Interplay between foraging behaviour, adult density and fruit ripeness determines the effectiveness of gibberellic acid and host-marking pheromone in reducing susceptibility of grapefruit to infestation by the Mexican fruit-fly, Anastrepha ludens

Abstract

The potential of gibberellic acid (GA₃) and host-marking pheromone as management tools for control of Mexican fruit-fly (Anastrepha ludens) was evaluated in the field. Varying numbers of GA₃-treated and untreated “Ruby Red” grapefruit were hung in branches of field-caged citrus trees and exposed to four different densities of gravid A. ludens females (1, 5, 15 and 30 individuals per cage) over the entire harvest season (October to February). Infestation was not lowered by GA₃-treatment when fly density was set at 0.06, 0.19 and 0.38 females per fruit. Results depended mainly on fruit ripeness and female density. A reduction in infestation (almost eight-fold) was recorded at a fly density of one female per 200 fruit (0.0005 female/fruit rate), when fruit was treated with 15 ppm of GA₃ (applied once) and exposed to flies early in the harvest season (November). At a higher GA₃ concentration (20 ppm applied twice) and a fly density of 30 females per 100 fruit (0.3 female/fruit rate), no statistically significant reduction in damage was recorded. Late in the season, when untreated fruit were overripe (i.e. were of poor quality), there was a tendency for females to preferentially oviposit into GA₃-treated (and therefore superior quality) fruit. We also tested the combined effect of GA₃ and host-marking pheromone and pheromone-treated fruit on the oviposition behaviour of A. ludens and found that the presence of pheromone, with or without GA₃, reduced infestation to nearly zero. Wediscuss our findings in the context of the interplay between oviposition behaviour, fly density and fruit ripeness (i.e. the season) and the complexities involved in the design of biorational fruit-fly management schemes.

Keywords:

• Anastrepha ludens
• biorational pest management
• Citrus paradisi
• Diptera: Tephritidae
• fly density
• gibberellic acid

Acknowledgements

We thank the Bigurra-Armida family for allowing us to work in their citrus grove. We also thank Anabel Dávila, Norma Lozada, Isabel Jácome, Jaime Piñero, Graciano Blas, Fernando Gómez, Alejandro Vázquez, Octaviano Díaz and Cesar Ruíz for technical assistance. Rogelio Macías-Ordóñez provided expert advice on data analysis and ran some of the statistical tests reported here. We also thank John Sivinski, Francisco Díaz-Fleischer, Caroline Fowler, and three anonymous referees for comments on earlier drafts of the manuscript. Finally, we thank Alberto Anzures for helping us format the manuscript and all the figures. Mention of a commercial or proprietary product does not constitute an endorsement by any of the authors or institutions. We would like to acknowledge for financial support: the United States Department of Agriculture (Grant 58-6615-3-006), Fondo de Estudios de Investigaciones Ricardo J. Zevada and Secretaría de Agricultura, Ganadería, Desarrollo Rural y Pesca – Instituto Interamericano de Cooperación para la Agricultura (SAGARPA-IICA) through the Campaña Nacional contra las Moscas de la Fruta.