Name: Development and Challenges of Feeding Assays for Insect Pest Management (Video) | JoVE
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SM, YP, and VN acknowledge the fellowship awarded by the University Grants Commission, Government of India, New Delhi. RJ acknowledges the Council of Scientific and Industrial Research (CSIR), India, and CSIR-National Chemical Laboratory, Pune, India, for financial support under project codes MLP036626, MLP101526, and YSA000826.

H. armigera larvae were acquired from ICAR-National Bureau of Agricultural Insect Resources (NBAIR), Bangalore, India. A total of 21 second instar larvae were used for the present study.
1.&#160;Preparation of chickpea-based artificial diet
NOTE: A list of ingredients required for preparing an artificial diet is mentioned in Table 1.
<ol>
	<li>Weigh all the fractions separately in a beaker, as listed in Table 1</s...

Assessment of Phytochemical Effects on Helicoverpa armigera Through Feeding Assay

<ol>
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Laboratory bioassays are useful to predict outcomes and produce comparative toxicity data on several compounds in a short period at a reasonable cost. The feeding bioassay helps to interpret the interactions between insect-insecticide and insect-plant-insecticides. It is an efficient method for measuring the toxicity of a variety of substances that significantly simplifies the process of establishing the lethal dose 50 (LD50), lethal concentration 50 (LC50), or any other lethal concentration or dose...

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.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Agar Agar</td>
			<td>Himedia</td>
			<td>RM666</td>
			<td>Solidifying agent</td>
		</tr>
		<tr>
			<td>Ascorbic acid</td>
			<td>Himedia</td>
			<td>CMS1014</td>
			<td>Vitamin C source</td>
		</tr>
		<tr>
			<td>Bengal Gram</td>
			<td>NA</td>
			<td>NA</td>
			<td>Protein and carbohydrate source</td>
		</tr>
		<tr>
			<td>Casein</td>
			<td>Sigma</td>
			<td>C-5890</td>
			<td>Protein source</td>
		</tr>
		<tr>
			<td>Cholesterol</td>
			<td>Sisco Research Laboratories</td>
			<td>34811</td>
			<td>Fatty acid source</td>
		</tr>
		<tr>
			<td>Choline Chloride</td>
			<td>Himedia</td>
			<td>GRM6824</td>
			<td>Ammonium salt</td>
		</tr>
		<tr>
			<td>DMSO</td>
			<td>Sigma</td>
			<td>67-68-5</td>
			<td>Solvent</td>
		</tr>
		<tr>
			<td>GraphPad Prism v8.0</td>
			<td></td>
			<td></td>
			<td>https://www.graphpad.com/guides/prism/latest/user-guide/using_choosing_an_analysis.htm</td>
		</tr>
		<tr>
			<td>Methyl Paraben</td>
			<td>Himedia</td>
			<td>GRM1291</td>
			<td>Antifungal agent</td>
		</tr>
		<tr>
			<td>Multivitamin capsule</td>
			<td>GalaxoSmithKline</td>
			<td>NA</td>
			<td>Vitamin source</td>
		</tr>
		<tr>
			<td>Quercetin</td>
			<td>Sigma</td>
			<td>Q4951-10G</td>
			<td>Phytochemical</td>
		</tr>
		<tr>
			<td>Sorbic Acid</td>
			<td>Himedia</td>
			<td>M1880</td>
			<td>Antimicrobail agent</td>
		</tr>
		<tr>
			<td>Streptomycin</td>
			<td>Himedia</td>
			<td>CMS220</td>
			<td>Antibiotic</td>
		</tr>
		<tr>
			<td>Vitamin E capsule</td>
			<td>Nukind Healthcare</td>
			<td>NA</td>
			<td>Vitamin E source</td>
		</tr>
		<tr>
			<td>Yeast Extract</td>
			<td>Himedia</td>
			<td>RM027</td>
			<td>Amino acid source</td>
		</tr>
	</tbody>
</table>

developing a feeding assay system for evaluating the insecticidal effect of phytochemicals on helicoverpa armigera

Helicoverpa armigera, a lepidopteran insect, is a polyphagous pest with a worldwide distribution. This herbivorous insect is a threat to plants and agricultural productivity. In response, plants produce several phytochemicals that negatively impact the insect's growth and survival. This protocol demonstrates an obligate feeding assay method to evaluate the effect of a phytochemical (quercetin) on insect growth, development, and survival. Under controlled conditions, the neonates were maintained until the second instar on a pre-defined artificial diet. These second-instar larvae were allowed to feed on a control and quercetin-containing artificial diet for 10 days. The insects' body weight, developmental stage, frass weight, and mortality were recorded on alternate days. The change in body weight, the difference in feeding pattern, and developmental phenotypes were evaluated throughout the assay time. The described obligatory feeding assay simulates a natural mode of ingestion and can be scaled up to a large number of insects. It permits one to analyze phytochemicals' effect on the growth dynamics, developmental transition, and overall fitness of H. armigera. Furthermore, this setup can also be utilized to evaluate alterations in nutritional parameters and digestive physiology processes. This article provides a detailed methodology for feeding assay systems, which may have applications in toxicological studies, insecticidal molecule screening, and understanding chemical effects in plant-insect interactions.

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

Insect larvae fed on a diet containing 1,000 ppm quercetin showed a significant decrease in body weight of ~57% as compared to the control group (Figure 2A). The reduction in body weight resulted in a reduced body size of quercetin-treated larvae (Figure 2B). A notable reduction was observed in the feeding rate of quercetin-fed larvae as compared to the control (Figure 2C).
Also, larvae fed on quercetin s...

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This protocol describes the obligate feeding assay to evaluate the potentially toxic effect of a phytochemical on the lepidopteran insect larvae. This is a highly scalable insect bioassay, easy to optimize the sublethal and lethal dose, deterrent activity, and physiological effect. This could be used for screening eco-friendly insecticides.

Helicoverpa armigera, a lepidopteran insect, is a polyphagous pest with a worldwide distribution. This herbivorous insect is a threat to plants and ...