Nissan Island is presented as a cautionary case in which stopping an intensive wartime spraying program did not restore the ecology it had disrupted. Once spraying ceased, malaria-carrying mosquitoes reinvaded an island where their predators had been killed and were not yet re-established, leaving the way open to a tremendous population increase. The episode shows how chemical control can create a continuing dependence on intervention by removing the natural checks that might otherwise limit a pest.

Wartime spraying and its aftermath

During the Second World War, spraying on Nissan Island was carried on intensively. When hostilities ended, the spraying stopped. The shift from sustained chemical treatment to no treatment did not simply return the island to its earlier condition: the predators of the mosquitoes had been killed, and there had not been time for new populations to become established.

Reinfestation and ecological imbalance

Soon after spraying ceased, a malaria-carrying mosquito reinvaded. With its predators absent, it encountered conditions in which its population could expand dramatically. The book links the outbreak not just to the mosquito’s return but to the altered ecological circumstances left by the control campaign: the loss of predators and the delay before their populations could recover.

The chemical-control treadmill

Marshall Laird, who described the incident, compared chemical control to a treadmill: once people have stepped onto it, they may fear stopping because of what will follow. Nissan Island gives that warning a concrete form. Intensive spraying had eliminated predators as well as its intended targets; when treatment ended, the missing ecological checks helped a disease-carrying mosquito surge back. The case therefore frames pest control as an ecological process with consequences extending beyond the period of application.