Bidirectional interactions between beet armyworm and its host in response to different fertilization conditions

Area of Science:

• Agricultural Science
• Entomology
• Plant Physiology

Background:

• Crop plants face significant damage from pests like Spodoptera exigua, leading to economic losses.
• Fertilizer nutrient ratios, specifically nitrogen (N) and phosphorus (P), are known to affect plant defense mechanisms against herbivores.

Purpose of the Study:

• To investigate how different intensities and durations of Spodoptera exigua herbivory affect Brassica rapa biomass.
• To analyze the impact of varying N:P fertilizer ratios on Spodoptera exigua's enzyme activities in response to herbivory.

Main Methods:

• Experimentally manipulated N:P fertilizer ratios (1:5, 1:3, 1:1, 3:1, 5:1) applied to Brassica rapa.
• Exposed plants to varying intensities and durations of Spodoptera exigua herbivory.
• Measured host plant biomass (leaf, stem, root) and Spodoptera exigua enzyme activities (CAT, SOD, AChE, CarE).

Main Results:

• Compensatory leaf biomass growth observed with N:P = 3:1 fertilizer.
• Higher N proportion in fertilizer maintained stem biomass under herbivory.
• Antioxidant enzyme (CAT, SOD) activity was enhanced by N at low herbivory, but P became more critical at higher intensities.
• Acetylcholine esterase (AChE) activity was influenced by P at low defoliation and N at high defoliation.
• Carboxylesterase (CarE) activity showed reduced N influence with increased defoliation intensity.

Conclusions:

• Fertilizer N:P ratio significantly modulates plant-herbivore interactions.
• Plant biomass accumulation and pest enzyme responses are complexly regulated by nutrient availability and herbivory levels.
• Optimizing fertilizer N:P ratios can be a strategy to manage Spodoptera exigua impacts on crops like Brassica rapa.