RNA interference (RNAi) is a method of gene silencing where dsRNA is digested into small interfering RNA (siRNA) in the presence of enzymes. These siRNAs then target homologous mRNA sequences aided by the RNA-induced silencing complex (RISC). The mechanism of dsRNA uptake has been well studied and established across many living organisms including insects. In insects, RNAi is a novel and potential tool to develop future pest management means targeting various classes of insects including dipterans, coleopterans, hemipterans, lepidopterans, hymenopterans and isopterans. However, the extent of RNAi in individual class varies due to underlying mechanisms. The present review focuses on three major insect classes viz hemipterans, lepidopterans and coleopterans and the rationale behind this lies in the fact that studies pertaining to RNAi has been extensively performed in these groups. Additionally, these classes harbour major agriculturally important pest species which require due attention. Interestingly, all the three classes exhibit varying levels of RNAi efficiencies with the coleopterans exhibiting maximum response, while hemipterans are relatively inefficient. Lepidopterans on the other hand, show minimum response to RNAi. This has been attributed to many facts and few important being endosomal escape, high activity dsRNA-specific nucleases, and highly alkaline gut environment which renders the dsRNA unstable. Various methods have been established to ensure safe delivery of dsRNA into the biological system of the insect. The most common method for dsRNA administration is supplementing the diet of insects via spraying onto leaves and other commonly eaten parts of the plant. This method is environment-friendly and superior to the hazardous effects of pesticides. Another method involves submergence of root systems in dsRNA solutions and subsequent uptake by the phloem. Additionally, more recent techniques are nanoparticle- and Agrobacterium-mediated delivery systems. However, due to the novelty of these biotechnological methods and recalcitrant nature of certain crops, further optimization is required. This review emphasizes on RNAi developments in agriculturally important insect species and the major hurdles for efficient RNAi in these groups. The review also discusses in detail the development of new techniques to enhance RNAi efficiency using liposomes and nanoparticles, transplastomics, microbial-mediated delivery and chemical methods.

The basic principle of crop regulation is to manipulates the natural flowering and fruiting of guava plant in desired season of the year that contribute to increased fruit yield, quality, profitability and sustainability of the environment by reducing the use of the frequency of the pesticides. This concept is based on the fact that guava flowers are borne only on new, succulent, vigorously emerging vegetative growths. These new growth flushes can be either new emergences of lateral bud on older stems or extensions of already established terminals of various size and vigor. The crop regulation can be achieved by the adoption of the various practices like withholding irrigation after harvesting during the months of April-May in Northern Indian plains. This results in the shedding of flowers and the tree goes to rest. The basin of the tree is dug up, manured and irrigated in June. After about 30-35 days the tree put forth profuse flowering and fruit mature in winter. Terminal portion of the shoots up to 20 or 30 cm length should be pruned between 20 th to 30 th April. Always avoid severe pruning in guava. Apply the recommended dose of fertilizers during the month of June to encourage vegetative growth in July-August for getting maximum flowering during August-September for winter season crop. To regulate the guava crop, it is essential to reduce the fruit set during the rainy season and subsequently increase the fruit set during winter season by the use of different chemicals like NAA ethereal and urea etc. Key words:Crop regulation, Deblossoming, Guava, NAA, Water stress.Guava is most important commercial fruit crop grown in sub-tropical region of the Indian subcontinent. It gives an assured crop with very little care. Its cost of production is also low as compared to most of other commercial fruit crops. It has gained considerable prominence on account of its high nutritive value, cheap and easily availability at moderate prices. It is a good source of Vitamin C (150-200 mg/100 g of pulp). Guava fruit contains antioxidant factors and is known to control the systolic blood pressure. In guava, two distinct seasons of flowering, spring (March-April) and rains (June-July) occur from which fruits ripen during rainy and winter season respectively. In North Indian climate the rainy season crop of guava is poor in quality and nutritive value and is affected by many insect pests and diseases. The winter season fruits are superior in quality free from diseases and pests and give higher income. But it is advisable to take only one crop every year. This requires management of flowering to obtain the most desireable crop, by the methods like withholding irrigation, pruning, thinning of flowers by chemically or manually. The work carried out by various scientists on crop manipulation is reviewed under different sub heads. Why crop regulation:The rainy season crop of guava is poor in quality and crop is affected by many biotic and abiotic stresses as compared to winter season crop. The winter season crops which ripen f...

Sorghum shoot fly, Atherigona soccata,causes substantial economic losses in sorghum globally. Cultural practices and host plant resistance are effective measures for mitigating the losses caused by sorghum shoot fly. Therefore, we evaluated 32 sorghum genotypes consisting of a set of 10 restorer lines, 10 CMS (cytoplasmic male-sterile) lines and their respective maintainers exhibiting resistance/susceptibility to shoot fly along with resistant and susceptible checks under field conditions. The traits such as leaf glossiness, leaf sheath pigmentation, percentage plants with shoot fly deadhearts and number of shoot fly eggs per plant were used as morphological markers for selecting genotypes with resistance to shoot fly during the rainy and post rainy seasons of 2016 and 2017. The test material was also subjected to biochemical analysis (total soluble sugars, protein and tannin contents), while the leaf surface chemicals were analysed by GC-MS to identify the compounds associated with resistance/susceptibility to shoot fly. The genotypes differed significantly for all the traits, except percentage plants with shoot fly deadhearts during the 2016 rainy season. The genotypes ICSB 458, ICSA/B 467, ICSA/B 487, ICSA/B 14037, IS 18551 and ICSV 93046 exhibited moderate to high levels of resistance to shoot fly based on number of plants with shoot fly deadhearts, plants with shoot fly eggs and total number of shoot fly eggs. The shoot fly resistant genotypes ICSB 84, ICSA/B 467, ICSB 487, ICSB 14024, and IS 18551 had low shoot fly deadheart incidence, higher amounts of condensed tannins, soluble sugars, phenols and lower protein content as compared to the susceptible genotypes. Thirteen unique compounds were identified from leaf surface extracts by GC-MS which were associated with shoot fly resistance/susceptibility. While HPLC analysis revealed that Protocatechuic and coumaric acids were present in most of the sorghum genotypes, but their amounts were significantly greater in resistant as compared to the susceptible ones. The findings of the study highlight the importance of various morphological and biochemical traits conferring resistance to sorghum shoot fly, and these traits can be used as markers to identify shoot fly resistant genotypes for use in breeding programs.

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