**1. Introduction**

In 1962, *Silent Spring*, the book written by Rachel Carson, documented the detrimental effects on the environment of the indiscriminate use of synthetic pesticides [1]. The book claimed that DDT and other pesticides had been shown to cause cancer and that their agricultural use was a threat to wildlife, particularly birds. She explicitly accused chemical industry of spreading misleading information and public officials of accepting industry claims unquestioning about

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consequences. Despite the fierce opposition by chemical companies, the book's impact on the American public was a seminal event for the environmental movement, spurring a reversal in national pesticide policy. Still the issue has great actuality, considering the recent debate [2– 4] about effects of neonicotinoids on honey bees and birds [5].

In 1972, DDT was banned on the agricultural uses in the US, and soon after in EU. Before DDT was banned, more than 600,000 tonnes were applied in the US. The environmental movement led to the creation of the US EPA (Environmental Protection Agency). The first resistance episode concerned DDT in 1914 [6]. In May 2015, US President Obama, considering the final report of the Commission, stated the primary importance of antibiotic multiresistance, leading to the ban of the use of antibiotics in agriculture and farm practices. However, deep divide exists between American and European regulation of pesticides and other chemicals, many chemicals that are banned or strictly regulated in EU are permitted in the US.

Accordingly to the current definitions, resistance can be defined as "a heritable change in the sensitivity of a pest population that is reflected in the repeated failure of a product to achieve the expected level of control when used according to the label recommendation for that pest species" [7]. In this chapter, we will consider resistance as "the inherited ability of an organism to become tolerant to a dosage of the chemical that would be lethal to a definite species." Evidence for pesticide resistance in arthropods of agricultural and medical importance is an emerging threat. It is possible that in the next 20–30 years, all the synthetic pesticides now employed for pest control will lose their efficacy. Research on newer and safer control tools may be helpful in future scenarios for mankind, dramatically involving feed and food.

Synthetic insecticides are usually utilized to reduce damages caused by insects that destroy crops or transmit diseases. To be effective, an insecticide should be lethal to the majority of the individuals in a normal wild population. However, the insecticide can lose its efficacy, thus many pest populations developed resistance to the toxic effects [8]. This key point is only a further example of the consequences of human tendency to amplify the natural resources beyond any limit in order to obtain the maximum of the effects and not considering the consequences. The problem is inherent: the resistance is related to a massive and persistent use of pesticides, exactly like for antibiotics in microorganisms. Many species have resistant populations, which can resist to one or many treatments [9]. In the moment of the insecticide use, some individuals result resistant. Sensitive insects exposed to the insecticide will die, except the few resistant ones, which can continue to develop and proliferate. Continuing the use, they will be favored. More use of pesticide fuels the dominance of resistant populations. The consequence of the mechanism is that, in the right time, insecticides, once effective, are not sufficient in controlling insects [10]. Nowadays, the above definitions risk to be insufficient to describe the complex system that generates the resistance phenomenon to insecticides or the absence of any real efficacy in control of insect pests. The solution can be considered simply as "find the best weapon to kill the bacterium and solve the problem," as so far mainly considered. As in the general medicine, where the "chemical magic bullet" was considered the central solution for any disease, this approach is nowadays in crisis because the physiologic aspects are more complex and complicated by interactions at several levels. Resistance is the consequence of a series of events.

This chapter attempts to overcome the paradigm substance → replay of organism → resist‐ ance, in favor of a more complex approach, leading to integrated pest management. A focus on two current vector-borne emergencies was provided.
