Changes in antifungal defence systems during the intermoult period in the Colorado potato beetle

Area of Science:

• * Entomology
• * Insect Pathology
• * Host-Pathogen Interactions

Background:

• * The Colorado potato beetle (Leptinotarsa decemlineata) is a significant agricultural pest.
• * Understanding insect immune responses is crucial for developing biological control strategies against pests.
• * The intermoult period significantly influences insect susceptibility to pathogens.

Purpose of the Study:

• * To investigate changes in Colorado potato beetle larval defences during the intermoult period.
• * To assess the beetle's susceptibility to the entomopathogenic fungus Metarhizium robertsii at different developmental stages.
• * To correlate changes in cuticle properties and immune parameters with fungal resistance.

Main Methods:

• * Larval instars of the Colorado potato beetle were exposed to Metarhizium robertsii at 4-6h, 34-36h, and 84-86h post-moult.
• * Cuticle thickness, melanization, and epicuticular hydrocarbon content were measured.
• * Phenoloxidase activity, conidial adhesion, encapsulation rate, and haemocyte counts were analyzed.
• * Activity of detoxification enzymes in haemolymph and fat body was assessed.

Main Results:

• * Cuticle thickening occurred during larval growth, accompanied by decreased melanization and epicuticular hydrocarbons.
• * Resistance to Metarhizium robertsii increased, with reduced conidial adhesion.
• * Haemolymph showed elevated encapsulation rates and total haemocyte counts.
• * Detoxification enzyme activity shifted from haemolymph to fat body.

Conclusions:

• * Larval development in Colorado potato beetles leads to enhanced resistance against Metarhizium robertsii.
• * Changes in cuticle structure and immune system components contribute to increased host defence.
• * Understanding these developmental changes is key for optimizing biological control using entomopathogenic fungi.