## 3 Conclusions and Future Perspectives
Successful implementation of RNAi-based pest control strategies requires high efficacy of the dsRNA in inhibiting the growth of the target pest and also easy operation in the field. Therefore, optimal delivery systems for the dsRNA to the target pest are essential. Particularly in lepidopteran species, oral administration of dsRNA may not fully elicit the RNAi effect. [PERSON] et al. (2012) addressed this problem by synthesizing a cationic polymer compound, poly[\(N\)-(3-guanidinopropyl)-methacrylamide], to bind to RNA. When dsRNA was bound to this compound and administered to larvae of the fall armyworm, it showed moderate larval mortality. This carrier compound is thought to bind to the dsRNA and make it resistant to the attack of high-activity RNA-degrading enzymes in the insect gut. It has also been suggested that the complex of the polymer and dsRNA facilitates its transport into cells in the digestive tract. Similarly, [PERSON] et al. (2013) showed an increase in mortality after oral administration to _Spodoptera exigua_, a lepidopteran insect, of a dsRNA formulation using guanylated polymer nanoparticles to ensure the stability of the complex in the alkaline environment of the digestive tract. Recently, a new nanocarrier polymer/detergent formulation has been developed that allows dsRNA to quickly penetrate the insect body wall. In plant-chewing pests such as hemipteran aphids, dsRNA ingested orally is rapidly degraded by enzymes in the gut and hemolymph, making it difficult to achieve the full effect of RNAi. However, it was reported that the novel delivery system (dsRNA/nanocarrier/detergent formulation), in which the target dsRNA was bound to a cation dendrimer and covered with a detergent, promoted transdermal penetration of the target dsRNA into soybean aphids and induced the expected inhibitory RNAi effect ([PERSON], 2014). Refinement of compounds for the optimal delivery of RNA products \begin{table}
\begin{tabular}{l l l l} \hline \hline
**Host Microbe** & **Advantages** & **Disadvantages** \\ \hline \multirow{4}{*}{_Escherichia coli_} & - & High production yield of dsRNA & \\  & - & Easy genetic manipulation & - & Gram-negative bacterium \\  & - & Many examples of use as host strain for & with endotoxins \\  & & dsRNA production & & \\ \hline \multirow{4}{*}{_Pseudomonas syringae_} & - & Enables the efficient production of long RNAs of & \\  & & uniform length & - & Low production yield of dsRNA \\  & - & Preparation of RNA with high purity & & \\ \hline \multirow{4}{*}{_Corynebacterium_} & - & Very high production yield of dsRNA & & \\  & - & Robustness and proven performance in & - & Thick cell membrane \\  & & large-scale fermentation & & structure that makes RNA \\  & - & Non-pathogenic, non-endotoxic microorganism & & extraction difficult \\  & & (GRAS status) & & \\ \hline \multirow{4}{*}{_Chlamydomonas_} & - & Non-pathogenic, non-endotoxic microalgae & - & Low production yield of dsRNA \\  & & (GRAS status) & - & Concerns about release of living \\  & - & Use as live dsRNA-producing alga considered (mainly & - & GMOs into the environment \\  & & for use in aquaculture feed) & & \\ \hline \multirow{4}{*}{_Saccharomyces cerevisiae_} & - & Non-pathogenic, non-endotoxic eukaryote & & \\  & (GRAS status) & & \\ \cline{1-1}  & - & Proven performance in large-scale culture & - & Low production yield of dsRNA \\ \cline{1-1}  & - & Beneficial properties of microbial ingredients & & \\ \hline \multirow{4}{*}{Symbiotic bacteria (_Rhodococcus rhodati_, BFo2)} & - & Difficulties in constructing & \\ \cline{1-1}  & & dsRNA-producing bacteria with & & the limited available genetic \\ \cline{1-1}  & & coexisting in the gut of the target pest & & engineering tools \\ \cline{1-1}  & & - & Concerns about release of living \\ \cline{1-1}  & & GMOs into the environment & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Characteristics of typical microbial dsRNA expression systems.