Nature doesn’t stand still, and humankind’s restlessness has only accelerated the movement of species around the globe. The zebra mussel came to the Great Lakes as a stowaway in ship ballast water; the gypsy moth was accidentally introduced to the United States by a researcher interested in silkworms. While some have little impact where they’re introduced, and others can even increase biodiversity, many create tremendous ecological and economic harm.
According to the 2011 study “Economic Impacts of Non-Native Forest Insects in the Continental United States,” published in the online journal PLoS ONE, more than 450 introduced insect species are now established in U.S. forests. They frequently arrive with imported wood or live plants. Native trees often have little resistance to non-native insects, which also benefit from an absence of predators. They can thus spread rapidly, killing or damaging trees across wide areas.
To understand the impact of such pests and better inform management options, the researchers classified introduced insect species into three major groups and sorted the damages they caused into five cost categories, using a ten-year time horizon. The results of the study include:
- Wood-boring insects, including the highly destructive Asian longhorned beetle, represent the smallest group of invasive species yet are the most damaging. Such species annually incur more than $3.5 billion in losses, primarily to local governments ($1.7 billion) and homeowners ($1.59 billion). Other costs are born by forest landowners ($130 million) and the federal government ($92 million).
- Sap-feeding insects such as the hemlock wooly adelgid are the most numerous, but their costs are the smallest of the three groups, approximately $616 million annually. This is primarily born by homeowners, whose property values decline when trees are damaged or die.
- Insects that feed on foliage, including gypsy moths, cause $868 million in annual damages, also primarily to homeowners. They’re unlikely to kill trees unless defoliation occurs two years in a row or if it coincides with a drought.
- Of all the invasive insect species detected from 1980 to 2006, 56% were wood borers. Based on the observed rate of species introduction in the U.S., there is a 32% probability that another destructive species of wood-boring insect will arrive in the next decade.
While costs fall most heavily on municipal governments and homeowners, these constituencies are often not taken sufficiently into account when decisions are made, the authors note. One possible approach is import taxes or fees, which could be used to limit introduction of new species and control those that have already arrived.
Keywords: consumer affairs, economy, science, invasive species