Abstract
Plant secondary metabolites such as terpenes, phenolics, glycosides, and alkaloids play various functional roles including pigmentation, foliar and floral volatile synthesis, hormonal regulation, and direct and indirect defenses. Among these, phenolic compounds are commonly found in plants, but vary in the distribution of their specific compounds among plant families. Polyphenols, including anthocyanins and tannins, are widely distributed and have been well documented for their roles- primarily in plant pigmentation and also in plant defenses. However, commercialization of such compounds for use in insect pest management is severely hampered by expensive, inefficient, and time-consuming extraction protocols. Using a recently developed inexpensive and easy extraction method using the byproducts of pigmented (purple) corn processing, we examined whether the crude pericarp extract rich in polyphenols can affect the growth and development of tobacco hornworm (Manduca sexta L.) caterpillars. Our findings show that purple corn pericarp extract negatively affected M. sexta egg hatching and larval mass gain and prolonged developmental time compared to regular yellow corn extract or an artificial control diet. We also found that these effects were more severe during the early stages of caterpillar development. These results conclusively demonstrate that purple corn pericarp, an inexpensive by-product of the corn milling industry, is a valuable product with excellent potential as an insect antifeedant.
Highlights
Based on quantification methods described above, we found that purple corn pericarp extract contained significantly higher concentrations of anthocyanins
We found that a significant number of purple corn pericarp extract-fed caterpillars stayed away from the diet compared to those on either yellow corn extract and control diets or both, implying that purple corn pericarp extract was possibly the least preferred when compared to others (Supplementary Table S5 and Figure S1)
When the diets were switched, we found that control diet fed caterpillars continued to gain more mass compared to caterpillars we found that control diet fed caterpillars continued to gain more mass compared to caterpillars we found that control diet fed caterpillars continued to gain more mass compared to caterpillars switched totopurple corn diet diet importantly, we that switched to purple corn extract diet control from control diet
Summary
Plants produce a wide range of secondary metabolites that serve a gamut of functions.These include their role as floral scent that attracts pollinators [1,2,3,4], foliar volatiles that act as attractants or repellants for herbivores and predators [5,6,7,8,9], defensive toxins against herbivory [10,11,12,13,14], and in pigmentation [15,16]. Coumarins (1, 2-benzopyrones) are common in many dicotyledonous families, including the Apiaceae, Asteraceae, Fabaceae, Moraceae, Rosaceae, Rubiaceae, and Solanaceae, while catechol (1, 2-di-hydroxybenzene) and phloroglucinol (1,3,5-trihydroxybenzene) have been found in leaves of Gaultheria species (Ericaceae) and as a glucoside in the peel of various citrus fruits (Rutaceae) [26] These compounds play an important role in cell division, hormonal regulation, and various plant biochemical and physiological activities including protection from biotic and abiotic stresses [27,28,29]. Known for their potential defensive role against insect herbivores [33], there is a limited understanding of methods to commercially extract and use them as a biopesticide or herbivore deterrent
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