Comparative study of courtship in twelve phycitine moths (Lepidoptera: Pyralidae)

Abstract

The courtship behavior of 12 phycitine moths (Lepidoptera: Pyralidae) was studied using frame-by-frame analysis of video recordings. Behavioral transitions during courtship were quantified for selected species and kinematic diagrams of courtship sequences were constructed. Interspecific similarities in courtship behaviors were measured by calculating Euclidean distances between species based on 12 courtship characters and by clustering species according to UPGMA (unweighted pair-group method using arithmetic averages). The resulting phenogram revealed two major behavioral patterns in courtship: (1) interactive and (2) simple. The former was characterized by a complex sequence in which, typically, a male approached a pheromoneemitting female, engaged in a head- to- head posture with the female, and then brought his abdomen over his head and struck the female on the head and thorax. This action brought male abdominal scent structures into close proximity with the female antennae. The male then attempted copulation from the head- to- head position by a dorsolateral thrust of the abdomen toward the female genitalia. Males of these species possessed scent structures located either on the eighth abdominal segment, or in a costal fold of the forewing, or both. Courtship in the second group was much more prosaic. After locating the female by response to her sex pheromone, the male simply attempted copulation by lateral abdominal thrusts under the female wing, without behavioral embellishments. Males of species exhibiting simple courtship had either no scent structures or structures that appeared vestigial. The grouping of species based on courtship characters was poorly correlated with taxonomic relationships, suggesting that the selective pressures governing the evolution and maintenance of courtship and male pheromones were distinct from those involved in the evolution of other morphological characters. While we argue that the primary force molding the evolution of courtship was an adaptive response to interspecific mating mistakes, we do not believe that isolation is brought about by the sequence of courtship behaviors themselves, due to the striking similarity in the sequence across several diverse species. Rather, these behaviors act to deliver more efficiently the male pheromonal message, which mayhave evolved for reproductive isolation.