The barrier protecting Hawai'i from invasive species is a weak one, and without prompt action by the state, the threat to our environment is sure to grow.

The danger comes primarily from invaders that destroy native species and agricultural crops grown locally. In some cases — the noisy coqui frog is a prime example — alien species become a chronic nuisance.

In an effort to reduce that risk of pest infestation, lawmakers last year passed a bill to establish a new fee that would fund increased inspections of cargo containers.

The new fee, which amounts to 50 cents per 1,000 pounds of freight, has yet to be rolled out fully. According to the state Department of Agriculture, only about half the cargo carriers have been paying into the fund and none of the airlines.

The fee took effect officially in August, after the bill passed and lawmakers voted to override Gov. Linda Lingle's veto. The Lingle administration has opposed the fee, largely because it is assessed on the basis of total weight, regardless of whether the cargo poses a risk of pest infestation.

Lingle makes a persuasive argument that the fee, as it's now calculated, would punish shippers of cargo — oil, for example, or frozen foods — that is relatively heavy but is not a likely carrier of invasive species.

She favors a more focused approach. Her policy office has considered financing inspections through a fund created with penalty assessments rather than a front-end fee.

This way, shippers would have the incentive to avoid penalties by more proactively inspecting the cargo themselves or fumigating containers before shipment.

It's unclear whether penalties alone would provide sufficient funds to finance adequate inspections. But lawmakers should certainly open that discussion when they convene next month.

A revision to the current fee structure that targets higher-risk cargo categories could be considered in tandem with penalties.

What's clear is that the state has to grapple with the problem and settle on a comprehensive funding scheme that can cover enhanced inspections without adding excessively to the cost of products.

Legislators and state officials also must resolve the difficulty in filling inspector positions with trained professionals. Agriculture officials are trying to deal with this problem by hiring technicians who can handle the parts of the job requiring less training.

Leaders must come to terms with the problem, and soon. A recent University of Hawai'i survey of plant nurseries that import its stock found plants infested with 29 alien species of snails and slugs, five of which had never been identified in the state before. This is just one sector of Hawai'i's vast load of imported goods, so the vulnerabilities to invasive species on multiple fronts can only be imagined.

There will be a cost that will be passed through to consumers, but lowering the risk of pests damaging crops and the native environment is an essential duty to be shouldered by state government.