Scientists have finally identified a small insect that has been sucking the life out of the nation's pine forests.

The sap sucking Essigella californica aphid has been defoliating up to 30 per cent of the forest canopy, costing the industry about $20 million a year in lost production.

Barrie May, a scientist from CSIRO joint venture company ENSIS, says a lot of time was spent in cherry pickers at the tops of trees to pinpoint the cause.

"Based on these results we're pretty confident in saying that aphids are responsible for most of the defoliation of radiata pine that we've seen over the last five years," he said.