Between January and December 2016, a survey was conducted in the foothills of Rancagua (VI Region, Chile, South America) to characterize the entomological fauna of the "Río de los Cipreses" National Reserve. The aim was to develop a baseline for the systematic study of invasive or quarantine phytophagous insect species, a very relevant problem in Chile. The survey followed the methodology of the field search for insects. The Reserve was visited during the summer and spring months, 1 to 2 times per month, with stays of 2 to 4 days, including nights. We worked in morning, afternoon and evening shifts, using low environmental impact traps. With the help of Conaf (Corporación Nacional Forestal, Chile) park rangers, representative sites with low pedestrian traffic were chosen and insects present in the foliage were observed, photographed and captured. Some interesting results were: a) the plant species "bollén" (Kageneckia oblonga) was the most attacked host, b) Hemiptera was the most frequent order, with 2 exotic genera of "mosquitas blancas" (Siphoninus, Aleurodicus) and c) pollenophagous cockroaches were observed.