Effects Of Long-term Exposure Upon Heavy Metal Zn²⁺ On Ecogenetic Parameters, Enzyme Activity And Protein Level Of The Aphid Sitobion Avenae

Heavy metal pollution exerts the strong selection pressure on the genetic evolution ofinsect population. To assess the long-term effects of Zn on the growth, development,fecundity, corresponding enzyme activities and protein content of Sitobion avenae （Fabricius）,and the heredity principle of the life history, the age-stage, two-sex life table was establishingto analysis the life history and the enzyme activities and protein content of the heavy metal,on1^st,5^th,10^th,15^thand20^thfor twenty successive generations. Then the study will show thelong-term effects of heavy metal pressures, thereby providing the theory of the molecularmechanisms and resistance mechanisms of heavy metal toxic effects, and the theory of thebiological monitoring and genetic evolution. The results include:1. Effects of long-term exposure upon zinc on the growth and development of S. avenae:With Zn²⁺long-term stress, the survival rate of the nymph was decreasing with the increasinggeneration; the first and the fourth instars were significantly shorten; the APOP wassignificantly higher than that of the control compared with the control groups. The resultindicated that the long-term Zn²⁺stress will result in the decline of the nymph survival rate,the acceleration of the nymph molt and the delay the fecundity.2. Effects of long-term exposure upon zinc on the adult longevity and fecundity of S.avenae: The female longevity was prolonged at low concentrations until the tenth generation,and then shortened in the following generations, which did not differ significantly withcontrol, and this illustrated that low concentration will result in the adaptation mechanisms.The female longevity of high Zn²⁺treatments was prolonged in the5^thgeneration, and thensignificantly shortened in the following generations, and at1600mg/kg, the longevity wasshortened to6.83d in the20^thgeneration; the fecundities of S. avenae female increased in the5^thgeneration and then decreased in the following generations under higher concentration.After the10^thgeneration, the fecundities of the four treatments began to show the inhibitioneffect and were significantly in the higher concentrations. It indicated that long-term exposedto zinc could shorten the adult longevity and decline the fecundity of S. avenae, and this wasan important way for the insects to defense the heavy metal.3. Significantly effects of long-term exposure upon zinc on life table parameters ofSitobion avenae （Fabricius）: the values of R0, r and λ in lower concentration （200and400 mg/kg） treatment reduced before the20^thgeneration while showing no difference comparedwith control; however, the values of higher concentration （800and1600mg/kg） treatmentwere increased in the5^thgeneration and then decreased rapidly and were lower than that ofcontrol. It could illustrate that high concentration played a brief role in promoting thereproductive capacity and population growth, and then strengthening inhibitory effects todecrease the reproductive potential and population growth rate. It indicated that the toxiceffects had been accumulated in the offspring in the development and population growth afterZn²⁺exposure upon the aphid.4. Significantly effects of long-term exposure upon zinc on enzyme activities: theprotective effect showed until to the9thgeneration, the activities of POD and SOD graduallyincreased and higher than that of the control in the four grade concentration of long-termexposed to zinc. The activities of CarE increased in the higher concentration while nosignificant effect in the low concentration. After the16^thgeneration, the zinc concentrationleads to the inhibitory of POD and CarE. At400mg/kg, the increase of CAT and SODactivities showed a protective effect on the living systems.5. Significantly effects of long-term exposure upon zinc on the protein content in S.avenae: The protein content of the treated S. avenae was significantly lower than the controlin the5^thgeneration while dramatic higher than the control after the16^thgeneration. Also thehigher concentration treatments were significantly higher than the lower concentration afterthe16^thgeneration. The protein content gradually increased in the Zn²⁺stress and high dosesof stress enhanced the protective effect.In conclusion, heavy metals had considerable effects on the survival rate, thedevelopment duration, reproductive capacity, defending enzymes and protein synthesis ofaphids, and the toxicity of low concentration was inferior to that of higher concentrationwithin each metal treatment. Meanwhile, the population development, defending enzymesand protein synthesis system of aphids showed the significant protective effect on livingsystems after the exposure upon zinc, and this indicated that aphids have gradually adapted tothe heavy metals.