Comparisons of morphometric traits associated with flight performance in two species of longhorn beetles, Monochamus alternatus and M. saltuarius (Coleoptera: Cerambycidae)

The longhorn beetles of Monochamus alternatus and M. saltuarius are the two principal vectors of Bursaphelencus nematodes that infect pine trees and cause pine wilt disease in Korea. The speed and directions of this spreading epidemic are determined by the dispersal of its insect vectors. To better understand the role of these beetles as vectors for pine wilt disease, we compared morphological and physiological traits associated with flight between M. alternatus and M. saltuaris beetles collected from six different populations. Various measures of wing morphologies (size and shape) and allometric relationships between different body parts were quantified to estimate key indices correlating with flight performance in these two insects (wing loading, thorax investment, flight muscle ratio, etc.). Results showed that M. alternatus beetles had greater thorax mass, flight muscle ratio and wing area than M.saltuarius. Wing loading was significantly lighter in M. alternatus versus M.saltuarius. The wing shape of M. alternatus was long and slender, which was designed to be aerodynamically efficient for long-distance flight, whereas that of M. saltuarius was much rounder. Collectively, our data indicate that M.alternatus are morphologically and aerodynamically more adapted for flight and dispersal than M. saltuaris, which has important implications for the prediction and management of pine wilt epidemic.