PS 36-78
Forest edges enhance mate-finding in the European gypsy moth, Lymantria dispar
Understanding the movement of individuals within a landscape is essential to identifying how habitat boundaries affect species abundances, ranges, and spread rates. Particularly in heterogeneous landscapes containing low-density populations, movement barriers due to fragmentation may reduce mate-finding ability in some species, while edge habitat may enhance mate-finding in others. The focus of this study is the effect of habitat type and habitat edge on mate-finding in an invasive defoliator, the European gypsy moth (Lymantria dispar), in fragmented forest. Gypsy moth invasion rates vary geographically and are negatively correlated with levels of fragmentation, suggesting a causal link. We hypothesized that mate-finding is reduced in fragmented forests. Adult European gypsy moths exhibit sex-specific movement with mate-finding by flighted males mediated through pheromones released by flightless females. We measured mate-finding in a male release-recapture experiment using female-baited traps. Baited traps were arranged in semicircular arrays 25m equidistant from a release point in fields, across forest edges (with a release from within and outside the forest), and in the forest interior at two sites within a fragmented, agricultural landscape at Blandy Experimental Farm (Boyce, VA). For purposes of data analysis we divided edge arrays into 5 trap types: forest, forest/edge, edge, field/edge, and field.
Results/Conclusions
Mate-finding was highest in forest edge arrays, intermediate in field arrays, and lowest in forest interior arrays. We found that mate-finding was highest in the forest traps (15m meters from the tree line) of both types of forest edge arrays and mate-finding monotonically decreased to the field traps. These results suggest that mate-finding is enhanced by forest edges, with the effect greatest several meters interior from the tree line. Since mate-finding was higher in field habitats than interior forest, we conclude that habitat fragmentation, at the small scale of this study, may enhance mate-finding in gypsy moth populations. If habitat fragmentation negatively affects gypsy moth mate-finding, it does so at larger scales than tested. These data do not support the hypothesis that mate-finding is the mechanism for the effects of habitat fragmentation on invasion rates. In contrast, these data suggest that low levels of habitat fragmentation may increase the spread of this non-native forest defoliator.