Effects of CO₂, O₃ and humidity on the biology of MPB and their symbiotic fungi.xlsx

Mountain pine beetles pose a substantial threat to North American pine forests, causing extensive tree mortality over large areas. Their tree-killing ability is closely linked to mass aggregation on host trees triggered <i>via</i> pheromones and dependence on their symbiotic fungi. However, the influence of a changing climate on the biology of mountain pine beetles and their co-evolved interactions with their fungal symbionts remains uncertain. To investigate this, male and female pairs of beetles were introduced into freshly cut logs from lodgepole pine trees and placed in controlled climate chambers with manipulated environmental conditions, including two levels of CO₂ (ambient vs. 1,000ppm), O₃ (ambient vs. 100ppb), and humidity (33% vs. 65%)The beetle-infested logs were left in these chambers for one month and then returned to ambient conditions until brood emergence. Emerging broods were collected for further analysis. Additionally, three species of fungal symbionts (<i>Grosmannia clavigera</i>, <i>Ophiostoma montium</i>, and <i>Leptographium longiclavatum</i>) were subjected to the same CO₂,O₃, and humidity conditions for five days. Lower humidity promoted mountain pine beetle reproduction and fungal growth. Elevated CO₂ accelerated larval growth and emergence while improving brood pheromone production. Elevated O₃ had a negative impact on mountain pine beetle reproduction and brood fitness while improving its immune responses to an entomopathogenic fungus (<i>Beauveria bassiana</i>). It also inhibited fungal growth and reproduction, whereas elevated CO₂ had varied (positive or negative) effects on fungal growth and ergosterol (proxy to fungal mass) production depending on the fungal species. Together, these findings suggest that climate change can potentially alter the interactions between mountain pine beetles and their fungal symbionts, highlighting the importance of understanding how climate change affects forest pests and their symbiotic relationships to develop effective management strategies in the future.