THE ABSOLUTE EFFICIENCY OF GYPSY-MOTH, LYMANTRIA-DISPAR (LEPIDOPTERA, LYMANTRIIDAE), MILK-CARTON PHEROMONE TRAPS

Catches by gypsy moth (Lymantria dispar (Linnaeus)) 'milk-carton' pheromone traps with (+)-disparlure were compared with estimates of the absolute aerial density of gypsy moths obtained using a suction trap of known absolute sampling efficiency. The mean number of male L. dispar caught per pheromone trap per day was found to be proportional to the 2/3 power of the suction trap's estimate of aerial density. We infer that the efficiency of the gypsy moth milk-carton pheromone trap is density-dependent, declining as aerial density increases. The significance of the density-dependent efficiency and the mode of action of attractant traps are discussed, and the problems of designing and building suction traps to standardize pheromone traps for other species are also considered. It is concluded that standardization is only possible when some basic biology is known because pheromone trap parameters are specific to the field behaviour of the species.