Prorandry in the Pine Looper, Bupalus Piniarius (Lep., Geometridae); an Explanatory Model

Abstract

A simulation model is presented which explains the occurrence of protandry (i.e. males emerge on average before females) in the pine looper Bupalus piniarius. The model calculates the fitness of the moths in relation to their date of emergence during the period of emergence. It is investigated how this fitness is affected by: a) the difference between the mean time of emergence of males and females, b) the age of the moths at copulation, c) the mortality rate and longevity of the moths, d) the flight activity of the males, and e) the density of the moths. The input of the model is based on field data and experimental results. The model shows that a) the difference and the mean time of emergence between males and females is maintained by selection of males, such that they on average emerge 2 days before the females, b) 95% of the females mate on the day of emergence, c) the flight activity of the males together with moth density has a significant effect on the difference in time of emergence between the sexes, d) age-dependent copulation success, mortality rate and longevity do not affect the difference in time of emergence between the sexes. From the results it is concluded that mass trapping of males with pheromone traps does not decrease the percentage of females that mate. It is suggested that competitive mate searching has no effect on the occurrence of protandry.