Studying Ips sexdentatus Borner outbreaks in Italian coastal pine stands: technical issues of trapping in warmer climates

During the last few years the stenographer bark beetle Ips sexdentatus Borner has been causing serious damage to pine stands on the coast of Tuscany. Here, its populations have dramatically increased in numbers, exploiting the weakening of maritime pines by other pests as well as the increasing number of wildfires. Preliminary results of an ongoing multi-year study on I. sexdentatus population dynamics and its control in these areas have shown issues on the use of aggregation pheromones for monitoring and mass trapping. According to the manufacturer, dispensers should be replaced after 50 days, thus guaranteeing efficacy until the 50th day. This may be true for colder climates in inland pine stands, but the warmer summer temperatures on the coastline of South Tuscany deplete dispensers considerably faster. By dividing the traps in two groups (A and B) by starting to bait each group about 30 days apart, we assured the presence of adequately baited traps in the field, also verifying the differences in beetle catches for 10 months in 2017. While spring and fall temperatures of these areas do not seem to significantly affect dispensers’ nominal life, catches decreased noticeably after 30 days during summer. More specifically, when at the 50th day one group registered almost zero catches, the other one (20 days after its own bait renewal) still recorded 20-30 beetle catches per trap every 10 days. Thus, in warmer climates, the use of pheromone dispensers according to manufacturer instructions, may lead to errors in interpreting flight patterns and the number of I. sexdentatus generations per year. Thus, the study of this pest’s outbreaks in newly exploited areas must consider the adjusted life-span of pheromone dispensers, according to the local climate, for a proper interpretation of the flight curves, and to better address control strategies.