Pheromone production, male abundance, body size, and the evolution of elaborate antennae in moths

Abstract

The males of some species of moths possess elaborate feathery antennae. It is widely assumed that these striking morphological features have evolved through selection for males with greater sensitivity to the female sex pheromone, which is typically released in minute quantities. Accordingly, females of species in which males have elaborate (i.e., pectinate, bipectinate, or quadripectinate) antennae should produce the smallest quantities of pheromone. Alternatively, antennal morphology may be associated with the chemical properties of the pheromone components, with elaborate antennae being associated with pheromones that diffuse more quickly (i.e., have lower molecular weights). Finally, antennal morphology may reflect population structure, with low population abundance selecting for higher sensitivity and hence more elaborate antennae. We conducted a phylogenetic comparative analysis to test these explanations using pheromone chemical data and trapping data for 152 moth species. Elaborate antennae are associated with larger body size (longer forewing length), which suggests a biological cost that smaller moth species cannot bear. Body size is also positively correlated with pheromone titre and negatively correlated with population abundance (estimated by male abundance). Removing the effects of body size revealed no association between the shape of antennae and either pheromone titre, male abundance, or mean molecular weight of the pheromone components. However, among species with elaborate antennae, longer antennae were typically associated with lower male abundances and pheromone compounds with lower molecular weight, suggesting that male distribution and a more rapidly diffusing female sex pheromone may influence the size but not the general shape of male antennae.

The Evolution of Body Size, Antennal Size and Host Use in Parasitoid Wasps (Hymenoptera: Chalcidoidea): A Phylogenetic Comparative Analysis

“…In insects generally, larger antennae are typically associated with greater numbers of olfactory receptors [14] resulting in greater sensitivity and acuity to chemical signals [60,61]. Since chemical signals are the primary means by which chalcidoid wasps locate their hosts, including hemipterans [62,63], this may indicate some feature of hemipteran chemical communication, such as reduced amount of chemicals produced, or more volatile chemicals produced [64], that selects for greater sensitivity and hence antennal size in the parasitoid. In particular, parasitoids of true bugs rely on long-range kairomones from nontarget instars (most are egg parasitoids) and host-plant synomones induced by host feeding [65].…”

Investment in sensory structures, testis size, and wing coloration in males of a diurnal moth species: trade‐offs or correlated growth?

“…Larger, more elaborate male antennae are associated with species of moths that exist at low population densities, suggesting that sexual selection favors traits facilitating the rapid detection of mates that are highly dispersed and difficult to locate (Symonds et al. 2012). In diurnal moths, mate location by males may also involve visual searching (Charlton and Cardé 1990; Sarto i Monteys et al.…”

Earwigs (Labidura riparia) mimic rotting-flesh odor to deceive vertebrate predators

“…Moth species with greater body size are associated with higher pheromone titers in females, suggesting costs that smaller-bodied species are less able to maintain (Symonds et al 2011). A positive relationship between body weight and semiochemical amounts was found in females of cotton aphid Aphis gossypii, plant bug Lygus hesperus, moth Neoleucinodes elegantalis, and wasp parasitoid Leiophron uniformis, suggesting metabolic costs that were difficult to achieve by smaller individuals (Byers 2005(Byers , 2006Jaffe et al 2007;Byers and Levi-Zada 2011).…”