General Commission for Scientific Agricultural Research-
Lattakia Research Center
Tishreen University, Faculty of Agriculture
The study was carried out at the laboratories of Lattakia Research Centre and Faculty of Agriculture, Tishreen University in order to understand how the resistance of red mites to acaricides develops through knowing the reasons which lead to grow it in addition to the auxiliary effects. Accordingly, the research look for possible practical procedures to delay growing resistance against pesticides in individual strains of red mites from one side, and to control the appearance of strains to decrease its damages from the other side. This will share in control of the resistant strains through modifying the practical effects which cause developing the resistance (decrease the selective pressure). On the basis of damages of the resistance which results from genetic and biological effects, which are out of control. This must be taken into consideration.
The study has contained the following:
1. Experiments to determine the efficacy of some modern compounds according to the used concentrations practically on individuals of adult and deutonymph from the strain of resistance the two-spotted mite (Tetranychus urticae Koch) to Dimethoate organophosphate compound. The acaricides are: (Abamectin, Azocyclotin, Biphenthrin, Fluphenoxuron, Carbosulfan and Bromopropylate).
2. Experiments to explain the effects of many practical procedures (treatments) on efficacy of tested pesticides on individuals of the studied resistant strain.
The performed practical procedures have concluded nine different treatments as the following:
a) Direct treatment the resistant of adult to Dimethoate (treatment A).
b) Direct treatment the resistant of deutonymph to Dimethoate (treatment A1).
c) Treatment of the resistant adult to Dimethoate after stopping the selective pressure on it for five months (treatment B1).
d) Treatment of the resistant adult to Dimethoate after stopping the selective pressure on it for five months to replace pressure in other materials respectively (treatment B2).
e) Treatment of the resistant adult to Dimethoate after stopping the selective pressure on it for five months and then return the pressure again for two months (treatment B3).
f) Treatment of the resistant adult to Dimethoate after stop the selective pressure for 10 months (treatment B4).
g) Direct treatment of the resistant adult to Dimethoate with mixture of tested acaricide and antiecdysis compounds (treatment C1).
h) Direct treatment of the resistant adult to Dimethoate with mixture of tested acaricide and extract of (Melia- azedarach) as antifeedant (treatment C2) .
i) Direct treatment of the resistant deutonymph to Dimethoate with mixture of tested acaricide and antiecdysis compounds (treatment C3).
The study shows the effect of performed treatments on average mortality (%) caused by the tested acaricides of the individuals of sensitive and resistant strains.
Additional experiments were carried out to appear the differences between efficacy of compounds that were used in the study through the variety in the degree and the clearness of external symptoms of the treated plants in acaricides and which were infected by the individuals of resistant strain, and this support the results.
The results of performed experiments with leaf-disk method of Phaseolus vulgaris and treated with immersion for 5 seconds in solution of acaricides before removing the mites to it. Abamectin was the best among the tested compounds for all performed treatments with mortality 100% during 24 hours from the treatment in resistant the individuals of adult and deutonymph and without significant differences between sensitive and resistant strains.
This result shows high efficacy of Abamectin in controlling the resistant strains, and it is equal to efficacy of Bromopropylate (standard control). After Abamectin came Azocyclotin and Biphenthrin with significant differences for the first, the final average of mortality 89.12%, 92.92%, for the first and 76.41%, 83,63% for the second in individuals of resistant strain of adult and dentonymph respectively.
It was significant differences between the three mentioned compounds and the other tested compounds, the lowest efficacy was of Fluphenoxuron with adult and Carbosulfan with deutonymph.
On the other hand, the experiments have proved the equality of the final mortalities (%) of Abamectin with treatments A, B1, B2, B3, B4, C3, A1 which was 100%, while the efficacy was decreased with C3 (97.30%) and C1 (71.30%).
The best treatment was B4 (94.83%) then A1 (92.92%) with Azocyclotin.While C2 (90.47%) was the first, then B4 (85.78%), the third was B2 (84.96%) with Biphenthrin.
The first treatment with Fluphenoxuron was C2 (49.41%), then A1 (39.34%), and the third treatment was B4 (19.40%).
The result with Carbosulfan was not enough except treatment C2 (58.76%) which was the best, then B4(32.04%) ,and the third was C3(25.88%) respectively.
The efficacy of standard control Bromopropylate was complete except C3 (80.94%) and C1(75.26%) when mixed it with the half recommended quantity for Bromopropylate and antiecdysis compounds on dentonymph and adult respectively.
Generally, the results showed the treatment C2 (direct treatment with mixture acaricide and extract as antifeedant ) was the first, then B4 (direct treatment of resistant individually after stopping selective pressure for 10 months).
One important result which the study has showed it that treatment C2 (using mixture antiecdysis compounds and antifeedant against adult) was before direct treatment of deutonymph with antiecdysis compounds alone.
This shows the importance of antifeedants and planted extracts of materials that are natural and safe. However, adding antifeedant to antiecdysis compounds gave good results with adult comparing with deutonymph.
The results with Carbosulfan have emphasized the importance of antifeedants, and the treatment C2 was the best among the other treatments.
It is clear that practical procedures are very important to control the resistant red mite to acaricides especially stop selective pressure of pesticides for enough period (treatment B4) and using mixture of pesticides and Antifeedants (treatment C2) and using materials respectively (treatment B2) besides to direct treatment (A) was the last among the treatments except the two treatments C1 (with all pesticides) and C3 (with Azocyclotin). The treatment (A) was equal to treatments (B1, B1, B2, B3, B4, C2, A1) only when using Abamectin and standard control Bromopropylate, that is because of increasing the efficacy of used concentrations of the two compounds. There are no significant differences among treatments.
Finally, the experiments of external symptoms emphasize the results of performed tests with the different treatment.