Pine Pitch Canker and Insects: Regional Risks, Environmental Regulation, and Practical Management Options

Abstract

Pine pitch canker (PPC), caused by the pathogenic fungus Fusarium circinatum (Nirenberg and O' Donnell), is a serious threat to pine forests globally. The recent introduction of the pathogen 2 of 34 to Southern Europe and its spread in Mediterranean region is alarming considering the immense ecological and economic importance of pines in the region. Pines in forests and nurseries can be infected, resulting in severe growth losses and mortality. The pathogen is known to spread in plants for planting and in seeds, and results from recent studies have indicated that F. circinatum may also spread through phoretic associations with certain insects. With this review, we aim to expand the current understanding of the risk of insect-mediated spread of PPC in different parts of Europe. Through the joint action of a multinational researcher team, we collate the existing information about the insect species spectrum in different biogeographic conditions and scrutinize the potential of these insects to transmit F. circinatum spores in forests and nurseries. We also discuss the impact of environmental factors and forest management in this context. We present evidence for the existence of a high diversity of insects with potential to weaken pines and disseminate PPC in Europe, including several common beetle species. In many parts of Europe, temperatures are projected to rise, which may promote the activity of several insect species, supporting multivoltinism and thus, further amplifying the risk of insect-mediated dissemination of PPC. Integrated pest management (IPM) solutions that comply with forest management practices need to be developed to reduce this risk. We recommend careful monitoring of insect populations as the basis for successful IPM. Improved understanding of environmental control of the interaction between insects, the pathogen, and host trees is needed in order to support development of bio-rational strategies to safeguard European pine trees and forests against F. circinatum in future.

Global Geographic Distribution and Host Range of Fusarium circinatum, the Causal Agent of Pine Pitch Canker

“…Combined with information regarding introduction pathways, it can also help prevent further introductions by focusing quarantine measures and monitoring efforts where they are most effective. Given the risks posed by the movement of the pathogen, there is an urgent need for routine surveillance of Pinus and other species known to be susceptible to F. circinatum, as well as research on the importance of soil, native insects, and asymptomatic nursery plants for the spread of the disease [166]. Without maintained levels of surveillance, it is highly probable the pathogen will continue spreading to new areas and extending its host range.…”

Pine Pitch Canker (PPC): Pathways of Pathogen Spread and Preventive Measures

“…Many other insects (e.g., shoot and foliage feeders, bark beetles, wood and root borers, suckers and predators) have also been recognized as potential carriers or vectors of PPC in European and non-European countries [98][99][100].…”

“…The short-distance flight of insect vectors limits the dispersal of the pathogen to local scale. However, insects can act as wounding agents providing an entry point for the disease [98] that favors PPC establishment. In forest or plantations, a reliable method of monitoring the population of insect vectors is the use of volatile compounds such as pheromones [154].…”

“…In forest or plantations, a reliable method of monitoring the population of insect vectors is the use of volatile compounds such as pheromones [154]. Interventions for the control should be adapted to the different Forest Management Approaches, considering the gradient of management intensity allowed in each silvicultural system [98]. Due to the increasingly restricted use of pesticides in EU forests [155], mechanical controls are gaining more interest.…”

“…Strategies such as the elimination of coarse woody debris colonized by insects before their emergence or the avoidance of storage of freshly cut logs in forests have shown effective results [156][157][158]. Recently, literature-based recommendations in the management of insect vectors of PPC have been compiled by Fernández-Fernández et al [98,99]. In international trade, the suppression of the long-distance spread of potential insect vectors implicates the debarking of conifer wood destined for packaging material [159].…”