Attraction of Mexican Fruit Flies (Diptera: Tephritidae) to Lures Emitting Host-Fruit Volatiles in a Citrus Orchard

Abstract

Better lures for the Mexican fruit fly are needed because existing lures are cumbersome to use and last less than two weeks in traps. Robacker et al. (1992) developed an attractant (CEHO) for the Mexican fruit fly (Anastrepha ludens Loew) containing four components of volatiles from fruit of chapote amarillo (Sargentia greggii S. Wats.), a natural host of the fly. The attractant was more attractive than Torula yeast in McPhail traps during flight-chamber tests. The purpose of this paper is to report evaluation of a novel formulation of CEHO as an attractant for the Mexican fruit fly in a citrus orchard. Lures were prepared using a membrane-based formulation described previously for synthetic pheromone of Toxotrypana curvicauda (Gerstaecker) (Heath et al. 1996). CEHO chemicals (1,8-cineole, ethyl hexanoate, hexanol, and ethyl octanoate, all >98% pure) were obtained from Aldrich Chemical Company (Milwaukee, WI). Two loadings of the chemicals were prepared. Loading A contained 25 ,ul and B contained 100 tl of a 10:1:1:10 mixture of CEHO chemicals in the sequence listed above. Tests were conducted in a citrus orchard in Weslaco, Texas. Laboratory culture Mexican fruit flies (origination Morelos, Mexico, 1953) were used. Flies were irradiated with 70-85 Gy (7Cs source) 1-2 days before adult eclosion. Two thousand 2-13 day old flies (sex ratio approximately 1:1) were released evenly throughout the orchard twice each week. Flies were fed sugar and water until release. Ten linear blocks of four trees each were selected in the orchard. Six blocks contained Meyer lemon and four blocks contained naval orange trees. Baits were tested in McPhail traps (Baker et al. 1944) that were hung one to a tree. Each block contained 3-4 traps: 1-2 CEHO treatments; a water blank; and a standard Torula yeast trap. Torula yeast traps contained three Torula yeast/borax pellets (Sit-Khem Corp., Michigan City, IN) in 300 ml of water. CEHO lures were suspended in the entrance holes on the undersides of traps. CEHO traps, and water blanks, contained 300 ml of amber-colored water prepared from red, yellow and green McCormick food colors (McCormick & Co., Inc., Baltimore, MD) to mimic the color of Torula yeast. The water also contained 0.01% Triton (Rohm and Haas Co., Philadelphia, PA) as a wetting agent. Traps were washed and flies were counted each week for four weeks. Positions of treatments within blocks were randomized for the first week, then moved sequentially within each block each week. Torula yeast and amber-colored water were replaced each week. CEHO lures were reused each week for four weeks. Three experiments were conducted. Experiment 1 treatments were: CEHO (A); CEHO (B); Torula yeast; and water. Each lure type was replicated 80 times (10 blocks x 4 weeks for each of 2 sets of lures) from April 22 to June 16, 1994. The orchard contained scattered mature fruit and only a little new fruit at the beginning of the experiment, and nearly full grown immature fruit by the end. Experiment 2 treatments