Effects Of Parasitism Of Ovomermis Sinensis On The Encapsulation Capacity Of Helicoverpa Armigera Hemocytes

The hemocytes of insects can encapsulate invaders efficiently,but some parasitic organism can breakthrough encapsulation and parasitize on insects successfully.The mechanism that parasitic wasp avoid encapsulation have been known,however how the mermithid nematode avoid encapsulation is unknown.We have established Ovomermis sinensis/Helicoverpa armigera parasitic system and researched the effects of parasitism of O.sinensis on the encapsulation capacity of H.armigera hemocytes by injecting Sephadex A-25 beads into host and observing the encapsulation grade of beads. Encapsulation is a immunoreaction involved hemocytes,so their amount will directly affect the procession of encapsulation.Thus we investigated the effects of parasitism on host hemocytes(include total hemocytes amount,plasmatocytes amount,granular cell amount and spherule cell amount).Plasmatocytes are the predominant cell that participate in encapsulation.The spreading function of plasmatocytes and associated cytoskeleton function are the fundamental factors for plasmatocytes to attach and encapsulate on the parasitic organisms.Thus we also investigated the effects of parasitism on plasmatocytes spreading ability and plasmatocytes cytoskeleton.The results are below:1)O.sinensis have greatly impaired the encapsulation capacity of host after parasitized.Compared to control group,the encapsulation index which inflect the encapsulation capacity have been reduced after parasitized and the significant level reached P≤0.05 at 48h,but reached P≤0.01 at 24h,72h,96h.The encapsulation index of parasitized group continuously reduce after 48h and the index number reduce to the half of control group at 96h.2)O.sinensis greatly increase the total hemocyte amount and plasmatocyte amount. For parasitized group,total hemocytes are continuously raising from 24h to 72h and reach maximum at 72h.but the total hemocytes begin to reduce after 72h and reach minimum at 144h.The plasmatocyte amount is higher than control group at all the time spots after parasitized,but granular cell amount is higher at 72h and spherule cell amount is higher at 24h respectly.3)O.sinensis have not affected plasmatocytes spreading rate after parasitized,but the morphology of spreading plasmatocytes become abnormal.The spreading plasmatocytes appeared many particles around the nuclear at 120h,144h after parasitized.4)The parasitism of O.sinensis cause the plasmatocytes cytoskeleton abnormal.The plasmatocytes cytoskeleton morphology appear many bright spots around the nuclear under the fluorescence microscope at 24h,48h.But at 144h there are many hollow holes in fluorescence photo of plasmatocytes cytoskeleton and phase contrast photo.We have revealed that the O.sinensis actively suppress encapsulation capacity of host by breakdown the plasmatocytes cytoskeleton.