| The relationship between environmental stress, developmental instability and fluctuating asymmetry has been a controversy in the world. Any physical, biological, or chemical change in water quality can adversely affect aquatic living organisms. Population changes of aquatic insects regarded as bioindicators are not only important to assess water quality, but also their morphological changes are helpful to analyze water quality. We achieved a series of significant results from studying fluctuating asymmetry of bilaterally symmetrical aquatic insects affected by nonpoint pollution of agriculture.1. Effects of temperature stress and pesticide exposure on fluctuating asymmetry and mortality of higher instar of larvae Copera annulata (selys) (Odonata: Zygoptera)Although there have been some investigations into the effects of insecticide on the level of fluctuating asymmetry (FA) of adult damselflies, the cooperative effects of environmental factors on FA of larval damselflies were known little. This paper explored effects of exposure to temperature and pesticide on larval development of the damselfly Copera annulata (Selys). A conventional life history trait (mortality) and developmental instability (estimated by calculating fluctuating asymmetry of bilaterally symmetrical structures) were used to measure stresses in this paper. The results showed that temperature and different concentrations of pesticide produced significant effects only on developmental stability of some characters. The FA values of three traits decreased at lower concentrations, then increased slowly with increased insecticide doses. The FA values of four traits decreased slowly with increased temperatures. However, the interaction between different concentrations of insecticide and temperature was complicated and only produced significant effects on five traits. Insecticide treatment did not significantly affect mortality of the larvae of damselfly. However, mortality was significantly positively associated with temperature. There were significantly negative associations between mortality and the FA values of three traits. These results may be caused by higher mortality and short rearing time although we did not find the significant effects of concentrations on mortality. Therefore, we speculate FA may be induced if larval damselflies were treated during longer term and FA has potential as a more specific bioindicator of stresses if we guarantee enough longer rearing time without higher mortality under stressful environment.2. Effects of the mixture of avermectin and imidacloprid on developmental stability of lower instar of larvae Copera annulata (Odonata: Zygoptera)This study explored the effects of mixture of avermectin and imidacloprid on the level of fluctuating asymmetry (FA) and mortality of Copera annulata larvae. The results showed that the mortality of larval damselflies treated with different concentrations of insecticide did not differ significantly. The level of FA of two traits demonstrated significantly different with different treatments whereas the others did not show any differences. There was a significantly negative relationship between the first femur length and the absolute difference between its right and left sides. There was not a relationship between the absolute difference between the right and left sides of all traits and their body size. FA was not associated with mortality. Our results emphasized the need for making further study combined with other methods such as fitness, physiological and biochemical method and molecular biology before FA-based biomonitoring can be responsibly and effectively implemented.3. Relationship between exposure to an insecticide and fluctuating asymmetry in a damselfly (Odonata, Coenagriidae)In this study, we explored the effects of pesticide on fluctuating asymmetry (FA) levels and mortality of Ceriagrion sp. larvae. The results showed that the mortality of larval damselflies treated with pesticide was significantly higher than that treated with tap water which had been aerated for 48h, but there were no significant differences among mortality of larvae treated with different concentrations of pesticide. Meanwhile, we found that the level of FA of the first tibia length, one of the seven bilaterally symmetrical traits (First femur length, First tibia length, Second femur length, Second tibia length, Third femur length, Third tibia length and Prementum width), differed significantly with different treatments, whereas the others did not show any significant differences. The Bonferroni (Dunn) t Tests revealed that FA of the first tibia length at 15×10-9mg l-1 was significantly higher than that at 1.5×10-9 mg l-1 and control. There was no significant relationship between trait size and the absolute difference between their right and left sides. There was also no significant relationship between body size and the absolute difference between right and left sides. Trait size was significantly positively correlated with body size. FA was not associated with mortality. Therefore, we concluded that FA of the first tibia length of Ceriagrion sp. larvae may be induced by sublethal doses of pesticides. That is to say, its FA may be regarded as an indicator of reflecting the level of pesticide stress.4. Effects of nonpoint pollution of agriculture on bilaterally symmetrical traits of Cinygmina rubromaculata and