Effects of bait age and prior protein feeding on cumulative time dependent mortality of Anastrepha ludens (Diptera: Tephritidae) exposed to GF-120 Spinosad baits.

Authors: Mangan, Robert

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/28/2008
Publication Date: 6/12/2009
Citation: Mangan, R.L. 2009. Effects of bait age and prior protein feeding on cumulative time dependent mortality of Anastrepha ludens (Diptera: Tephritidae) exposed to GF-120 Spinosad baits. Journal of Economic Entomology. 102(3):1157-1163.

Interpretive Summary: GF-120 is a bait/insecticide mixture developed for killing fruit fly adults. The bait was developed in a cooperative agreement research project with Dow Agro-Science for area-wide programs of fruit fly management or eradication, and is composed of a mixture of hydrolyzed proteins, sugar, thickeners, and additives to enhance attraction of flies to the bait and to induce feeding by adults. The insecticide in the bait is Spinosad, which is purified from cultures of a micro-organism and is registered as an organic insecticide by USDA and several European organic product registries. The bait functions by attracting adult flies to the bait and inducing feeding. Insecticide concentration is too low to induce mortality by contact so the insects must feed in order to control populations. A series of experiments were performed to determine the time periods for mortality to take place and the effects of prior feeding by adults and exposure of the bait to air (bait aging) for attraction feeding to occur. Results showed that the insects are not attracted to the bait and may be repelled for periods up to 8 hours after fly exposure to freshly applied drops. If the bait drops are exposed to air for 24 hours prior to exposure to the insects, mortality during the first 8 hours is significantly greater. During the first 8 hours, flies that had been fed protein survived longer than flies that were protein starved. After 24 hours, prior feeding had no effect and at 48 hours all flies on both aged and fresh drops had more than 95% mortality. These results explain discrepancies between other published results showing low mortality in laboratory tests of the bait when exposure periods were less than an hour.

Technical Abstract: A fruit fly bait to attract and kill adult fruit flies (GF-120, Dow Agro-Science) was tested to determine effects of pre-treatment diet and ageing of GF-120 bait prior to use on cumulative mortality rates of the Mexican fruit fly (Anastrepha ludens (Leow), Tephritidae). Bait effectiveness depends on components to attract flies (hydro-lyzed protein, ammonium acetate), induce feeding (sugar), a number of conditioners (vegetable oils, polyethylene glycol, thickeners, adjuvants), and a toxin (0.008% spino-sad). Original laboratory experiments to test and optimize the GF-120 formulation were based on 24h, 48h, and 72h cumulative mortality assessments. The experiments reported here were designed to examine the impact on time-dependent cumulative mortality of 1) protein feeding by adults prior to exposure to bait and 2) whether the attractant-phagostimulatory function of the bait changed after bait exposure to air, specifically whether freshly applied or 24 hr-aged bait induced greater mortality in flies. In the first experiment, “protein-starved” and “protein-fed” flies both experienced varying overall cumulative mortality at all evaluation time points (4, 8, 24, 28 hr). These experiments used different laboratory stocks of GF-120. Pre-treatment diet had no significant effect on mortality for any of the sample periods. Overall mortality rates were below 10% for 4 and 8h exposure periods, but mortality in all treatments increased to 89-93% by 24hr, and 99% by 48hr. In a second test, GF-120 baits were either freshly-prepared or aged in air for 24h prior to presentation to the flies in cages. Sub-treatments comprised of protein-fed vs. protein-starved flies were included in this test as well. The 24 hr-aged bait killed significantly more flies at 4 and 8h observations than did the freshly prepared bait. Protein-starved flies had significantly higher mortality at 4h and marginally higher mortality at 8h than non-protein-starved flies. However, by 24 and 48h there were no significant differences among treatments and overall morality rose to 99-100% by 48hr. These results may explain differences noted in previous publications where fruit fly mortality to GF-120 was reported as unusually low as well as reports of bait ineffectiveness for protein-fed flies. Many of these studies used cumulative mortality assessments of less than 8 hrs., thus potentially significantly underestimating the efficacy of the GF-120 bait. The current formulation of GF-120 was designed to provide maximum attraction and phagostimulation to flies, as well as maximum persistence, and additives supplements were added to repel beneficial insects. Previous publications show that although these functions were achieved, some additives, particularly ammonium acetate, were known to be very close to a concentration that initially inhibits fruit fly feeding. Freshly applied GF-120 bait may be slightly repellent to fruit flies for the first 4-8h after application, yet these high initial concentrations of ammonium acetate promote maximum residual efficacy of the bait. The overall impact of any initial repellency of GF-120 appears negligible as judged by overall cumulative mortality at later evaluation time points.