Comparative Studies On Host Fitness, Defensive Enzymes And Symbionts Of The Three Rice Planthoppers

The rice planthoppers are the most important pests on paddy rice. Nilaparvata lugens(St?l),Sogatella furcifera (Horvath)and Laodelphax striatellus (Fallén)are the main rice planthoppers in China. Their biological performances are very different when reared on different host plants. In order to find out mechanisms causing the differences, we studied the survival rate, adult weight, terms of detoxification enzymes, and activities of protective enzymes of rice planthoppers reared on four rice varieties (TN1, IR42, Wujing3 and RHT) and a weed (Echinochloa. crusgalli ). In addition, a comparative study on the endosymbionts of these rice planthoppers was also conducted. The main results are as follows:1. On the four rice varieties (TN1, IR42, Wujing3 and RHT) and the weed (E. crusgalli), the survival rate of three kinds of planthoppers were significantly different. N. lugens had a highest survival rate reared on TN1, followed by IR42 and Wuyujing3. The lowest survival rate was observed reared on RHT. S. furcifera and L. striatellus had significantly higher survival rates reared on TN1 as well as on Wuyujing3. Interestingly, these two kinds of rice planthoppers reared on E. crusgalli even had higher survival rate than that reared on TN1 and Wuyujing3.The survival rates reared on RHT and IR42 were significantly lower. The weight of newly emerged adults showed the same trend along with the outcomes of the survival rates.2. The activities of glutathione S-transferase (GST) and microsomal mixed function oxidases (MFO) at adult stage, and those of carboxylesterase (CarE), superoxide dismutase (SOD) and peroxidase (POD) at adult stage were significantly different. The similar outcomes were also observed at the nymph stage. The effects of host plants on the activities of five defensive enzymes were also different among these rice planthopper species. The activities of these five defensive enzymes of L. striatellus were mostly affected. In comparing, S. furcifera was moderately affected and N. lugens was slightest affected. It was in accordant with the host range of the three planthoppers. However, we also found that these rice planthoppers had the similar host fitness. But the activities of the five tested enzymes were different, both at adult and nymph stages. These results indicated that there was no a constant relation between fitness and activity of detoxification and protective enzymes reared on different host plants and different developmental stages.3. The infection rates of seven endosymbionts of three planthoppers were also compared. The infection rates of Arthrobacter and Chryseobaterium were high in all of three kinds of planthoppers (83.3% - 96.6%). The infection rates of these two endosymbionts were similar among three planthoppers. But, the infection rates of other five endosymbionts, Serratia, Wolbachia, Arsenophonus, Acinetobacter and Cardinium hertigiiersal were significant different among these planthoppers. The infection rate of, at least, one of planthoppers was≤30% for the obove five endosymbionts. The infection rates of Serratia and Wolbachia in S. furcifera and L. striatellus were higher than in N. lugens. The infection rate of C. hertigii and Acinetobacter in S. furcifera is higher than in N. lugens and in L. striatellus. Arsenophonus was detected in all tested N. lugens populations, while it is rarely detected in S. furcifera and in L. striatellus. Thus, we concluded that the infected species of endosymbionts and infection rates were different among rice planthoppers. Furthermore, the infection rates of same endosymbiont were also different among geographic- and host-associated populations within same planthopper species.