Cinygmina obliquistrita larve (Ephemeroptera, Heptageniidae)By analyzing the impact of nonpoint pollution of agriculture on bilaterally symmetrical traits of mayfly larve such as Cinygmina rubromaculata and Cinygmina obliquistrita, we concluded that FA values of five traits (first femur length, first femur width, first tibia length, first tibia width and first tarsus length) of C. rubromaculata living downstream were significantly lower than that living upstream, and that FA values of first tibia length of C. obliquistrita living downstream were significantly higher than that living upstream. We compared again the variation of fluctuating asymmetry of two mayflies living downstream, the results showed that FA value of first tibia width of C. obliquistrita was significantly higher than that of C. rubromaculata. Therefore, we speculated that C. obliquistrita larvae were more sensitive to polluted water than C. rubromaculata, and that C. rubromaculata belongs to tolerable species. The variation of fluctuating asymmetry is not only correlated with the degree of nonpoint pollution of agriculture, but also is affected by tolerable degree of indicatory organisms. FA values of organisms are the lowest under the optimal environment.5. Influence of nonpoint pollution of agriculture in Anji County on bilaterally symmetrical traits of Cheumatopsyche trifascia Li adults (Trichoptera, Hydropsychidae)We studied the influence of nonpoint pollution of agriculture in Anji County on bilaterally symmetrical traits of Cheumatopsyche trifascia Li adults. The results showed that there were significantly negative correlation between the absolute asymmetry of the left and right sides and mean trait size of total length of antennal segments II ,III and IV and second tibia length. We found the levels of fluctuating asymmetry of a minority of traits of female and male adults were significantly different. FA values of fifth fork length of male adults in site one were significantly higher than that of female adults. However, for total length of segments II, HI and IV of maxillary palpus in site one, first tibia length in site two, total length of segments II ,III and IV of maxillary palpus and fifth fork length in site three and total length of antennal segments II ,III and IV in site four, FA values of female adults were higher than that of male adults. Our most important results were FA values of total length of segments II ,III and IV of maxillary palpus and total length of antennal segments II ,III and IV of female adults living downstream were significantly higher than that living upstream, so was FA value of total length of segments II ,III and IV of maxillary palpus of male adults.6. Effects of insecticide on bilaterally symmetrical traits of Limnephilidae sp (Trichoptera) larvae forty one days after exposedWe compared their fluctuating asymmetry and mortality forty one days after Limnephilidae sp larvae were exposed to insecticide. The results showed that there was significantly negative relationship between the absolute difference of the left and right sides and mean trait size of the length of tarsal claw of middle leg. We found eighteen traits were significantly affected by different concentrations of insecticide. FA values of other traits except the length of tarsal claw of middle leg decreased at lower concentrations and increased at higher concentrations when compared with control. Bonferroni (Dunn) t tests showed that mortality at 180×10-8mg/L was significantly higher than that of control. But no statistically significant differences were observed in mortality obtained from paired tests with two lower concentrations and control or highest concentration. We also found no significantly relationship between fluctuating asymmetry and mortality. In conclusion, lower concentrations of insecticide did not hold back the development of Limnephilidae sp larvae, but promote their symmetrical growth. Higher concentration of insecticide disturbed their development and make their fluctuating asymmetry increase.7. The chronic effect of insecticide on fluctuating asymmetry of Limnephilidae sp (Trichoptera) larvaeMonitoring water quality using fluctuating asymmetry of aquatic insects have received little attention in China. Consequently, we studied the effects of insecticide on Limnephilidae sp larvae. One hundred and ten days after Limnephilidae sp larvae were exposed to insecticide, we analyzed morphological variation of bilaterally symmetrical traits. The results showed that there was no statistically significant relationship between the absolute difference of left and right sides and their mean trait size. Insecticide had significant effect on two traits such as the length of abdominal segment III and the length of tarsal claw of middle leg. For the length of abdominal segment HI, the Bonferroni (Dunn) t Tests revealed that its FA value at 2.02×10-6 mg/L was significantly higher than that of control. For the length of tarsal claw of middle leg, it indicated that FA value at 20.2×10-6 mg/L was significantly higher than that at 2.02×10-6 mg/ and control. Different concentrations of insecticide had significant effect on mortality of Limnephilidae sp larvae. We found no significant difference of mortality between 2.02×10-6 mg/L and control, but mortality increased with increasing insecticide doses. The significant relationship between FA and mortality