Entomology was the first department to be established, together with seven other departments at the College of Agriculture in 1909. It remained a purely teaching department for the first five years, with a lone teacher and an offering of two one-year courses, zoology and economic entomology, each credited for 10 units. With the offering of plant pathology in 1917, both economic entomology and plant pathology became one-semester offerings by 1918.
Through the pioneering services of American entomologists and later by Filipinos, the department gradually built up its course offerings which by 1927 included Introductory Economic Zoology, Vertebrate Zoology, Introductory Economic Ichthyology, Economic Entomology, Insect Collection and Elementary Entomology, Insects Affecting Field Crops, Insects Affecting Sugar Cane, Special Problems, Seminar, Undergraduate Thesis, and Graduate Thesis, all of which were handled by a staff of seven. By 1929, the department had produced 15 BS and 2 MS students.
The Philippines, being tropical, was a haven of a tremendous diversity of insects about which collections started to accumulate. At first the department collections were largely undetermined and were generally useless to science. With the coming of pioneer American entomologists, foremost of whom was C.F. Baker (1912-1927), an agronomist by profession but an avid insect enthusiast at heart, the collections flourished. Dr. Baker embarked on extensive collecting in the country and some parts of Borneo and accumulated the single biggest insect collection in the world from which numerous publications by foreign insect taxonomists were derived. As a result of his untiring efforts, the Philippines, especially Mt Makiling became well known in the world literature of entomology, with over 500 papers published on Philippine insects. Unfortunately, after his death in 1927, his whole collection was deposited in the U.S. National Museum, both a loss which left the department deprived of this treasure, and a blessing, because the remaining department collection was burned during the second world war.
As early as 1915-1916, the department was witness to one of the initial historic successes of biological control when some American entomologists visited Los Baños and discovered a parasitic wasp, Scolia manilae Ashmead, which when introduced to Hawaii led to the control of the white grub, Anomala orientalis Waterhouse, to the satisfaction of Hawaii sugarcane planters. As a gesture of appreciation, the Hawaiian Sugar Planters' Association donated funds for the construction of an insectary to promote entomological research in the country.
The department of entomology was under the tutelage of American entomologists from 1909 to 1922, and was later headed by Filipinos beginning with Dr. L.B. Uichanco (1923-1956). The department, as the College did, suffered losses and setbacks during the war (1941-1944), and began the long and tedious task of restoration in 1945. These rehabilitation efforts were enhanced by the two phases of the Cornell-Los Baños contract (1952-1969) which resulted in the improvement of facilities and courses and the academic improvement of the department faculty. Eventually, the College of Agriculture graduated into an autonomous University of the Philippines Los Baños in 1972, at which time the zoology courses were transferred to the department of zoology of the new College of Sciences and Humanities (now the College of Arts and Sciences).