Changes in haemolymph parameters and insect ability to respond to immune challenge during overwintering

Area of Science:

• Insect physiology and immunology
• Overwintering biology
• Climate change impacts on insects

Background:

• Overwintering presents significant energetic challenges for temperate insects, potentially leading to reduced immune function.
• The harlequin ladybird (Harmonia axyridis) is a model organism for studying overwintering adaptations.
• Understanding immune system changes during overwintering is crucial, especially in the context of climate change.

Purpose of the Study:

• To investigate physiological and immunological parameters in overwintering harlequin ladybirds.
• To assess the impact of winter temperature regimes on immune parameters in laboratory-reared beetles.
• To evaluate changes in immune inducibility and physiological status in field-collected beetles before and after overwintering.

Main Methods:

• Laboratory experiments: Monitored haemocyte concentration in beetles exposed to different winter temperatures.
• Field experiments: Measured haemocyte concentration, total protein, and antimicrobial activity in naive vs. Escherichia coli-challenged beetles before and after overwintering.
• Statistical analysis of physiological and immunological data to determine significant changes and differences.

Main Results:

• Haemocyte concentration significantly decreased during overwintering, with limited effects of temperature regimes in laboratory settings.
• In field-collected beetles, immune challenge prior to overwintering increased haemocyte concentration and antimicrobial activity, but this effect diminished post-overwintering.
• Total protein concentration increased during overwintering, with higher levels in females than males; immune response capacity was generally reduced after winter.

Conclusions:

• Overwintering significantly reduces the capacity of insects to mount an immune response.
• The ability to respond to immune challenges is compromised after the overwintering period.
• Findings highlight the vulnerability of insect immune systems during winter, with implications for population dynamics and climate change adaptation.