Invasive insects 101
Stories of invasive tree-killing insects here in Canada are pervasive. You can read about many of them here on this site. Emerald ash borer, brown spruce longhorned beetle, Asian longhorned beetle and, more recently, hemlock woolly adelgid are just a few. The impact, both economic and ecologic, of many of these insects is, or will be, profound.
In the US, there has been an average of 2.5 new non-native forest insects per year over the past 150 years, and yet the chance of an alien insect surviving and establishing when it arrives here in North America is actually very low. There are few different reasons for this. Environmental conditions may not be suitable for them - too hot, too cold, too variable - or they may arrive during unfavourable weather. They may not find an appropriate food source - either because there are no suitable food sources, or because they cannot locate it. Or, they may not be able to locate a mate. Alternatively, they may survive and reproduce but their populations remain low and they eventually die off.
Even if they do establish, not all insects in a new range will become a problem. Many just join the insect community and never, or rarely, become noticeable. The probability of an insect becoming a successful invader is thought to follow the rule of tens, i.e., about one in ten introductions persist, and about one in ten of those become a problem. So, about one in one hundred introductions are problem insects. However, those problem invasive insects are often inordinately costly both economically and ecologically. Unfortunately, it is difficult to predict which invaders will be successful in establishing.
Most modern-day invasive insects arrive here accidentally. These insects primarily arrive with the importation or movement of materials: wood packaging materials (pallets, crates, spools etc) and live plant material (nursery stock) are the primary pathways, but also shipping containers, firewood, raw lumber with bark, Christmas trees, personal property and vehicles. Wood packaging material has long been an important pathway for movement of invasive insects and likely the source of emerald ash borer and Asian longhorned beetle introductions. Wood packaging is typically made of low quality wood which is often infested by insects. New wood packaging treatment protocols came into place in 2006 to reduce the risk this pathway poses (ISPM #15). These are measures taken in the country where the products are exported, and proof of treatment is required by countries receiving shipments. Since these measures were implemented, fewer shipments are found with infested materials, however some do persist. This could be because some insects survive the ISPM #15 treatment protocols, non-compliance (intentional or unintentional), or because the wood packaging becomes infested after treatment.
Although much of the risk of movement of invasive species is through trade and commercial movement of infested materials, individuals do play a part. Burning firewood where you buy it, and inspecting vehicles and contents for invasive species before you depart from a location play an important role in stopping the spread of invasive species.