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Double-stranded RNA (dsRNA)-degrading enzyme (dsRNase) is one of the negative factors influencing the RNA interference (RNAi) effect in Colorado potato beetle (CPB). We have previously shown that plastid-mediated RNAi (PM-RNAi) can be utilized to control CPB. In this study, we aimed to test whether silencing dsRNase could increase the RNAi effect in CPB via PM-RNAi. We generated transplastomic potato (Solanum tuberosum) plants expressing dsRNA targeting shibire (dsSHI) of CPB. St-dsSHI plants (transplastomic plants expressing dsSHI) showed much less potent RNAi response than transplastomic potato plants expressing dsRNAs targeting CPB Shrub (St-dsSHR) or β-Actin (St-dsACT), two CPB-resistant transplastomic lines generated previously. The three types of transplastomic lines have weak (St-dsSHI), moderate (St-dsSHR) and strong (St-dsACT) resistant levels to CPB. Treatment with in vitro-synthesized dsdsRNase1/2 (a fusion dsRNA targeting dsRNase1 and dsRNase2 of CPB) led to enhanced suppression of dsRNase1 and dsRNase2 in CPB larvae fed with St-dsSHI plants and dsRNase2 in CPB larvae fed with St-dsSHR plants. St-dsSHR or St-dsSHI plants showed significantly reduced CPB larva weight or damaged area by CPB feeding. These results demonstrate that dsRNase-silencing approach could improve the effect of PM-RNAi when the silencing of target genes has weak or moderate strength of the insecticidal effects. The findings provide a new proof-of-concept to enhance crop resistance to insect herbivores to via an “RNAi-of-RNAi” approach. [ABSTRACT FROM AUTHOR]

Agricultural ecosystems are extremely vulnerable to invasions by various pestiferous organisms. Bactrocera dorsalis is one of the invasive insect pests on fruits and vegetables in southern China, gradually spreading northward in past decades. To clarify its risk to damage to the northern fruits, the performance and fitness of the first and third reared generations of B. dorsalis were studied with two-sex life table on northern fruits (apples and peaches as dominant fruits) and southern fruit (oranges as appropriate host). Furthermore, the preference of host and oviposition selection were also conducted in laboratory experiments. Also, the CLIMEX model was used to comprehensively assess its potential risk in northern orchards. It was found that B. dorsalis had high fitness on peaches and good-performance on apples within first and third generations. This implies that peaches and apples are liable to become one of its most favorable hosts in northern orchards. The simulation based on CLIMEX model showed B. dorsalis had a high population growth potential in summer and autumn in some regions of northern China, where the life cycle can be completed and two simulated occurrence peaks last two to three months from early June to late July and from mid-late August to early September, long enough to cause serious harm. Projection for its distribution by 2080 indicated that the suitable area for B. dorsalis would further expand northward. Innate ability of B. dorsalis in flight, adaptability and wide range of hosts is conducive to its diffusion into new habitats, and external causes including harm concealment within fruits, frequent transportation were also discussed. Therefore, monitoring of B. dorsalis occurrence in northern orchards is necessary, combined with strict quarantine and control efforts, to avoid its further expansion and the consequent economic losses. [ABSTRACT FROM AUTHOR]