Toxicity Effects of Melia azedaracht and Peganum harmala Extract Emulsions on The Eggs and Adults of The Cowpea Southern Beetle, Callosobruchus maculatus

Abstract

The experiments were conducted at the Integrated Pest Control Laboratories affiliated with the Ministry of Science and Technology at Al-Tuwaitha, with the aim of preparing emulsions of the alcoholic extracts of both Melia azedarach and Peganum harmala. The active compounds in the oil extracts were identified using a GC-Mass spectrometry. The experimental design followed was the complete randomized design, using three concentrations of the prepared emulsions (1000, 2000 and 3000 ppm) and with three replicates, to study their toxic effects on the eggs and adults of the southern cowpea beetle C. maculatus. The GC-Mass results indicated the presence of 48 compounds in Melia azedarach oil, with the highest content for the compound n-Hexadecanoic acid (25.12%), followed by oleic acid (15.60%), and tetradecanoic acid (8.05%), whereas the cyclotetrasiloxane and octamethyl had the lowest content (0.10%). Various derivatives of Azaderachtin were also detected. 59 chemical compounds were also detected in Peganum harmala oil, with the highest content for n-hexadecanoic acid (20.12%), followed by oleic acid (7.86%), tetradecanoic acid (5.63%), whereas decane had the lowest content (0.11%). The toxicity effect study showed that the highest rate of unhatched eggs was due to the Melia azedarach oil emulsion (64.32%), when used at a concentration of 3000 ppm. As for the Peganum harmala oil emulsion, the highest rate of unhatched eggs was 54.79% when a concentration of 3000 ppm was used. Moreover, the highest adult’s mortality rate was achieved when Melia azedarach oil emulsion was used at a concentration of 3000 ppm, and reached 87.5% 72 hours after treatment. Meanwhile, the highest mortality rate of insect adults was obtained when using Peganum harmala oil emulsion at a concentration of 3000 ppm (33.33%) 72 hours after treatment. It was evident that the oil emulsions of both Melia azedarach and Peganum harmala were highly efficient in controlling the insect, and their efficiency increased with the increase in concentration and duration of exposure. It can be concluded that the natural extracts investigated in this study can be used as environmentally friendly and safe alternatives to chemical pesticides in combating the southern cowpea beetle Callosobruchus maculatus.

Keywords:

Oil extracts, emulsions, southern cowpea beetle, Callosobruchus maculatus.