Individual Pheromone Signature in Males: Prerequisite for Pheromone-Mediated Mate Assessment in the Central American Locust, Schistocerca Piceifrons

Abstract

Living in high-density groups of animals has advantages and disadvantages for mating. The advantage of facilitated mate finding is compromised by difficulties in protecting a suitable partner from competitors. Thus, males regularly are faced with increased competition for sperm, and females with harassment by males at high population densities. To cope with these problems, mating tactics and mate choice mechanisms have to be adjusted. An adaptation to gregarious condition observed in locusts includes the use of male-emitted pheromones. Males of the Central American locust, Schistocerca piceifrons, release sex-specific volatiles, which were identified as phenethyl alcohol (synonym: phenyl-ethyl-alcohol, 2-phenyl-1-ethanol, 2-phenylethanol, PEA), (Z)-3-nonen-1-ol (3-Nol), and (Z)-2-octen-1-ol (2-Ool). The emission of the two major compounds, PEA and 3-Nol, was restricted to crowded conditions. Furthermore, the release of both volatiles was coupled to males reaching sexual maturity, indicating a function in reproductive behavior. However, neither the single substances nor their mixtures were attractive or repellent to the locusts. Instead, females prefer the sperm of high pheromone-emitting males to fertilize their ova. In this way, the male-specific volatiles act as mate assessment pheromones utilized in a context of cryptic female choice. This function is well supported by the highly variable but individual-specific emission rates of the three compounds. Schistocerca piceifrons males release a virtually unique personal pheromone signature, a prerequisite for mate assessment pheromones.

One hundred years of phase polymorphism research in locusts

“…Detailed analyses by Seidelmann et al (2000; and Seidelmann and Ferenz (2002) showed that this substance is released from wings and legs and can be considered a mating regulator or "courtship inhibiting pheromone" as it prevents additional mating between females and other males. In a different species Schistocerca piceifrons, Stahr and Seidelmann (2016) showed that females preferentially mate with males emitting a high concentration of the volatiles phenylethyl alcohol (PEA) and (Z)-3-nonen-1-ol (3-NOL) and this also affected successful hatching of their larvae. Recently, a careful study of Guo et al (2020) identified 4-vinylanisole or 4-methoxystyrene as an aggregation pheromone in Locusta migratoria.…”