Efficacy of natural oils against the biological activity on Callosobruchus maculatus and Callosobruchus chinensis (Coleoptera: Tenebrionidae)
Authors: Sabbour Magda Mahmoud Amin 
Published: December 2019

Abstract
Background
Callosobruchus maculatus and C. chinensis (Coleoptera: Tenebrionidae) are dangerous insects to stored grains. They are controlled by chemical insecticides, which cause a lot of harmful diseases and pollute the environment. Essential oils are a new trend for controlling of storage pests.

Methods
The nano-encapsulation process was carried out by polymerization technology. The tested nano-oils were experimented at tested concentration (0.5%) for their insecticidal activities against the third-instar larvae of tested insects. After 7 days of exposure, accumulative mortality percentages were calculated in the treated and untreated control. Also, the tested nano-oils were sprayed to the foam granules and were mixed with 2 g foam/100 g cow pea for testing the oviposition inhibitory effects of the tested oils. Additionally, the experiment was designed to test the latent effect of the tested oils against C. maculatus and C. chinensis on foam as surface protectant after 90-day intervals.

Results
After 7 days of treatments, the accumulations of C. maculatus were 61.2, 42.0, 46.6, and 35.5% after being treated with rosemary, catnip, garlic, and citronella oil, respectively, as compared to 0.3% in the control. When C. chinensis were treated with corresponding oils, the accumulations obtained 68.9, 44.1, 49.9, and 37.9% as compared to 0.1% in the control. When both the target insect pests, C. maculatus and C. chinensis, were treated with the tested nano-oils, results showed that the accumulations of C. maculatus recorded 82.2, 55.8, 66.3, and 46.3% when treated with nano-rosemary, nano-anis, nano-garlic, and nano-citronella as compared to 0.1 in the control. When the corresponding nano-oils were applied against C. chinensis, the accumulations obtained 89.7, 42.8, 70.9, and 48.9% as compared to 0.1% in the control. When the tested oils and their nano were tested against C. maculatus life cycle, the number of eggs laid/female were significantly decreased to 6.4 ± 9.89 eggs/female after nano-rosemary treatments as compared to 299.9 ± 9299 eggs/female in the control. The adult emergence decreased to 1% after nano-rosemary treatments as compared to 100% in the control. The malformations of the insect significantly increased after nano-rosemary and nano-anis to 100% as compared to 0% in the control. The same results obtained when C. chinensis were treated with different tested oils. The number of eggs C. chinensis laid/female was 8.3 ± 1.0 eggs/female as compared to 298.9 ± 7.89 eggs/female in the control.

Conclusion
This work research indicate that some essential oils might be useful for managing C. maculatus and C. chinensis in enclosed spaces because of their fumigant harmful action. Plant essential oils and their active ingredient have potentially high bioactivity against a range of the target insect pests. Furthermore, they are highly selective to C. maculatus and C. chinensis. Incorporation of essential oils into a controlled release nano-formulation prevents rapid vaporization and degradation, increases constancy, and preserves the lower effective dosage/application. Treated foam with nano-rosemary and nano-garlic oils and covering gunny bags provided many efficient effects against tested insects.