Ips sexdentatus Mass-Trapping: Mitigation of Its Negative Effects on Saproxylic Beetles Larger Than the Target

Abstract

Research Highlights: We investigated the negative effects of bark beetle mass trapping, especially non-target catches among the target’s natural enemies. Slot traps modified with mesh screen and escape windows were tested to improve their selectiveness. Background and Objectives: Two of the main natural enemies of bark beetles, Thanasimus formicarius (L.) and Temnoscheila caerulea (Olivier), are frequently trapped in high numbers in Ips sexdentatus (Böerner) pheromone traps, along with other saproxylic insects; this may lead to much larger pest populations in the successive 4–20 beetle generations. From 2016–2019, during I. sexdentatus mass-trapping in a pine forest of Tuscany (Italy), non-target catches were tallied. Trap modifications were evaluated to mitigate non-target catches, especially those concerning bark beetles’ natural enemies. Materials and Methods: A total of 25 bark-beetle slot traps were placed about 75 m apart in a pine stand infested by I. sexdentatus. Traps were baited with I. sexdentatus aggregation pheromone, whose main components are ipsenol, ipsdienol, and 2-methyl-3-buten-2-ol. Catches were collected every 10 days from March to December. In 2019, 13 traps were modified by applying a 6-mm mesh screen on top of the collection container and by providing three 60 mm × 8 mm escape windows immediately above the screen. These “modified traps” and their captures were considered separately from the 12 remaining “standard traps.” All bark beetle species were recorded, as well as all beetle species > 8 mm. Results: Overall, target catches amounted for <10% of the total beetle catches. The most-collected species was the bark beetle Orthotomicus erosus Wollaston. Trap modification allowed the escape of larger species, resulting in the reduction of the average size of caught specimens. Even though non-target catches among predators were still high, the proportion of major predators (T. formicarius and T. caerulea) to bark beetles showed a statistically significant reduction of predator catches in modified traps, an encouraging outcome. Conclusions: Trap modifications may mitigate the problem of non-target catches during mass trapping, especially reducing catches of beetle species larger than the target. However, the key is to schedule mass trapping only during those seasons when the target adults are more active than the main predator adults, thus limiting their catches and, consequently, the negative effects on pest management and biodiversity.

Verbenone Affects the Behavior of Insect Predators and Other Saproxylic Beetles Differently: Trials Using Pheromone-Baited Bark Beetle Traps

“…From 2014 onward, the increased availability of pine trees weakened by the maritime pine bast scale Matsucoccus feytaudi (Ducasse) led to a notable rise in the population density of I. sexdentatus. Furthermore, the bark beetle Orthotomicus erosus (Wollaston) was also favored, even on pines already infested with I. sexdentatus or the other major pine bark beetle, Tomicus destruens (Wollaston), as well as on those trees highly stressed by abiotic factors [14]. Starting in 2016, phytosanitary measures, such as the prompt cutting of infested trees and mass trapping, were carried out, negatively affecting the population density of I. sexdentatus, which was reduced to sustainable levels in 2022 [14].…”

“…Furthermore, the bark beetle Orthotomicus erosus (Wollaston) was also favored, even on pines already infested with I. sexdentatus or the other major pine bark beetle, Tomicus destruens (Wollaston), as well as on those trees highly stressed by abiotic factors [14]. Starting in 2016, phytosanitary measures, such as the prompt cutting of infested trees and mass trapping, were carried out, negatively affecting the population density of I. sexdentatus, which was reduced to sustainable levels in 2022 [14]. However, trappings were planned again in 2023 to continue monitoring both I. sexdentatus and O. erosus.…”

“…The collection of catches occurred every 14 days from March to October with pheromone renewal every 28 days, approximately 20 days earlier than the dispensers' expected lifespan. Deviating from the manufacturer's instructions (50 days) was necessary since dispensers deplete faster in Tuscany's coastal pine stands due to the warm climate [15].…”

Different responses of Monochamus galloprovincialis and three non-target species to trap type, colour, and lubricant treatment

“…Traps used for monitoring M. galloprovincialis often capture non-target insects (Pajares et al 2004, Francardi et al 2009, Jurc et al 2012, 2016, because different species often respond similarly to volatiles released by host trees (Francardi et al 2009, Boone et al 2018 and by other insect taxa (Bakke & Kvamme 1981, Allison et al 2001, Heber et al 2021, and furthermore, these volatiles may act synergistically (Pajares et al 2004). However, the capture of nontarget species raises several issues related to trap functionality and, more importantly, could reduce populations of beneficial species such as predators, thus limiting their ability to regulate pest populations (Bracalini et al 2021). Therefore, trap optimization should focus not only on trap effectiveness in capturing target species but also on minimizing captures of nontarget taxa, particularly beneficial insects.…”

Recent Advances in the Monitoring, Assessment and Management of Forest Pathogens and Pests

“…Additional studies are needed to better understand how to improve their efficacy, while reducing undesirable effects. Bracalini et al [24], for example, have investigated the negative effects of Ips sexdentatus Böerner mass trapping, especially non-target catches among the target's natural enemies. They tested slot traps modified with mesh screens and escape windows to improve their selectiveness, demonstrating how trap modifications may mitigate the problem, especially for beetles larger than the target.…”