Trirhabda Virgata Research Articles

Eco-evolutionary processes affecting plant-herbivore interactions during early community succession.

The quality and outcome of organismal interactions are not only a function of genotypic composition of the interacting species, but also the surrounding environment. Both the strength and direction of natural selection on interacting populations vary with the community context, which itself is changed by these interactions. Here, we test for the role of interacting evolutionary and ecological processes in plant-herbivore interactions during early community succession in the tall goldenrod, Solidago altissima. We use surveys in a large-scale field experiment with repeated plots representing 6years of early oldfield succession and reciprocal transplant common garden experiments to test for the relative importance of rapid evolution (genetic) and environmental changes (soil quality) in affecting mean plant resistance and growth phenotypes during community succession. While plant growth varied strongly with soil quality over the first 5years of agricultural abandonment, plant secondary metabolism, and herbivore resistance varied minimally with the soil environment. Instead, mean composition and abundance of plant secondary compound bouquets differed between S. altissima plants from populations collected in communities in the first ("early") and sixth ("intermediate") years of oldfield succession, which was reflected in the feeding preference of the specialist herbivore, Trirhabda virgata, for early succession lines. Moreover, this preference was most pronounced on poorer quality, early succession soils. Overall, our data demonstrate that plant quality varies for insect herbivores during the course of early succession and this change is a combination of altered genotypic composition of the population and phenotypic plasticity in different soil environments.

Plant communication in a widespread goldenrod: keeping herbivores on the move

Summary Plant communication has been documented in over 35 plant species spanning 16 families to date; however, the underlying mechanisms through which it shapes plants' ecological interactions remain less clear. Using a combination of field/laboratory bioassays, headspace volatile and leaf chemical analyses in tall goldenrod (Solidago altissima), we tested the hypothesis that plant‐to‐plant communication affects the performance, feeding and movement behaviour of herbivores by changing plants' chemical phenotypes. We found that plant communication accelerates herbivore movement between host plants while simultaneously reducing herbivory. This suggests that plant communication can limit herbivore loads by keeping herbivores on the move between host plants. We demonstrate that volatile chemicals emitted from herbivore‐attacked plants are sufficient to explain metabolic responses in and ecological consequences for the exposed neighbour plant. Volatile profiles of beetle (Trirhabda virgata)‐damaged and undamaged plants show substantial compositional differences, especially in sesquiterpene emission, indicating that these differences have the potential to provide neighbouring plants with specific information about herbivores in the vicinity. Despite qualitative and phenological differences in plants' metabolic responses to herbivory‐induced volatile organic compounds (VOCs) and feeding herbivores, herbivores nonetheless respond similarly to directly damaged plants and plants exposed to VOCs from damaged neighbours as if they were of equivalently poor quality. This study suggests that by enlarging the spatial scale at which induced resistance affects the distribution of plant chemical phenotypes in plant populations, VOC‐mediated plant communication alters the movement behaviour and performance of herbivores. A lay summary is available for this article.

Herbivore pressure on goldenrod (Solidago altissima L., Asteraceae): its effects on herbivore resistance and vegetative reproduction

Summary1. Ecological and physiological costs of resistance to herbivory are core concepts in the study of plant–insect interactions, but identifying them remains challenging. These costs are most obvious when trade‐offs in resource allocation occur between different growth and resistance traits.2. We used plant genotypes collected from long‐term herbivore exclusion plots and from plots with natural herbivory. We evaluated putative trade‐offs between resistance to two different herbivore species (the larvae of the beetle Trirhabda virgata and the moth Spodoptera exigua), and between resistance and growth as a potential outcome of differential natural selection.3. We hypothesized that long‐term exclusion of herbivores would result in differential natural selection on plant resistance traits that are expressed by marked differences in mean resistance between plants from populations with and without herbivores. The results supported this hypothesis. Genotypes from herbivore exclusion plots were less resistant to the more common herbivore in the system, T. virgata, than genotypes from control plots. In contrast, the genotypes from the two herbivory regimes were equally resistant to the rarer S. exigua caterpillars. As a consequence, resistance to one herbivore species did not correlate with resistance to another, suggesting independent evolution of resistance to multiple herbivores.4. Plant growth correlated positively with resistance to Trirhabda, but not to Spodoptera, and only in plants from herbivore exclusion plots, leading us to reject the hypothesis of a growth resistance trade‐off.5. Synthesis. Our results suggest that correlations between growth and resistance are context dependent and may only be apparent in populations relieved from certain natural pressures, such as in natural populations relieved from natural selection by herbivores.

