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Sublethal Effects of Methoxyfenozide and Chlorfluazuron on Spodoptera Exigua (hübner)

Author: ZhangQiaoLi
Tutor: WangDongSheng
School: Shanghai Ocean University,
Course: Crop Genetics and Breeding
Keywords: Methoxyfenozide Chlorfluazuron Spodoptera exigua Sublethaleffect
CLC: S482.3
Type: Master's thesis
Year: 2013
Downloads: 13
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Abstract


Beet armyworm, Spodoptera exigua (Lepidoptera: Noctuidae), is widerlydistributed in the subtropics and temperate regions and have serious damage or disasterrecord in all continents. Chemical control is one of the main means of control of beetarmyworm. The insect growth regulators(IGRs) is acted on specific physiologicalprocesses in insects, such as molting, formation of new cuticle, less harmful tonon-target organism and environment. Meanwhile, it is not easy for IGRs to cause thepest resistance than many broad-spectrum insecticides. It is widely used to controlLepidoptera pest such as beet armyworm. In this paper three experiments on thesublethal effects of two insecticides, methoxyfenozide and chlorfluazuron, onSpodoptera exigua were described. The effects on development, survival, andreproduction of Spodoptera exigua that survived exposure to an LC10and LC30concentration of methoxyfenozide and chlorfluazuron were observed. Then the activityof glutathione-s-transferase and acetylcholine esterase in5th instars were measured andthe content of glyceriden、protein and soluble sugar in hemolymph and fat body in5thinstars, pupae and adult of this pest were determined. These studies are helpful to thecomprehensive understanding of the control function of methoxyfenozide andchlorfluazuron to beet armyworm and have guiding significance to the rationalapplication in the field.The results show as follows:1. The LC10and LC30of methoxyfenozide were estimated at1.365mg/L and2.951mg/L separately for2ndinstars larvae of spodoptera exigua. The LC10and LC30value ofchlorfluazuron were0.0042mg/L and0.0125mg/L separately.2. The effects on development, survival, and reproduction were observed in secondinstars of this pest that survived exposure to an LC10and LC30concentration ofmethoxyfenozide. Treated with LC10and LC30concentration of methoxyfenozide, thelarvae developmental duration was delayed for1.3d and2.0d, respectively. But therewas no influence on the larvae developmental duration of offspring, pupa weigh and pupa duration. Significant impact on survival was observed. The survive rate to the firstday of adult emergence of the control was81.9%, that was58.7%and26.1%treatedwith LC10、LC30. Adults from the methoxyfenozide treatment did not show reducedfecundity, but the appearance of oviposition peak was delayed compared with untreatedcontrol insects. Effect of the methoxyfenozide treatment on life table parameters of thebeet armyworm Spodoptera exigua was evaluated. The intrinsic rate of increase (rm)and finite rate of increase (λ) of the parental and offspring were decreased. Moreover,the generation time (T) and the population doubling time (Dt) were prolonged. Andthese effects on the life table parameters were positively correlated with the treatingconcentration and faded away with the development. We concluded that the sublethaleffects of methoxyfenozide are likely to have a significant impact on S. exiguapopulations.3. The sublethal concentration of chlorfluazuron could delay the larvaldevelopment. But the inhibiting effect only worked in parental and F1generation.Treated with LC10、LC30, the female pupa weigh increased in parental generation. Andthe effects disappeared in offspring. Concerning to the rate of survive, the sublethalconcentration of chlorfluazuron decreased the survive rates of parental and F1generation. With the treating concentration increasing, the fecundity of beet armywormreduced. Furthermore, in parental generation the intrinsic rate of increase of the treatinggroups was lower significantly than that of the control. The intrinsic rates of increaseand the finite rate of increase were negatively related with the treat concentration. Andthe generation time and the population doubling time were prolonged with theconcentration increasing.4. The activities of glutathione-S-transferase and acetylcholine esterase were lowerthan the control in treating48h. However, the two enzymes’ activities increasedremarkably after72h. It could deduce that the sublethal concentration ofmethoxyfenozide had the ability to promote the activities of the two enzymes. But whenlarval was treated with the sublethal concentration of chlorfluazuron, the effects on theenzymes’ activity was not obvious.5. After being treated with the sublethal concentration of methoxyfenozide, thecontent of triglyceride in the hemolymph of5th instars was lower than that of control.The effect on the protein content was opposite. And the soluble sugar content of the treatment and control had no significant difference. Treated with LC10, the contents oftriglyceride in fat body of larval, prepupa and pupa were lower than that of control,which presumed that the LC10of methoxyfenozide could inhibit the synthesis oftriglyceride or promote the transformation of triglyceride. At the LC30, the effect was assame as the LC10except the larval period. And the protein content was less than thecontrol.The sublethal concentration of chlorfluazuron could decrease the content oftriglyceride in hemolymph. But the protein content of LC30treatment was much morethan that of the control, and the opposite situation existed in the low concentrationtreatment. The sublethal concentration of chlorfluazuron on the content of soluble sugarwas not obvious. Furthermore, in the fat body, the contents of triglyceride and protein intreatment were lower than that in control. It suggested that the chlorfluazuron couldprevent from synthesizing of energy materials, namely triglyceride and protein. Butthere was less influence on the content of soluble sugar utilized directly.

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CLC: > Agricultural Sciences > Plant Protection > Pesticide ( chemical control ) > Various pesticides > Pesticides
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