documented among moths despite providing insights into the ecology and behaviour of species in which they occur. I studied polyphenism of forewing pattern (maculation) in Ochrogaster lunifer Herrich-Schaffer as it relates to the distribution and nesting behaviour of caterpillars. In south-eastern Australia, ground-nesting (g-n) and canopy-nesting (c-n) forms are the most commonly observed. Nests keep g-n larvae warmer but c-n larvae cooler during the day when they are not foraging; they also provide protection from lower ambient humidity during the day. Females of both behavioural forms have the simplest wing pattern comprising a single spot of silvery white (unpigmented) scales below the areole and delimited by veins M-1 and M-3. The female pattern occurred most frequently in males from g-n populations which are dominant at higher latitudes. Males from c-n populations, which are dominant at lower latitudes, commonly have wings with one or more streaks of unpigmented scales (reduced melanisation), but some can have the female pattern. Some g-n males can exhibit the streaked pattern if caterpillars develop at lower latitudes. Streaked males weigh less and live longer than spotted males. The weight of gravid females of the g-n form was positively correlated with latitude (Bergmann cline) while those of gravid females of the c-n form were negatively correlated with latitude (converse Bergmann cline). Females of both forms are capital breeders (oviposit once and die), but g-n females lay greater numbers of smaller eggs than c-n females. Although the two behavioural forms do not overlap substantially, adults interbreed under lab conditions and can produce fertile eggs. Significant reaction norms between latitude and streaking indicate that male wing pattern is a shared polyphenism while female wing pattern is a conserved, static trait. Nest temperature and group size probably have interactive effects on the expression of male wing polyphenism and female body size but understanding them will require rearing larvae on different hosts under artificial temperature, humidity and lighting regimes.