Abstract
The present study was conducted to investigate the toxicity of Aerosil 200® (fumed silica nanoparticles) and leaf extracts of four plants, Cinnamomum camphora, Matricaria chamomilla, Mentha arvensis, and Trigonella foenum-graecum against Thrips tabaci (Lind.) (Thysanoptera: Thripidae) in onion fields, as well their allelopathic effects on onions; moreover, the chlorophyll, phenol, and protein contents were determined in onions. This study was performed in completely randomized plots. After a growth period of 1 month, bioassay investigations and molecular polymorphism in T. tabaci by RAPD-PCR were performed, and total chlorophyll, phenol, and protein concentrations were investigated in onion plants posttreatment as well. The initial reduction% of the T. tabaci population in onion fields after application of a high concentration of nanoparticles (Aerosil 200® (4 ml/l)) and 8000 ppm concentrations of the four plant extracts were 83.66, 81.08, 86.92, 74.49, and 91.38%, respectively, whereas their persistence effects were 73.18, 67.78, 71.46, 66.94, and 78.29%, respectively. Furthermore, the total chlorophyll contents in onions treated with the nanoparticles and four plant extracts were 1.35, 1.17, 1.09, 1.07, and 1.18 mg/g, respectively; additionally, the concentrations of phenols were 4.65, 3.15, 3.15, 2.85, and 3.70 mg/g in onions treated with C. camphora, M. chamomilla, M. arvensis, T. foenum-graecum, and Aerosil 200®, respectively. The C. camphora extract was the most potent, as it increased the protein content in the onion plants, while the Aerosil 200® decreased the protein content in onions. In addition, DNA-RAPD showed that the polymorphism percentages were 73, 71, and 67% when treated with high concentrations of C. camphora and M. arvensis extracts and Aerosol 200®, respectively. T. foenum-graecum and M. chamomilla extracts induced the least polymorphism (17 and 16%, respectively). Overall, this study indicated that these plant extracts as well as the nanoparticles in Aerosil 200® could be used to reduce onion infestations of T. tabaci in the field environment.
Highlights
The onion (Allium cepa L.) is an important vegetable crop cultivated worldwide
Average number of T. tabaci after treatment The results presented in Table 2 showed that the average number of T. tabaci adults ranged from 46.9 ± 4.4 to 28.55 ± 5.9 in the untreated control, while it ranged from 2.95 ± 0.9 to 9.55 ± 1.7, 8.45 ± 3.1 to 12.9 ± 4.2, 4.75 ± 1.9 to 11.95 ± 4.4, and 6.45 ± 3.7 to 12.65 ± 3.9 when 8000 ppm C. camphora, M. chamomilla, M. arvensis, and T
The most effective treatment was that with the C. camphora extract, so it considered the standard toxicant and given arbitrary index value of 100 units, and the reduction effect of tested compounds descended in the following order: C. camphora, M. arvensis, Aerosil 200®, T. foenum-graecum, and M. chamomilla
Summary
The onion (Allium cepa L.) is an important vegetable crop cultivated worldwide. Egypt is considered the largest dehydrated onion source in Africa and the Middle East. Plants offer a different and alternative source of insect biocontrol agents, as they contain a wide range of bioactive materials, and many of such compounds are selective or have no harmful effects on nontargeted organisms as well as the environment, unlike synthetic insecticides. Some of these bioactive materials have been shown to have repellent, antifeedant, and toxic effects and induce enzymatic changes in insects (Adakole and Adeyemi 2012). This study was carried out to evaluate the effect of plant extracts and Aerosil 200® nanoparticles in reducing onion infestations of T. tabaci in the field using bioassays and molecular tools
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