3 Ecological Impacts of Insecticides Francisco Sánchez-Bayo Centre for Ecotoxicology, University of Technology Sydney, Australia 1. Introduction Substances capable of killing insects and other pests were discovered by the Persians some 2500 years ago, but it was the Green Revolution since the 1950s that fostered the development of new synthetic pesticides to cope with the demands of the explosive human population. We have now reached 7 billion people and managed to reduce starvation in many underdeveloped countries. In fact, the world’s agricultural productivity has increased 2.6-fold but the arable area has increased only by 10%, mostly at the expense of our forests (FAO 2004). Synthetic insecticides applied to a full range of crops soon started to have side effects in the surrounding natural ecosystems. The direct effects of insecticides on arthropod communities, and the birdlife that depends on them, was brought into question by Rachel Carson as early as 1962. It is not coincidence that the birth of the environmental movement and ecotoxicology was thus linked from its very beginnings to the widespread use of synthetic pesticides in agriculture and forestry. These fears became reality when the unrestrained over-use of these ‘wonder chemicals’ in Indonesia and the Philippines led to the collapse of their rice crops in the early 1970s. The destruction of predators within the complex food web of rice ecosystems released the pressure on pest species such as plant hoppers (Nilaparvata lugens), which devastated the crops. This love affair with chemicals ended when the Indonesian government banned many insecticides and restricted the use of other pesticides (Daryanto 1998). From then onwards farmers were encouraged to foster natural enemies that can control or at least avoid the onset of pests in agricultural ecosystems. Pesticides were not to be used alone, but in combination with other biological and agronomic practices that protect the ecosystem. Thus, the Integrated Pest Management (IPM) strategies, first proposed by the Food and Agricultural Organisation (FAO) of the United Nations in October 1965, started to replace the conventional Green Revolution practices. However, to grow enough food for us all is a major challenge faced by modern agriculture. Because the relentless expansion of our cities often demands that old, fertile agricultural land be converted to urban dwellings, our planet is actually running out of suitable land to grow food for the future generations. This chapter deals with the known ecological impacts of insecticides on terrestrial and aquatic ecosystems, without consideration of the economic benefits that they may have. We must accept that pest control and disease eradication are complex issues that will never be resolved without causing problems to the environment –and there are not simple solutions to complex problems. Our aim should be to minimise the environmental impacts to levels that are acceptable by the society and bearable by the ecosystems. www.intechopen.com