Toxicity, developmental and histological effects of monoterpenes on peach fruit fly, Bactrocera zonata (Diptera: Tephritidae)

In the present study, the toxicity of three oxygenated monoterpenes, viz., (R)-carvone, (R)-camphor and (1R, 2S, 5R)-menthol was evaluated against the adults of the peach fruit fly, Bactrocera zonata (Saunders). Effects of these monoterpenes on oviposition, adult longevity and ovarian development have also been studied. The tested compounds revealed strong toxic effect against the adults of B. zonata. Nevertheless, (-)-carvone showed higher insecticidal activity than (1R, 2S, 5R)-menthol and (R)-camphor. Moreover, the tested monoterpenes induced significant reduction in female longevity at 20 and 50 mg/kg compared with control, with (-)-carvone being the most effective monoterpene. In addition, egg deposition was completely inhibited when the adults were treated with (-)-carvone at 20 and 50 mg/kg, and (1R, 2S, 5R)-menthol and (R)-camphor at 50 mg/kg. Histological studies indicated that monoterpenes induced delay in the development of ovarioles of females that fed on artificial diet treated with 20 and 50 mg/kg of compounds. Changes, such as empty egg chambers; constricted germarium, vacant spaces between ovarioles and failure of oocyte formation were observed.