Submitted to: Crop Protection Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 22, 2005
Publication Date: February 16, 2006
Citation: Mangan, R.L., Moreno, D.S., Thompson, G. 2006. Bait dilution, spinosad concentration, and efficacy of GF-120 based fruit fly sprays. Crop Protection Journal. 25:125-133.
Interpretive Summary: The most widely used and effective method for managing fruit fly (family Tephritidae) pests is by killing adults with insecticide bait sprays. Eradication programs and effective management programs require that these baits be applied over all areas where the pest threatens fruit crops. In order to minimize ecological and health dangers from broad spectrum insecticides that have been used in management and eradication programs, we developed a bait that is attractive to the flies and induces feeding and has at least 10,000 times lower mammalian toxicity than the recommended organophosphate insecticide bait. This bait was developed under a cooperative agreement between USDA-ARS Weslaco, Texas and Dow AgroSciences to use a very low concentration of the insecticide spinosad (80 mg/liter) and a mixture of hydrolyzed proteins, sugar oils and other additives in the GF120 bait. This bait may be applied aerially or by ground for fruit fly management or as part of an eradication program. In this study we addressed three questions: How long will the bait be effective after application? How much can the complete GF120 bait be diluted? Can the concentration of spinosad in the bait be reduced? We performed a series of field cage and laboratory tests to address these questions. The standard GF120 bait was found to be fully effective for 14 days in Texas summer conditions after application and the bait did not significantly diminish in effectiveness until 20 days post application. The spinosad insecticide was equally effective at concentrations of 800 and 80 mg/liter, but bait toxicity declined and at 8 mg/liter. When the complete bait was diluted with water, we found that a 4 fold reduction in bait concentration, slightly, but not significantly, reduced bait effectiveness, but an 8 fold dilution did not kill flies better than the control (no insecticide). These results showed that spray intervals can be 2 to 3 weeks (with no rain), but dilution of more than 4 fold will greatly reduce effectiveness of the bait.
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 GF120 is a mixture of the insecticide spinosad, microbially hydrolyzed protein, sugars, adjuvants and a series of conditioners. Bait is formulated to have both an attractant and feeding stimulant function. Tests were designed to determine maximum spray interval and effects of bait or spinosad dilution for function of the bait in attracting flies and reducing the population in field cages. 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, we found that 8 mg AI liter(-1) bait did not differ from the control (no spinosad). Concentrations of 80 mg liter(-1) had significantly lower rapid kill than 800 mg liter(-1), but the two concentrations did not significantly differ in numbers of survivors over a four day treatment period. Effects of spinosad concentrations and aging effects on the bait in field cages showed significant differences among spinosad concentrations and bait ages for knockdown of flies, but 80 and 800 mg spinosad liter(-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 did not significantly reduce attraction or knockdown. The undiluted bait was superior to 8 fold dilution, but did not differ from 4 fold dilution.