Growth And Detoxification Response Of Gypsy Moth Under Cadmium And Lead Stress

Lymantria dispar belongs to the family Lepidoptera.It is a worldwide forestry pest with a wide range of distribution,eating habits,heavy damage,and larve.In order to explore the occurrence trend of forest pests in the case of increasingly serious heavy metal pollution,and supplementary theoretical basis for prevention and control of forest pests in heavy metal polluted areas,the cadmium(Cd)and lead(Pb)were added to artificial feed.We measured the growth,reproduction,detoxification enzyme(ACP,AKP,GST)activity,and glutathione(GSH)content of larvae under Cd,Pb single stress(Cdl:7.5 mg/kg?Cd2:10.5 mg/kg;Pbl:55 mg/kg?Pb2:90 mg/kg?Pb3:125mg/kg)or combined stress(M1:Cd1×Pb1?M2:Cd1×Pb2?M3:Cd1×Pb3?M4:Cd3×Pb1?M5:Cd3×Pb2?M6:Cd3×Pb3),the concentration of Cd and Pb in different parts(head,insect cuticle,fat bodies and heamolymph,gut)of gypsy moth larvae also has been measured.(1)With the increased stress time,the inhibition of Cd and Pb stress on the growth and development of gypsy moth gradually appeared.The inhibition of larval body weight,body length and head width increased with stress time.Compared with the control group,the 3rd instar larvae had no significant change(P<0.05),the 4th instar larvae were inhibited,but the low mass fraction treatment group had no significant decrease(P>0.05),the high mass fraction treatment group had significant decrease(P<0.05),and the 5th instar larvae had significant decrease(P<0.05).The weight of pupae and the amount of eggs laid by adults decreased with the increase of Cd and Pb contents,while the survival rate,pupation rate and emergence rate of larvae were not affected significantly,only the survival rate and emergence rate of M6 treatment group decreased significantly(P<0.05).The inhibiting effects of compound stress on 4th and 5th instar larvae body weight,body length,head width were stronger than those of single stress at the same concentration,but there were no significant differences in 3rd instar larvae.Under compound stress,the pupa weight and egg laying amount was significantly lower than that of single stress at the same concentration,but the larval survival rate,pupation rate and pupae emergence rate were not affected.(2)The detoxification physiology of gypsy moth larvae under Cd and Pb stress can produce stress response.ACP activity gradually decreased with time increased,compared with the control group,there no significant change was observed in the 3rd instar larvae(P>0.05).The 4th and 5th instar larvae decreased,and the 4th instar larvae Cd2,Pb3,M3,M4,M5 and M6 treatments decreased significantly(P<0.05),while all the 5th instar larvae treated groups decreased significantly(P<0.05).AKP activity decreased with the increase of Cd and Pb content in the 3rd,4th and 5th instar larvae.The 3rd and 5th instar larvae were significantly lower than those in the control group(P<0.05),and the 4th instar larvae in the M5 and M6 treatment groups were lower than those in the control group(P<0.05).The activity of GST increased first and then decreased with the increase of larval instar,that is,the 3rd instar larvae increased significantly with the increase of Cd and Pb content(P<0.05),and the 4th and 5th instar larvae decreased with the increase of Cd and Pb content.The 4th instar larvae only had no significant difference between Cdl and control group(P>0.05),but the 5th instar larvae had no significant difference between Cdl,Pb1 and M1 treatment group and control group(P>0.05).Cd and Pb stress caused stress changes in GSH content of 3,4 and 5 instar larvae.(3)The concentrations of Cd and Pb in different parts of gypsy moth were different.The concentrations of Cd and Pb in head,insect cuticle,fat bodies and heamolymph,gut of larvae were positively correlated with the mass fractions of Cd and Pb,and there were significant differences between the treatments(P<0.05).Under single stress,the order of Cd concentration in four tissues was gut>fat bodies and hemolymph>head>insect euticle;The eoncentration of Pb in all tissues changed with the change of Pb mass fraction.The enrichment order of Pbl treatment group was insect cuticle>gut>fat bodies and hemolymph>head,and that of Pb2 was fat bodies and hemolymph>gut>insect cuticle>head,and that of Pb3 was fat bodies and hemolymph>gut>head>insect cuticle.Compared with the single stress of the same mass fraction,the enrichment of two heavy metals in different tissues of Gypsy moth larvae under different stresses.However,there is a threshold for the total enrichment of the Cd and Pb,that is,one party rises and the other party must decrease.The Cd content in the head decreased and the Pb content increased.The Cd content in the insect cuticle increased and the Pb content decreased.There was no significant change in Cd and Pb in the gut,fat bodies and heamolymph.In conclusion,under heavy metal stress,although the detoxifying enzyme activity and GSH content of gypsy moth may produce stress response,but the heavy metals will accumulate and store in different organs of gypsy moth,and the detoxifying enzyme activity of gypsy moth will be inhibited with the prolongation of stress time.This inhibits the growth and eggs laid of the gypsy moth,and ultimately inhibits the growth of its population,which is inhibited to a certain extent.