The ability to establish successfully in a new area can vary considerably among species. In addition to the well-recognized importance of propagule pressure in driving the rates of establishment of biological invaders, the life history strategy of a species can also affect establishment success, such as in the extent to which Allee effects (positive densitydependence), and environmental and demographic stochasticity manifest themselves. We quantified the establishment success of Adelges tsugae
, a non-native insect currently invading North American hemlock. We inoculated eastern hemlock host trees with varying densities of this parthenogenetic insect, from 1 to >500 progrediens ovisacs. The number of settled sistens (the subsequent generation) was positively related to the initial density. More interesting, however, was that we recorded successful establishment from released progrediens ovisacs, and the subsequent initiation of the next generation (sistens), in ≈39 % of host trees inoculated with 1 ovisac. The observation that successful establishment can be accomplished by a single ovisac produced by a single individual has important implications in the invasion dynamics and management of A. tsugae
Hemlock woolly adelgid
Tobin, Patrick C.; Turcotte, Richard M.; Snider, Daniel A. 2013. When one is not necessarily a lonely number: initial colonization dynamics of Adelges tsugae on eastern hemlock, Tsuga canadensis. Biological Invasions. 15(9): 1925-1932. https://doi.org/10.1007/s10530-013-0421-3.