Summary This paper examines the entomological investigations carried out by the French naturalist Henri-Louis Duhamel du Monceau during a series of insect epidemics that ravaged France in the second half of the eighteenth century.1 This article began as a paper for Pamela H. Smith's ?Knowledge in Transit? graduate seminar. I would like to thank the participants of that seminar for comments and feedback. I would also like to thank Pamela Smith, Carl Wennerlind, Anya Zilberstein, Christopher L. Brown, Charly Coleman, Matthew (...) Jones, Peter Walker and Melissa Morris for their suggestions and comments on this paper. Finally, thanks to Vanessa Copeland for invaluable assistance in the archives in Paris. The author acknowledges support from the Social Sciences and Humanities Research Council of Canada and the Graduate School of Arts and Sciences, Columbia University. It shows how a particularly fierce invasion of caterpillars in the Angoumois region in the 1760s sparked theoretical debates about the nature of animal generation between academic naturalists, farmers, provincial officials and amateur naturalists. As part of a wider effort to reform agricultural production in France, Duhamel du Monceau sought to eliminate vernacular understandings of insect generation and to reform local pest control techniques. In his attempt to develop a body of pest-control knowledge grounded in the systematic observation of insect generation, however, Duhamel du Monceau relied heavily on the efforts of amateur naturalists. The paper shows how he mobilized a nation-wide network of entomological observers, and collected specimens and observational reports from farmers, improving landlords and local officials throughout France. Some informants did not only act as ?mere? observers, but formulated their own causal claims about insect generation that sometimes contradicted those of their metropolitan counterpart. Finally, it demonstrates that a ?patriotic? discourse that joined agricultural improvement and civic virtue provided a powerful impetus for the formation of collaborative relationships between academic naturalists, state officials and enlightened agricultural improvers. (shrink)