Multi-trophic interactions and niche partitioning of the hemlock woolly adelgid predator-prey community in their native western North American range

How specialist predator communities interact with each other and prey in the native range is critical to inform management and biological control of introduced pests, but is often lacking. We studied three candidate biocontrol agents of the invasive hemlock woolly adelgid, Adelges tsugae (HWA) and test hypotheses about niche partitioning between these predators. Five populations of HWA, their suite of specialist predators (Laricobius nigrinus, Leucotaraxis argenticollis and Le. piniperda), and predator-prey phenological synchrony were studied over two years in their native western North American range. Specialist predators were present throughout HWA oviposition. Heterospecific Leucotaraxis flies showed temporal niche separation as immatures, while La. nigrinus beetles overlapped with both species of Leucotaraxis. We observed only one annual generation of HWA in both years, in contrast to bivoltine population in the introduced range. Such differences could influence predator-prey phenological synchrony when released in the introduced range. Larval La. nigrinus showed patterns of negative spatial cooccurrence with Leucotaraxis spp. immatures, providing evidence of resource partitioning during times of overlap. These findings support using Leucotaraxis fly predators in conjunction with La. nigrinus beetles to enhance biocontrol of HWA in eastern North America. Differences in prey voltinism between western (native) and eastern (introduced from Japan) lineages of HWA may contribute to variation in the outcome of predator-prey interactions. We recommend release of Leucotaraxis spp. in combination with La. nigrinus in the introduced range and emphasize the complexity of community interactions between the in the native and introduced range.