الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
 |  | from | 132 |  |  |
| | | from | 132 | | |
Abstract
The pesticides have a vital role in the integrated pest management of Spodoptera littoralis, (Abd-El-Aziz and Salama 2020). Chlorpyrifos and Cypermethrin are the most commonly used insecticides in our country to manage such a pest (Bagni et. al. 2020, El-Sheikh 2012). Which led to the emergence of insect resistance to these pesticides and thus increasing the lethal doses, which increase pesticide residues in agricultural crops. (Pagliuca et. al. 2005). There have been numerous sample preparation methods documented for determining pesticide residues in food. A well-known sample cleaning technique called QuEChERS (quick, easy, cheap, effective, robust, and safe) for measuring insecticide residues with certain sorbents. The common sorbents used were Octadecyl silica (C18), primary secondary amine (PSA) and graphitized carbon black (GCB) (Durak 2020).
The study’s objectives were improvement of the established (QuEChERS extraction method) that used for determination of Chlorpyrifos and Cypermethrin residues, which are used to control the cotton leafworm S. littoralis that infests potato and tomato crops, by making a modification in QuEChERS method to increase its efficiency in detecting residues of chlorpyrifos and cypermethrin in tomato and potato crops.
Modification of the conventional QuEChERS were made through conversion of commercially available sorbents of Octadecyl silica (C18), Graphitized Carbon black (GCB) and primary secondary amine (PSA) to their corresponding nanoparticles, C18-NPs, GCB-NPs and PSA-NPs by ball milling technique and used in the sample purification step to filter out more unwanted impurities that prevent the GC-MS/MS device from accurately detecting the ratio of pesticide residues in tomato and potato samples.
The fourth larval instar of Spodoptera littoralis of both the L (lab) and F (field) strains, were reared and then subjected to bioassays to measure the efficacy of the two insecticides. LC50 and LC90 were calculated. Resistance Ratio (R.R.) were measured for each insecticide through mathematical equation using LC50 of both lab and field strains.
The LC50 of the cotton leafworm S. littoralis was calculated when using chlorpyrifos insecticide, it was 0.55 and 190.3 for the laboratory and field strain respectively, while the LC50 when using cypermethrin insecticide was 16.97 and 100 for the laboratory and field strain respectively. The cotton leafworm, Spodoptera littoralis, was found to be resistant to both chlorpyrifos and cypermethrin, where the field strain was 346 times more resistant to chlorpyrifos than the laboratory strain, while the field strain was 5.89 times more resistant to cypermethrin than the laboratory strain.
A modification was made to QuEChERS method by converting the three sorbents C18, PSA and GCB to the corresponding nanoparticles. characterization of these nanoparticles was carried out using the device XRD, FTIR, BET and TEM, and the results of the XRD analysis were that There was no clear change in the three adsorbent materials used after converting them to nano size. The results of the FTIR analysis showed that there was no change in the chemical composition of C18 and PSA, while there was a slight change in the composition of GCB after converting it to nano size. When photographing the three samples before and after converting them to nano size using a transmission electron microscope, it became clear that the three materials had reached to the nano size. While the results of the BET analysis were, the surface area of the sorbents increased after converting them to the nanoform, as the surface area of C18 increased from 208.72 to 487.01 after converting to nano, and the surface area of PSA increased from 196.09 to 464.09 after converting to nano, and the surface area of GCB increased from 221.34 to 519.41 after converting to nano.
The results showed that silica octadecyl (C18) nanoparticles absorbed a high percentage of unwanted impurities in the potato sample and thus detected the residues of chloropyrifos and cypermethrin with higher efficiency in the potato sample, while the primary secondary amine (PSA) nanoparticles absorbed a high percentage of unwanted impurities in the tomato sample, therefore, chlorpyrifos and cypermethrin residues were detected with higher accuracy in the tomato sample.