In recent years, the research on the potential of using RNA interference (RNAi) to suppress crop pests has made an outstanding growth. However, given the variability of RNAi efficiency that is observed in many insects, the development of novel approaches toward insect pest management using RNAi requires first to unravel factors behind the efficiency of dsRNA-mediated gene silencing. In this review, we explore essential implications and possibilities to increase RNAi efficiency by delivery of dsRNA through non-transformative methods. We discuss factors influencing the RNAi mechanism in insects and systemic properties of dsRNA. Finally, novel strategies to deliver dsRNA are discussed, including delivery by symbionts, plant viruses, trunk injections, root soaking, and transplastomic plants.

https://biblio.ugent.be/publication/8503128/file/8503129.pdf

RNAi efficiency, systemic properties, and novel delivery methods for pest insect control : what we know so far

Molting is critical for growth, development, reproduction, and survival in arthropods. Complex neuroendocrine pathways are involved in the regulation of molting and may potentially become targets of environmental endocrine disrupting chemicals (EDCs). Based on several known ED mechanisms, a wide range of pesticides has been developed to combat unwanted organisms in food production activities such as agriculture and aquaculture. Meanwhile, these chemicals may also pose hazards to nontarget species by causing molting defects, and thus potentially affecting the health of the ecosystems. The present review summarizes the available knowledge on molting-related endocrine regulation and chemically mediated disruption in arthropods (with special focus on insects and crustaceans), to identify research gaps and develop a mechanistic model for assessing environmental hazards of these compounds. Based on the review, multiple targets of EDCs in the molting processes were identified and the link between mode of action ...

/pdf/ecdysone-receptor-agonism-leading-to-lethal-molting-4eyqfxl8pi.pdf

Ecdysone Receptor Agonism Leading to Lethal Molting Disruption in Arthropods: Review and Adverse Outcome Pathway Development.

Transcriptional response provides insights into the effect of chronic polystyrene nanoplastic exposure on Daphnia pulex.

Cloning of heat shock protein genes (hsp70, hsc70 and hsp90) and their expression in response to larval diapause and thermal stress in the wheat blossom midge, Sitodiplosis mosellana

Intermittent food shortages are commonly encountered in the wild. During winter or starvation stress, mammals often choose to hibernate while insects—in the form of eggs, mature larvae, pupae, or adults opt to enter diapause. In response to food shortages, insects may try to find sufficient food to maintain normal growth and metabolism through distribution of populations or even migration. In the face of hunger or starvation, insect responses can include changes in behavior and/or maintenance of a low metabolic rate through physiological adaptations or regulation. For instance, in order to maintain homeostasis of the blood sugar, trehalose under starvation stress, other sugars can be transformed to sustain basic energy metabolism. Furthermore, as the severity of starvation increases, lipids (especially triglycerides) are broken down to improve hunger resistance. Starvation stress simultaneously initiates a series of neural signals and hormone regulation processes in insects. These processes involve neurons or neuropeptides, immunity-related genes, levels of autophagy, heat shock proteins and juvenile hormone levels which maintain lower levels of physiological metabolic activity. This work focuses on hunger stress in insects and reviews its effects on behavior, energy reserve utilization, and physiological regulation. In summary, we highlight the diversity in adaptive strategies of insects to hunger stress and provides potential ideas to improve hunger resistance and cold storage development of natural enemy insects. This gist of literature on insects also broadens our understanding of the factors that dictate phenotypic plasticity in adjusting development and life histories around nutritionally optimal environmental conditions.

/pdf/insect-behavior-and-physiological-adaptation-mechanisms-4j017yhwa5.pdf

Insect Behavior and Physiological Adaptation Mechanisms Under Starvation Stress

RNA interference (RNAi) is an effective gene-silencing tool and double stranded RNA (dsRNA) is considered a powerful strategy for gene function studies in insects. In the present study, we aimed to investigate the function of trehalase (TRE) genes (TRE 1-1, TRE 1-2 and TRE-2) isolated from the brown planthopper Nilaparvata lugens, a typical piercing-sucking insect in rice and investigate their regulating roles in chitin synthesis by injecting larvae with dsRNA. The results showed that TRE1 and TRE2 had compensatory function and the expression of each increased when the other was silenced. The total rate of insects with phenotypic deformities ranged from 19.83 to 24.36% after dsTRE injection, whereas the mortality rate ranged from 14.16 to 31.78%. The mRNA levels of genes involved in the chitin metabolism pathway in RNA-Seq and DGEP, namely hexokinase (HK), glucose-6-phosphate isomerase (G6PI) and chitinase (Cht), decreased significantly at 72 h after single dsTREs injection, whereas two transcripts of chitin synthase (CHS) genes decreased at 72 h after dsTRE1-1 and dsTREs injection. These results demonstrated that TRE silencing could affect the regulation of chitin biosynthesis and degradation, causing moulting deformities. Therefore, expression inhibitors of TREs might be effective tools for the control of planthoppers in rice.

/pdf/functional-characterization-of-three-trehalase-genes-2e5a9kt8ac.pdf

Functional characterization of three trehalase genes regulating the chitin metabolism pathway in rice brown planthopper using RNA interference.

BACKGROUND
RNA interference combined with digital gene expression (DGE) analysis can be used to study gene function. Trehalose-6-phosphate synthase (TPS) plays a key role in the synthesis of trehalose and insect development.

