Female pheromonal chorusing in an arctiid moth, Utetheisa ornatrix

Abstract

We report an unusual case of communal sexual display in the arctiid moth Utetheisa ornatrix that we designate ''female pheromonal chorusing.'' As in most moths, female U. ornatrix release a long-distance sexual advertisement pheromone during a nightly activity period. We arranged U. ornatrix females in 2 types of signaling conditions: grouped and solitary. When the females were grouped with neighboring signaling females (grouped), they initiated pheromone release sooner, continued release with less interruption and over a longer total period, and performed the release with faster abdominal pumping than observed in isolated females (solitary). This differs from the usual form of sexual communication in moths: female (chemical) signalers, male receivers, and a general lack of interaction among females. At mating, male U. ornatrix transfer a large spermatophore that may enhance female reproductive success and which represents either mating effort or paternal investment. This action results in an extended postmating male refractory period leading to a female-biased operational sex ratio. We argue that this biased sex ratio generates intrasexual competition among females, to which they respond by elevating signaling effort such that the likelihood of at least matching their neighbors' signals is increased. In the field, U. ornatrix are clustered around patches of host plants, and we also explore the possibility that pheromonal chorusing is driven by cooperation among groups of related-or nonrelated-females.

Conspecific females promote calling behavior in the noctuid moth, Pseudaletia adultera

“…Females of the arctiid moth U. ornatrix form aggregations of calling individuals and adults of both sexes are attracted to the pheromone source in a dose‐dependent manner, thus as a large chorus will attract more receptive males, individual females could increase their probability of mating by joining other calling females (Lim & Greenfield, , ). Pseudaletia adultera females do not start calling for several days post‐emergence, a trait that has been associated with migratory species (McNeil, ).…”

“…As most of the noctuid species exhibiting female autodetection are considered migrants, it is possible that females of migratory species, when arriving in a new habitat where the density of males is unknown, use a form of chorusing as a strategy to attract males to a site with a high concentration of pheromones. However, if this is a strategy used, there may still be female‐female competition for certain positions within the chorus, as this would influence access to approaching males, as noted in the case of U. ornatrix (Lim & Greenfield, , ).…”

Mating failures as a consequence of sexual selection on females

“…Note that the competition for mates definition used here contrasts with that of recent reviews that dilute the concept of sexual selection on females to include any sort of social competition to reproduce (Clutton-Brock, 2007Shuker, 2010). This is either a form of passive attraction (Arak, 1988) of males to the most prominent signal of a group of non-interacting females (the usual case in moths; Lim & Greenfield, 2008) or a more active form of choice of certain females by males (probably more likely when females increase signalling effort in response to nearby competitorse.g., the arctiid moth Utetheisa ornatrix L., in which females appear to be competing for nutritious male spermatophores; Lim & Greenfield, 2007). Most of the hypotheses can be related to some form of sexual selection on females.…”

Geographic and Temporal Variation in Moth Chemical Communication

“…Many female moths can perceive their own pheromone as well as pheromone compounds of other species (e.g., Ljungberg et al 1993; Schneider et al 1998; Groot et al 2005b; Hillier et al 2006). Also, most female moths produce their sex pheromone de novo every night (e.g., Raina 1989; Rafaeli 2002; Jurenka 2003), and can modulate the time and temporal patterning of pheromone release (calling) in relation to environmental conditions (Schal and Cardé 1985; Lim et al 2007) and presence of conspecifics (Conner et al 1980; Lim and Greenfield 2007, 2008). Hence, it may be possible that females can vary their biosynthesized as well as emitted pheromone blend to some extent depending on the prevailing olfactory cues in their habitat.…”