Population divergence in nutrient-temperature interactions in Pieris rapae.

Area of Science:

• Ecology
• Insect Physiology
• Evolutionary Biology

Background:

• Larval host plant quality and temperature significantly impact insect herbivore physiology and life-history traits.
• Local variations in these factors can lead to local adaptation, but comparative studies between populations are rare.

Purpose of the Study:

• To investigate how diet macronutrient ratio (protein to carbohydrate) and temperature affect larval growth, development, and survival of two invasive Pieris rapae populations from different North American climates.
• To compare the sensitivity of these populations to nutritional and thermal variations.

Main Methods:

• A fully factorial experiment was conducted using three temperatures (18°C, 25°C, 32°C) and three artificial diets varying in protein-to-carbohydrate ratio (low, balanced, high).
• Larval growth, development, survival, and pupal mass of Pieris rapae were measured.

Main Results:

• Dietary effects on life-history traits were more pronounced at lower temperatures and varied between the subtropical and temperate populations.
• The subtropical population showed reduced survival on a low-protein diet at cold temperatures.
• Larvae from the temperate population were less sensitive to diet changes across all temperatures, though both populations performed poorly on the low-protein diet.

Conclusions:

• The impact of imbalanced nutrition on insect herbivores is temperature-dependent.
• Geographic populations of Pieris rapae in North America exhibit distinct sensitivities to nutritional balance and temperature, indicating local adaptation.