Influence of polyploidy on insect herbivores of native and invasive genotypes of Solidago gigantea (Asteraceae)

Herbivores are sensitive to the genetic structure of plant populations, as genetics underlies plant phenotype and host quality. Polyploidy is a widespread feature of angiosperm genomes, yet few studies have examined how polyploidy influences herbivores. Introduction to new ranges, with consequent changes in selective regimes, can lead to evolution of changes in plant defensive characteristics and also affect herbivores. Here, we examine how insect herbivores respond to polyploidy in Solidago gigantea, using plants derived from both the native range (USA) and introduced range (Europe). S. gigantea has 3 cytotypes in the US, with 2 of these present in Europe. We performed bioassays with generalist (Spodoptera exigua) and specialist (Trirhabda virgata) leaf-feeding insects. Insects were reared on detached leaves (Spodoptera) or potted host plants (Trirhabda) and mortality and mass were measured. Trirhabda larvae showed little variation in survival or pupal mass attributable to either cytotype or plant origin. Spodoptera larvae were more sensitive to both cytotype and plant origin: they grew best on European tetraploids and poorly on US diploids (high mortality) and US tetraploids (low larval mass). These results show that both cytotype and plant origin influence insect herbivores, but that generalist and specialist insects may respond differently.

Abnormal elytra, wings and other structures in a female Trirhabda virgata (Chrysomelidae) with a summary of similar teratological observations in the Coleoptera

An abnormal female of Trirhabda virgataLECONTE is described from the Province of Quebec with the following anomalies: short, apically narrowed, suturally widely apart elytra; reduced, swollen (incapable of flight) hind wings; stout met-endosternite; apically truncate scutellum; peculiar membrane (with characteristic setae) enclosing portion of hind wings, stretched across them over the thorax dorsally; strongly sclerotized abdomen, especially the pygidium; and inside the abdomen, gut slender and reproductive organs compact. Similar observations are summarized for certain species of the Coleoptera belonging to the families Buprestidae, Carabidae, Cerambycidae, Chrysomelidae, Cleridae, Curculionidae, Dytiscidae, Melyridae, Scaphidiidae and Scarabaeidae.

Disarming the paradox of sublethal plant defense against insects: Trirhabda virgata larval development time and leaf tissue loss on Solidago altissima

AbstractAlthough the fitness benefits of traits that kill herbivores are obvious, the contention that sublethal antiperformance traits have evolved as plant defenses has proved more controversial. Traits that slow herbivore development seem particularly paradoxical, given the common assumption that a protracted feeding period will lead to greater total consumption. Whereas this assumption is superficially reasonable, there is very little evolutionarily relevant evidence to suggest that plants on which larval development is slower actually lose more tissue. For the assumption underlying the sublethal‐defense paradox to be valid, plant traits that affect larval development time and tissue loss must be positively correlated genetically within natural plant populations. In this study, we examined the relationship between larval development time of the beetle Trirhabda virgata LeConte (Coleoptera: Chrysomelidae) and plant tissue loss by its host plant Solidago altissima L. (Asteraceae). Plant genets on which the larval development time was longer ended up losing less leaf area than plant genets that allowed quicker larval development. This negative genetic correlation contradicts the common assumption that greater sublethal resistance leads to increased tissue loss. Combined with other hypothesized benefits of sublethal resistance, this result suggests that antiperformance traits may constitute a more potent form of resistance than is generally acknowledged.

