Monday, April 30, 2012

The Red Menace Grows

The Red Army menace grows even as the government cuts the budget....
The total area in Taiwan affected by exotic red fire ants has increased by nearly 50 percent since 2003, but despite the growing infestation, the government budget for pest control was cut from last year’s NT$40 million (US$1.36 million) to NT$20 million this year.

Listed among the world’s top 100 most-invasive species, the ants, native to South America, were discovered in Taiwan in 2003 and have alarmed residents by quickly spreading through urban areas in Greater Taipei, Taoyuan, Hsinchu, Miaoli and Chiayi counties.
Fire ants, often called red ants, first appeared in Taiwan in 2003. According to a landmark genetic study, fire ants are spreading out of the US into the world along global trade routes. The US is in fact the origin for all subsequent transmissions, a total of eight separate waves. The Taiwan case was special: while other transmissions went directly from the southern US outward to places like New Zealand, the Taiwan-bound group of ants came to California before continuing on to Taiwan. The article above describes:
Biologists had certainly considered this United States–bridgehead scenario of invasions, Ross says, “but without data, it was anybody’s guess.” To track the invasions, an international research team analyzed ants from 2,144 colonies in a total of 75 places in 11 countries and looked at several kinds of genetic information, including dozens of DNA markers.

“Most studies don't come close to those numbers,” says Goodisman.

Ross explains that looking closely at fire ants in their native range in South America revealed 322 distinct genetic types. Only 11 of those types were found in the southern United States, including three that were very rare in the native range. Yet the populations from newly invaded territories had combinations of the three rare variants from those U.S. types, not the others left behind in South America. Additionally, the researchers ran computer models of how gene patterns in populations change as invaders bud off into new territories. The scenarios that fit the data best, alas, showed the United States as the source, Ross says.

This analysis raises the possibility that the rigors of invading the United States and then of moving on toward world domination have winnowed out weaklings and less invasive ants. Populations now erupting from the United States could be specially adapted as super-invaders, Ross says.
Fire ants like disturbed terrain, of which there is plenty on the overdeveloped Beautiful Island. When disturbed, they attack aggressively in swarms, and their venom can cause shock and even death in a small percentage of cases. Arriving in Chiayi and Taoyuan in 2003 in what appears to be two separate infestations, they quickly spread across Taoyuan county and are now entrenched in urban areas around the island but especially in the north. In 2006, to help root out the problem, Taiwan began to train beagles to smell out fire ant nests.

According to this 2009 paper, the core of the infestation in the north is in Taoyuan: Dayuan, Jhongli, Luiju, Taoyuan, Bade and Pingjhen, but it reaches well into Hsinchu county. The figure below gives a glimpse of their distribution:

Polygyne and monogyne refer to their social organization of nests that have multiple queens and single queens, respectively. Note that dead center of the infestation in the north is Taoyuan International Airport. The authors argue that the infestation in Chiayi came entirely from ants with two or more queens per social unit, and that the nests with single queens are a later development, implying that the island was infested twice, seemingly in the same year. They also say that while the infested area in Chiayi is basically stagnant, the one in the north is expanding at a constant rate. Brr.....
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