feeding assay to evaluate the effects of quercetin on helicoverpa armigera growth and development

Assessment of Phytochemical Effects on &lt;em&gt;Helicoverpa armigera&lt;/em&gt; Through Feeding Assay

The biotic factors that affect crop productivity are mainly pathogenic agents and pests. Several insect pests cause 15% to 35% of agricultural crop loss and affect economic sustainability practices1. Insects belonging to the orders Coleoptera, Hemiptera, and Lepidoptera are the major orders of devastating pests. The highly adaptive nature of the environment has benefited lepidopterans in evolving several survival mechanisms. Amongst lepidopteran insects, Helicoverpa armigera (Cotton bollworm) can feed on around 180 different crops and cause significant damage to their reproductive tissues2. Worldwide, H. armigera infestation has resulted in a loss of around $5 billion3. Cotton, chickpeas, pigeon peas, tomatoes, sunflowers, and other crops are hosts for H. armigera. It completes its lifecycle on different parts of host plants. Eggs laid by female moths get hatched on the leaves, followed by their feeding on vegetative tissues during larval stages. The larval stage is the most destructive due to its voracious and highly adaptable nature4,5. H. armigera shows a global distribution and encroachment to new territories due to its remarkable attributes, such as polyphagy, excellent migratory abilities, higher fecundity, strong diapause, and the emergence of resistance to existing insect control strategies6.
Diverse chemical molecules from terpenes, flavonoids, alkaloids, polyphenols, cyanogenic glucosides, and many others are widely used for the control of H. armigera infestation7. However, frequent application of chemical molecules imparts adverse effects on the environment and human health due to the acquisition of their residues. Also, they show a detrimental effect on various pest predators, resulting in an ecological imbalance8,9. Therefore, there is a necessity to investigate safe and eco-friendly options for chemical molecules of pest control.
Natural insecticidal molecules produced by plants (phytochemicals) can be used as a promising alternative to chemical pesticides. These phytochemicals include various secondary metabolites belonging to the classes alkaloids, terpenoids, and phenolics7,10. Quercetin is one of the most abundant flavonoids (phenolic compound) present in various grains, vegetables, fruits, and leaves. It shows feeding deterrent and insecticidal activity against insects; also, it is not harmful to natural enemies of pests11,12. Thus, this protocol demonstrates the feeding assay using quercetin to assess its toxic effect on H. armigera.
Various bioassay methods have been developed to evaluate the effect of natural and synthetic molecules on an insect&#39;s feeding, growth, development, and behavioral patterns13. Commonly used methods include the leaf disk assay, choice feeding assay, droplet feeding assay, contact assay, diet covering assay, and obligate feeding assay13,14. These methods are classified based on how pesticides are applied to insects. The obligate feeding assay is one of the most commonly used, sensitive, simple, and adaptable methods to test probable insecticides and their lethal dose14. In an obligate feeding assay, the molecule of interest is mixed with an artificial diet. This provides consistency and control over the diet composition, generating robust and reproducible results. Important variables affecting feeding assays are the developmental stage of the insect, choice of insecticide, environmental factors, and sample size. The duration of the assay, interval between two data recordings, frequency and amount of diet fed, health of insects, and handling skill of operators can also influence the outcome of feeding assays14,15.
This study aims to demonstrate the obligate feeding assay to evaluate the effect of quercetin on H. armigera survival and fitness. Assessment of various parameters, such as insect body weight, mortality rate, and developmental defects, will provide insights into the insecticidal effects of quercetin. Meanwhile, measuring nutritional parameters, including the efficiency of conversion of ingested food (ECI), efficiency of conversion of digested food (ECD), and approximate digestibility (AD), will highlight the antifeedant attributes of quercetin.

Author Spotlight: Development and Challenges of Feeding Assays for Insect Pest Management 

Developing a Feeding Assay System for Evaluating the Insecticidal Effect of Phytochemicals on Helicoverpa armigera

This study is conducted to develop a simple and cost-effective feeding assay method for evaluating the effect of various natural molecules, including phytochemicals for their antifeedant and insecticidal properties against thieving insects, and identified potential molecules from these assay can be evaluated in field condition for pest management. Multiple assays have been developed to evaluate the effect of synthetic and natural molecules on insect feeding, growth, development, and behavior, further assays have been designed, such as dip case tool, diet covering assay, contact assay, droplet feeding assay, choice feeding assay, and lip dish test for insecticide evaluation, Maintaining uniform experimental conditions, addressing issues, like infection and cannibalism, ensuring even phytochemical distribution in larval diet, tracking, feeding behavior accurately, and determining optimal phytochemical concentrations post challenges, batch variation, and experimental design complexities must be managed. Additionally, transitioning from the lab assist to the field application, considering formulation and scalability is demanding.In the obligatory feeding assay, a large number of molecules can be tested simultaneously with a large number of insect sample sizes. The advantage of this feeding assay is that the test compound is mixed with an artificial diet, thus we have control over diet composition, which provides robust and reproducible results.

Watch this Scientific Journal Video about Feeding Assay to Evaluate the Effects of Quercetin on Helicoverpa armigera Growth and Development at JoVE.com

Feeding Assay to Evaluate the Effects of Quercetin on Helicoverpa armigera Growth and Development  

Feeding Assay to Evaluate the Effects of Quercetin on Helicoverpa armigera Growth and Development

To begin, keep Helicoverpa armigera neonates in the plastic breeding chamber covered with a muslin cloth in the insect culture room. Then gently transfer newly emerged neonates using a fine paintbrush on a freshly prepared, chickpea based artificial diet for growth. For the feeding assay, collect 21 second instar larvae for the control and treatment set.Cut previously prepared control and quercetin containing diet into small pieces, and record the weight of the diet and the insect's body. Carefully transfer the insect into the culture vial, add the respective diet into the vial, and let the insect feed. From the second day till the 10th day, record the weight of the insect body followed by a given diet, uneaten diet, and frass.Count the live and dead larvae and pupae on day 10. To record and analyze the data, compare the insect body weight between the control and treatment groups using a student t test Plot a Kaplan-Meier curve for survival percentage using the graphing software using live dead larvae and pupae count. Then calculate the percent pupation and compare larval development and nutritional indices.In the present study, the insect larvae fed with quercetin containing diet showed a significant decrease compared to the control group, thereby resulting in reduced body size. Also, a notable reduction was observed in the feeding rate of quercetin fed larvae compared to the control. Furthermore, there was a significant decrease in percent pupation in quercetin fed larvae suggesting developmental retardation upon treatment.For insects fed on the quercetin containing diet, the efficiency of conversion of ingested food to body matter was reduced by approximately 9%compared to the control. The efficiency of conversion of digested food was reduced by approximately 49%compared to the control. The approximate digestibility in quercetin fed insects was increased by 5%compared to the control.

feeding-assay-to-evaluate-effects-quercetin-on-helicoverpa-armigera

Research

JoVE Journal

Biology

67 Views.  CSIR-National Chemical Laboratory. To begin, keep Helicoverpa armigera neonates in the plastic breeding chamber covered with a muslin cloth in the insect culture room. Then gently transfer newly emerged neonates using a fine paintbrush on a freshly prepared, chickpea based artificial diet for growth. For the feeding assay, collect 21 second instar larvae for the control and treatment set.Cut previously prepared control and quercetin containing diet into small pieces, and record the weight of the diet and the insect's bo...