most severe form of malaria) cases increased from 45% to 85%. Although habitat modification played a role, the telling factor was migration. Migrants brought with them strains of malaria to which the local population, and many of the migrants, had no immunity (Cruz Marques, 1987). Malarial outbreaks have a large economic impact on the financial viability of the mining and logging operations. At one mine, a 12% reduction in income occurred due to absenteeism, and profits for the company were reduced by the same amount (Vosti, 1990). Many species of mosquitoes prefer to feed on animals rather than humans. Destruction of animal habitats, and a decline in the number of wild animals forces the mosquitoes to feed on domestic animals and humans. The frequency of human feeding has a marked influence on malarial transmission. In 1975, a PNG government entomologist, Dr. Margaret Spencer (Spenser, 1975), drew attention to the probable increase in malarial mosquito breeding due to forest clearing. She writes: "There is no doubt that forest clearing will increase the breeding potential for malarial mosquito vectors in the Golgol area or northern Papua New Guinea, largely by creating man-made breeding places. These will be many and various, e.g. standing water left in holes caused by up-rooted tree stumps, in bulldozer and other tracks, wheel ruts, and roadside ditches, ruts caused by dragging of logs, and blocking of roadside drainage." In heavily forested inland areas of Papua New Guinea the main malarial vector is Anopheles koliensis, which breeds in semi-permanent