PhD Student, Pennsylvania State University
Climate change is widely recognized as the leading challenge. Temperature and other environmental factors can strongly influence plants and thus have implications for other trophic levels. Temperature is predicted to rise by 2-5°C by the end of the century. Elevated temperature may affect both insect and plant performances to alter the outcome of plant-herbivore interaction. Despite the importance, limited work has investigated the biotic interactions with elevated temperature. Here we explored how increasing temperature affects the plant-herbivore interactions in a model crop species tomato, Solanum lycopersicum against tomato fruit worm, Helicoverpa zea. In particular, two questions were addressed: a) How will elevated temperature affect the development and defense strategies in plants? b) How will this affect (both direct and indirect) the herbivore performance?
Results: a) Plant Performance: • Elevated temperature decreased the shoot and root biomass by 18% and 14 % in 30°C, and 65% and 38% in 35°C respectively • Higher temperature significantly reduced plant height and the rate of photosynthesis.
b) Defensive Proteins and Glandular Trichome Density • A significant 23 and 63 % higher PPO activity (constitutive) was observed with plants grown at 30°C compared with 25°C and 35°C. • In response to caterpillar feeding (induced) PPO activity was 1 and 31% higher in 30°C compared with 25°C and 35°C . • Constitutive TPI activity were insignificant between treatments, however induced TPI activities fell by 7.4 and 24.4 % at 30°C and 35°C with respect to highest recorded at 30°C. • Trichome density was highest among the plants grown at 30°C, followed by 25°C and 35°C.
c) Herbivore Performance: • Direct effect: Prolonged development and increased body mass at lower temperatures. • Indirect effects (mediated via hostplant quality): Plants grown at elevated temperature hindered the growth of larvae
• Elevated temperature affects the plant growth rates, which alters the concentration of defensive compounds and density of glandular trichomes.
• At 35°C, a temperature well above the optimal growth temperature of 25°C, plant growth, PPO, TPI and trichome density were lowest indicative of the super-optimal thermal stress.
• The growth rate increased linearly due to direct effect of temperature but the host-plant quality affected growth, resulting from an interactive effect of primary/secondary metabolites and trichome density
Abstract: Climate warming will fundamentally alter basic life history strategies of many ectothermic insects. In the lab, rising temperatures increase growth rates of lepidopteran larvae but also reduce final pupal mass and increase mortality. Using in situ field warming experiments on their natural host plants, we assessed the impact of climate warming on development of monarch (Danaus plexippus) larvae. Monarchs were reared on Asclepias tuberosa grown under 'Ambient' and 'Warmed' conditions. We quantified time to pupation, final pupal mass, and survivorship. Warming significantly decreased time to pupation, such that an increase of 1 °C corresponded to a 0.5 day decrease in pupation time. In contrast, survivorship and pupal mass were not affected by warming. Our results indicate that climate warming will speed the developmental rate of monarchs, influencing their ecological and evolutionary dynamics. However, the effects of climate warming on larval development in other monarch populations and at different times of year should be investigated.
Pub.: 04 Nov '15, Pinned: 02 Nov '17
Abstract: Rising temperatures can influence the top-down control of plant biomass by increasing herbivore metabolic demands. Unfortunately, we know relatively little about the effects of temperature on herbivory rates for most insect herbivores in a given community. Evolutionary history, adaptation to local environments, and dietary factors may lead to variable thermal response curves across different species. Here we characterized the effect of temperature on herbivory rates for 21 herbivore-plant pairs, encompassing 14 herbivore and 12 plant species. We show that overall consumption rates increase with temperature between 20 and 30 °C but do not increase further with increasing temperature. However, there is substantial variation in thermal responses among individual herbivore-plant pairs at the highest temperatures. Over one third of the herbivore-plant pairs showed declining consumption rates at high temperatures, while an approximately equal number showed increasing consumption rates. Such variation existed even within herbivore species, as some species exhibited idiosyncratic thermal response curves on different host plants. Thus, rising temperatures, particularly with respect to climate change, may have highly variable effects on plant-herbivore interactions and, ultimately, top-down control of plant biomass.
Pub.: 27 May '14, Pinned: 02 Nov '17
Abstract: Climate change can profoundly alter species' distributions due to changes in temperature, precipitation, or seasonality. Migratory monarch butterflies (Danaus plexippus) may be particularly susceptible to climate-driven changes in host plant abundance or reduced overwintering habitat. For example, climate change may significantly reduce the availability of overwintering habitat by restricting the amount of area with suitable microclimate conditions. However, potential effects of climate change on monarch northward migrations remain largely unknown, particularly with respect to their milkweed (Asclepias spp.) host plants. Given that monarchs largely depend on the genus Asclepias as larval host plants, the effects of climate change on monarch northward migrations will most likely be mediated by climate change effects on Asclepias. Here, I used MaxEnt species distribution modeling to assess potential changes in Asclepias and monarch distributions under moderate and severe climate change scenarios. First, Asclepias distributions were projected to extend northward throughout much of Canada despite considerable variability in the environmental drivers of each individual species. Second, Asclepias distributions were an important predictor of current monarch distributions, indicating that monarchs may be constrained as much by the availability of Asclepias host plants as environmental variables per se. Accordingly, modeling future distributions of monarchs, and indeed any tightly coupled plant-insect system, should incorporate the effects of climate change on host plant distributions. Finally, MaxEnt predictions of Asclepias and monarch distributions were remarkably consistent among general circulation models. Nearly all models predicted that the current monarch summer breeding range will become slightly less suitable for Asclepias and monarchs in the future. Asclepias, and consequently monarchs, should therefore undergo expanded northern range limits in summer months while encountering reduced habitat suitability throughout the northern migration.
Pub.: 24 Feb '15, Pinned: 02 Nov '17
Abstract: For insect herbivores, rising temperatures lead to exponentially higher metabolic rates. As a result, basic nutritional demands for protein and carbohydrates can be altered at high temperatures. It is hypothesized that temperature‐driven increases in metabolic nitrogen turnover will exacerbate protein limitation by increasing metabolic nitrogen demand. To test this hypothesis, the present study examines whether metabolic nitrogen turnover at higher temperatures causes protein limitation of a generalist herbivore, the beet armyworm Spodoptera exigua Hübner (Lepidoptera : Noctuidae). Third‐instar S. exigua larvae were reared at 25 and 30 °C on three artificial diets of varying protein : carbohydrate ratios (23 : 26, 17 : 26 and 6 : 26 %P : %C, respectively) and their growth rates, metabolic nitrogen demand and consumption rates were measured. Warming was found to lead to temperature‐induced protein limitation of the S. exigua larvae by increasing metabolic nitrogen demand at the same time as reducing nitrogen digestion efficiency. Because climate change is increasing atmospheric temperatures rapidly worldwide, it is suggested that a better understanding of how temperature change can influence metabolic demands will provide key information for predicting herbivore growth rates and foraging strategies in the future.
Pub.: 09 Apr '16, Pinned: 02 Nov '17