Knockout of ecdysis triggering hormone receptor (ETHr) gene adversely affects the nymphal molting and adult reproduction in Bemisia tabaci.

Bemisia tabaci (Gennadius) is one of the most dangerous polyphagous pests in the world causing damage to various crops by sucking sap during the nymphal and adult stages. Chemical management of whiteflies is challenging because of the emergence of pesticide resistance. RNA interference has been well established in whitefly to study the functions of various genes. G-protein coupled receptors (GPCRs) are important targets for development of new generation insecticides. In this study, Ecdysis triggering hormone receptor (ETHr) gene expression was recorded in different stages of whitefly and its function has been studied through RNAi. The expression of ETHr is highest in third-instar nymphs followed by other nymphal instars, pupae and newly emerged adults. Silencing of ETHr resulted in significantly higher adult mortality (68.88%), reduced fecundity (4.46 eggs /female), reduced longevity of male and female (1.05 and 1.40 days, respectively) when adults were fed with dsETHr @ 1.0 µg/µl. Silencing of ETHr in nymphs lead to significantly higher mortality (81.35%) as compared to control. This study confirms that ETHr gene is essential for growth and development of whitefly nymphs and adults. Hence, it can be future target for developing dsRNA based insecticides for management of whitefly.

Potential of RNA interference in the study and management of the whitefly, Bemisia tabaci.

Whiteflies cause considerable losses to crops, directly by feeding, and indirectly by transmission of viruses. The current control methods consist of a combination of different control tactics, mainly still relying on unsafe and non-ecofriendly chemical control. RNA interference (RNAi) is a post-transcriptional gene-silencing strategy in which double-stranded RNA (dsRNA), corresponding specifically to a target gene, is introduced in a target organism. Research on RNAi in the previous decade has shown its success as a potential insect control strategy, which can be highly species-specific and environment friendly. In whiteflies, the success of dsRNA delivery through the oral route opened possibilities for its management through plant-mediated RNAi. To date, several genes have been targeted in whiteflies through RNAi and these assays demonstrated its potential to manage whiteflies at lab level. However, further research and investments are needed to move toward an application at field level. In this review, for the first time, we collected the literature on genes targeted for silencing via RNAi in whiteflies and discuss the potential of RNAi in whitefly pest control. We also discuss likely delivery methods, including transgenic in planta delivery and symbiont-mediated delivery, and its potential for studying and interfering with insecticide resistance mechanisms and virus transmission by whiteflies.

Molecular phylogenetic analysis of mango mealybug, Drosicha mangiferae from Punjab.

Mealybugs (Hemiptera: Pseudococcidae) are major pests of a wide range of crops and ornamental plants worldwide. Their high degree of morphological similarity makes them difficult to identify and limits their study and management. In the present study, four Indian populations of mango mealybug (mango, litchi, guava from Gurdaspur and mango from Jalandhar) were analyzed. The mtCOI region was amplified, cloned, the nucleotide sequences were determined and analysed. All the four species were found to be D. mangiferae. The population from Litchi and Mango from Gurdaspur showed 100% homologus sequence. The population of Guava-Gurdaspur and Mango-Jalandhar showed a single mutation of 'C' instead of 'T' at 18th and 196th position, respectively. Indian populations were compared with populations from Pakistan (21) and Japan (1). The phylogenetic tree resulted in two main clusters. Cluster1 represent all the 4 populations of Punjab, India, 20 of Pakistan (Punjab, Sind, Lahore, Multan, Faisalabad and Karak districts) with homologous sequences. The two population collected from Faisalabad district of Pakistan and Japan made a separate cluster 2 because the gene sequence used in analysis was from the COI-3p region. However, all the other sequence of D. mangiferae samples under study showed a low nucleotide divergence. The homologus mtCO1 sequence of Indian and Pakistan population concluded that the genetic diversity in mealybug population was quite less over a large geographical area.

Isolation and characterization of novel phorate-degrading bacterial species from agricultural soil.

Based upon 16S rDNA sequence homology, 15 phorate-degrading bacteria isolated from sugarcane field soils by selective enrichment were identified to be different species of Bacillus, Pseudomonas, Brevibacterium, and Staphylococcus. Relative phorate degradation in a mineral salt medium containing phorate (50 µg ml(-1)) as sole carbon source established that all the bacterial species could actively degrade more than 97 % phorate during 21 days. Three of these species viz. Bacillus aerophilus strain IMBL 4.1, Brevibacterium frigoritolerans strain IMBL 2.1, and Pseudomonas fulva strain IMBL 5.1 were found to be most active phorate metabolizers, degrading more than 96 % phorate during 2 days and 100 % phorate during 13 days. Qualitative analysis of phorate residues by gas liquid chromatography revealed complete metabolization of phorate without detectable accumulation of any known phorate metabolites. Phorate degradation by these bacterial species did not follow the first-order kinetics except the P. fulva strain IMBL 5.1 with half-life period (t1/2) ranging between 0.40 and 5.47 days.