Coping with crowds: density-dependent disease resistance in desert locusts

Area of Science:

• Ecology
• Evolutionary Biology
• Entomology

Background:

• Parasite transmission often increases with host population density.
• Natural selection may favor disease resistance mechanisms that respond to density cues.
• Density-dependent prophylaxis predicts higher resistance in crowded individuals.

Purpose of the Study:

• To investigate density-dependent prophylaxis in the desert locust (Schistocerca gregaria).
• To determine if crowded locusts exhibit enhanced resistance to the entomopathogenic fungus Metarhizium anisopliae var. acridum.
• To explore the physiological basis of this enhanced resistance.

Main Methods:

• Rearing desert locusts under crowded versus solitary conditions.
• Challenging locusts with Metarhizium anisopliae var. acridum.
• Measuring locust survival rates.
• Assessing antimicrobial activity in locust hemolymph.
• Monitoring thermal preferences and behavioral fever responses.

Main Results:

• Locusts reared under crowded conditions showed significantly higher resistance to Metarhizium anisopliae var. acridum compared to solitary locusts.
• Enhanced pathogen resistance in crowded locusts correlated with elevated antimicrobial activity.
• No significant differences were observed in thermal preferences or behavioral fever responses between the two groups.

Conclusions:

• The study provides evidence for density-dependent prophylaxis in the desert locust.
• Elevated antimicrobial activity is a key mechanism underlying enhanced disease resistance in crowded locusts.
• Findings have implications for understanding locust plague dynamics and developing effective biocontrol strategies.