Controlling Activites Of The Essential Oils Against Three Main Stored-product Pests

In recent years, grain storage at farmer's level has increased steadily every year coupled with a high grain production. Today, the use of synthetic insecticides for the protection of stored crop products has declined significantly due mainly to its toxicity to warm-blooded animals and insects are becoming resistant to it. One alternative to synthetic insecticides is insecticide plants. The essential oils are volatile secondary metabolites that plants produce for their own needs other than nutrition. In general they are complex mixtures of organic compounds that give characteristic odor and flavor to the plants. In this paper, the fumigant, contact toxicity, repellence and population inhibition against Sitophilus zeamaise Motschulsky, Rhizopertha dominica and Cryptolestes pusillus were studied. In addition, the respiratory intensity and physiological mechanisms were investigated. The main results are as follows: 1. Controlling activities of 9 essential oils against 3 stored-pnoduct insect pests 1.1 Fumigation on adult of stored product insects pestsFumigant toxicities of the essential oils of Citrus tangerina, Citrus limon, Citrus hongheensis, Litsea cubeba, Mentha spicata, Pinus tabulaeformis, Cinnamoum camphora, Melaleuca alternifolia, Eucalyptus globules on adults of maize weevil, Sitophilus zeamaise Motschulsky were investigated at the dosage of 16ul/L and under the exposure times of 24 h, 36 h, 48 h, and 60 h, respectively. The results proved that fumigation efficacies of the essential oils of Cinnamoum camphora, Melaleuca alternifolia, Citrus limon, Mentha spicata, and Pinus tabulaeformis were better than those of the other four essential oils. And Cinnamoum camphora oil got the best fumigation toxicity. The LC₅0S of the maize weevil adults fumigated by Cinnamoum camphora oil under the exposure times of 12 h, 24 h, 36 h, 48 h, and 60 h were 31.43, 11.26. 6.16, 2.72 and 1.11 1/L, respectively. The LT50S under the exposure concentration of 8,16,32 L/L were 33.78,24.86 and 9.93h, respectively.Fumigant activity of Cinnamoum camphora on adults of Sitophilus zeamaise Motschulskyblended with maize were carried out. The responding LC₅0s under the exposure times of 12 h, 24 h, 36 h, 48 h, and 60 h were 39.9059, 24.3095, 20.1385, 19.6320 and 15.2589 L/L, respectively, higher than those without maize. The LT₅0s under the exposure concentration of 12, 16, 24uL/L were 160.78, 25.57 and 24.85h, respectively..The fumigant toxicities of the 9 plant essential oils against adults of Rhizopertha dominica F. have been researched. The results showed that 4 plant essential oils of Eucalyptus globules, Citrus limonum, Melaleuca alternifolia C. tangerina resulted in higher adult mortality of Rhizopertha dominica and E. globules oil obtained the best efficacy (96.7% adult mortality) at a dosage of 160μ 1/L and under the exposure time of 24 hours. Adult mortality fumigated by E. globules oil reached up to 100% under the exposure time of 36 hours. The values of LC₅0 of the Rhizopertha dominica F. fumigated by E. globules oil under the exposure times of 24h, 36h, 48h, 60h and 72h were 35.907, 31.050,' 24.067, 23.396, 20.420ul/L, respectively. The LT50 of the under the exposure concentrition of 15, 30, 40 L/L were 103.46, 33.66, 24.69h, respectively.The Fumigant toxicities of the essential oils on adults of flat grain beetle; Cryptolestes pusillus Schonherr were investigated at the dosage of 40uL/L and under the exposure times of 12h, 24h, 36h, 48hand 60h, respectively. The results proved that fumigation-efficacies of the essential oils of Citrus tangerina, Melaleuca alternifolia, Citrus limcn, Mentha spicata, and Pinus tabulaeformis were better than those of the other four essential oils. And Eucalyptus globules oil possessed the best fumigation toxicity. The LC50S of the small flat adults fumigated by Eucalyptus globules oil under the exposure times of 12 h, 24 h, 36 h, 48 h, and 60 h were 15.29. 