By Jan TenBruggencate
Advertiser Columnist

Sources of alien pest species sometimes turn up where you least expect them.

In a block of toxic bait aimed at controlling rats, Army environmental scientists found seeds of alien plants. Rats are not native to Hawai'i, and they are a serious problem in native ecosystems and raid Hawaiian bird nests. But in studies of rat bait, scientists found that controlling one pest could create another problem.

The research on the rat bait was conducted by the environmental division in the U.S. Army Garrison Hawai'i's Directorate of Public Works. The Army's researchers noted that rat bait blocks were made up primarily of seeds, but that the seeds were not identified. Instead, they were listed as "inert ingredients" on the packages.

Army horticulturist David Palumbo was asked to see if he could get the bait blocks to grow.

He tested two kinds: J.T. Eaton Bait Block and Ramik Mini Bars. Both use the pesticide diphacinone as their rat killers, and both list their only other contents as "inert ingredients." The labels make no mention of seeds and the possibility the material was viable and could sprout.

Palumbo said it was easy to recognize that seed material was a major constituent by looking at the bait blocks. He said the Ramik product seemed to contain primarily cracked corn and milled grain, while the Eaton product appeared to contain whole seeds.

"There's a lot of grass seed in it, and it looked like a problem," Palumbo said.

In the greenhouse, he found that seeds in the Eaton bait block sprouted quickly. The Ramik product never did produce a live plant.

The sprouted seeds appeared to be of the same species, a kind of morning glory. None of the grass seed found in the bait block germinated.

"I suspect the company buys their seed from a farmer, and that this plant is a weed in their grain fields," Palumbo said.

He grew the plant to maturity, collected seeds and grew another generation. Botanists at Bishop Museum were able to identify the morning glory as Ipomea triloba, a weed that is already present in Hawai'i.

"It is naturalized in the lowlands," Palumbo said.

He said none of the other kinds of plant seeds germinated, suggesting that the morning glory was tough enough to survive whatever seed sterilization technique the company uses.

As a result of the bait studies, Army environmental scientists have concluded that it's important to study the inert ingredients of rat control methods as well as the toxic materials themselves.

Jan TenBruggencate is The Advertiser's Kaua'i bureau chief and its science and environment writer. Contact him at (808) 245-3074 or jant@honoluluadvertiser.com.