Domestic Sea Trade Aids Wood-Boring Beetles’ Range Expansion
By Andrew Porterfield
Bark- and wood-boring insects rank among the top destroyers of trees and shrubs. One tactic that pest control officials have used to fend off these insects is to halt their entrance to a country at international ports. Recently, however, native species of wood-boring beetles have expanded their range within their normal biogeographic regions, leaving questions about how they got there and how to deal with the damage in their wake.
A group of Italian researchers led by entomologist Davide Rassati at the University of Padua found that two types of beetles, in the families Cerambycidae and Scolytinae, could travel within a single country thanks to stowing away on ships between ports, and they can easily travel from local forests to a port and be exported to anywhere outbound ships are traveling. Their research was published in December in the Journal of Economic Entomology.
Rassati and his team looked at three years of beetle trapping records, from 2012 to 2014, documenting transport between 12 Italian ports as well as travel of beetles from surrounding forests to nearby ports, to see how effectively these beetles travel. The research is the first to look at local travel and expansion in a species’ native region; most insect control methods have focused on international transport of exotic insects.
Trapping was conducted using black funnel traps, with three 12-unit traps at each port. The traps also were used in forests found within 6.1 miles (19 km) of each port. The records showed 52 species of scolytines and cerambycids, totaling 7,702 individual beetles. These were broken down to 39 scolytine species and 13 cerambycids. True bark beetles, particularly Orthotomicus erosus, were the most abundant scolytines. Among cerambycids, Spondylis buprestoides and Acanthocinus friseus were the most abundant species.
The highest species richness was recorded in the ports of Monfalcone and Trieste, while the highest number of individual beetles were in Ancona, Ravenna, and Salerno. Ancona and Palermo had the highest proportion of species shared between a port and surrounding forests.
The study found a new mechanism by which native species could move locally as well as outside its native country: Forests near ports are a wellspring of native species that easily move within pallets, crates, and other wood packaging. In addition, sea transport within one nation can promote range expansion of species where the animals are native. The role of national trade in moving native species within native biogeographical regions has not been thoroughly investigated.
“Our findings underscore the importance of identifying and recording not only exotic species trapped or intercepted at ports of entry but also native species,” the authors write.
In Italy, like the European Union, wood packaging shipped domestically does not have to be treated like wood used for international trade. Similarly, the United States does not require domestic treatments of wood for intra-country transport. This has left a door open for insects like wood-borers to invade wood packaging and expand their range. Insects that were not known for being able to actively disperse can show (and have shown) a disproportionate capacity for occupying more of their native range, which increases their ability to cause harm to trees and shrubs. Once these beetles infest a tree or shrub, it is often very difficult to eradicate them with pesticides, because they are physically protected by the bark of their target plant.
Journal of Economic Entomology
Andrew Porterfield is a writer, editor, and communications consultant for academic institutions, companies, and nonprofits in the life sciences. He writes frequently about agriculture issues for the Genetic Literacy Project. He is based in Camarillo, California. Follow him on Twitter at @AMPorterfield or visit his Facebook page.