| Beet armyworm, Spodoptera exigua (Hubner) , is widely distributed in the world. It is a polyphagous and gluttonous pest of 170 species of host plant. The damage, which was occurrent previously, has become gradually serious in some areas of the country since 1990, so has its resistance problem as a result of slathering insecticides.In recent years, Spodoptera exigua has arised very grievously in Chongqing, which impacts qualities and quantities of vagetables seriously. Applying synergists can enhance the activities and reduce the dosage of insecticides in large scale. It also can reduce the selective pressure and apply in resistant insect's preventing and controlling. We studied and discussed the joint action and synergism of synergists in Spodoptera exigua, in order to offer theoretical grounds of applying synergists. The main results are as follows: 1 Joint action of 5 synergists with 3 insecticidesSynergism of 5 synergists (PBO, DEM, TPP, NT, T) to beta-cypermethrin, chlorpyrifos, methmoyl were measured in Spodoptera exigua (Hubner) by spot test. Highest synergism(7.9 times )was obseverd between PBO and beta-cypermethrin within one hour after spotting, and the effect declined thereafter. Synergism increased with the dosage of PBO with the range of 10 to 20μg/larva and decreased at the dosage of 40μg/larva. The synergism between NT and beta-cypermethrin increased with the dosage of NT, the maximum being 4.4 times. However, NT showed virtually no synergistic effect to chlopyrifos and methmoyl. DEM showed satergistic effect to chlopyrifos (2.5 times) . Thad some synergistic effect to chlopyrifos only (2.5 times) . The research indicated that the same synergist had different synergism to different...
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