Double-Stranded RNA-Mediated Suppression of Trypsin-Like Serine Protease (t-SP) Triggers Over-Expression of Another t-SP Isoform in Helicoverpa armigera

High diversity of digestive proteases is considered to be the key factor in the evolution of polyphagy in Helicoverpa armigera. Serine proteases (SPs) contribute ~85% of the dietary protein digestion in H. armigera. We investigated the dynamics of SP regulation in the polyphagous pest, H. armigera using RNA interference (RNAi). HaTry1, an isoform of SP, expressed irrespective of the composition of the diet, and its expression levels were directly proportional to the larval growth rate. Therefore, HaTry1 was silenced by delivering 10 and 20 μg concentrations of double-stranded RNA through semi-synthetic diet. This led to a drastic reduction in the target gene transcript levels that manifested in a significant reduction in the larval weight initially, but the larvae recovered in later stages despite continuous dsRNA treatment. This was probably due to the compensatory effect by over-expression of HaTry13 (31-folds), another isoform of SP. Phylogenetic analysis of H. armigera SPs revealed that the over-expressed isoform was closely related to the target gene as compared to the other tested isoforms. Further, silencing of both the isoforms (HaTry1 and HaTry13) caused the highest reduction in the larval weight and there was no larval growth recovery. These findings provide a new evidence of the existence of compensatory effect to overcome the effect of silencing individual gene with RNAi. Hence, the study emphasizes the need for simultaneous silencing of multiple isoforms

African ancestry of New World, Bemisia tabaci-whitefly species

Bemisia tabaci whitefly species are some of the world’s most devastating agricultural pests and plant-virus disease vectors. Elucidation of the phylogenetic relationships in the group is the basis for understanding their evolution, biogeography, gene-functions and development of novel control technologies. We report here the discovery of five new Sub-Saharan Africa (SSA) B. tabaci putative species, using the partial mitochondrial cytochrome oxidase 1 gene: SSA9, SSA10, SSA11, SSA12 and SSA13. Two of them, SSA10 and SSA11 clustered with the New World species and shared 84.8‒86.5% sequence identities. SSA10 and SSA11 provide new evidence for a close evolutionary link between the Old and New World species. Re-analysis of the evolutionary history of B. tabaci species group indicates that the new African species (SSA10 and SSA11) diverged from the New World clade c. 25 million years ago. The new putative species enable us to: (i) re-evaluate current models of B. tabaci evolution, (ii) recognise increased diversity within this cryptic species group and (iii) re-estimate divergence dates in evolutionary time

Species-complex diversification and host-plant associations in Bemisia tabaci : a plant-defense, detoxification perspective revealed by RNAseq analyses

Insect‐plant associations and their role in diversification are mostly studied in specialists. Here, we aimed to identify macroevolution patterns in the relationships between generalists and their host plants that have the potential to promote diversification. We focused on the Bemisia tabaci species complex containing more than 35 cryptic species. Mechanisms for explaining this impressive diversification have focused so far on allopatric forces that assume a common, broad, host range. We conducted a literature survey which indicated that species in the complex differ in their host range, with only few showing a truly broad one. We then selected six species, representing different phylogenetic groups and documented host‐ranges. We tested if differences in the species expression profiles of detoxification genes, are shaped more by their phylogenetic relationships or by their ability to successfully utilize multiple hosts, including novel ones. Performance assays divided the six species into two groups of three, one showing higher performance on various hosts than the other (the lower‐performance group). The same grouping pattern appeared when the species were clustered according to their expression profiles. Only species placed in the lower‐performance group showed a tendency to lower the expression of multiple genes. Taken together, these findings bring evidence for the existence of a common detoxification “machinery”, shared between species that can perform well on multiple hosts. We raise the possibility that this “machinery” might have played a passive role in the diversification of complex, by allowing successful migration to new/novel environments, leading, in some cases, to fragmentation and speciation

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Potential of RNAi in insect pest managementHelicoverpa armigera is an important pest infesting a number of crops of high commercial value leading to huge economic losses globally. RNA interference (RNAi) is a potent tool for the control of insect pests and towards this objective, transgenic tomato expressing dsRNA of Juvenile hormone acid methyl transferase (JHAMT) gene of H. armigera was developed. The H. armigera larvae fed on HaJHAMT tomato leaves led to a severe (90%) down regulation of the cognate gene expression thus adversely affected the feeding and metamorphosis. Reduction in larval and pupal weight and inability to undergo complete metamorphosis were observed that led to larval-pupal intermediates and subsequently affected the eclosion. Thus, JH down regulation is an attractive target due to specificity to insects and its important role in insect growth and development to engineer insect resistance in crops using RNAi.Not Availabl

Not Available

Not AvailableHelicoverpa armigera is an important pest infesting a number of crops of high commercial value leading to huge economic losses globally. RNA interference (RNAi) is a potent tool for the control of insect pests and towards this objective, transgenic tomato expressing dsRNA of Juvenile hormone acid methyl transferase (JHAMT) gene of H. armigera was developed. The H. armigera larvae fed on HaJHAMT tomato leaves led to a severe (90%) down regulation of the cognate gene expression thus adversely affected the feeding and metamorphosis. Reduction in larval and pupal weight and inability to undergo complete metamorphosis were observed that led to larval-pupal intermediates and subsequently affected the eclosion. Thus, JH down regulation is an attractive target due to specificity to insects and its important role in insect growth and development to engineer insect resistance in crops using RNAi.Not Availabl