Pre-release consumption of methyl eugenol increases the mating competitiveness of sterile males of the oriental fruit fly, Bactrocera dorsalis, in large field enclosures

Abstract

The sterile insect technique may be implemented to control populations of the oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), when environmental concerns preclude widespread use of chemical attractants or toxicants. The goal of the present study was to evaluate whether the mating competitiveness of sterile B. dorsalis males could be increased via pre-release feeding on methyl eugenol. Males of the oriental fruit fly are strongly attracted to this plant-borne compound, which they ingest and use in the synthesis of the sex pheromone. Previous studies conducted in the laboratory and small field-cages have shown that males given methyl eugenol produce a more attractive pheromone for females and have a higher mating success rate than males denied methyl eugenol. Here, levels of egg sterility were compared following the release of wild-like flies and either methyl eugenol-fed (treated) or methyl eugenol-deprived (control) sterile males in large field enclosures at four over flooding ratios ranging from 5:1 to 60:1 (sterile: wild-like males). Treated sterile males were fed methyl eugenol for 1-4 h (depending on the over flooding ratio tested) 3 d prior to release. Eggs were dissected from introduced fruits (apples), incubated in the laboratory, and scored for hatch rate. The effect of methyl eugenol was most pronounced at lower over flooding ratios. At the 5:1 and 10:1 over flooding ratios, the level of egg sterility observed for treated, sterile males was significantly greater than that observed for control, sterile males. In addition, the incidence of egg sterility reported for treated sterile males at these lower over flooding ratios was similar to that noted for treated or control sterile males at the 30:1 or 60:1 over flooding ratios. This latter result, in particular, suggests that pre-release feeding on methyl eugenol allows for a reduction in the number of sterile flies that are produced and released, thus increasing the cost-effectiveness of the sterile insect technique.

Figure 1:

Total number of eggs collected from apples suspended in field enclosures with treated (provided methyl eugenol) or control (not provided methyl eugenol) sterile males of Bactrocera dorsalis at the four over flooding ratios (sterile: wild-like males) tested. Symbols represent means (± SE; n = 7). High quality figures are available online.

Figure 2:

Relative number of sterile (unhatched) eggs collected (% total eggs collected) for treated (provided methyl eugenol) and control (not provided methyl eugenol) sterile males of Bactrocera dorsalis at the four over flooding ratios (sterile: wild-like males) tested. Symbols represent means (± SE; n = 7). High quality figures are available online.

Figure 3:

Fried's Competitiveness Index (C) for treated (provided methyl eugenol) and control (not provided methyl eugenol) sterile males of Bactrocera dorsalis at the four over flooding ratios (sterile: wild-like males) tested. Symbols represent means ± SE; n = 7). High quality figures are available online.