| Hermitia illucens larvae,as a saprophagous insect,can transform animal manure into biomass rich in protein and fat.The larvae can be used as feedstock in animal husbandry and aquaculture because of high protein and fat content in the body.Therefore,research on the utilization of H.illucens larvae to convert organic wastes into high-quality animal feedstock have explosive increased.Heavy metal pollution in livestock manure has been a concern,but H.illucens can survive at a certain Cd concentration.This study is to investigate the effects of Cd on the biological and physiological characteristics of H.illucens,and provide basic information for the application of H.illucens to treat livestock manure.The main findings are showed as follows:1.Effect of Cd on the biological characteristics of H.illucensDifferent concentrations of Cd(0-800 mg/kg)had no significant effect on the survival of larvae,prepupae and pupae.However,the body type,duration and weight of larvae and the fecundity of adults had a significant difference when the concentration reached 100 mg/kg,and the impact was more significant with the concentration of Cd increasing.When the progeny continued to be treated with Cd,the body type,duration and weight of larvae were also affected significantly,but less remarkably than the parent.2.Effect of Cd on the physiological characteristics of H.illucensThe pH values of different parts of H.illucens larvae gut were determined.The pH of foregut was 6.9-7.5.The anterior,middle and posterior segments of midgut were5.5-5.7,2.0-2.2,8.1-8.4,respectively.The hindgut was 7.3-7.8.The Cd treatment affected the pH of the midgut,and the pH value increased significantly at 300 mg/kg and 700mg/kg for 24 h.The maximum pH was 2.6 and control was 1.9.Cd treatment makes fat body cells have no distinct outline,fat droplets disperse,the proportion of fat cells is small,the nucleus and fat body cells are smaller.The higher the concentration of Cd,the greater the impact.3.H.illucens enrichment of CdH.illucens can enrich Cd at a certain concentration,and the enrichment is related to the concentration of Cd.At 700 mg/kg,bioaccumulation factors(BAFs)were less than 1,and other treatment groups were more than 1.The amount of enrichment in different parts was different,BAFs < 1 in body wall and fat body,and BAFs > 1 in intestine.This study shows that H.illucens can tolerate a certain concentration of Cd,this tolerance can be transmitted to the offspring,so that the degree of impact on the offspring is reduced.A relatively higher concentration of Cd affects the pH value and fat droplet morphology in the midgut,and the larvae,especially the intestine,can enrich Cd.The results confirm the influence of Cd on the biological and physiological characteristics of black leeches. |
