The Effects Of Plumbum Stress On Reproduction And Vg Of Beet Armyworm

This paper is mainly to study the effects of different concentrations（0,0.3,4.8,76.8 mg/kg） of heavy metal plumbum (Pb²⁺) on the growth and development of beet armyworms for five consecutive generations.The vitellogenin gene of beet armyworms that was related to reproduction was cloned, and the relative expression levels of the vitellogeningene under the stresses of plumbum during the three growth stages of male and female larvae, pupa and imago. The results are as follows:（1） Under the Pb²⁺ stresses of different concentrations, the female-male ratio, gonadosomatic index, egg laying amount and egg hatchability of beet armyworms for five consecutive generations were effected in different degrees.Under the Pb²⁺ stresses of high concentration （76.8mg/kg）, the female-male ratio of the third generation of beet armyworms was significantly higher than that of control treatment, with the ratio of female moths reaching up to approximately 60%, but the ratios of the forth and the fifth generations were not significantly different from those of the control group. In thgroup of plumbum in lower concentration （4.8 mg/kg）, the female-male ratio of the forth generation of beet armyworms was memorably higher than that of control, with the ratio of female moths reaching up to approximately 64%, but the ratio of the fifth generation decreased dramatically and not significantly different from that of the control. However, in the treatment group of plumbum in the lowest concentration （0.3mg/kg）, the female-male ratios of all five consecutive generations were not significantly different from those of the control group. These indicate that during a certain period of time, high concentration Pb²⁺ can lead to feminization of beet armyworms, but the effects disappear gradually as the time went on.Under the stresses of Pb²⁺ in low concentration （0.3mg/kg）, the gonadosomatic index of female moths of the first generation of beet armyworms was 14% higher than that of the control. The egg number per female was also notably higher. There were about 80 grains more than the control. But the female moths’ gonadosomatic index and egg number per female of the forth and the fifth generations were both significantly lower than the control. Plumbum in high concentration （76.8mg/kg） notably reduced the gonadosomatic index of beet armyworms’ female moths and restrained the spawning. The outcome shows that after the Pb²⁺ stressesstress, the trends of the beet armyworms’ egg number per female and gonadosomatic index are consistent, which both appear that in a short period of time, the treatment of plumbum in low concentration （0.3mg/kg） generates the weight increment of the ovaries of beet armyworms’ female moths, promoting the spawning, but still restrains the development of ovaries as well as spawning along with the generations’continuation, and the treatment of plumbum in high concentration （76.8mg/kg） restrains the development of ovaries as well as spawning all the time.In the two treatment groups of which the plumbum concentrations were respectively 4.8mg/kg and 0.3mg/kg, the egg hatching rate of beet armyworms had been much lower than the control group since the second generation. In the treatment group with high concentration （76.8mg/kg） of plumbum, the egg hatching rates of five generations of beet armyworms were continuously and significantly lower than the control group, during the fifth generation, the egg hatching rate was even lower than the half of the control. It means that under the stressesof plumbum, the egg hatching rate of beet armyworms decreases linearly along with the increase of the concentration of plumbum and the generations’ continuation.（2）The full-length sequence of beet armyworm Vitellogenin （Vg） gene was cloned from beet armyworm by RACE. The full-length of Vg cDNA was 5612bp. There is an opening reading fragment（ORF） from 556th bp to 5340th bp, encoding 1761 amino acid. Its initiation codon is ATG and termination codon is TAA. The Vg was about 200.47KDa, and the isoelectric point was 8.71. After the analysis, the amino acids of the gene has 88% identity with those of Spodoptera litura,74% identity with Helicoverpa armigera and 73% identity with Mythimna separata.（3） Pb²⁺ stresses has different influences on the relative expression levels of vitellogenin （Vg） in each developmental stage of beet armyworms.At thelarval stage of beet armyworms:under the lower concentrations （0.3 and 4.8 mg/kg）, the gene expression of Vg of the fifth instar female was significantly lower than control. In the group with high concentration （76.8mg/kg）, the gene expression of Vg of the fifth instar femalewas consistently lower than the control group for five generations （exception for the second generation）. It means that the gene expression of Vg of female moths in the fifth instar decreases along with the increase of the concentration of plumbum and the generations’ continuation. Compared with female moths, the gene expression of Vg the fifth instar male was at a relatively low level, in the three treatments（0.,4.8 and 76.8mg/kg）, the gene expression of Vg of the fifth instar male was separately higher than the control group in the 5th generation, the 3rd-5th generation and the 2nd-4th generations. It indicates that Pb²⁺ stresses induce the expression of Vg ofmale moths in the fifth instar and the expression increases along with the increase of the generations’ continuation and the concentration of plumbum.In the pupal stage of beet armyworms:In the treatment group with low concentration （0.3mg/kg） of plumbum, the gene expression of Vg of the female pupaes was significantly lower than the control group in the forth and fifth generation. In the treatment groups with high concentrations （4.8 and 76.8mg/kg） of plumbum, the gene expression quantities of Vg of the female pupaes was separately in the Srd-5th generation and the third generation were notably higher than the control groups. It suggests that the treatment of plumbum of low concentration reduces the gene expression of Vg of female pupaes and vice versa. In the treatment groups with three graded concentrations （0.3,4.8 and 76.8mg/kg）, the gene expression of Vg of the male pupaes was significantly lower than the control group separately in the 3rd-5th, the 3rd-5th and the 2nd-5th generations. Pb²⁺ stressesof three different concentrations all reduced the gene expression of Vg of the male pupaes.In the adult stage of beet armyworms:In the treatment groups with three graded concentrations （0.3,4.8 and 76.8mg/kg）, the gene expression of Vg of the female adults was significantly lower than the control group respectively in the 4th-5th, the 3rd-5th and the 2nd-5th generations. Pb²⁺ stressesreduced the gene expression quantity of Vg of the female adults on the whole. In the treatment group with high concentration （76.8mg/kg） of plumbum, the gene expression of Vg of the male adults was significantly going up for all of the five generations. In the group with lower concentration （4.8 mg/kg） of plumbum, the gene expression quantity of Vg was notably higher than the control group in the fifth generation. Even in the group with the lowest concentration （0.3mg/kg） of plumbum, there was not any significant difference compared to the control group, Pb²⁺ stresses still increased the gene expression of Vg. It shows that Pb²⁺ stresses increases the gene expression quantity of Vg of male beet armyworms on the whole.