Genetic Structure And Female Flight Behavior Of Asian Gypsy Moth Populations From Different Geographic Regions

Gypsy moth, Lymantria dispar Linnaeus is one of the most recognized pests of forests and ornamental trees in the world because of the broad range of host tress and great damage. Based on the geographic distribution, host species of larvae and female flight ability, gypsy moth were classified into three subspecies:L. d. dispar (L.), L. d. asiatica Vnukovskij and L. d. japonica (Motschulsky), the common name for L. d. dispar is European gypsy moth, and for the latter two is Asian gypsy moth. Asian gypsy moth is considered as a greater threat than European gypsy moth based on the following reasons:Asian gypsy moth eggs have low chill requirement to fulfill diapause; larvae can feed on more host species than European gypsy moth larvae; and that females are capable of flying while European females could not fly. To investigate the genetic characterization of Asian gypsy moth from China, inter simple sequence repeat markers (ISSR) were employed to reveal the genetic diversity and genetic structure of different geographic gypsy moth populations; DNA barcoding was used to identify the geographic origin of all the populations. Besides, variation among female flight behavior of Asian gypsy moth from different countries was studied under different light intensity and time after scotophase. The main conclusions in this research are as follows:1. Genetic diversity of gypsy moths from China was relatively higher than that of European gypsy moth. Overall genetic diversity (Nei’s, H) was 0.2357, while the mean genetic diversity within geographic populations was 0.1845±0.0150. The results of our analyses investigating the degree of polymorphism, genetic diversity (Nei’s and Shannon) and genetic structure, suggest that individuals from Hebei may be better able to adapt to different environments and to disperse to new habitats. The observed genetic distance among the eight populations ranged from 0.0432 to 0.1034. Clustering analysis (using an unweighted pair-group method with arithmetic mean), revealed strong concordance between the strength of genetic relationships among populations and their geographic proximity. Analysis of molecular variance demonstrated that 25.43% of the total variability (FST= 0.2543, P< 0.001) was attributable to variation among geographic populations.2. There were a few samples from China exhibiting genetic relatedness to gypsy moth from Europe or Siberia, Russia, on mitochondrial DNA (mtDNA) COI haplotype. The restriction site markers showed that two Chinese populations had both Asian and European haplotypes. DNA barcode sequence divergence between the Asian populations and the European populations was three times greater than the variation within each group. Using Bayesian and parsimonious network analyses, nine previously unknown barcode haplotypes were documented from China and a single haplotype was shared by 55% of the Chinese and some Far Eastern Russian and Japanese individuals. Some gypsy moths from two Chinese populations (Guizhou and Liaoning) showed genetic affinity with mtDNA haplotypes from Siberia, Russia, suggesting there could be a cryptic new subspecies in Lymantria dispar or human aided movement of moths between these two locations at an earlier point in time.3. Time intervals after the start of scotophase had a significant effect on the female flight propensity, and both the flight propensity and flight capability varied among different populations. Female flight propensity, time to initiate walking, fanning, and flying, and duration of fanning differed significantly among geographic populations. Females were less likely to voluntarily fly during the 0-1 h time interval after the start of scotophase than during the later time intervals (1-2 h and 2-3 h), suggesting flight is at least partially regulated by an endogenous rhythm. Light intensity did not significantly affect the proportion of females that voluntarily flew, but did impact the timing of the walking and fanning preflight behaviors. The interaction between light intensity and time interval after the start of scotophase had a significant effect on the proportion of females that fanned. The proportion of females with sustained flight capability varied among the populations evaluated, indicating the female flight capability is not fixed in one subspecies or population. These results may aid in determining the risk of Asian gypsy moth dispersal, but further work is needed to assess other factors that play a role in flight propensity.This study provides genetic and female flight behavior information, which is crucial in evaluating the distribution, population dynamics and dispersal risk of this important pest species of global concern.