Chemical variability of Cypress (cupressus lusitanica) essential Oil and its insecticidal efficacy against Musca Domestica L.

Abstract

Housefly, Musca domestica Linnaeus (Muscidae) is a household pest that is primarily controlled by chemical insecticides that often affect the environment and promote insecticide resistance. As a safer alternative to the chemical insecticides, plants of Cupressaceae family are often used locally to repel houseflies (HFs) in different parts of Rwanda and Uganda. However, studies on their chemical characterization and bioactivity are limited. This study aimed at assessing the chemical variability and insecticidal efficacy of essential oils (EOs) from C. lusitanica Mill. (Cupressaceae) growing in three agro-ecological zones (AEZs) of Rwanda. The specific objectives were to: (i) Compare the yields of EOs from C. lusitanica leaves collected from three AEZs in Rwanda, (ii) analyze the major chemical components of obtained EOs, and (iii) evaluate their insecticidal activity against houseflies. Fresh leaves of C. lusitanica were judgmentally collected from Burera, Huye and Kayonza districts representing highlands (HLZ), midlands (MLZ) and lowlands (LLZ) zones, respectively. Steam distillation was used to extract the EOs and the average yields as per AEZ were calculated. The chemical components of EOs were analyzed using Fourier Transform Infrared (FT-IR) Spectroscopy and Gas Chromatography-Mass Spectrometry (GC-MS), while insecticidal activity was evaluated by exposing adult houseflies separately to test solutions (90, 70, 50 and 30% v/v) for 6, 12 and 24 h. Acetone and Dichlorvos (DDVP, 77%) insecticide served as test controls. The lethal doses (LD50 and LD90) of tested solutions obtained via Probit analysis and Repellency percentages (PR) were recorded. Significantly higher (P= 0.02) EOs yield was from LLZ (Kayonza) (0.39 ± 0.01% v/w) when compared to HLZ (Burera) (0.27 ± 0.02% v/w) that was not significantly different (P= 0.13) from MLZ (Huye) EOs yield (0.34 ± 0.02% v/w). FT-IR results indicated the presence of C-H stretch for alkanes (2950-2850 cm-1 ), C=O bend for aldehydes (1720-1740 cm-1 ), Ketones (1720-1705 cm-1 ), and Carboxylic acids (1725-1700 cm-1 ), C=C for alkenes (̰~1640 cm-1 ) and C-C stretch for Aromatics (900-800 cm-1 ) in the EOs. GC-MS results revealed the dominance of Sabinene, Myrcene and α-Pinene for EOs from HLZ; Umbellulone, δ-3-Carene and Sabinene for EOs from MLZ; and γ-Terpinene, Umbellulone and Bornyl acetate for EOs from LLZ. DDVP insecticide showed significantly higher fumigant (LD50 of 0.015 to 0.002 ppm and LD90 of 0.52 to 0.20 ppm) and contact (LD50 of 0.01 to 0.001 ppm and LD90 of 1.03 to 0.19 ppm) toxicities against adult houseflies exposed for 6 to 24h. EOs from LLZ showed the highest contact toxicity on houseflies exposed for 24 h (LD50=0.08 ppm; LD90=16.26 ppm), while EOs from HLZ showed the lowest toxicity in 6 h of exposure (LD50 = 0.64 ppm; LD90 = 706.21ppm). EOs from MLZ showed toxicity with LD50 values of 0.41 to 0.15 ppm and LD90 of 453.24 to 22.01 ppm in 6 to 24 h of exposure. Fumigant toxicity followed a similar trend (LLZ: LD50=0.15 ppm; LD90=24.79 ppm for houseflies exposed for 24 h; HLZ: LD50=1.90 ppm; LD90=1250.21 ppm after 6 h of exposure; and MLZ EOs with LD50 of 0.66 to 0.28 ppm; and LD90 of 521.36 to 80.65 ppm in 6 to 24 h of houseflies’ exposure. The repellent activity indicated that fewer adult houseflies were repelled at low dose (30% v/v) of EOs for 6 h, with MLZ EOs recording higher PR (42.77 ± 2.79) than LLZ (40.47 ± 0.62) or HLZ (36.81 ± 2.39). However, over 70% of houseflies were repelled at high dose (90% v/v) of EOs for 24 h (MLZ: 79.52 ± 3.30, LLZ: 75.62 ± 1.37, and HLZ: 70.38 ± 3.20%). At all tested doses, less than 14% and over 97% of houseflies were repelled by Acetone and DDVP, respectively. The variation of yields and chemical components as well as promising insecticidal activities were observed for EOs of C. lusitanica from the three study-based AEZs. The promising findings of this study call for further research into the biosafety of C. lusitanica EOs for use as safer insecticide against housefly.