Raspberry ketone supplements provided to immature male Queensland fruit fly, Bactrocera tryoni (Froggatt), increase the amount of volatiles in rectal glands

Abstract

Raspberry ketone (RK) supplements provided together with sugar and yeast hydrolysate accelerate sexual maturation and increase mating success of Queensland fruit fly (‘Qfly’) males. However, the mechanisms underlying this enhanced mating ability are currently unknown. Volatiles are an important element of Qfly sexual calling and courtship and so changes in volatiles quantity or quality may be involved, and the present study investigated this possibility. Flies were fed a diet of sugar only (S) or yeast hydrolysate mixed with sugar (YH + S) (1:3) that contained 0% RK (control) and 5% RK (treated) for 2 days after emergence. Volatile compounds were extracted from rectal glands when flies were 6, 8, 10, 20, and 30 days old. Males fed on RK exhibited a significant increase in total volatile production in rectal glands compared to RK-unfed males (control). Males fed on RK with YH + S produced significantly higher amount of volatiles than males fed on RK with sugar only. Males fed on YH + S diet produced more volatiles in the presence of RK compared to males fed on YH + S diet only. Two compounds, N-(3-methylbutyl)acetamide and N-(3-methylbutyl)propanamide were dominant in endogenously produced rectal gland volatiles comprising ca. more than 90% of the total amount in both RK-fed and control males. Considering exogenous and endogenous compounds together, unaltered RK was dominant along with these two endogenous compounds in RK-fed males in rectal gland until 30 days of age in both diet groups.