Investigating the insecticidal and repellent activity of Crocus sativus petal on Tribolium confusum (Col. Tenebrionidae) adults and its chemical constituents

Saffron (Crocus sativus) petals are used as an organic agent in agricultural industries. In the present study, the insecticidal activity and repellent effect of the saffron plant petal extract was investigated on the confused flour beetles (Tribolium confusum Jacquelin du Val.). Storage pests are one of the important issues of storing products from harvest to consumption contributing to 10-30% of damages to the products. The flour bug T. confusum is a pest found all over the world, causing great damage to various crops such as flour, beans, etc. every year. These pests have a high reproduction rate and it is necessary to protect the stored products from their contamination. In recent years, many studies have been conducted on the insecticidal and repellent effects of plant essential oils, and some of these compounds have been introduced as suitable candidates for pest management, especially in warehouses. Research on the biological properties of plant essential oils can lead to the identification of new biological insecticides compatible with organic agriculture. A large number of plants (17,500 species) and their secondary metabolites have physiological and behavioral effects on many pests, especially storage pests, such as repellent effects, respiratory effects, and inhibition of nutrition and spawning. In some cases, plant insecticides function as an interesting substitute for industrial insecticides in pest management as a safer option for humans and the environment. In terms of agricultural pest management, plant insecticides have been adapted as the best option to preserve organic food products in developed countries.

Maceration method was used for extraction, and methanol was applied as a solvent. After 72 hours, the contents of each container were filtered twice using filter paper and the resulting extract was stored in the refrigerator. The experiments were carried out at 27±1°C, 65±5% relative humidity, and in the dark. The T. confusum was obtained from the Entomology Laboratory of the Department of Plant Medicine, Zakaria Razi Laboratory, Islamic Azad University, Science and Research Unit. For the fumigant toxicity, the adults were exposed to 100, 500, 1000, 10000, 50000 and 100000 ppm of methanol extract of saffron and mortality rate was recorded 4, 5, 6 and 7 days after exposure. While, for the repellency test, the adults were exposed to the concentrations of 4.2, 5.27, 6.34 and 7.41% and the repellency was checked 4, 5, 6 and 7 days after exposure.

Saffron flower petals extract caused fumigant toxicity in T. confusum adults. According to the analysis of statistics, the mortality rate increased with increasing concentration and exposure time. In addition, the mean repellency of saffron petal extract against adults when exposed to the concentrations of 4.20, 5.27, 6.34, and 7.41% was 13.33, 18.33, 23.33, and 26.66 % respectively. The chemical analysis of the extract by GC MS device showed that the main volatile compounds in the saffron petal extract were C8H16 (Cyclopentane Propyl npr), C8H18 (Hexane 3, 3 dimethyl), C8H18 (Octane Octane) and C16H34 (Hexadecane).

Saffron petal extract causes fumigant toxicity in T. confusum adults, and mortality increases with increasing concentration and duration of exposure to the extract. Since repellents can be considered as one of the new methods in controlling stored-products insect pests, the repellency of saffron petal extract was evaluated in T. confusum adults. The repellency of saffron petal extract on T. confusum adults increased with increased time of exposure. The chemical compounds of saffron petals confirm the presence of terpenoids, ethyl acetate, methanol, and aqueous extract of saffron petals. The presence of these chemical compounds proves the antibacterial properties of saffron petal extract.