Pimentel began his career at Cornell studying pest control and DDT in house flies. During his time in Puerto Rico, he studied the introduced mongoose. Early work, such as on herbicides, is still cited today. At the intersection of agriculture and
food security, Pimentel was concerned about the effects of chemical inputs and modern farming techniques on production in agriculture. Pimentel also warned that
human overpopulation is a function of food availability. In his later years, he took an interest in the environmental effects of global warming. In 1961, Pimentel published on several important topics in ecology, including diversity-stability, spatial patterns, and community structure. It was also the year that he presented his model integrating population dynamics and genetics that he called genetic feed-back. He later presented data for it. It was one of the earliest attempts at mathematically combining genetics with population dynamics. Half a century later, it was cited as a paper that presaged the currently hot field of eco-evolutionary dynamics. Pimentel's forays into the environmental field came out of his experiences on various government panels and study groups, especially his year as an ecological consultant to the
Office of Science and Technology. His study of the energy inputs into the productions of corn was published during the energy crisis of 1973 and became his most cited paper ever. It was followed up by a study of the energy inputs to beef production. By then, he was on his way to becoming a voice that was listened to on a variety of environmental issues through the numerous studies that he led and published, the results of which always could, and were, inspected and revised. He was not a scientist who shied away from controversy or feared contradicting established views. Early in his career, he took on the biological control establishment by suggesting that native pests could be controlled by introducing new parasites and predators, based on his observations of successful control of pests in new associations and his genetic feedback model. It was not an idea that was readily accepted, however, particularly by California biocontrol experts. They admitted that, "Outstanding biological control successes have sometimes been achieved ... by the use of natural enemies whose hosts belong to different species or genera from the pests they are needed to control," but they then rejected (pp 47–49) Pimentel's work on genetic feedback as an explanatory mechanism involved in biocontrol by insect parasites and predators. Undaunted, Pimentel continued to support and document the use of new associations in biocontrol. This practice has been called "new association biological control" as opposed to "classical biological control". Pimentel was a pioneer in tabulating the energy cost, fossil fuel in particular, of food production. When his suggestion that "energy was going to be important to agricultural research in the future" was rebuffed as an area of study by a 1968 National Academy of Science Panel on which he served, Pimentel set about to put together the needed data himself by creating a graduate research course to do so using his own students. Coming out during the 1973 energy crisis, the paper on energy inputs to corn production received much attention and helped to launch a number of studies and papers, including many by Pimentel and his colleagues. That paper then putatively initiated the controversy over the net energy and environmental impacts of gasohol crops. Pimentel took great solace in having had his work reviewed by "26 top scientists and engineers" Pimentel claimed criticism such as that raised by
Bjørn Lomborg, was only a disagreement on details, rather than conclusions, stating he was correct anyway despite the fact that the numbers he used in his calculations later turned out to be wrong. ==Biomass fuels==