Survey Of Natural Enemie Of Pseudaulacaspis Pentagona (Targioni-Tozzetti) And Predation Potential Of Its Dominant Species

Pseudaulacaspis pentagona(Targioni-Tozzetti) is the main pest of fruit trees such as peach tree,plum tree,apricot tree and others,among which peach trees are seriously damaged in recent years.Biological control by conservation of natural enemies of this pest can be an effective approach to control it.In this paper,after investigation of assembly of natural enemies in Kashi,Xinjiang,experiments were carried out in biology,functional responses,and spatial pattern of individuals of two dominant pradtors,Chilocorus geminus Zaslavskij and Cybocephalus nipponicus(Endrody-Younga).The main findings are as follows:1.Field survey was carried out on natural enemies of Pseudaulacaspis pentagona(Targioni-Tozzetti) in Tazihong town,Shule county,and Awaiti town,Shufu county,Kashi.The survey uncovered eight natural enemy species,Which came from six families in four orders of two classes.The natural enemies include(ⅰ) six predaceous arthropods,Cybocephalus nipponicus(Endrody-Younga),Chilocorus geminus Zaslavskij,C. dunhuangensis Tian and Stethorus Punctillum Weise from Coleoptera,and Chrysopa shansiensis Kuwayama from Neuroptera,and Icius courtaulidi Bristowe from Salticidae,Araneae;and(ⅱ) two parasitoid wasps,Encarsia berlesei Howard and Cerapteroceroides similis Ishii two predaceous beetles dominated the natural enemy assembly based on population size and dominance index,including C. geminus and C.nipponicus.2.The investigation of population dynamics made over the season showed that the two predaceous insects closely succeeded the scale pest both in time and abundance.When the population of P.pentagona increased gradually,C.geminus and C.nipponicus multiplied thereafter in abundance.This observation suggests that C.geminusand C.nipponicus have the potential of suppressing P.pentagona population in general,and its larval population in particular.3.Function responses were studied in labotatory,and searching efficiency and mutual interference were estimated for adults and larvae of C.geminus and adults of C.nipponicus.The results showed that function responses can be best fitted by Holling typeⅡresponse model.The numer of P.pentagona consumed in a fixed time increased with the prey density,and then approached an asymptote.With the density of P.pentagona increasing,the searching efficiency of C.geminus Zaslavskij and C.nipponicus decreases.The predation rates of C.geminus and C.nipponicus decreased with the density of P. pentagona.With the density of P.pentagona increasing,the predation rate desreased.The best matching density between C.geminus and C.nipponicus and P.pentagona can be projected by using the Holling-Ⅲmodel,which can be used as a reference for setting the ratio between benefitial insects and the pest.4.Spatial distribution of individuals was estimated for adult,lava and pupa of C.geminus and adult of C.nipponicus on peach trees.The research showed that aggregated pattern was fitted based on measures including I(Moore value),M~*/m(Lloyd value),C_a value,C value,K value,M~*-m regression analysis law, and Toyar power rule.Estimated Blackith(λ) showed that the aggregation of adult C.geminus may createdby environmental factors,lava and pupa of C.geminus and adult of C.nipponicus by their own habits and environmental factors.The best sampling size was fitted by Iwao model for lava and pupa of C. geminus and adult of C.nipponicus.