RESULTS
DGE analysis revealed that the expression of nine or four chitinase genes was reduced significantly 48 h after NlTPS1 and NlTPS2 knockdown by RNAi, respectively. Additionally, abnormal phenotypes were noted, and approximately 30% of insects died. HK and G6PI2 expression decreased significantly whereas GFAT, GNPNA and UAP expression increased significantly 72 h after NlTPS1 and NlTPS2 knockdown. PGM1 expression decreased significantly after TPS2 knockdown, whereas PGM2 expression increased significantly and the expression of three CHS genes decreased 48 h after TPS1 knockdown. The mRNA expression of all 12 chitin degradation genes decreased 48 h after NlTPS1 and NlTPS2 treatment, and Cht2, Cht3, Cht6, Cht7, Cht10 and ENGase levels remained significantly decreased up to 72 h after NlTPS1 and NlTPS2 knockdown.

CONCLUSIONS
These results demonstrate that silencing of TPS genes can lead to increased moulting deformities and mortality rates owing to the misregulation of genes involved in chitin metabolism, and TPS genes are potential pest control targets in the future. © 2016 Society of Chemical Industry

Knockdown of two trehalose-6-phosphate synthases severely affects chitin metabolism gene expression in the brown planthopper Nilaparvata lugens

Suppressing the activity of trehalase with validamycin disrupts the trehalose and chitin biosynthesis pathways in the rice brown planthopper, Nilaparvata lugens.

RNA interference is a very effective approach for studies on gene function and may be an efficient method for controlling pests. Trehalase is a key gene in the chitin biosynthesis pathway in insects. Five trehalase genes have been cloned in Tribolium castaneum, though it is not known whether the detailed functions of these trehalases can be targeted for pest control. The functions of all five trehalase genes were studied using RNAi, and the most important results showed that the expression of all 12 genes decreased significantly from 12 to 72 h compared with the control groups, except GP1 at 72 h, when the expression of the TcTre2 gene was suppressed. The results also revealed different abnormal phenotypes, and the observed mortality rates ranged from 17 to 42 %. The qRT-PCR results showed that the expression of TPS, GS, two GP, CHS1a and CHS1b genes decreased significantly, while that of the CHS2 gene decreased or increased after RNAi after the five trehalases were silenced at 48 h. In addition, TPS gene expression decreased from 12 to 72 h after dsTcTre injection. These results demonstrate that silencing of any individual trehalase gene, especially Tre1-4 and Tre2 gene can lead to moulting deformities and a high mortality rate through the regulation of gene expression in the chitin biosynthesis pathway and may be a potential approach for pest control in the future.

/pdf/knockdown-of-five-trehalase-genes-using-rna-interference-20zn8e75ss.pdf

Knockdown of five trehalase genes using RNA interference regulates the gene expression of the chitin biosynthesis pathway in Tribolium castaneum

The main function of small heat shock proteins (sHSPs) as molecular chaperones is to protect proteins from denaturation under adverse conditions. Molecular and physiological data were used to examine the sHSPs underlying cold-hardiness in H. axyridis. Complementary DNA sequences were obtained for six Harmonia axyridis sHSPs based on its transcriptome, and the expression of the genes coding for these sHSPs was evaluated by quantitative real-time PCR (qRT-PCR) in several developmental stages, under short-term cooling or heating conditions, and in black and yellow females of experimental and overwintering populations under low-temperature storage. In addition, we measured water content and the super cooling and freezing points (SCP and FP, respectively) of H. axyridis individuals from experimental and overwintering populations. The average water content was not significantly different between adults of both populations, but the SCP and FP of the overwintering population were significantly lower than that of the experimental population. Overall, the six sHSPs genes showed different expression patterns among developmental stages. In the short-term cooling treatment, Hsp16.25 and Hsp21.00 expressions first increased and then decreased, while Hsp10.87 and Hsp21.56 expressions increased during the entire process. Under short-term heating, the expressions of Hsp21.00, Hsp21.62, Hsp10.87, and Hsp16.25 showed an increasing trend, whereas Hsp36.77 first decreased and then increased. Under low-temperature storage conditions, the expression of Hsp36.77 decreased, while the expressions of Hsp21.00 and Hsp21.62 were higher than that of the control group in the experimental population. The expression of Hsp36.77 first increased and then decreased, whereas Hsp21.56 expression was always higher than that of the control group in the overwintering population. Thus, differences in sHSPs gene expression were correlated with the H. axyridis forms, suggesting that the mechanism of cold resistance might differ among them. Although Hsp36.77, Hsp16.25, Hsp21.00, and Hsp21.62 regulated cold- hardiness, the only significant differences between overwintering and experimental populations were found for Hsp16.25 and Hsp21.00.

/pdf/molecular-cloning-and-induced-expression-of-six-small-heat-22raiqfnhh.pdf

Qida Shen

Papers

Functional characterization of three trehalase genes regulating the chitin metabolism pathway in rice brown planthopper using RNA interference.

Knockdown of two trehalose-6-phosphate synthases severely affects chitin metabolism gene expression in the brown planthopper Nilaparvata lugens

Suppressing the activity of trehalase with validamycin disrupts the trehalose and chitin biosynthesis pathways in the rice brown planthopper, Nilaparvata lugens.

Knockdown of five trehalase genes using RNA interference regulates the gene expression of the chitin biosynthesis pathway in Tribolium castaneum

Molecular Cloning and Induced Expression of Six Small Heat Shock Proteins Mediating Cold-Hardiness in Harmonia axyridis (Coleoptera: Coccinellidae)