had not been detected. In sum, long term of insecticide treatment influenced the development of bilaterally symmetrical traits of Limnephilidae sp larvae.8. Acute Toxicities of Four New Insecticides to the Fourth Instar Larvae Chironomus flaviplumus Tokunage (Diptera: Chironomidae)The acute toxicity of four new insecticides (Fengsheng, Daowei, Yamankexing and Shuwei) was evaluated using Dipteran fourth instar larvae, Chironomus flaviplumus Tokunage, of the family Chironomidae. The results showed that 48 h acute toxicity of YK was the highest (LC50 = 0.0041 mg/L) among the four insecticides tested. Different concentrations of the four insecticides had significant effects on survival rates of the Chironomus flaviplumus Tokunage larvae except for FS (24 h toxicity). For each insecticide, the difference of survival rates of chironomid larvae of 24 h, 48 h, 72 h and 96 h exposure was significant. For each day, the effects of four insecticides on larval survival were also significant. In conclusion, these insecticides severely affected survival of chironomid larvae. The active patterns of the four insecticides were different, in which larvae exposed to FS died slowly during four days. The serious impacts of insecticides on chironomid larvae in this study may help promote monitoring and assessing water quality in China.9. A study of variation of bilaterally symmetrical traits of Chironomus flaviplumu (Diptera, Chironomidae) exposured to insecticideFluctuating asymmetry (FA) of Chironomus flaviplumu adult was employed to assess water quality after they emerged. Their larvae were reared in water containing insecticide. We found there were statistically significantly negative correlations between the absolute difference of left and right sides and mean trait size of tarsus III length of foreleg and tarsus IV length of foreleg. Insecticide had significant effects on four traits such as the length of femur of foreleg, the length of tibia of foreleg, tarsus II length of foreleg, second fork length of the fore wing. For the length of femur of foreleg, FA value at 1.62×10-4 mg/L was significantly higher than that of control. For the length of tibia of foreleg, FA value at control was higher than that at 16.2×10-4mg/L. This may be caused by type I error. For tarsus II length of foreleg, FA values at 1.62×10-4 mg/L and 16.2×10-4mg/L were significantly higher than that of control. For second fork length of the fore wing, FA value at 16.2×10-4 mg/L was significantly higher than that at 1.62×10-4mg/L and control. Different concentrations of insecticede had significant effects on emergence rate of adults. There was not significant difference of emergence rate between 1.62×10-4 mg/L and control, but higher concentrations of insecticide had significantly affected emergence rate of adults. Emergence rate decreased with increasing concentrations of insecticide. Pearson correlation indicated that there was significantly negative relationship between FA of first fork length of the fore wing and emergence rate. That is to say, the higher FA, the lower emerence rate.10. Potential of using fluctuating asymmetry of Chironomus flaviplumus (Diptera, Chironomidae) adult as a bioindicator to evaluate water qualityWe studied emergence rate and variation of bilaterally symmetrical traits of Chironomus flaviplumus adults after the last instar of larvae were exposed to different concentrations of insecticide. The results showed that insecticide had significant effects on emergence rate of adults. We found no significant difference of emergence rate between lower concentrations of insecticide and control. But emergence rates at higher concentrations of insecticide were significantly different from that of control. Emergence rate decreased with increasing concentrations of insecticide. There was no significant correlation between the absolute asymmetry of left and right sides and mean trait size. Insecticide had significant effects on three traits such as tarsus I length of foreleg, tarsus III length of foreleg and first fork length of the fore wing. For tarsus I length of foreleg, FA values at 120×10-4 mg/L and control were higher than that at 12×10-4mg/L. The latter may be due to type I error. For first fork length of the fore wing, FA value at 120×10-4 mg/L was higher than that at 12×10-4 mg/L and control. We found no correlation between fluctuating asymmetry and emergence rate. Anyway, we think FA has potential in water quality assessment.In conclusion, higher concentrations of insecticide had acute toxic impact on aquatic insects. As the biological indicators of water environment, aquatic insects even could not survive in severely polluted water body. Lower concentrations of insecticide could bring subacute and chronic tixicity to aquatic insects. Toxic response may be showed by decreasing emergence rate, increased mortality, and variation of bilaterally symmetrical traits of some sensitive species, etc. We even found the difference of fluctuating asymmetry under stress but not other biological indicators. It is important for us to study fluctuating asymmetry to indicate environmental stresses and reveal the evolution of organisms. Studying varition of bilaterally symmetrical traits of aquatic insects living in polluted water can promote and improve water quality assessment and monitoring systems in China. |
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