Ravindra Mahadappa Aurade

Computational reverse chemical ecology: virtual screening and predicting behaviorally active semiochemicals for Bactrocera dorsalis.

BackgroundSemiochemical is a generic term used for a chemical substance that influences the behaviour of an organism. It is a common term used in the field of chemical ecology to encompass pheromones, allomones, kairomones, attractants and repellents. Insects have mastered the art of using semiochemicals as communication signals and rely on them to find mates, host or habitat. This dependency of insects on semiochemicals has allowed chemical ecologists to develop environment friendly pest management strategies. However, discovering semiochemicals is a laborious process that involves a plethora of behavioural and analytical techniques, making it expansively time consuming. Recently, reverse chemical ecology approach using odorant binding proteins (OBPs) as target for elucidating behaviourally active compounds is gaining eminence. In this scenario, we describe a “computational reverse chemical ecology” approach for rapid screening of potential semiochemicals.ResultsWe illustrate the high prediction accuracy of our computational method. We screened 25 semiochemicals for their binding potential to a GOBP of B. dorsalis using molecular docking (in silico) and molecular dynamics. Parallely, compounds were subjected to fluorescent quenching assays (Experimental). The correlation between in silico and experimental data were significant (r2 = 0.9408; P < 0.0001). Further, predicted compounds were subjected to behavioral bioassays and were found to be highly attractive to insects.ConclusionsThe present study provides a unique methodology for rapid screening and predicting behaviorally active semiochemicals. This methodology may be developed as a viable approach for prospecting active semiochemicals for pest control, which otherwise is a laborious process.

Oviposition site-selection by Bactrocera dorsalis is mediated through an innate recognition template tuned to γ-octalactone.

Innate recognition templates (IRTs) in insects are developed through many years of evolution. Here we investigated olfactory cues mediating oviposition behavior in the oriental fruit fly, Bactrocera dorsalis, and their role in triggering an IRT for oviposition site recognition. Behavioral assays with electrophysiologically active compounds from a preferred host, mango, revealed that one of the volatiles tested, γ-octalactone, had a powerful effect in eliciting oviposition by gravid B. dorsalis females. Electrophysiological responses were obtained and flies clearly differentiated between treated and untreated substrates over a wide range of concentrations of γ-octalactone. It triggered an innate response in flies, overriding inputs from other modalities required for oviposition site evaluation. A complex blend of mango volatiles not containing γ-octalactone elicited low levels of oviposition, whereas γ-octalactone alone elicited more oviposition response. Naïve flies with different rearing histories showed similar responses to γ-octalactone. Taken together, these results indicate that oviposition site selection in B. dorsalis is mediated through an IRT tuned to γ-octalactone. Our study provides empirical data on a cue underpinning innate behavior and may also find use in control operations against this invasive horticultural pest.

Modulatory Effect of Citrate Reduced Gold and Biosynthesized Silver Nanoparticles on α-Amylase Activity

Amylase is one of the important digestive enzymes involved in hydrolysis of starch. In this paper, we describe a novel approach to study the interaction of amylase enzyme with gold nanoparticles (AuNPs) and silver nanoparticles (AgNPs) and checked its catalytic function. AuNPs are synthesized using citrate reduction method and AgNPs were synthesized using biological route employing Ficus benghalensis and Ficus religiosa leaf extract as a reducing and stabilizing agent to reduce silver nitrate to silver atoms. A modulatory effect of nanoparticles on amylase activity was observed. Gold nanoparticles are excellent biocompatible surfaces for the immobilization of enzymes. Immobilized amylase showed 1- to 2-fold increase of activity compared to free enzyme. The biocatalytic activity of amylase in the bioconjugate was marginally enhanced relative to the free enzyme in solution. The bioconjugate material also showed significantly enhanced pH and temperature stability. The results indicate that the present study paves way for the modulator degradation of starch by the enzyme with AuNPs and biogenic AgNPs, which is a promising application in the medical and food industry.

Salicylic Acid Induces Changes in Mango Fruit that Affect Oviposition Behavior and Development of the Oriental Fruit Fly, Bactrocera dorsalis.

