There is no argument to the fact that insect herbivores cause significant losses to plant productivity in both natural and agricultural ecosystems. To counter this continuous onslaught, plants have evolved a suite of direct and indirect, constitutive and induced, chemical and physical defenses, and secondary metabolites are a key group that facilitates these defenses. Polyphenols—widely distributed in flowering plants—are the major group of such biologically active secondary metabolites. Recent advances in analytical chemistry and metabolomics have provided an opportunity to dig deep into extraction and quantification of plant-based natural products with insecticidal/insect deterrent activity, a potential sustainable pest management strategy. However, we currently lack an updated review of their multifunctional roles in insect-plant interactions, especially focusing on their insect deterrent or antifeedant properties. This review focuses on the role of polyphenols in plant-insect interactions and plant defenses including their structure, induction, regulation, and their anti-feeding and toxicity effects. Details on mechanisms underlying these interactions and localization of these compounds are discussed in the context of insect-plant interactions, current findings, and potential avenues for future research in this area.

The role of disturbance in accelerating weed growth is well understood. While most studies have focused on soil mediated disturbance, mowing can also impact weed traits. Using silverleaf nightshade (Solanum elaeagnifolium), a noxious and invasive weed, through a series of field, laboratory, and greenhouse experiments, we asked whether continuous mowing influences growth and plant defense traits, expressed via different avenues, and whether they cascade into offspring. We found that mowed plants produced significantly less number of fruits, and less number of total seeds per plant, but had higher seed mass, and germinated more and faster. When three herbivores were allowed to feed, tobacco hornworm (Manduca sexta) caterpillars, gained more mass on seedlings from unmowed plants, while cow pea aphid (Aphis craccivora), a generalist, established better on mowed seedlings; however, leaf trichome density was higher on unmowed seedlings, suggesting possible negative cross talk in defense traits. Texas potato beetle (Leptinotarsa texana), a co-evolved specialist on S. elaeagnifolium, did not show any differential feeding effects. We also found that specific root length, an indicator of nutrient acquisition, was significantly higher in first generation seedlings from mowed plants. Taken together, we show that mowing is a selective pressure that enhances some fitness and defense traits and can contribute to producing superweeds.

Bioactive compounds such as polyphenols in plants have been well studied for their potential insecticidal activities. These are considered as safe alternatives against chemical pesticides because of their lower persistence in environment, lower toxicity to humans and other organisms. However, they are present constitutively in lower amounts in plants and have to undergo complicated extraction methodshampering their commercial exploitation in pest management. Using an inexpensive extraction method developed to recover polyphenol-rich liquid extract from purple corn pericarp, we recently documented that this extract has anti-feeding effects that cascade from larval to adult stages in a model herbivore tobacco hornworm (Manduca sexta). However, M. sexta does not feed on corn or any other major crops other than the species in the nightshade family (Solanaceae). In this study, we explored the same idea but using a generalist and common herbivore on corn, the fall armyworm (Spodoptera frugiperda). We found that purple corn pericarp extract inhibited the larval growth and development as well as negatively affected the pupal stages of S. frugiperda. However, unlike on M. sexta, time to complete larval life cycle was unaffected. Our findings confirm the toxicity of this extract on a generalist, economically important herbivore, but also suggest potential species-specific effects that should be explored further.

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The ability to visualize cell and tissue morphology at a high magnification using scanning electron microscopy (SEM) has revolutionized plant sciences research. In plant-insect interactions studies, SEM based imaging has been of immense assistance to understand plant surface morphology including trichomes (plant hairs; physical defense structures against herbivores (Kaur and Kariyat, 2020a, 2020b; Watts and Kariyat, 2021), spines, waxes, and insect morphological characteristics such as mouth parts, antennae, and legs, that they interact with. While SEM provides finer details of samples, and the imaging process is simpler now with advanced image acquisition and processing, sample preparation methodology has lagged. The need to undergo elaborate sample preparation with cryogenic freezing, multiple alcohol washes and sputter coating makes SEM imaging expensive, time consuming, and warrants skilled professionals, making it inaccessible to majority of scientists. Here, using a desktop version of Scanning Electron Microscope (SNE- 4500 Plus Tabletop), we show that the “plug and play” method can efficiently produce SEM images with sufficient details for most morphological studies in plant-insect interactions. We used leaf trichomes of Solanum genus as our primary model, and oviposition by tobacco hornworm (Manduca sexta; Lepidoptera: Sphingidae) and fall armyworm (Spodoptera frugiperda; Lepidoptera: Noctuidae), and leaf surface wax imaging as additional examples to show the effectiveness of this instrument and present a detailed methodology to produce the best results with this instrument. While traditional sample preparation can still produce better resolved images with less distortion, we show that even at a higher magnification, the desktop SEM can deliver quality images. Overall, this study provides detailed methodology with a simpler “no sample preparation” technique for scanning fresh biological samples without the use of any additional chemicals and machinery.