Print PagePlant physiology is altered dramatically when plants are water stressed. Nitrogen (N) availability, digestible carbohydrates, and nutrients all change when plants are water limited and changes in the availability of these resources may affect insect herbivores. Currently, we are unable to accurately predict herbivore response to host water-deficit stress. The literature suggests contrasting responses for even the same herbivore guild, such as piercing-sucking aphids and thrips. Several studies suggest an increase in herbivore survivorship under stress, while others report the opposite. However, the degree and duration of water stress may determine the effect of water stress on host plant quality for herbivores. Huberty & Denno (2004) conducted a meta-analysis of herbivore response and concluded that pulsed stress increases host plant quality for piercing-sucking insects. They hypothesized that N availability was increased by water stress and that plant turgor increases when plants recover from stress. The increased turgor pressure associated with plant recovery from stress allows herbivores to access the excess N. In contrast, continuous stress produces a constant decline in turgor pressure, reducing herbivore feeding efficiency. In this study, we examined the effects of pulse and continuous stress on cotton (Gossypium hirsutum) physiology and herbivore abundance over a stress gradient.
Results/Conclusions
Our objectives were to 1) explicitly differentiate the effects of pulsed and continuous stress on herbivore abundance via cotton and 2) to determine the physiological parameters in cotton that may be associated with herbivore performance. Anti-stress enzymes and herbivore abundance were quantified on continuously stressed, pulse stressed, and non-stressed plants. Our results show that the abundance of western flower thrips (Frankliniella occdientalis) was significantly higher on pulse stressed plants versus continuously and non-stressed plants. The average production of the anti-stress and defense compound peroxidase was much higher in pulsed stressed plants than continuous and non-stressed plants. Furthermore, we determined that several physiological parameters of cotton metabolism (i.e. photosynthetic rate, stomatal conductance) may be indicators of herbivore performance. Our study supports that the duration of water stress may play a key role in determining its effects on herbivore performance. This study will help us more accurately predict herbivore response to water stressed plants and provide insight into how water availability influences plant-insect interactions.
