Lymantria dispar

Pheromone-baited traps are the primary method for detecting and delimiting new isolated gypsy moth populations in previously uninfested areas. Pheromone-baited traps are a very sensitive tool that can be used to detect very low density populations that could not be detected using any other method. Every year, over 300,000 traps are deployed in the USA for detection/delimitation alone (Tobin et al., 2012). When a new population is detected using pheromone traps, it is a common practice to make a search for gypsy moth life stages in order to confirm the presence of a reproducing population. However, given the difficulty of detecting low-density populations in this way, life stages cannot always be found in all populations.
Larvae on foliage are easily distinguishable from other defoliators. Late in the year, host pupae and egg masses on tree trunks indicate gypsy moth infestation. Egg mass counting is a common practice for monitoring infested areas to estimate population density and predict future outbreaks. In North America, the detection of gypsy moth outbreaks is also based on aerial defoliation surveys.