Revisiting plant defense-fitness trade-off hypotheses using Solanum as a model genus

Plants possess physical and chemical defenses which have been found to deter herbivores that feed and oviposit on them. Despite having wide variety of defenses which can be constitutive or induced, plants are attacked and damaged by insects associated with different mouthparts and feeding habits. Since these defenses are costly, trade-offs for growth and defense traits play an important role in warding off the herbivores, with consequences for plant and herbivore growth, development and fitness. Solanum is a diverse and rich genus comprising of over 1,500 species with economic and ecological importance. Although a large number of studies on Solanum species with different herbivores have been carried out to understand plant defenses and herbivore counter defenses, they have primarily focused on pairwise interactions, and a few species of economic and ecological importance. Therefore, a detailed and updated understanding of the integrated defense system (sum of total defenses and trade-offs) is still lacking. Through this review, we take a closer look at the most common plant defense hypotheses, their assumptions and trade-offs and also a comprehensive evaluation of studies that use the genus Solanum as their host plant, and their generalist and specialist herbivores from different feeding guilds. Overall, review emphasizes on using ubiquitous Solanum genus and working toward building an integrated model which can predict defense-fitness-trade-offs in various systems with maximum accuracy and minimum deviations from realistic results

Are epicuticular waxes a surface defense comparable to trichomes? A test using two Solanum species and a specialist herbivore.

Although plants possess a suite of structural defenses, most studies have focused on trichomes. Trichomes can have both pre- and post-ingestive effects and have been consistently found to reduce herbivory. Along with trichomes, a few studies have focused on epicuticular waxes as an important defense; however, manipulated comparisons examining herbivore growth and development is limited. In this study, using two Solanum species (Solanum glaucescens and Solanum macrocarpon) that vary in both defenses, we tested the hypothesis that variation in defenses will affect herbivore feeding, primarily by restricting feeding commencement. We used electron microscopy together with a series of plant- and diet-based manipulative experiments, using tobacco hornworm (Manduca sexta; Lepidoptera: Sphingidae) as the herbivore. We found that S. glaucescens leaves had significantly fewer trichomes and significantly higher wax content when compared to S. macrocarpon. We also found that S. glaucescens waxes acted as a strong physical barrier resulting in lower mass gain and higher mortality of caterpillars compared to S. macrocarpon. Artificial diet manipulation experiments also suggested the possible toxicity of waxes. Collectively, we show that epicuticular waxes can play a significant role as a strong surface barrier and should be examined further

Examining the Role of Buzzing Time and Acoustics on Pollen Extraction of Solanum elaeagnifolium

Buzz pollination is a specialized pollination syndrome that requires vibrational energy to extract concealed pollen grains from poricidal anthers. Although a large body of work has examined the ecology of buzz pollination, whether acoustic properties of buzz pollinators affect pollen extraction is less understood, especially in weeds and invasive species. We examined the pollination biology of Silverleaf nightshade (Solanum elaeagnifolium), a worldwide invasive weed, in its native range in the Lower Rio Grande Valley (LRGV) in south Texas. Over two years, we documented the floral visitors on S. elaeagnifolium, their acoustic parameters (buzzing amplitude, frequency, and duration of buzzing) and estimated the effects of the latter two factors on pollen extraction. We found five major bee genera: Exomalopsis, Halictus, Megachile, Bombus, and Xylocopa, as the most common floral visitors on S. elaeagnifolium in the LRGV. Bee genera varied in their duration of total buzzing time, duration of each visit, and mass. While we did not find any significant differences in buzzing frequency among different genera, an artificial pollen collection experiment using an electric toothbrush showed that the amount of pollen extracted is significantly affected by the duration of buzzing. We conclude that regardless of buzzing frequency, buzzing duration is the most critical factor in pollen removal in this species

Field data on plant growth and insect damage on the noxious weed Solanum eleaegnifolium in an unexplored native range

In this data article, we provide a novel data set on plant growth, insect damage levels, and herbivore community of the noxious and invasive weed Solanum eleaegnifolium (Solanaceae). The data is collected from disturbed and un-disturbed urban populations of the species from one of its unexplored native range in Southern United States (South Texas). The data include plant height measurements, insect damage levels, GPS coordinates of the populations, and their disturbance status. Additional data includes the number of chewing herbivore (specialist herbivore Texas potato beetle (Leptinotarsa texana; Chrysomelidae), their eggs, and any lepidopteran caterpillars found on the plants

Morphological characterization of trichomes shows enormous variation in shape, density and dimensions across the leaves of 14 Solanum species

