Abstract
Using of plant essential oil that coevolved as a defense mechanism against agriculture insects is an alternative means of controlling many insect pests. In order to repel brown planthoppers (BPHs), the most notorious rice insect pest, a new film based on guar gum incorporated with citral (GC film) was formulated, which was effective while being environmentally friendly. In this paper, the effect and mechanism of GC film repellency against BPHs were determined. Repellent activity test and olfactory reaction analysis showed that GC film had repellency effect against BPHs, with repellency of 60.00% and 73.93%, respectively. The result of olfactory reaction indicated that GC film repellency against BPHs relied on smell. EPG analysis showed the proportion and mean duration of np waveform were significantly higher than in CK and increased following the treatment concentration, which indicated that GC film affected the recognition of BPHs to rice. Further analysis by RNA sequencing analysis showed a total of 679 genes were significantly upregulated and 284 genes were significantly downregulated in the BPHs fed on the rice sprayed with GC film compared to control. Odorant-binding protein (OBP) gene 797 and gustatory receptor gene (GR)/odorant receptor (OR) gene 13110 showed a significant decrease in differential expression and significant increase in differential expression, respectively. There were 0.66 and 2.55 differential expression multiples between treated BPHs and control, respectively. According to the results described above, we reasoned that GC film repellency against BPHs due to smell, by release of citral, caused the recognition difficulties for BPHs to rice, and OBP gene 797 and GR/OR gene 13110 appeared to be the crucial candidate genes for GC film repellency against BPHs. The present study depicted a clear and consistent repellency effect for GC film against BPHs and preliminarily clarified the mechanism of GC film as a repellent against BPHs, which might offer an alternative approach for control of BPHs in the near future. Our results could also help in the development and improvement of GC films.
Highlights
Licensee MDPI, Basel, Switzerland.The brown planthopper (BPH, Nilaparvata lugens Stål, Hemiptera: Delphacidae) is an oligophagous insect that feeds only on wild rice (Oryza rufipogon Griff.) and cultivated rice (Oryza sativa L.), primarily on cultivated rice, which is one of the world’s most important food crops and a staple food for over half of the population in Asian countries
The olfactory reaction analysis showed a similar pattern to that of the feeding choice test, for the repellency increased with the treated concentration of GC film-forming emulsion, and 73.93% repellency was recorded at the highest concentration (Figure 2b)
Film has a repellency effect against brown planthoppers (BPHs), and olfactory reaction analysis indicated GC film repellency against BPHs relies on smell
Summary
The brown planthopper (BPH, Nilaparvata lugens Stål, Hemiptera: Delphacidae) is an oligophagous insect that feeds only on wild rice (Oryza rufipogon Griff.) and cultivated rice (Oryza sativa L.), primarily on cultivated rice, which is one of the world’s most important food crops and a staple food for over half of the population in Asian countries. The use of chemical insecticides is still the main strategy for BPH management. The search for alternative and environmentally friendly strategies to control BPH has been an increasing interest. One strategy relies on the use of plant secondary metabolites that have coevolved as a defense mechanism against agriculture insects [8,9]
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