Re-counting

Insect species are much fewer than previously estimated

 
Published: Friday 31 May 2002

scientists have recently made a drastic downward revision of the number of insect species they believe the Earth contains. Instead of about 30-million-plus species previously estimated, the researchers say there are probably no more than four to six million insect groups. The new estimate stems from a six-year comprehensive study conducted in New Guinea's rainforest of plants eaten by insects. An international team of researchers had conducted the study.

The main discovery by the researchers is that insects are much less fussy feeders than realised. Instead of eating only individual plant species, most insects are far more varied in their taste. The team compared insect communities feeding on 51 plant species. They collected 50,734 leaf-chewing insects from 51 plant species. Scientists used to assume that each plant-eating insect species tended to feed on one plant species, or very few. This made them conclude that the number of herbivorous insect species should be linked to the number of plant species. But the New Guinea group found that this was was a false assumption.

"Most insects turn out to be specialised not to plant species, but rather to a genus (a group of species) or a family (a group of genera) of plants," said George Weiblen, a plant biologist from the University of Minnesota, usa, and the principal plant expert in the research team. "Our estimates bring some reality to predictions about declining biodiversity in the sense that the consequences for insect herbivores of losing a particular host plant species may not be as dire as previously thought. However, that is no reason to ignore the decreasing number of species worldwide," Weiblen added.

The number of insects identified so far is between one and two million. At present, there is no money for making a complete catalogue to summarise information from collections across the world.

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