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Abstract
Study aimed to throw light ~on the possibility of build up resistance in field strains of Bemisia tabaci, to insecticides with novel modes of action. The main results of this study were:
1. Testing the susceptibility of different field strains (Fayoum, Beheira, Dakahliya, Gharbaia) Collected during ’2000, 2001 seasons at the early and the end cotton growing season. The results showed.
a- The level of resistance to all tested compounds, in season 2000 was less than in 2001 season for most insecticides.
b. Neonicotinoid insecticides, thdimethoxam and imidacloprid. Were more toxic than the tested insecticides for all strains in both years.
c. Fayoum strain exhibited high level toward most tested insecticide.
2. Biological performance of certain pest control agent to B.tabaci under field conditions. Wis trial was carried out in the Etay El Baroud in Beheira g.overnorate in the 2000 and 2001 seasons. The results summarized showed that. The imidacloprid was the most effective compound for both adult and immature stages, in both years 2000 and 2001 while profenofos was the least effective.
3. Laboratory selection pressure applied for Beheira strain to build up resistance toward profenofas and thiamethoxam. The level of selection pressure was Lc5o for each compound. After selection for eleven generation the revel of resistance to thiamethokain was 188.91 fold and for profenofos 7.20,41 fold.
4. There was no cross resistance between thiamethoxam and thiocyclum, buprofezin. Howeverthere was profenofos resistant strain showed cross resistance with all tested chemicals except thiocyclam. and buprofezin.
5- laboratory studies were directed to explore the mechanisms of resistance in Bemisia tabaci by usinr enzyme. inhibitors, DEF as an inhibitor of hydrolytic estrases, PB as an inhibitor mixed function oxidases (MFO), DM is an inhibitor of glutathione &transfers and TCP is an inhibitors of nonspecific esterase’s. The synergist were mixed at different ratios 50ppm 10 pm with LF59. of the tested insecticide Data of synergic a . especially at the concentration 5Oppm
tction showed that DR 9.66) had synergistic effect to thiamethoxam resistant strain. While in a profenfos resistant strain high level of synergistic was occurred with PB at all levels of mixing. These result indicatecl the role of detoxification enzymes in the mechanism of resistance in which esterases and mixed function oxidases play an important roles in the resistance to thiamethaxom and profenofos respectively.
6. Eldetrophoretic patterns of proteins In thiamethaxom resistance strain isolated 62 bands ’With diffrent molecular weiiht (M.V) ranged from 11. 2to 1140KDa. In case
of profenofos resistance strain was separated into 86 different bands their
molecular weight (M. ranged from 4.1 to 150 KDa.
b) Electrophoresins ata (tiamethaxom resistant strain) showed that the
esterases were detected in generations 3,5,8,9 but slight esterases were
noted in generations 2,4 6 7 11 While in case of proFeiifos resistant
Strain the esterasesre aetecied in ’generations 5 6 7,8,9,11.
7. Proposal Sequences of insecticides applications as an strategy for resistance
management the results showed that, the rogram with sequence of lambda¬ cyhalothrin, profenofos, imidactoprid an buprofegin was the best PT9grams.
Key words: Bemisia tabaci, Resistance, Cross resistance, Novel insecticides.