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During the last three decades of the 19th century, the Colorado potato beetle (Leptinotarsa decemlineata) became the most harmful nuisance to crop production in North America. Exchanges between American and French entomologists, which began to take place during the phylloxera disaster, allowed for the methods of eradication of insects regarded as harmful to cross the Atlantic and circulate in France. From then on, the vegetal species protected from pests by arsenicals –the first large-scale chemical insecticides– grew in numbers. In some cases, such as for fruit trees, the consequences on beekeeping were instantaneous on both sides of the Atlantic. Although it was obvious that broad-spectrum active substances were toxic to all beneficial arthropods, it seems that as early as the beginning of the 20th century, many producers balked at taking into account the warnings and advice from entomologists.