Fertilizing Corn With Manure Decreases Caterpillar Performance but Increases Slug Damage

Area of Science:

• Agricultural Science
• Entomology
• Soil Science

Background:

• Farmers increasingly use manure as a fertilizer alternative to inorganic options.
• Previous studies suggest manure reduces plant herbivore susceptibility, but underlying mechanisms are not fully understood.

Purpose of the Study:

• To investigate the impact of cow manure versus NPK fertilizer on caterpillar performance and plant traits.
• To evaluate the effects of manure and cover crops on herbivore damage and performance in field conditions.

Main Methods:

• Greenhouse experiment: Corn fertilized with cow manure or NPK fertilizer, followed by feeding trials with fall armyworm (Spodoptera frugiperda) and black cutworm (Agrotis ipsilon).
• Field experiment: 3-year study with a 2x2 factorial design including wheat cover crops and manure/NPK fertilizer treatments.
• Measurements included caterpillar mass gain, plant nutritional content, plant defenses, field herbivore damage, and neonate caterpillar performance on field-collected leaves.

Main Results:

• Manure reduced mass gain in black cutworm and smaller fall armyworm caterpillars in the greenhouse.
• In field trials, manure-fertilized plots showed increased herbivore damage, particularly from slugs, despite reduced fall armyworm performance on manure-treated leaves.
• No significant increase in micronutrients or enhanced plant defenses were observed in manure-treated plants.

Conclusions:

• Cow manure can confer resistance to certain herbivores, but this effect can be diminished by habitat conditions.
• The benefits of manure for pest resistance may be context-dependent and not universally applicable across different environments and herbivore types.