Franklin William Pettey, an American entomologist with a Bachelor of Arts (BA) degree in entomology, came to South Africa in 1910 to work for the Department of Agriculture. He was stationed at the agricultural school at Elsenburg, near Stellenbosch, where he lectured in zoology and entomology. Later the department awarded him a scholarship that enabled him to go to Cornell University in the United States for postgraduate work, and to return with a doctoral degree in entomology. Around this time he published 'A revision of the genus Sciara of the family Mycetophilidae (Diptera)' in the Annals of the Entomological Society of America (1918), in which he reported finding 31 new species of this genus of fungus gnats in the insect collection of Cornell University.
Pettey remained at Elsenburg until about 1930. During this time he conducted pioneering work on the control of codling moths with arsenate of lead. His publications on this work included 'The fruit shed in relation to the control of the Codling Moth' and 'Insect enemies of the Codling Moth in South Africa and their relation to its control' (South African Journal of Science, 1919, Vol. 16, pp. 193-196 and pp. 239-257); Arsenical spray experiments for the control of Codling Moth in pears at Elsenburg (Department of Agriculture, Science Bulletin No. 26, 1922), and several more publications of the Department of Agriculture on the same topic in 1916, 1926 and 1930. Other departmental publications by him dealt with the control of the quince borer (1917), red scale in pear orchards (1925), pear mealy bugs (1930) and the fruit fly (1932).
Pettey later played a leading role in the biological control of prickly pears in the Eastern Cape. In 1932 he was sent to Australia to obtain a colony of the Cactoblastis moth, which had been used to great effect in that country to control prickly pears. Cactoblastis stations were set up at Graaff-Reinet (1933), Uitenhage (1935) and Fort Beaufort (1936), where the work was carried on vigorously for 15 years. Pettey was initially stationed at Graaff-Reinet, but then moved to Uitenhage. As the species of prickly pear and the ecology of the Eastern Cape differed from those in Australia, and the moths had many natural enemies here, progress was slow and on the whole the project was not a success. Much more successful was the cochineal, Dactylopius opuntiae, which was first released in Uitenhage in 1938 and virtually wiped out the prickly pear in the dry inland areas of the Karoo, though it did not flourish near the coast. Pettey remained in charge of the prickly pear eradication project when he retired in 1947, until the work was stopped in 1952. His publications on the topic included The biological control of prickly pears in South Africa and The boring beetles of prickly pear in South Africa (Department of Agriculture, Science Bulletin, 1948 and 1953). He received the Senior Captain Scott Memorial Medal of the South African Biological Society for this work in 1953.
Pettey was a foundation member of the Entomological Society of Southern Africa in 1937. He became a member of the South African Association for the Advancement of Science in 1915, and was a member of the Royal Society of South Africa by 1917. In 1916 he became a foundation member of the South African Biological Society.