Shoot beetle damage to Pinus yunnanensis monitored by infrared thermal imaging at needle scale

Aims To explore the feasibility of thermal infrared technology for monitoring the shoot beetle damage to Yunnan pine (Pinus yunnanensis), the relationship between temperature and biochemical and/or physiological factors of healthy and damaged shoots of Yunnan pine was analyzed.Methods The temperatures were extracted with the software FLIR-TOOLS from the thermal images of damaged shoots. The temperature differences between damaged shoots and healthy shoots (ΔT) in the same thermal image were analyzed. The relationships between ΔT and physiological and biochemical parameters were used to clarify the mechanism that caused needle temperature increase with infested duration.Important findings Results indicated: (1) The chlorophyll and water content of damaged shoots decreased with the infested duration, and the chlorophyll content decreased faster than water content; (2) The net photosynthetic rate (P_n), stomata conductance (G_s) and transpiration rate (T_r) also decreased with infested duration, and the temperature difference between needle and atmosphere (ΔT_l-a) increased with infested duration; (3) ΔT reached the maximum at 14:00 to 15:00; the temperature differences of lightly-infested, mid-infested and heavily-infested needles reached 0.6, 0.7 and 2.5 °C, respectively; (4) A strong negative correlation was found between ΔT and G_s, water content. Our study concluded that the water imbalance of damaged needles caused needle temperature changes. Therefore, thermal infrared technology could be applied to monitor shoot beetle damage of Yunnan pine at different stages.