Toxicity And Detoxification Mechanism Of Megaselia Scalaris On Heavy Metal Cadmium

Cadmium is an important heavy metal pollutant,which not only has a direct toxic effect on humans and organisms,but also can be enriched in organisms and migrate between organisms through the food chain,affecting the ecosystem.Insects are diverse and widely distributed,and play an important role in the food chain.They are not only heavy metal consumers and accumulators,but also heavy metal transmitters.Studying the toxicological reactions of organisms under cadmium stress is of great significance for bioremediation and biological monitoring of heavy metals.In this study,M.scalaris was used as the test object.The toxic effects of Cd²⁺on the species and its physiological response mechanism to Cd²⁺were dealed comprehensively with the aspects of ontogeny,internal anatomy,enzymology and molecular biology.The main results are as follows:(1)The body length,body weight,pupation rate,adult emergence rate and life span of parental M.scalaris under Cd²⁺at different concentrations were significantly decreased with the increase of stress concentration(P<0.05).Compared with the control group,Cd²⁺stress significantly prolonged the developmental period and pupal period of M.scalaris parents(P<0.05)and had a dose effect.Compared with the control group,Cd²⁺stress had a significant effect on the female-male ratio of M.scalaris parent adults(P<0.05).In summary,Cd²⁺stress can inhibit the growth and development of M.scalaris,and may also change the population structure of M.scalaris.Compared with the control group,there were no significant differences in body length,body weight,pupation rate,pupal stage and adult eclosion rate,life span,developmental period and sex ratio of M.scalaris offspring larvae that were no longer under Cd²⁺stress(P>0.05).It shows that the influence of Cd²⁺stress on the growth and development of M.scalaris at the individual level is eliminated in the offspring.(2)Cd²⁺can change the morphology and color of the digestive tract of M.scalaris larvae.The digestive tract of the larvae had more yellowing than the control group,especially the midgut,after 5d of feeding Cd²⁺with a concentration of 60?g/g artificial diet.Many granular structures were clearly observed densely distributed inside the intestinal wall.After measurement,it is found that Cd²⁺can change the length and diameter of the larvae's midgut,and damage the structure of the digestive tract.It is speculated that Cd²⁺can impair the digestive function of M.scalaris larvae.(3)Antioxidant enzymes are the early response of M.scalaris body to resist the toxic effects related to oxidative stress induced by Cd²⁺.Compared with the control group,with the increase of the treatment time,the activity of the antioxidant enzyme CAT of M.scalaris showed a promotion-inhibition trend,and the activity of the antioxidant enzyme SOD changed to medium and low concentrations group(7.5,15,30?g/g)showed a promotion-inhibition trend,the high concentration(60?g/g)group showed an inhibitory trend,the activity of antioxidant enzyme GSH-PX showed a promotion-inhibition in the low concentration(7.5?g/g)group,and the medium-high concentration group(15,30,60?g/g)showed an inhibitory trend;among them,GSH-PX had a faster and more sensitive reaction than SOD and CAT;the MDA content in M.scalaris continued to increase,showing a certain concentration effect and time effect relationship.These results indicate that Cd²⁺stresses the larvae to produce and accumulate a large amount of ROS,which affects the activity of antioxidant enzymes,breaks the steady state of redox in the worms,induces oxidative stress,and lipid peroxidation occurs.M.scalaris causes oxidative damage to the body.(4)After different concentrations of Cd²⁺,The TL,DNAT%,TM and OTM of M.scalaris somatic DNA increased with the increase of Cd²⁺treatment concentration and time,indicating that the damage degree of M.scalaris DNA increased with the increase of Cd²⁺treatment concentration and time,and there were significant concentration-effect and time-effect relationship.The above results showed that Cd²⁺could cause M.scalaris DNA damage and lead to DNA strand break,which had genotoxicity.The degree of DNA damage had an effect relationship with the concentration and time of Cd²⁺treatment.(5)Combined with the correlation analysis of the detection indicators,the time sequence of the physiological response of M.scalaris to heavy metal Cd²⁺is:antioxidant enzyme activity and oxidative stress,DNA damage,tissues and organs,individual indicators,population indicators.Finally,according to the difficulty of practical operation,it is recommended that the sensitive physiological and biochemical indexes of the toxicity effect of M.scalaris on heavy metal Cd²⁺are GSH-PX enzyme activity,MDA content,TM value,pupation rate and eclorescence rate.In this study,M.scalaris was used as the research object,and its accumulation metabolism and detoxification metabolism mechanism under heavy metal cadmium stress were discussed from the ontogenetic,internal anatomy,enzymology and molecular levels for the first time,provides the oretical support and data reference for better understanding of the biotoxicological process of heavy metal cadmium and its transport process in urban ecosystem.