Spatial Pattern Of Wheat Aphids And Propylaea Japonica In Wheat Field&Lethal And Sublethal Research Of Insecticides On Wheat Aphids

In order to conservation and utilization of natural enemies of wheat aphids in fields.Wheat aphids and Proplaea japonica were sampled by grid method and ecological niche.And geostatistical method was used to analyzed the spatial patterns of wheat aphids and P.japonica and the relationships between them.The results showed that population dynamics of aphids and P.japonica was similar across the season.The P.japonica population significantly correlated with the aphids and the coefficient was 0.930.This indicate that aphids abundance has a positive impacts on that of P.japonica.In addition,both aphids and P.japonica had large ecological niche breadth and the niche overlap between them increased with increased densities of aphids,peak value reaching 0.52.The spatial patterns of wheat aphids and P.japonica also changed according to the densities of aphids during the entire sampling date.Aphids showed random distribution in the lower density.However,in the higher density,the semivariograms of aphids and P.japonica can be best simulated by exponential model,indicating aggregative distribution of their population.The 2D–maps of spatial distribution stimulated by Block Kriging interpolation can intuitively show the spatial distributions of aphids and P.japonica in the wheat field.People use chemical methods control the pests when they occur enormously.Rhopalosiphum padi(L.)is principal species of wheat aphid infesting wheat in many countries.Neonicotinoid insecticides,like imidacloprid,are now widely used for controlling wheat aphids worldwide.However,sublethal effects of imidacloprid on this aphid have not been fully investigated.Here,sublethal effects of imidacloprid on biological parameters of R.padi were investigated using an age-stage,two-sex life table approach;effects on five enzymes activities were also determined.Wheat aphids and Proplaea japonica were sampled by grid method and ecological niche and geostatistical method was used to analyzed the spatial patterns of wheat aphids and P.japonica and the relationships between them.The results showed the LC10,LC20 and LC25 of imidacloprid to aphid adults were 0.0053,0.0329 and 0.0659 mg L-1,respectively.The development duration of 1st instar nymphs,pre-oviposition period and adult longevity were significantly prolonged by these sublethal doses.The LC20 delayed female oviposition period.However,sublethal concentrationssignificantly decreased survival rate of aphid pre-adults.The intrinsic rate of increase(r),net reproductive rate(R0),and finite rate(?)all decreased at sublethal concentrations,whereas mean generation time(T)increased.SOD activity was inhibited at LC20 and LC25,whereas CAT activity increased at LC20 and LC25,and Ach E activity increased at LC20,P450 activities significantly increased in LC25.Based on these findings,the biological parameters and enzyme activities of R.padi offspring were clearly negatively affected when sublethal concentrations of imidacloprid were sprayed on parental adults.All in all,Wheat aphids and P.japonica have strong similarity in temporal population dynamics and spatial distribution.Thus,the wheat aphids management should comprehensively take into account the population relationships,spatial pattern and biological control services of the natural enemy P.japonica.sublethal concentrations of imdacloprid not only increase the death rate of the next generation,but also delay the development and reduced the fecundity.These results indicate that imidacloprid serve as spraying and seeding treatment,except kill the targets,the residuce of imidacloprid in palnts still can influence the survival rates,development and fecundity of the next generation,decrease the population quantity.