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Switchgrass (Panicum virgatum L.) Yield and Photosynthetic Response to Simulated Insect Defoliation and Grasshopper (Orthoptera: Acrididae) Feeding
Insect herbivory can affect morphology and physiological functions of plants. Defoliation caused by herbivores may alter photosynthetic rates of remaining plant tissues or reduce the leaf area and limit the photosynthate needed to fulfill the energy and nutritional requirements of the plants. The reduction in plant leaf area may reduce the quality and quantity of biomass, which is critical for bioenergy crops. Plants may also compensate for herbivory losses utilizing their energy and resulting in less vigorous plants. Two switchgrass (Panicum virgatum L.) cultivars, Shawnee (upland) and Kanlow (lowland), were evaluated for yield response to simulated leaf-mass consumption. The data showed no significant effect of up to 80% simulated insect defoliation on the yield of switchgrass under suitable weather conditions. During the first year of the study with abundant rainfall, a significant reduction in leaf area index (LAI) did not result in a significant effect on switchgrass yield. However, the following year, drought occurred and resulted in significant yield reduction, along with reductions in LAI and percent light interception. Switchgrass cultivars (Shawnee and Kanlow) were tested for their photosynthetic response to simulated leaf injury. Mechanical defoliation with different insect feeding patterns was applied to individual leaves to determine the effect on photosynthetic rates. No significant differences among various patterns of tissue removal were recorded in Kanlow. However, during 2011, double edge cutting treatment significantly reduced the photosynthetic rates in Shawnee. Significant reductions in photosynthetic rates were recorded over time in Kanlow for both years. Photosynthetic rates differed significantly between the years even prior to treatment, likely as a result of water stress in the second year. The actual feeding rates of nymphs and adults of red-legged grasshopper, Melanoplus femurrubrum (DeGeer) (Orthoptera: Acrididae) were quantified. The average leaf area consumed and the weight gained by each stage of grasshopper were measured after three days of feeding. The results of the study indicated that the third instar of M. femurrubrum consumed the maximum amount per unit of body weight per day while the maximum weight gain was observed in adults and the fifth instars. These results may explain the higher metabolic rates and digestive efficiencies of early instar grasshoppers. The study results suggest control of grasshoppers at early stages is needed to avoid potential economic losses.
Mustafa, Fatima, "Switchgrass (Panicum virgatum L.) Yield and Photosynthetic Response to Simulated Insect Defoliation and Grasshopper (Orthoptera: Acrididae) Feeding" (2013). ETD collection for University of Nebraska - Lincoln. AAI3561388.