Time-dependent stress evidence in dynamic allocation of physiological metabolism of Nilaparvata lugens in response to elevated CO2

Bottom-Up Effects of Drought-Stressed Cotton Plants on Performance and Feeding Behavior of Aphis gossypii

Drought, a major stress for crop plants, is expected to increase in frequency due to climate change. Drought can alter crop growth and levels of secondary plant metabolites, which in turn can affect herbivores, but this latter point is still controversial. This study used three different polyethylene glycol (PEG-6000) levels (0%, 1%, and 3%) to simulate drought stress and evaluated their effects on cotton plants and the impacts on the performance of the cotton aphid Aphis gossypii. Cotton plants under drought stress showed decreased water content, above-ground biomass, and nitrogen content and increased soluble protein, soluble sugar, and tannin contents. Based on analysis of the developmental time and fecundity data from individuals and at the population level, a significantly lower fecundity and population abundance of A. gossypii were detected on cotton plants with drought stress, which supports the "plant vigor hypothesis". The poor development of A. gossypii is possibly related to lower xylem sap and phloem ingestion under drought stress. In addition, the increased tannin content of cotton plants induced by drought and lower detoxification enzyme activities of A. gossypii may have affected the responses of aphids to drought-stressed plants. Overall, the results showed that drought stress altered the physiological characteristics of the cotton plants, resulting in adverse bottom-up effects on cotton aphid performances. This implies that the adoption of drip irrigation under plastic film that can help alleviate drought stress may favor the population growth of cotton aphids.

Effects of Elevated CO2 on the Fitness of Three Successive Generations of Lipaphis erysimi

Simple Summary

Global warming caused by the increase in atmospheric CO₂ concentration is becoming a major environmental issue. Lipaphis erysimi is one of the most damaging pests of cruciferous crops worldwide, and L. erysimi has strong adaptability to the environment and reproductive capacity. The age-stage, two-sex life table is currently used by many researchers in place of the traditional age-specific life table, providing many details such as fitness and potential damage. In this study, the individual fitness and population dynamics parameters of three successive generations of L. erysimi were analyzed using the age-stage, two-sex life table. The results show that a high CO₂ concentration had a cumulative effect on the survival rate and fecundity of L. erysimi, and elevated CO₂ had a negative effect on the individual fitness parameters of L. erysimi. The life expectancy (e_xj) is significantly lower in elevated CO₂ than that in ambient CO₂ treatment in the three successive generations, indicating that L. erysimi was more sensitive to CO₂ concentration and the life of L. erysimi was shortened under elevated CO₂. Additionally, we can find that elevated CO₂ has a short-term effect on the population parameters, including the intrinsic rate of increase (r) and finite rate of increase (λ) in L. erysimi. Through the data from this experiment, we believe that the individual and population fitness of L. erysimi will be decreased under elevated CO₂, which indicates that the damage caused by L. erysimi may be reduced in the future with increasing CO₂ levels.

Abstract

To assess the effect of elevated CO₂ on the development, fecundity, and population dynamic parameters of L. erysimi, the age-stage, two-sex life table was used to predict the individual fitness and population parameters of three successive generations of L. erysimi in this study. The results show that a significantly longer total pre-adult stage before oviposition (TPOP) was observed in the third generation compared with the first generation of L. erysimi under the 800 μL/L CO₂ treatment. The fecundity is significantly lower in the 800 μL/L CO₂ treatment than that in the 400 μL/L CO₂ treatment in the third generation of L. erysimi, which indicates that elevated CO₂ had a negative effect on the individual fitness parameters of L. erysimi. Additionally, the life expectancy (e_xj) is significantly lower under the 800 μL/L CO₂ treatment than that under the 400 μL/L CO₂ treatment in the three successive generations. A significantly higher intrinsic rate of increase (r) and finite rate of increase (λ) were found in the second generation compared with those in the first and third generations of L. erysimi under the 800 μL/L CO₂ treatment. Moreover, significantly lower r and λ were observed under the 800 μL/L CO₂ treatment compared with those under the 400 μL/L and 600 μL/L CO₂ treatments in the first generation of L. erysimi, which indicates that elevated CO₂ has a short-term effect on the population parameters (r and λ) of L. erysimi. Our experiment can provide the data for the comprehensive prevention and control of L. erysimi in the future with increasing CO₂ levels.

Elevated CO2 concentration affects survival, but not development, reproduction, or predation of the predator Hylyphantes graminicola (Araneae: Linyphiidae)

Elevated CO₂ concentrations can change the multi-level nutritional relationship of the ecosystem through the cascading effect of the food chain. To date, few studies have investigated the effects of elevated CO₂ concentration on the Araneae species through the tritrophic system. Hylyphantes graminicola (Araneae: Linyphiidae) is distributed widely in Asia and is a dominant predator in cotton fields. This study investigated chemical components in the food chain of cotton (Gossypium hirsutum)-cotton aphid (Aphis gossypii)-predator (H. graminicola) and compared the development, reproduction, and predation of H. graminicola under ambient (400 ppm) and elevated concentration of CO₂ (800 ppm). The results showed that the elevated CO₂ concentration increased the chemicals of cotton and cotton aphid, but it did not affect the nutrients, development, reproduction, and predation of the spider. However, the survival rate of the spider was significantly decreased in elevated CO₂. The results will further our understanding of the role of natural enemies in an environment with elevated CO₂ concentration.