Assessing Methyl Eugenol and Dietary Protein on Peach Fruit Fly, Bactrocera zonata Saunders (Diptera: Tephritidae) Males for Enhancing the Effectiveness of SIT Application

Abstract

Methyl eugenol (ME) naturally occurs in several plant species. It strongly attracts males of many Bactrocera species. The peach fruit fly, Bactrocera zonata Saunders (Diptera: Tephritidae) is endemic to South and Southeast Asia. The species is a quarantine pest and interferes with the international trade of horticultural produce. The male annihilation technique (MAT) incorporating the ME is an environmentally benign technique that can be used to suppress B. zonata population. Due to certain limitations of MAT, the sterile insect technique (SIT) has been used to eliminate several pests successfully and has the potential to be applied against B. zonata. The SIT inherently relies upon mass rearing of males of the target insects, sterilizing them with ionizing radiations and releasing them in the target area where mating of the sterile males with wild females will not produce offspring. The sustained releases of sterile males can lead to eradication/suppression of the target population. For the success of SIT, sterile males must be competitive, and the increased mating success of sterile males can enhance the efficiency of SIT. ME can increase the mating success of several Bactrocera species males but the necessary knowledge on how ME can be utilized to increase B. zonata male mating success for enhancing the efficiency of SIT was not available. The simulation model suggested that the simultaneous application of MAT and SIT can enhance the cost-effectiveness of fruit fly control programmes manifold. The objectives of the current studies were to assess, i) Effect of methyl eugenol on B. zonata male age-dependent response and mating success, ii) ME delivery system, adoptable in SIT operational programs, and assess the ME delivery system for suppressing the subsequent response of ME treated males to ME-baited traps for simultaneous application of MAT and SIT, iii) Effect of methyl eugenol treatment and dietary protein on B. zonata male mating success, and iv) Effect of methyl eugenol treatment and dietary protein on B. zonata male survival. The results showed that males initiated their mating at 8 days of age and attained the highest mating success at 16 days of age. A proportion of immature males responded to ME, the percentage of responders increased with age and the maximum response was observed during the sexual maturity age. ME treatment at sexual maturity age significantly enhanced the male mating success over untreated males. The males treated with ME at a sexually immature age (5 days; a standard protocol of holding males in sterile males holding and release facility), achieved significantly higher mating success after reaching sexual maturity age. These findings suggested that B. zonata males can be treated with ME at 5 days of age in sterile male holding and release facilities and released in the field to achieve higher mating success after attaining sexual maturity. Owing to ME-feeding impracticable, ME-aromatherapy which is a practicable delivery system in sterile male holding and release facility was developed. The ME-aromatherapy given at 5 days of age yielded higher mating success of males, after attaining sexual maturity. The ME aromatized males also exhibited reduced response to ME-baited traps. ME-aromatherapy will allow the simultaneous application of MAT and SIT. For assessing the effect of dietary protein and ME, the males were provided with a) dietary protein and ME (ME+P+) b) dietary protein (ME-P+) only, c) sugar-only diet and ME (ME+P-), and d) untreated (ME-P-) and their mating success was evaluated in the field cages. The protein fed males treated with ME at sexual maturity age achieved higher mating success over protein-fed or protein-deprived males and ME did not enhance mating success of protein-deprived males. The ME+P+ males that were fed on dietary protein for 5 days of age, treated with ME and then switched to a sugar-only diet, achieved higher mating success over ME-P+, ME+P- and ME-P- males after attaining sexual maturity age. The study showed that prerelease dietary protein and exposure of ME at 5 days of age is sufficient for males to achieve higher mating success and this protocol is expected to enhance the efficiency of SIT application in the field. In the last section of the current study, the effect of ME and dietary protein on the survival of B. zonata males was investigated. The males were fed for 5 days on their respective diets and were assessed under extreme scenarios of the absence of food and water and then with access to water. The results showed that sugar-fed males (ME-P-) had significantly more survival than other males. The protein-fed males (ME-P+) had the lowest survival. The present study also indicated that ME+P+ males had less survival than sugar-fed males, however, they performed better than the males of other treatments. The current study indicated that ME-aromatized males had better survival than ME-fed males. ME-aromatherapy can be adopted as a ME delivery system in sterile male holding and release facilities and such treatment enhances male mating success, with a positive effect on male survival. The current study developed the protocols for treating B. zonata males with ME that will enable the simultaneous application of MAT and SIT and enhance the efficiency of the control programme incorporating the SIT.