Trichomes are the epidermal appendages commonly observed on plant surfaces including leaves, stem and fruits. Plant trichomes have been well studied as a structural plant defence designed to protect plants against abiotic and biotic stressors such as UV rays, temperature extremities and herbivores. Trichomes are primarily classified into glandular and non-glandular trichomes, based on the presence or absence of a glandular head. The plant genus Solanum is the largest genus of family Solanaceae that houses ~3500 species of ecological and economic importance have a diverse set of trichomes that vary in density and morphology. However, due to the incomplete and contradictory classification system, trichomes have subjective names and have been largely limited to be grouped into glandular or non-glandular types. Through this study, we did a complete workup to classify and characterize trichomes on both adaxial and abaxial leaf surface of 14 wild and domesticated species of the genus Solanum. Using electron microscopy, statistical analyses and artistic rendition, we examined finer details of trichomes and measured their density and dimensions to compile a detailed data set which can be of use for estimating the variation in trichome types, and their density, with consequences for understanding their functional roles. Our study is the first of its kind that provides us with a better and well-defined classification, density and dimension analysis to complete the morphological classification of trichomes on both leaf surfaces of a diverse range of members in Solanum genus

Efficiency of using electric toothbrush as an alternative to a tuning fork for artificial buzz pollination is independent of instrument buzzing frequency

Background: Breeding programs and research activities where artificial buzz-pollinations are required to have primarily relied upon using tuning forks, and bumble bees. However, these methods can be expensive, unreliable, and inefficient. To find an alternative, we tested the efficiency of pollen collection using electric toothbrushes and compared it with tuning forks at three vibration frequencies—low, medium, and high and two extraction times at 3 s and 16 s- from two buzz—pollinated species (Solanum lycopersicum and Solanum elaeagnifolium). Results: Our results show that species, and extraction time significantly influenced pollen extraction, while there were no significant differences for the different vibration frequencies and more importantly, the use of a toothbrush over tuning fork. More pollen was extracted from S. elaeagnifolium when compared to S. lycopersicum, and at longer buzzing time regardless of the instrument used. Conclusions: Our results suggest that electric toothbrushes can be a viable and inexpensive alternative to tuning forks, and regardless of the instrument used and buzzing frequency, length of buzzing time is also critical in pollen extraction

The Known and Unknowns of Aphid Biotypes, and Their Role in Mediating Host Plant Defenses

Insect species are subjected to disparate selection pressure due to various biotic and abiotic stresses. Management practices including the heavy use of chemical insecticides and introduction of insect-resistant plant cultivars have been found to accelerate these processes. Clearly, natural selection coupled with human intervention have led to insect adaptations that alter phenotypes and genetic structure over time, producing distinct individuals with specialized traits, within the populations, commonly defined as biotypes. Biotypes are commonly found to have better fitness in the new environment and, in the case of aphids, the most commonly studied system for biotypes, have the ability to successfully infest previously resistant host plants and new species of host plants. Although a large number of studies have explored biotypes, the concept for defining biotypes varies among scientists, as we lack a consistency in estimating biotype behavior and their variation within and between biotypes. The concept of biotypes is even more complicated in aphid species (Aphidoidea), as they undergo parthenogenetic reproduction, making it difficult to understand the source of variation or quantify gene flow. In this review, we aim to illuminate the concept of biotype and how it has been used in the study of aphids. We intend to further elaborate and document the existence of aphid biotypes using sugarcane aphid (Melanaphis sacchari) as a model to understand their differences, level of variation, evolution, and significance in pest management

The Multifunctional Roles of Polyphenols in Plant-Herbivore Interactions

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

Development and testing of artificial membranes for rearing of Rhipicephalus microplus, the Southern Cattle Fever Tick

The southern cattle fever tick, Rhipicephalus microplus, is a livestock pest worldwide in tropical and subtropical climates, including South Texas, and can vector Babesia spp., the causal agents of bovine babesiosis. Artificial rearing methods for R. microplus are needed, especially for rearing specialist tick parasitoids that are under evaluation for classical biological control. In this study, we tested the efficiency of artificial feeding of R. microplus larvae, nymphs, and adults on a siliconized substrate (goldbeater’s membrane, lens paper, or Hemotek), or on nonsiliconized goldbeater’s membrane or Hemotek. Other variables tested were a warm water bath, incubator, positioning blood above or below ticks, using various attractants to stimulate attachment to membrane, incubating with or without 5% CO2, changing static blood once a day versus peristaltic pumping of blood, and using heparinized versus defibrinated blood. Peristaltic pumping of blood across the membrane inside the incubator significantly increased larval attachment. We found that up to 25% percent of these life stages would attach to the siliconized goldbeater’s membrane and feed, although none molted or completed their entire life cycle. A red color observable in the “fed” ticks’ legs seemed to indicate that bovine hemoglobin had penetrated the gut and entered the hemolymph of the ticks. We were successful rearing unfed nymphs to the engorged stage, which is the pre-requisite for rearing Ixoidiphagus tick parasitoids. Suggestions for future experimentation for rearing R. microplus on artificial membranes are discussed