Impact of Cymbopogon flexuosus (Poaceae) essential oil and primary components on the eclosion and larval development of Aedes aegypti (Diptera: Culicidae)

Abstract

The current study describes the effects of sub-lethal concentrations and constituent compounds (citral and geranyl acetate) of Cymbopogon flexuosus essential oil (EO) on the development of Aedes aegypti (L.) eggs and larvae. To demonstrate the ovicidal activity of EO, we treated embryonated eggs with 6, 18, and 30 mg.L-1 and larvae with 3 and 6 mg.L-1 EO concentrations. Citral and geranyl acetate were evaluated at 18, 30, and 42 mg.L-1 and compared with commercial growth inhibitors (diflubenzuron and methoprene) at 3 and 6 mg.L-1 concentrations. For each treatment, we measured larval head diameter, siphon length, and body length. To complement the morphological analysis, we examined concentrations of moult hormone (MH) and juvenile hormone III (JH III) using high-performance liquid chromatography (HPLC) coupled to mass spectrometry. The EO decreased egg hatching at all concentrations: 6 mg.L-1 in 45.3%; 18 mg.L-1 in 23.3%, and 30 mg.L-1 in 34.6%. EO also altered molting among larval instars and between larvae and pupae, with an increase in the length (3 mg.L-1: 6 {+/-} 0.0 mm; 6 mg.L-1: 6 {+/-} 0.7 mm) and head width (3 mg.L-1: 0.8 {+/-} 0 mm; 6 mg.L-1: 0.8 {+/-} 0.0 mm) compared with the control group (length: 5.3 {+/-} 0 mm; head width: 0.7 {+/-} 0.0 mm). We did not detect chromatographic signals of MH and JH III in larvae treated with C. flexuosus EO or their major compounds. The sub-lethal concentrations C. flexuosus EO caused a similar effect to diflubenzuron, decreasing hormone concentration, extending the larval period, and death.