The Oriental fruit fly, Bactrocera dorsalis (Hendel) is an important quarantine pest around the globe. Although measures for its control are implemented worldwide through IPM and male annihilation, there is little effect on their population. Hence, there is a need for new strategies to control this minacious pest. A strategy that has received negligible attention is the induction of ‘natural plant defenses’ by phytohormones. In this study, we investigated the effect of salicylic acid (SA) treatment of mango fruit (cv. Totapuri) on oviposition and larval development of B. dorsalis. In oviposition choice assays, gravid females laid significantly less eggs in SA treated compared to untreated fruit. Headspace volatiles collected from SA treated fruit were less attractive to gravid females compared to volatiles from untreated fruit. GC-MS analysis of the headspace volatiles from SA treated and untreated fruit showed noticeable changes in their chemical compositions. Cis-ocimene and 3-carene (attractants to B. dorsalis) were reduced in the headspace volatiles of treated fruit. Further, reduced pupae formation and adult emergence was observed in treated fruit compared to control. Increased phenol and flavonoid content was recorded in treated fruit. We also observed differential expression of anti-oxidative enzymes namely catalase (CAT), polyphenoloxidase (PPO) and peroxidase (POD). In summary, the results indicate that SA treatment reduced oviposition, larval development and adult emergence of B. dorsalis and suggest a role of SA in enhancing mango tolerance to B. dorsalis.

Evaluation of synthetic oviposition stimulants to enhance egg collection of the oriental fruit fly, Bactrocera dorsalis (Diptera: Tephritidae)

Tephritid flies are pests of horticultural importance throughout the globe. The oriental fruit fly, Bactrocera dorsalis (Hendel), is particularly feared because it attacks many commercial fruits and vegetables causing huge economic losses. The sterile insect technique (SIT) can be an effective, target-specific and economically feasible control method. However, implementation of SIT depends on mass production of high-quality insects. Production of superior quality eggs is of foremost importance in insect mass production. However, present protocols make use of fruit juices or fruit domes that attract saprophytic insects or microorganisms, reducing the quality of eggs. Furthermore, fermentation of juices is known to decrease oviposition efficiency, and daily sanitation of oviposition devices is required. Here, in a laboratory-scale study, we evaluate the effectiveness of four synthetic oviposition stimulants (OS) of B. dorsalis for egg production in dual choice tests, using oviposition devices similar to those used in mass rearing. Results indicated that γ-octalactone, benzothiazole, octen-3-ol and ethyl tiglate significantly increased egg laying compared to controls (water). Of these, γ-octalactone was particularly effective and elicited a 263-fold increase in oviposition on treated oviposition devices compared to control. Our findings demonstrate the potential of using OSs to improve the efficiency and cost effectiveness of mass production of B. dorsalis.

Centuries of domestication has not impaired oviposition site-selection function in the silkmoth, Bombyx mori

Oviposition site-selection in insects is mediated through innate recognition templates (IRTs) tuned to specific chemical cues. These cues aid gravid insects in choosing suitable oviposition sites and may even enhance the fitness of their offspring by warding off predators and parasitoids. However, studies on the evolution of oviposition site-selection and cues instigating oviposition in domesticated insects remain elusive. Using the interaction between the silkmoth, Bombyx mori, and its host plant mulberry, Morus alba, as a model system, we demonstrate that centuries of domestication of silkmoth has not impaired its oviposition site-selection function. Silkmoths significantly preferred mulberry leaves to filter paper as oviposition sites. Oviposition assays with filter paper, filter paper treated with leaf volatiles and leaf alone proved that surface texture was not a significant criterion for oviposition site-selection, but volatile cues were. Oviposition assays with electrophysiologically active compounds from mulberry revealed that two of the volatiles, valencene and α-humulene, aided moths in choosing suitable oviposition sites and enhanced egg-laying significantly. Moreover, we show that generalist egg-parasitoids are strongly repelled by valencene and α-humulene. Our results demonstrate that IRTs tuned to cues that aid crucial functions like oviposition site-selection are less likely to be impaired even after centuries of domestication.

Glimpses of Semiochemical Research Applications in Indian Horticulture: Present Status and Future Perspectives

Pests of horticulture importance are evolving rapidly with changing climatic conditions, intensive farming practices, and constant selection pressures exerted through insecticides. With worldwide interest in environmental protection, chemical insecticides have become objects of scientific and popular protest. Critics charge chemical insecticides of their danger in provoking the development of resistant strains of pests, sabotaging ecological systems, and poisoning the environment. These liabilities of chemical insecticides have paved way to nonchemical methods, which use natural processes and mechanisms against insect pests. Of several natural processes available for exploitation of management of insect pests, semiochemicals are less exploited inspite of their ability in making integrated pest management (IPM) programs sustainable in the long run. The past, present, and future of integrating these viable alternatives with IPM programs against horticultural insect pests in India is discussed.