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INTRODUCTION: Food-based protein baits are the primary tool used against fruit flies. GF-120® is composed of the toxicant spinosad and SolBait, which is a food-based attractant and phagostimulant for fruit flies. Since 2009, it has become the sole compound permitted for the control of Medfly in citrus orchards in Israel. In this study, we characterized various aspects of the effectiveness of GF-120 to Medfly. METHODS: The Medflies in most of the tests were held on sugar only and water, and starved for 20 h prior the test. Tests were carried out in ventilated 270 ml plastic containers, 10 flies/ container (x 5 replicate/ treatment). Drops of GF-120® diluted in water and/ or SolBait, were applied with a micropipette on glass slides that were offered to the flies for 2 h. Mortality was determined 24 h later with respect to the mortality of controlled flies. For studying natural exposure of GF-120 to sunlight, drops of aerial spraying mixture (1:1 in water) were applied on the upper surface of peripheral leaves on the sunny side of citrus trees. The leaves then were picked at different periods and subjected to the toxicity assay. RESULTS: Spinosad generated two distinctive dose- mortality responses: (a) when ingested with bait (GF- 120), (b) upon contact without bait (Tracer® Ultra) (Fig. 2). Males were slightly, but not significantly, more susceptible than females (Fig. 3). The droplet size of GF- 120 also plays a role in the toxicity (Fig.4). Drops in the field exposed to the sun lost most of their toxicity within 10 days (Fig. 5). In addition, drops of GF-120 disappeared off the leaves in time, most likely due to the consumption of insects (Fig. 1 & 6). The mortality of wild flies, which tolerate starvation for a few days, was related to the amount of consumed compound, hence depended on the fly‟s „appetite‟ (Fig. 7). Well-fed flies barely touched the drops, hence were almost unaffected. This characteristic sheds light on „sanitation‟ in the orchard from a different aspect: neglected fruit may serve as a source of nourishment for the fly that competes with the GF-120 in the orchard and reduces its effect. TOXICITY OF BAITED SPINOSAD TO MEDFLY: FROM THE LABORATORY TO APPLICATION Y. Gazit, S. Gavriel, R. Akiva and D. Timar The “Israel Cohen” Institute for Biological Control, Plant Production and Marketing Board, Citrus Division, Israel. [email protected] Figure 2: Dose mortality curves of two Spinosad based compounds: The effect of Spinosad (Tracer® Ultra) was determined by contact (mostly) and that of GF-120 after an ingestion assay. R 2 = 0.9558 R 2 = 0.8954 0 20 40 60 80 100 0.1 1 10 100 1000 10000 Dose (ppm) Mortality (% ± SE) Spinosad GF-120 R 2 = 0.8428 0 20 40 60 80 100 0 5 10 15 Time (days) Mortality (% ± SE) Figure 5: Toxicity of 3 μl drops of GF-120 and water (1:1) that were applied on citrus leaves facing the sun to Medflies as a function of time. R 2 = 0.9151 0 20 40 60 80 100 0 5 10 15 Time (days) Number of drops (% ± SE) GF-120 Malathion Figure 6: Disappearance of 3 μl drops containing either GF- 120 in water (1:1) or malathion (aerial spraying ULV formulation of Fyfanon mixed with Buminal 27: 38) that were applied on citrus leaves in a commercial orchard. R 2 = 1.000 R 2 = 0.999 0 20 40 60 80 100 0 1 2 3 4 5 6 Dose (ppm) Mortality (% ± SE) Females Males Figure 3: Dose mortality curves of GF-120 to Medfly (females and males). Figure 4: Medfly mortality as a function of size of GF-120 drops and time. Fine (0.23 mm Ø) drops were sprayed from a distance with a home sprayer and large, 5 μl drops (~5 mm Ø), were applied with a micro-pipette. Asterisks indicate significant differences at P<0.05(*) and P<0.01(**) according to LSMeans Student's t test. R 2 = 0.9404 R 2 = 0.8141 0 20 40 60 80 100 0.01 0.10 1.00 10.00 100.00 Time (d) Mortality (% ± SE) spray large drops * * ** Figure 7: Consumption of GF-120 and the conscience mortality rate, as a function of Medfly starvation. The fly‟s ingestion was evaluated by subtracting the intact drops from the initial number. R 2 = 0.9707 R 2 = 0.9447 0 20 40 60 80 100 0 30 60 90 120 150 180 Starvation (h) Mortality (% ± SE) 0.0 0.5 1.0 1.5 2.0 Consumption (drops/fly) Mortality(%) Drops/fly Figure 1: drops of GF-120 in water (1:1) (left) or baited malathion (Fyfanon with Buminal 27: 38) (right) 7 d after being applied on citrus leaves in an orchard. P - 31
