Bait dilution, spinosad concentration, and efficacy of GF-120 based fruit fly sprays

We tested persistence and effects of dilution of a hydrolyzed protein edible insecticide bait for control of tropical fruit flies (Tephritidae). The bait, commercially marketed as GF-120, is a mixture of the insecticide spinosad, a microbially hydrolyzed protein, sugars, adjuvants and a series of conditioners. Bait is formulated to have both an attractant and feeding stimulant function. In experiments to determine the maximum persistence of the commercial formulation we found that if bait is protected from rain but exposed to other environmental factors (heat, sunlight, humidity) the bait remained effective for about 14 days in field cages. In a laboratory cage test experiment to determine the effects of spinosad concentration in the commercial bait after exposure to field conditions, concentrations of 8 mg AI l−1 bait did not differ from the control (no spinosad). Concentrations of 80 mg l−1 had significantly lower knockdown (kill flies within 2 h) than 800 mg l−1, but the two concentrations did not significantly differ in numbers of survivors over a 4 day treatment period time. Field cage tests showed significant differences among spinosad concentrations and bait ages for knockdown of flies but 80 and 800 mg spinosad l−1 were similar for rates of survival over 4 day tests. A final test was performed to measure the effects of bait+insecticide dilution on function of the bait after 14 days aging in the field cage. Results showed that a four-fold dilution of the complete bait did not significantly reduce attraction or knockdown. The undiluted bait was superior to eight-fold dilution but did not differ from four-fold dilution.