Effects Of Parasitization By Cotesia Ruficrus Haliday (Hymenoptera: Braconidae) On Development And Biochemical Metabolism Of The Host Cnaphalocrocis Medinalis Guenée(Lepidoptera: Pyralidae)

Cnaphalocrocis medinalis Guenée is one of the major pests of rice and biological control is a feasible alternative strategy for controlling this pest. Cotesia ruficrus Haliday is one of the major parasitoids of Cn. medinalis larvae, but there is little research about Cn. medinalis and C. ruficrus. The effects of parasitization by C. ruficrus on host food consumption, development, nutritional metabolism and humoral immunity were studied in this dissertation. The major results are as follows: 1. Effect of parasitization by C. rufucrus on host food consumption and utilizationLaboratory studies were set up to investigate effects of parasitization by endoparasitoid C. ruficrus, on food consumption, weight gain, fecal matter and food utilization of the penultimate instar larva of Cn. medinalis using gravimetric method. The parasitization by C. ruficrus resulted in a reduction in the amount of food consumed, weight gain, fecal matter and in the food utilization performed. Total food consumption by parasitized larvae was about 70% of that consumed by unparasitized ones and the amount of fecal matter was significantly reduced. The food utilization of parasitized host larvae differed from the unparisitized ones with lower the efficiency of conversion of ingested(ECI) and the efficiency of convension of digested(ECD). But parasitism by C. ruficrus significantly increased the approximate digestibility(AD) of the host. Meanwhile, the relative growth rate(RGR) of the parasitized larvae was higher than the control larvae. 2. Developmental interactions between C. ruficrus and different instar larvae of Cn. medinalisDevelopmental interactions between C. ruficrus and different instar larvae of Cn. medinalis were studied in the laboratory. This part of study aimed at figuring out parasitism performances of C. ruficrus for different Cn. medinalis larvae and parasitismassociated effects on host growth. C. ruficrus parasitized 2, 3, 4 instar hosts, and we recorded parasitoid survival rate, development duration and clutch size. Changes of parasitized host weights were also measured. C. ruficrus could paratize all 3 instar hosts and its survival rates increased with host instar. The results showed that the parasitoids starting parasitism in the fourth-instar larvae had the shortest development duration and highest fecundity. The clutch size of C. ruficrus also increased with host instar. The growth of parasitized larvae was significantly inhibited, compared with unparasitised ones, irrespective of the host instar at oviposition. Parasitized host larvae attained the maximum weight earlier than unparasitized ones. Parasitoid load was significantly correlated with initial host weight. In addition, the maximum weight of host-parasitoid complex was significantly correlated with parasitoid clutch size. 3. Effect of parasitization by C. ruficrus on host larval nutritional metabolismWithin the observation time(12 h, 24 h, 48 h, 72 h, and 96 h) of Cn. medinalis being parasitized, the protein content in the hemolymph of parasitized host larvae was significantly lower than that of unparasitized larvae. But the significant difference occurred at 48 h, 72 h, and 96 h after host larvae were parasitized. The total carbohydrates free in the host hemolymph of parasitized larvae were more than that in controls at 12 h after host larvae was parasitized but without significant difference. However, the total carbohydrates free in the host hemolymph of parasitized larvae were significantly lower than that in unparasitized larvae at 24 h, 48 h, 72 h, and 96 h after host larvae were parasitized. The fat content in parasitized host larvae was significantly lower than the control at 48 h, 72 h, and 96 h after host larvae were parasitized. But the fat content in parasitized host larvae was significantly higher than the unparasitized larvae at 24 h after host larvae were parasitized. 4. Effect of parasitization by C. ruficrus on host humoral immune systemThe melanization of host hemolymph was significantly inhibited by parasitism. The black change rates in parasitized host larvae conspicuously decreased, while in the host hemolymph in unparasitized larvae reached to 100%. With the increase of observation time, the black change rates of hemolymph gradually decreased which were all lower than that in unparasitized larvae.The change tendency of the activities of phenoloxidases in host hemolymph in parasitized larvae and unparasitized ones was different with 12 h, 24 h, 48 h, 72 h, and 96 h after host larvae were parasitized. The activities of phenoloxidases in parasitized host hemolymph were significantly inhibited by parasitism. The activities of phenoloxidases in unparasitized host hemolymph increased with time, while the activities of phenoloxidase in the parasitized larvae hemolymph experienced increase and then decrease.