The peach fruit fly (PFF), Bactrocera zonata, is a serious insect pest infesting fruits and vegetables. The insecticidal activity of three monoterpenes, namely, (R)-camphor, (R)-carvone, and (1R,2S,5R)-menthol, was evaluated on the second-instar larvae of B. zonata. In addition, the latent effects of monoterpenes on pupation, adult emergence, deformation, oviposition, adult longevity, and ovarian development were also examined. The three tested monoterpenes showed pronounced insecticidal activity against B. zonata larvae with (R)-carvone being the most potent toxicant. When the second-instar larvae of B. zonata were treated with monoterpenes at concentrations of 20, 50, and 70 mg/kg for 72 h, significant reduction in pupation and adult emergence was observed. The three monoterpenes caused complete suppression of adult emergence at 100 mg/kg. Moreover, monoterpenes induced complete inhibition of egg deposition at all tested concentrations. Some adult deformations were also noticed at 20, 50, and 70 mg/kg. However, (R)-carvone was more effective than (1R,2S,5R)-menthol and (R)-camphor on the examined biological parameters. On the other hand, histological examination of the ovaries of emerged females from larvae that fed on diet treated with (R)-carvone, (1R,2S,5R)-menthol, and (R)-camphor at 20 and 50 mg/L indicated that both concentrations caused retardation in the development of ovarioles. It is clear that all the egg chambers are empty; the germarium region is constricted at base due to the failure of oocyte formation. Many vacant spaces were present between ovarioles.
