Abstract
The application of plant-derived essential oils has been revealed to proficiently insect pest control agents, meaningfully decreasing the side-effects caused by chemical insecticides. In the present study, the toxicity of essential oil isolated from Dracocephalum kotschyi has been assessed against cowpea weevil (Callosobruchus maculatus Fabricius) as one of the most damaging and cosmopolitan insect pest of stored beans. The other objective of current study was to identify the chemical composition of D. kotschyi essential oil as one of the medicinal plants endemic to Iran. Bioassays results revealed sound fumigant toxicity of essential oil, in which a concentration of 16.41 μl/l produced up to 50% insect mortality after 72 h. Increases in concentrations of the essential oil and exposure times augmented the insect susceptibility so that the highest mortality (96.25%) was achieved at a highest tested concentration (44.12 μl/l) after 72 h. A concentration of 44.12 μl/l was enough to achieve the 50% mortality of tested insects within 10.761 h. The 24 h-LC50 value of essential oil was 24.947 μl/l which decreased to 17.794 μl/l after 72 h. Gas chromatography-mass spectrometry (GC-MS) analysis of the essential oil exposed terpenes including geranyl acetate, citral, z-citral, methyl geranate, limonene, α-pinene and α-campholenal were the main components. Based on the results of present study, the terpene rich essential oil of D. kotschyi may be considered as promising alternative to the synthetic chemicals for C. maculatus management. 
 Keywords: Callosobruchus maculatus, chemical profile, essential oil, Dracocephalum kotschyi, toxicity.
Highlights
Cowpea weevil, Callosobruchus maculatus Fabricius (Coleoptera: Chrysomelidae), is a primary insect pest of legume grains which causes high quantitative and qualitative losses on legumes including notable decreases in weight, nutritional value, and the potential of seed germination (Badii et al, 2011)
The current study aimed to investigate the fumigant toxicity of D. kotschyi essential oil against C. maculatus, hoping that it could be considered as a new botanical-derived insecticide
Analysis of variance revealed that the tested concentrations of D. kotschyi essential oil including 11.76, 16.41, 22.82, 34.74 and 44.12 μl/l (F = 225.319 and p < 0.0001) and the 24, 48 and 72 h-exposure time (F = 104.328 and p < 0.0001) had statistically significant effects on the mortality of C. maculatus
Summary
Insect rearing: The original populations of C. maculatus were collected from infested cowpea seeds from Moghan Region (Ardabil province, Iran). To prevent flocking of the insects and infesting of rearing jars, old seeds were substituted with new ones monthly. Plant materials and extraction of ssential oil: Foliage of Dracocephalum kotschyi was collected at flowering stage from Esfahan, Iran. Fumigant toxicity: The bioassays were performed with 20 one to seven day-old unsexed C. maculatus adults in 340 ml glass jars, sealed with a screw cap, as fumgant chamber. Jars without essential oil concentration asigned as the controls. Four replicates were subjected to each concentration and dead insects were counted after 24, 48 and 72-h exposure times. Probit analysis was used to estimate LC50 (Lethal Concentrations to kill 50% of insect), LT50 (Lethal Time to kill 50% of insect), the data heterogeneity and the regression lines detailes using SPSS software version 24
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