Changes in Transcriptome and Gene Expression in Sogatella furcifera (Hemiptera: Delphacidae) in Response to Cycloxaprid.

The white-backed planthopper, Sogatella furcifera (Horváth), causes substantial damage to crops by direct feeding or virus transmission, especially southern rice black-streaked dwarf virus, which poses a serious threat to rice production. Cycloxaprid, a novel cis-nitromethylene neonicotinoid insecticide, has high efficacy against rice planthoppers, including imidacloprid-resistant populations. However, information about the influence of cycloxaprid on S. furcifera (Hemiptera: Delphacidae) at the molecular level is limited. Here, by de novo transcriptome sequencing and assembly, we constructed two transcriptomes of S. furcifera and profiled the changes in gene expression in response to cycloxaprid at the transcription level. We identified 157,906,456 nucleotides and 131,601 unigenes using the Illumina technology from cycloxaprid-treated and untreated S. furcifera. In total, 38,534 unigenes matched known proteins in at least one database, accounting for 29.28% of the total unigenes. The number of coding DNA sequences was 28,546 and that of amino acid sequences in the coding region was 22,299. In total, 15,868 simple sequence repeats (SSRs) were identified. The trinucleotide repeats accounted for 45.1% (7,157) of the total SSRs and (AAG/CTT)n were the most frequent motif. There were 359 differentially expressed genes that might have been induced by cycloxaprid. There were 131 upregulated and 228 downregulated genes. Twenty-two unigenes might be involved in resistance against cycloxaprid, such as cytochrome P450, glutathione S-transferase (GST), acid phosphatase (ACP), and cadherin. Our study provides vital information on cycloxaprid-induced resistance mechanisms, which will be useful to analyze the molecular mechanisms of cycloxaprid resistance and may lead to the development of novel strategies to manage S. furcifera.

Occurrence characteristics of Echinochloa and its response to long-term fertilization in paddy fields of yellow soil.

We studied the characteristics of Echinochloa and its response to variation of rice yield and soil properties under long-term fertilization in paddy field of yellow soil, based on a 23-year long-term fertilization experiment in Scientific Oberving and Experimental Station of Arable Land Conservation and Agricultural Environment (Guizhou), Ministry of Agriculture. The occurrence characteristics of Echinochloa (density, panicle number per plant, totle panicles, seed number per panicle, 1000-seed mass and seed mass per panicle) of ten treatments including CK, N, PK, NK, NP, NPK, 1/4MNP, 1/2MNP, M (manure), MNPK were examined. The results showed that the characteristics of Echinochloa significantly varied with long-term different fertilization. The highest density, panicle number per plant and total panicles of Echinochloa were attained in the MNPK treatment, followed by the 1/4MNP treatment. Compared with the NPK treatment, the density of Echinochloa was significantly decreased in no fertilizer treatment (CK) and unbalanced chemical fertilizer treatments (N, PK, NK, NP). The panicle number per plant significantly increased in organic fertilizer treatments (1/4MNP, 1/2MNP, M, MNPK). Both the density and total panicles of Echinochloa were positively correlated with rice yield. The occurrence characteristics of Echinochloa were positively correlated with soil organic matter, total N, total P, available N, available P and available K. Results from path analysis showed that soil total N had a direct positive effect on panicle number per plant and soil total P content was the main factor affecting the density and total panicles of Echinochloa. Soil available K content was the factor with strongest influence on seed number per panicle and seed mass per panicle. We concluded that the occurrence characteristics of Echinochloa varied with long-term different fertilization. The density, panicle number per plant and total panicles of Echinochloa could be increased with appling cow manure. Soil total P was the direct influencing factor for the variation of density and total panicle of Echinochloa in paddy field of yellow soil.

Expression Differences of Resistance-Related Genes Induced by Cycloxaprid Using qRT-PCR in the Female Adult of Sogatella furcifera (Hemiptera: Delphacidae).

As a newer cis-nitromethylene neonicotinoid pesticide at present, cycloxaprid has good industrialization prospects, including the management of imidacloprid-resistant populations, because this chemical have an excellent efficiency against rice planthoppers. Sogatella furcifera (Horváth) is the most economically important pest of rice worldwide and has developed resistance to many insecticides. This study focused on the expression change of these resistance genes, induced by cycloxaprid, involved in metabolic detoxification and receptor protein. Twenty-two differentially expressed genes (DEGs) that may be related with the insecticide resistance were found in the transcriptome of S. furcifera, including 2 cytochrome P450 genes, 2 glutathione S-transferase (GST) genes, 1 acid phosphatase (ACP) gene, 12 decarboxylase genes, 2 glycolipid genes, 1 cadherin gene, and 2 glycosyltransferase genes, which were up- or downregulated in response to an exposure of cycloxaprid. Furthermore, two P450 genes (CYP4 and CYP6 family, respectively), two decarboxylase genes, and one glycosyltransferase gene were validated by qRT-PCR. Expression differences of these genes verified successfully by qRT-PCR in response to different concentrations and times treated with cycloxaprid could explain the insecticide resistance mechanism under cycloxaprid stress in S. furcifera.

Monitoring Trends in Insecticide Resistance of Field Populations of Sogatella furcifera (Hemiptera: Delphacidae) in Guizhou Province, China, 2012-2015.

Sogatella furcifera (Horváth) is a migratory insect that is one of the most important pest species on rice in many Asian countries. Control of S. furcifera (Hemiptera: Delphacidae) primarily depends on the use of chemical insecticides, and with this extensive reliance on pesticides, determining the degree of resistance of S. furcifera populations to the chemicals used for its control is essential. In this study, the resistance level to six conventional insecticides in five populations of S. furcifera from Guizhou Province was monitored yearly using the rice-stem dipping method in 2012-2015 to precisely understand current resistance levels and to estimate trends in the development of insecticide resistance in S. furcifera in Guizhou. Overall, S. furcifera from five regions in Guizhou showed a trend toward decreased susceptibility to isoprocarb (resistance ratio [RR] 0.82-3.59), susceptibility to low resistance against thiamethoxam (RR 0.27-9.69), susceptibility to moderate resistance to imidacloprid (RR 0.71-26.06), and decreased susceptibility to moderate resistance to chlorpyrifos (RR 4.63-19.58). The resistance to pymetrozine (RR 10.48-84.65) was moderate to high, and that to buprofezin (RR 6.36-412.43) was low to very high. In conclusion, the use of buprofezin and pymetrozine to control S. furcifera should be reduced in Guizhou Province, whereas prudent use at a reasonable frequency of chlorpyrifos and imidacloprid can continue. Isoprocarb and thiamethoxam are the best choices for effective management of S. furcifera. Rotations using alternative insecticides with different modes of action are recommended for regions in which resistance is at a moderate level.