RNA interference-mediated knockdown of some genes involved in digestion and development of Helicoverpa armigera

Helicoverpa armigera is a significant agricultural pest and particularly notorious for its resistance to many types of common insecticides. RNA interference (RNAi) is a mechanism of post-transcriptional gene silencing and trigged by double-strand RNA (dsRNA), has become a widely used reverse genetics and potent tool for insect pest control. In this study, the effect of ingestion and injection delivery methods of dsRNA related two important enzyme genes, α-amylase (HaAMY48, Ha-AMY49) and juvenile hormone esterase (Ha-JHE), were examined on growth and development of H. armigera. After 24, 48, 72 and 96 h of feeding bioassay, significant down regulation was observed about; 56, 68, 78, 80.75% for HaAMY48, 60, 70, 86.5 and 96.75%, for Ha-AMY49 and 14, 27.5, 23 and 31.7% for Ha-JHE, respectively. The results for injection assay was 61.5, 71.5, 74 and 95.8% for Ha-AMY48; 70, 88, 91.5 and 97.7% for Ha-AMY49 and 22, 61, 75 and 74% for Ha-JHE after 24, 48 and 72 h of last injecting, respectively. Larvae that treated with dsRNA, fed or injected, lost more than half of their weight. 50% mortality in treated larvae was observed in the case injection bioassay with dsHa-JHE and 59% of larvae that fed of dsRNA-treated cubes survived. DsHa-AMY48 and 49 have significant mortality, but mixing of them is more effective in both bioassays. Injection bioassay has a potent inhibitory effect on α-amylase-specific activity about more than 87% in treated larvae with mix of dsHa-AMY48 and 49. Adult malformation percent was evaluated for feeding (28, 35.5 and 43% for Ha-AMY48, 49 and Ha-JHE, respectively) and injection bioassay (23, 42 and 29% for Ha-AMY48, 49 and Ha-JHE, respectively). All these finding suggest that Ha-AMY48, Ha-AMY49 and Ha-JHE can be new candidates to scheming effective dsRNAs pesticide for H. armigera control.

Knockdown of Helicoverpa armigera protease genes affects its growth and mortality via RNA interference

Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae), the cotton bollworm, is a destructive pest which is famous for its resistance to a variety of insecticides. RNA interference is a posttranscriptional gene silencing mechanism that has become a popular tool to control insect pests, triggered by double-stranded RNAs (dsRNAs). The effect of ingestion and injection delivery methods of dsRNA related to some protease genes including Trypsin (Ha-TRY39 and Ha-TRY96), Chymotrypsin (Ha-CHY), and Cathepsin L (Ha-CAT) on growth and development of H. armigera was investigated in this study. All protease genes encoded full ORFs and were expressed in all H. armigera larvae stages and tissues. In both injection and feeding bioassays, Ha-RNAi CHY's performance outperformed that of other protease genes. CHY enzyme activity in the midgut of larvae was significantly reduced after treatment with ds-HaCHY. Oral administration of ds-CHY also resulted in significant mortality of H. armigera larvae. However, because of the high RNase activity in the midgut lumen of lepidoptera, a large amount of dsRNA was needed to effectively kill instars of H. armigera. To reduce dsRNA degradation, bacterial expression and dsRNA formulation were used. After oral administration, it was toxic to H. armigera larvae. Before oral administration, bacterial cells were sonicated to increase dsRNA release. The RNA interference efficiency of sonicated bacteria was significantly increased, resulting in higher larval mortality when administered orally. All of these findings point to Ha-CHY as a new candidate for developing an effective dsRNA-based pesticide for H. armigera control.

Differential Inhibition of Helicoverpa armigera (Lep.: Noctuidae) Gut Digestive Trypsin by Extracted and Purified Inhibitor of Datura metel (Solanales: Solanaceae)

The cotton bollworm, Helicoverpa armigera Hubner (Lep: Noctuidae), is an economically important pest of numerous major food crops worldwide. Protease inhibitors from plants, expressed constitutively in transgenic crops, have potential for pest management as an alternative to chemical pesticides. In this study, a protease inhibitor was isolated, purified, and characterized from Datura metel L. seeds. The purity of the isolated inhibitor was confirmed by reverse-phase high-performance liquid chromatography, and activity staining showed one major peak and one clear activity band for the protein. Electrophoretic studies following gel filtration and ion-exchange chromatography revealed two and one bands for purified proteins, respectively. Partial biochemical characterizations of the purified inhibitor were determined. Maximum inhibitory activity was observed at 40-45°C (optimal temperature) when tested against gut extracts of fourth to sixth instar H. armigera larvae. Thermo-stability of the trypsin inhibitor against sixth instar larval midgut trypsin was observed up to 50°C when incubated for 30 min and 2 h. Among metal ions tested, Fe2+, Cu2+, and Mn2+ were found to decrease the trypsin inhibitory activity, whereas Hg2+, Mg2+, K+, Zn2+, Na+, Ca2+, and Cd2+ were found to significantly increase the inhibitory effect. This trypsin inhibitor showed competitive inhibition where the apparent value of Michaelis-Menten Km increased, but the value of Vmax remained unchanged.

A amylase activity of nymphal stages of sunn pest, Eurygaster integriceps Puton (Hemiptera: Scutelleridae)

Wheat production in Iran has changed substantially over the past one or two decades with development of higher-yielding cultivars and improved methods of planting. Sunn pest, Eurygaster integriceps (Heteroptera: Pentatomidae), is the most important cereal pest in Iran. Sunn pest like other insect pests of wheat lives on a polysaccharide-rich diet and depends to a large extent on effectiveness of their alpha-amylases for survival. alpha-amylase (1-4-alpha-D-glucan glucanohydrolase) hydrolyses starch, and related polysaccharides by randomly cleaving internal alpha-1,4-glucosidic linkages and has a major role in the utilization of polysaccharides. The recent increase in study of insect digestive enzymes seems to make sense in the realization that the gut is the major interface between the insect and its environment. Hence, an understanding of digestive enzyme function is essential when developing methods of insect control such as the use of enzyme inhibitor's and transgenic plants to control phytophagous insects. The aim of the current study is to identify and characterize alpha-amylase activity in order to gain a better understanding of its digestive physiology, which hopefully will lead to new strategies of the insect control. In order to analyze a-amylase activity adult and different nymphal stages were collected from wheat field from Karaj area and midgut complex from these individuals were dissected under a light microscope in ice-cold saline buffer (0.006M NaCl). After homogenization in buffer, homogenate was centrifuged at 15000 g for 20 min at 4 degrees C. The supernatant was pooled and stored at -20 degrees C for subsequent analysis. alpha-amylase activity was assayed by the dinitrosalicylic acid (DNS) procedure using soluble starch as substrate (starch 1%). Our result showed that enzyme activities in different nymphal stages (first, second, third, fourth and fifth stadium) were 0.19, 0.78, 1.21, 1.23, 1.25 units/mg protein, respectively.