EXTENDING THE RESOURCE CONCENTRATION HYPOTHESIS TO PLANT COMMUNITIES: EFFECTS OF LITTER AND HERBIVORES

We extend the resource concentration hypothesis (herbivorous insects are more likely to find and stay in more dense and less diverse patches of their host plants) to plant communities. Specifically, whenever superior plant competitors spread to form dense stands, they will be found and attacked by their specialist insect enemies. This will decrease host plant abundance, causing a reduction in standing crop biomass, which will indirectly increase subordinate competitors and plant species richness. In this study, we found that a native, specialist chrysomelid beetle (Trirhabda virgata) in an old-field community decreased total standing crop biomass, leading to an increase in plant species richness. This reduction in biomass was due solely to a reduction in the biomass of the beetle's host plant, meadow goldenrod (Solidago altissima), which was the dominant plant species in this community. Our results demonstrate that when a superior competitor increases in density, the per-stem impact of herbivores increase...

Interactions between goldenrod (Solidago altissima L.) and its insect herbivore (Trirhabda virgata) over the course of succession.

Consumers can mediate the composition of plant communities and alter ecosystem processes. Although herbivores usually increase N availability in the short term, they might decrease it in the long term. I investigated the long-term effect of insect herbivores on leaf tissue quality and soil N availability in goldenrod (Solidago altissima) fields using two approaches: (1) I compared plots from which herbivores had been excluded for 17 years with adjacent plots that had experienced normal levels of herbivory, and (2) I examined a chronosequence of nine goldenrod fields representing three successional stages: early, middle, and late. These parallel approaches showed that, in the long term, herbivores decrease the quality of leaf litter and soil N availability in goldenrod fields. These long-term effects appear to compensate for various short-term effects that increase N availability in the soil (e.g., added frass, increased light penetration). Furthermore, herbivores decrease leaf litter quality and N availability by reducing the quality of leaf tissue within the same species. This pattern may result from insect herbivores preferentially grazing on plants with a high N content thereby increasing the amount of recalcitrant litter over the course of succession.

PERFORMANCE OF TRIRHABDA VIRGATA (COLEOPTERA: CHRYSOMELIDAE) ON THREE POTENTIAL HOSTS

AbstractThe suitability of three potential host plants, Solidago canadensis L. var. canadensis (Asteraceae), Solidago graminifolia (L.) Salisb., and Aster lateriflorus L. (Asteraceae), for the goldenrod beetle, Trirhabda virgata LeConte was determined by measuring several fitness components during the T. virgata life cycle. Neonate larvae were collected from S. canadensis plants and transplanted onto S. canadensis, S. graminifolia, and A. lateriflorus and maintained in field enclosures until the last instar was reached. Once brought into the laboratory, larvae were fed their assigned host plant until pupation. Following emergence, adults were weighed and separated into mating pairs to record oviposition and longevity. Eggs were kept in the laboratory until the following spring, when first instar larvae were taken into the field and re-established on their assigned host, and the experiment was repeated for 2 years. Larval survival and rate of development was not affected by the host plant. Mean weight of adults at emergence was greater on S. canadensis than on either S. graminifolia or A. lateriflorus. Two components of adult fitness, postmating longevity and realized fecundity, were measured. Longevity of adult female T. virgata was not affected by the host plant. Fecundity of T. virgata reared on A. lateriflorus and S. graminifolia was lower than the fecundity of females reared on S. canadensis. These results are consistent with the hypothesis that both intrinsic plant quality and the mobility of the foraging stage are important in the evolution of host range in T. virgata. These experiments were repeated over a 3-year period, using offspring from the survivors of the previous year for the 2nd and 3rd years. Over this time, individuals experienced "laboratory adaptation," and both accepted and increased their performance on previously unacceptable food plants.