6.44, 6.55, 3.32 and 1.29 L/L, respectively. The LT50S of the under the exposure concentration of 4, 8 and 12 L/L were 45.48, 27.28 and 17.64h, respectively.1.2 Contact toxicity, repellency activity and population inhibitien of 9 essential oils on Sitophilus zeamaise MThe population inhibition, repellency activity and contact toxicity of 9 plant essential oils extracted from Citus reticulata, C. hongheensis, C. limon, Cinnamoum camphora, Citsea chbeba. Eucalyptus globules, Mentha spicata, Pinus spicata and Melaleuca alternifolia on adults of Sitophilus zesmaise motschulsky were studied. Compared to the other 7 essential oils, the efficacy of the essential oils from Cinnamoum camphora and Eucalyptus globules were better. The lethal rate of contact activity was over 50% at the concentration of 1mg/cm2, while under the exposure concentration of 4 mg/cm , adult mortality treated with Cinnamoum camphora and Eucalyptus globules amounted to 93.33% and 96.67%, respectively. The essential oils of Cinnamoum camphora and C. limon showed fairly good repellencies to adult of Sitophilus zeamaise Motschulsky and all the repellence grades reached grade V at the concentrations of 200 g/cm2, 400 g/cm2 and 800 g/cm2 after 24h. Cinnamoum camphora,Mentha spicata and Pinus tabulaeformis oils suggested better repellence activity than those of the other essential oils. The results of population inhibition activity indicated that the inhibition rate of Litsea cubeba, Cinnamoum camphora and Metaleuca alternifolia oils all amounted to 90%, and Cinnamoum camphor a oils expressed the best inhibition toxicity at a dosage of 0.1%.2.Effects of essential oils on respiratory intensity and energy sources of stored products insect pests2.1 Effects of essential oils on respiratory intensity and respiratory quotient (RQ) of stored products insect pestsThe difference of fresh weight, respiratory metabolites and respiratory quotient of Sitophilus zeamaise treated with Cinnamoum camphora oils at the concentrations of 4, 8,16ul/L and under 2,4,8h fumigating were compared. The results indicated that at the same concentration, with fumigation time increase, the fresh weight decreased and the decrease rate of weight was 17% at the dose of 16ul/L and under the exposure time of 2h; at the same treatment time, with the concentration increased the fresh weight loss was higher, consistent with the change trend of CO2 output and oxygen consumption of insects, wherera, the tendency of RQ was different.The difference of fresh weight, respiratory metabolites and respiratory quotient of Rhizopertha dominica adult treated with Eucalyptus globules oil at the concentrations of10, 20, 30μl/L and under 4, 8, 16. 32h fumigation time were also compared. The results showed that at the same concentration, the fresh weight decrease with time increase at the same treatment time, and the decrease rate of weight was 5% at the dose of 30ul/L under the exposure time of 4h, as the concentration increased the fresh weight loss was decreased, consistent with the change trend of CO2 output and oxygen consumption of insects2.2 Effects of essential oils on energy reserves of stored products insect pestsBesides a minority from physical energy (sunshine and heat), most of energy required in life activity of insects originates from chemical energy of hydrocarbon, lipids, protein and other energy sources in insect. The study showed that the triglyceride was the main stored energy sources of Sitophilus zeamaise. The content of per insect decreased significantly under the impact of Cinnamoum camphora oils and the change tendency in accordance with that of the weight loss. Under the same concentration, the content of soluble hydrocarbon declined with the exposure time wherera the soluble protein content varied not significantly. At the same fumigation time, and with the increase of concentration the content of soluble hydrocarbon went up significantly and the soluble protein content first rose and then descended.The study showed that the triglyceride was the main stored energy sources of Rhizopertha dominica. The content per insect decreased significantly under the impact of Eucalyptus globules oil and...