The pine shoot beetle Tomicus piniperda as a plausible vector of Fusarium circinatum

The pine shoot beetle, Tomicus piniperda, is a potential vector of the pitch canker disease pathogen. The insect could transmit the pathogenic fungus during its maturation or regeneration feeding on the shoots of healthy pine crowns.

Abstract

Fusarium circinatum, the causal agent of pitch canker disease, currently affects Pinus radiata in northern Spain, causing pitch-soaked cankers and tree death. Although several species of the family Scolytinae have been reported as vectors of this pathogen, the role of the pine shoot beetle T. piniperda remains unclear. The general objective of this study was to determine whether T. piniperda is a vector for the pitch canker pathogen F. circinatum. For this purpose, Leach’s postulates (1) an association between T. piniperda and trees affected by pitch canker disease; (2) regular visits by T. piniperda to healthy P. radiata trees; (3) presence of the pathogen on the insect in nature; and (4) transmission of the pathogen to disease-free host material under controlled conditions. Fresh green shoots with feeding galleries were collected from the ground, breeding galleries were collected from diseased trunks and insects were collected during their dispersion flights. A laboratory experiment was conducted in which specimens of T. piniperda were inoculated with the pathogen prior to feeding on shoots. In the field, T. piniperda was found to be associated with both diseased and healthy P. radiata trees, and F. circinatum was found to be present, at low rates, on the exoskeleton of T. piniperda. In the laboratory experiment, evidence of the ability of T. piniperda to transfer the pathogen to healthy shoots was found. The study findings indicate T. piniperda as a plausible vector of this pathogen. We postulate for the first time a potential relationship between the life cycles of T. piniperda and F. circinatum.