Effects of Population Density on Long‐Distance Dispersal in the Goldenrod Beetle Trirhabda Virgata

Recent theoretical and empirical studies suggest that an animals's long—distance dispersal behavior can have a major influence on its population dynamics. In this study I examined the role of dispersal in the population dynamics of a goldenrod leaf beetle, Trirhabda virgata. I measured the long—distance emigration rates of this beetle in the field under different population densities. I manipulated densities of Trirhabda larvae early in the season to create crowded, heavily defoliated host patches and uncrowded, lightly defoliated patches. Newly emerged, teneral beetles were added to these two density treatments and their long—distance emigration rates were measured. Beetles flew from host patches that had high densities of adults and heavy damage caused by larvae. No flight was detected from low—density patches with little defoliation. Beetles that had developed in these crowded and uncrowded patches were placed on lush, undefoliated plants as teneral adults. Their emigration rates did not differ. In a final experiment, female beetles were placed on plants with or without mates. The plants were one of two types, either heavily defoliated or lush. On lush plants, females without mates showed a stronger tendency to leave than females that had access to mates. On defoliated plants, females left at high rates whether or not mates were present. These experiments indicate that long—distance emigration is triggered by conditions experienced during the teneral phase. Heavy host defoliation inflicted by high population densities appears to induce flight. This density—dependent emigration should reduce local population pressure and result in the spread of local outbreaks across a larger area. The influence of dispersal on population dynamics will vary depending on the pattern of beetle densities across the region.

Timing of Dispersal and Ovarian Development in Goldenrod Leaf Beetles Trirhabda virgata and T. borealis1

The two goldenrod leaf beetles, Trirhabda virgata LeConte and T. borealis Blake (Coleoptera: Chrysomelidae), flew only during a brief, postteneral period, when each population was at peak density. Cessation of flight coincided with the period of rapid maturation of oocytes. The sex ratio of flying individuals was strongly skewed toward females, although males and females were equally abundant in each population at large. Most beetles were captured just above the goldenrod vegetation (at 1 m above ground); the number of captures decreased with increasing height above ground. Females tended to fly higher than males. The role of dispersal by flight in Trirhabda habitat colonization and population dynamics is discussed.

Plant Protection as a Consequence of an Ant‐Membracid Mutualism: Interactions on Goldenrod (Solidago Sp.)

In central New York, two chrysomelid beetles, Trirhabda virgata and T. borealis, frequently cause severe defoliation of tall goldenrod, Solidago altissima. This plant is also the primary host of Publilia concava (Membracidae), a sap—feeding treehopper that is tended by ants, especially Formica spp. Staged encounters indicate that Formica ants attack adult Trirhabda beetles on goldenrod stems bearing membracids. Such stems escape defoliation by Trirhabda, and show greater mean height increment and seed production than their nearest neighbors without ants. The degree of plant protection depends on the duration of Formica presence. During Trirhabda outbreaks, only stems bearing Formica ants for most of the season are likely to produce flowers and seeds. While Formica ants do not exclude Trirhabda larvae from goldenrod stems, they do deter feeding; plants with Formica ants experience significantly less defoliation by larvae than neighboring stems without ants. Two smaller, less aggressive an species (Prenolepis imparis and Myrmica sp.) do not affect either larval or adult beetle densities.

Association between Leaf Beetles1 and Meadow Goldenrods (Solidago spp.) in Central New York

The chrysomelid fauna associated with meadow goldenrods ( Solidago spp.) in central New York is composed of 9 specialists (species that feed only on goldenrods and asters), 4 generalists, and 7 “incidentals.” This diverse fauna of goldenrod feeders is the outcome of independent evolution in several taxa. The food habits, seasonal abundance, and life histories of the common beetles in the association are described. Two specialists, Trirhabda virgata LeConte and T. borealis Blake, account for 86% of all beetles collected in weekly samples taken over 3 growing seasons. Ovipositing Ophraella conferta (LeConte) and Microrhopala vittata (Fabr.) discriminate against s. graminifolia, but use other goldenrods (S. altissima, S. gigantea, S. juncea, and S. rugosa) nonpreferentially. The unique phenology and growth form of S. juncea may prevent it from being more fully utilized by Exema canadensis Pierce. During the 3-yr study, densities of T. virgata, T. borealis, and O. conferta increased, while those of Nodonota margaretae Schultz and Paria thoracica (Melsheimer) declined.