Selective Toxicity And Sublethal Effect Of Different Indoxacarb Isomers Against Plutella Xylostella And Chrysoperla Sinica

Indoxacarb,as a new oxadiazine insecticide,has been widely used in the control of lepidoptera with its unique insecticidal mechanism.It has two different isomers,namely（+）-S-indoxacarb（hereafter referred to as（+）-stereoisomer）and（-）-R-indoxacarb（hereafter referred to as（-）-stereoisomer）.（+）-stereoisomer is effective and has insecticidal activity,while（-）-stereoisomer is ineffective and does not have insecticidal activity.The indoxacarb used in agriculture mainly consists of two kinds of isomers 3:1 or 1:1 mixed racemic.With the increasing use of insecticides,more and more attention has been paid to their effects on pests and enemies.In present,the main application method of indoxacarb in the field is spraying.When killing the lepidoptera pests such as diamondback moth（Plutella xylostella）,chronic toxicity may occur to them with the decrease of the concentration.To understand the acute toxicity and sublethal effects of different indoxacarb isomers on diamondback moth and lacewing（Chrysoperla sinica）,the acute toxicity and sublethal effects of（+）-stereoisomer and（-）-stereoisomer on the two insects were studied.The main findings are as follows:1.The acute toxicity of（+）-stereoisomer and（-）-stereoisomer to diamondback moth and lacewing was determined.The LC₅₀ values of（+）-stereoisomer to diamondback moth and lacewing were 3.52 mg/L and 1.16 mg/L,respectively.The LC₅₀ values of（-）-stereoisomer against diamondback moth were 403.69 mg/L and more than 2000mg/L for lacewing.2.The sublethal effects of（+）-stereoisomer and（-）-stereoisomer on diamondback moth and lacewing were studied.The results showed that at LC₂₅ concentration of two isomers of indoxacarb,（-）-stereoisomer was the recommended dose for treatment of lacewing in the field,the acute toxicity of indoxacarb,to diamondback moth was low,but it had significant effects on pupal weight,pupal period,eggs per female and emergence rate,and had certain effects on the growth and reproduction of diamondback moth.Although（-）-stereoisomer had almost no acute toxicity to lacewing,it had significant effects on pupal weight,pupal period,eggs per female,eggs hatchability,larval survival rate,and adult survival rate.Compared with the control,the pupal weight was reduced by 29.75%,and the pupal period was prolonged by33.66%.Eggs per female,eggs hatchability,larval survival rate,and adult survival rate were significantly reduced.（+）-stereoisomer had significant effects on the growth,population quantity,and fecundity of diamondback moth and lacewing.3.The results showed that both isomers of（+）-stereoisomer and（-）-stereoisomer could decrease the predatory ability of lacewing,and（+）-stereoisomer had the greatest effect on the predatory ability.Under the LC₂₅ concentration of two isomers of indoxacarb（R-indoxacarb is the recommended dose for the treatment of lacewing in the field）,the instantaneous attack rate of lacewing larvae under the influence of（-）-stereoisomer decreased 46.81%,the time to deal with prey increased 1.9 times,and the maximum feeding amount decreased by 63.37%.The instantaneous attack rate of lacewing larvae decreased by 44.68%,the time to deal with prey increased by 4.2 times,and the maximum predation amount decreased by 80.80%under the influence of（+）-stereoisomer.In conclusion,（+）-stereoisomer of indoxacarb has high insecticidal activity and low sublethal effect on non-target natural enemies.（-）-stereoisomer had low insecticidal activity and had a great influence on the growth,development,and reproduction ability of lacewing.It was suggested to develop the indoxacarb with a high content of（+）-stereoisomer,which could not only improve the efficacy of indoxacarb but also reduce the effect of indoxacarb on the natural enemy insect,lacewing.