Plant Stress in Determining Attack Rates of Herbivorous Chewing Insects

Plants in stressful environments tend to be more asymmetrical, have reduced defenses, and are more vulnerable to herbivory. Stressful conditions are also detrimental to free-living herbivorous insects, which are sensitive to climatic variations like extreme temperatures and dry periods. In the Cerrado, different phytophysiognomies range from open to closed and structurally complex areas, simulating a gradient of environmental harshness. This study examines the relationship between fluctuating asymmetry (FA) and herbivory in Qualea parviflora and Eugenia dysenterica across five Cerrado areas. We tested the Plant Stress Hypothesis (PSH) and the Environmental Harshness Hypothesis (EHH), investigating their interaction. Specifically, we assessed how stressful conditions influence plants, herbivory rates, and the richness and abundance of herbivorous insects, considering species composition variation among phytophysiognomies. Results showed significant differences in structural complexity among areas, with campo rupestre < cerrado sensu stricto < cerradão. FA per plant varied with increasing complexity for Q. parviflora but not for E. dysenterica. Leaf area removed differed between species but did not vary significantly with complexity. Leaf area removed decreased with increasing FA in Q. parviflora but increased with FA and complexity interaction in E. dysenterica. Contrary to predictions, free-living herbivore richness and abundance were higher in the most stressed phytophysiognomy, with species composition variation mainly influenced by the substitution process.