There have been many notable successes in the natural control of weeds. The general consensus is that any contribution to a reduction in current control costs and efforts that outweighs the cost of the programme should be considered a success. A recent review of natural control programmes revealed an average cost: benefit ratio in excess of 1:200 and though there was some variation, all were found to be positive. A good example is the use of the weevil Cyrtobagous salviniae to control Salvinia weed in Sri Lanka. This plant was introduced into the country during WWII to prevent enemy aircraft from identifying waterways. It did the job so well that almost all water-bodies in the country were affected. The weevil was released in 1986 and within four years it destroyed around 80% of weed infestations. Since its discovery this weevil has been a successful control agent against this weed in more than 10 tropical countries around the world and is still working today.