SYNERGISM AMONG SOME INSECTICIDES AND ERGOSTEROL BIOSYNTHESIS INHIBITING FUNGICIDES AGAINST PECTINOPHORA GOSSYPIELLA (SAUND.)

Abstract

The toxicity of organophosphorus insecticide chlorpyrifos, pyrethroid insecticide cypermethrin, insect growth regulators, chlorfluazuron and biocide as a natural products spinosad increased when mixed with the ergosterol biosynthesis inhibiting (EBI) fungicides to newly hatched larvae of Pectinophora gossypiella. This study was carried out by feeding newly hatched larvae on artificial diet treated with different concentrations of the tested compounds either alone or in mixtures with EBI fungicide or IGR. Interestingly, these fungicides did not kill the larvae up to 100 ppm, moreover 20 ppm of each EBI fungicide with concentrations of the insecticides increased the toxicity of these insecticides. Also, all data indicated that the calculated LC50 of the insecticides alone were higher than the insecticides and fungicides or IGR. For instance, chlorpyrephos at 6.25 ppm caused 90.0 % larval mortality and 100.0 % larval mortality when mixed with 20 ppm of each fungicides or 3 ppm when mixed with IGR. The LC50 of chlorpyrifos alone were higher than that of chlorpyrifos when mixed with EBI fungicides and chlorfluazuron as IGR. For example, chlorpyrifos had LC50 equal 2.89 ppm, but 0.88, 0.48, 0.26, 0.26, and 0.13 ppm when mixed with difenoconazol, tetraconazol, imazalil, fenarimol and chlorfluazuron respectively. Also, the insecticidal action increased by 3.2, 6.02, 14.45, 11.11, 22.23 folds when mixed with the latter fungicides or the insect growth regulators. Cypermethrin at 25 and 12.5 ppm resulted in 81.66 and 78.33 % larval mortality when used alone, while these concentrations caused 100.0% larval mortality when 20 ppm of each fungicide or 3 ppm of IGR added to these concentrations. The LC50 values decreased when cypermethrin mixed with EBI fungicides or IGR, the LC50 were 1.95, 0.85, 1.01, 0.65 and 1.5 ppm when mixed with difenoconazol, tetraconazol, imazalil, fenarimol and chlorfluazuron compared with 3.01 ppm when cypermethrin used alone. Also, the insecticidal action increased by 1.54, 3.45, 2.98, 4.63, and 2.01 folds when mixed with the mentioned fungicides or the IGR respectively. Chlorfluazuron at 6.5 ppm caused 86.66 % larval mortality after 72 hr post treatment but the same concentration caused 100 % larval mortality after 48 hr from treatments when mixed with the latter EBI fungicides. LC50 values were 0.61, 0.11, 0.36 and 0.29 ppm respectively, compared with 1.01 ppm when used alone, insecticidal action increased by 6.01, 9.18, 2.85 and 3.48 folds respectively. Spinosad at 7.5 ppm caused 85.0 % larval mortality but the same concentration induced 100.0 % larval mortality when mixed with imazalil and fenarimol as EBI fungicides or chlorfluazuron as IGR and caused 95.08 and 98.33 when mixed with both difenoconazol and tetraconazol as EBI fungicides. LC50 values were decreased to 0.51, 0.41, 0.76, 0.61 and 0.56 ppm when was mixed with difenoconazol, tetraconazol, imazalil, fenarimol and chlorfluazuron respectively, compared with 1.54 ppm when used alone, insecticidal action was increased by 3.08, 3.21, 1.97, 2.56, and 2.75 folds respectively. These results suggested that EBI fungicides and the IGRs enhanced the insecticidal activity of chlorpyrifos, cypermethrin and spinosad against the pink bollworm P. gossypiella.