Understanding Eurasian gypsy moth (Lymantria dispar L.) population dynamics at low densities is important to understanding the process of range expansion in this invasive species. The gypsy moth is subject to depressed mating success in low-density populations, which may reduce the rate of range expansion. A previous study using female-baited delta traps found that male gypsy moths located mates at forest edges at a higher rate than in interior forest, suggesting that vegetation may affect mate-finding success. However, it was not clear how delta traps affect mate-finding ability nor how the results translate to female mating success. The goal of this project was to quantify the effects of delta traps and understory cover on female location by males and mating success. We compared males captured in female-baited delta traps to mating success of tethered females in a mass male-release experiment. Female-baited delta traps and tethered females were alternated in eight locations in a circular plot 24 meters from the male release point. The relationship between delta trap catch of males and female mating success, and the effects of understory cover, were quantified using a Bayesian framework.
Results/Conclusions
The number of males locating females in delta traps increased with number of males released. The probability of female mating success increased with the number of males caught in delta traps; however, greater understory vegetation density lowered the probability of female mating success. Delta traps baited with females reduced the male’s ability to find a female by approximately 67%; thus, female-baited delta trap catch counts tend to underestimate the ability of males to locate and mate with females. Understory vegetation reduced the male’s ability to locate a female, and reduced the effectiveness of delta traps even more. The vegetation effect was primarily due to the density of understory stems with diameters of 2.0-6.0 centimeters. We demonstrated the inhibiting effects of delta traps and understory cover on mate-finding and provide an adjustment algorithm to estimate mating success. These results suggest that understory cover may reduce range expansion of gypsy moth by inhibiting mating success. This study may be useful in optimizing management strategies to slow the spread of this iconic invader.