BUENOS AIRES - Some 350 exotic species introduced into Argentina's ecosystems at different times are causing serious changes to the environment, warns the local affiliate of the World Wildlife Fund (WWF).

The problem involves animals such as beavers, starlings, fish species like the carp, and also plants, such as the black acacia, originating from North America. These are all species that reproduce rapidly and jeopardize the development of Argentina's native flora and fauna.

Law prohibits the introduction of species into Argentine territory, but it is difficult to prevent, given the country's extensive borders, and the challenges of containing those that have already arrived as they continue to grow, says the 'Fundación Vida Silvestre.'

BOGOTA - Colombia's Environment Ministry presented a work plan for this year geared towards protecting wetlands, bodies of water and marshes that cover 712,216 hectares of the country's territory.

The program, financed by the Inter-American Development Bank, the government Environmental Investment Fund and World Wildlife Fund, has a budget of some 400,000 dollars.

Wetlands are bodies of fresh, brackish or salt water, of natural or artificial origins, and are considered the world's most productive ecosystems.

MEXICO CITY - For decades, the monarch butterfly has been faced with the progressive destruction of the forests in Mexico that serve as its wintering and mating grounds, but now it confronts a fatal threat: loggers have begun spraying pesticides.

Thousands of monarch butterflies were found dead in the reserves designated for them in Michoacán state, poisoned by insecticides, denounced writer Homero Aridjis, leader of the Group of 100, an environmental group here.

''It was a sickening aggression, such a thing had never occurred before,'' he told Tierramérica.

The Federal Prosecutor's Office for Environmental Protection considered that the most likely cause was an untimely frost. ''Perhaps the Prosecutor's Office is taking about a previous case, but there is no doubt that the latest killing was from pesticides,'' Aridjis responded.

Monarchs are famous for their yearly arrival in Mexico after as much as a 3,000-km trip from the forests of Canada and the United States. They winter here, where they mature and mate.

HAVANA - Herons, ducks and 'yaguasas,' among other aquatic birds, are aiding - not damaging - the rice paddies where they seek food, concluded Cuban researchers, who promote the protection and conservation of these species.

''These birds are natural agents of biological control because they are an efficient counterweight to pests and, contrary to popular beliefs, they do not eat rice that has gone to seed,'' affirmed Martín Acosta, of the University of Havana's School of Biology.

In Cuba, 97 species of aquatic birds live permanently or seasonally, of which 70 inhabit rice-growing sites and the adjacent wetlands, which cover a total 120,000 hectares on the island.