In February 1938 a severe caterpillar outbreak stripped 800 ha of natural forest on Mt Lawu, East Java.[1] In 1990 a conifer aphid had infested over 80% of Kenya's forests—just three months after it was first discovered.[2] In Ghana, the yield loss of cocoa attributable to insect infestation is estimated at 25-30% per annum, and may be as high as 75% in farms attacked by pests and left unattended for over three years.[3] Meanwhile, in Europe and North America Dutch elm disease has been spreading since 1910: by 1990 very few mature elms were left in Britain or much of continental Europe.[4]