Submitted to: Florida Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/12/1997
Publication Date: N/A
Citation: Interpretive Summary: The susceptibility of grapefruit to fruit flies threatens export of this commodity and requires extensive intervention to prevent infestation. Scientists at the Center for Medical, Agricultural and Veterinary Entomology, in cooperation with other scientists from ARS, APHIS, and Mexico collaborated to perform field tests to establish the efficacy of gibberellic acid (GA) treatment of grapefruit as a means of reducing fruit susceptibility to the Caribbean fruit fly. GA treatment delayed peel senescence and thereby reduced fruit susceptibility to the caribfly, but did not interfere with internal ripening of the fruit. In addition, late-season fruit drop was reduced by about 50%. Treatment costs for this EPA-approved agent were several times lower than the benefits obtained. This approach could provide a good alternative to use of malathion bait sprays for certification of Florida groves as being fly-free, for use in the $200 million grapefruit export market.
Technical Abstract: Field trials were conducted to evaluate use of gibberellic acid (GA) (a senescence-retarding plant growth regulator) on 'Marsh' grapefruit as a means of reducing fruit susceptibility to the Caribbean fruit fly, Anastrepha suspensa (Loew). Rates of application of GA and an adjuvant surfactant were optimized, as well as spray volume, using commercial air blast equipment (speed sprayers). In addition to evaluating susceptibility of treated vs. untreated fruit to fruit fly attack, a number of horticultural parameters also were measured, including fruit peel puncture resistance, peel color, internal ripening, leaf drop and spontaneous fruit drop. Ability to artificially degreen GA-treated and untreated fruit using ethylene gas also was measured. Susceptibility of treated grapefruit to attack by the Caribbean fruit fly under near- natural conditions was significantly reduced without causing adverse effects on leaf drop or internal ripening. GA-treated fruit could be successfully degreened when needed, and late season fruit drop was reduced. Use of this plant growth regulator already is approved by the U.S. Environmental Protection Agency, and it could prove very useful in reducing the likelihood of grapefruit being infested by the Caribbean fruit fly during the mid- to late-season when they are most susceptible. The results are discussed in light of their contribution to the possible development of biorational fruit fly management approaches and economic benefits that might be obtained.