Quantitative Association of Bark Beetles with Pitch Canker Fungus and Effects of Verbenone on Their Semiochemical Communication in Monterey Pine Forests in Northern Spain

Abstract

The association between 11 species of bark beetles (Coleoptera: Scolytinae) and one weevil (Coleoptera: Entiminae) with the pitch canker fungus, Fusarium circinatum Nirenberg and O'Donnell, was determined by crushing beetles on selective medium and histone H3 gene sequencing. Pityophthorus pubescens (Marsham) (25.00%), Hylurgops palliatus (Gyllenhal) (11.96%), Ips sexdentatus (Börner) (8.57%), Hypothenemus eruditus Westwood (7.89%), Hylastes attenuatus Erichson (7.40%), and Orthotomicus erosus (Wollaston) (2.73%) were found to carry the inoculum. In addition, the root weevil Brachyderes incanus L. (14.28%) had the second highest frequency of occurrence of the fungus. The responses of the insects to a range of verbenone doses were tested in field bioassays using funnel traps. Catches of P. pubescens, a species colonizing branch tips of live trees, were significantly reduced in a log-linear dose-dependent relationship. Catches of I. sexdentatus, an opportunistic species normally attacking fresh dead host material, were also gradually reduced with increasing verbenone dose. Catches of Tomicus piniperda L., O. erosus, Dryocoetes autographus (Ratzeburg), H. eruditus, Xyleborus dryographus (Ratzeburg), Hylastes ater (Paykull), Hylurgus ligniperda (F.), H. attenuatus, and B. incanus were not significantly affected by verbenone. The effects of verbenone were consistent with differences in host-age preference. Semiochemical disruption by verbenone in P. pubescens and I. sexdentatus could represent an integrated pest management strategy for the prevention of the spread of pitch canker disease between different stands. However, several species associated with F. circinatum were unaffected by verbenone, not supporting this compound for prevention of the establishment of potential vectors in Northern Spain.

A genetically homogenous population of Fusarium circinatum causes pitch canker of Pinus radiata in the Basque Country, Spain

“…In California, engraver beetles (Fox et al 1991) and twig beetles (Storer et al 2004) are thought to play critical roles as vectors and wounding agents, whereas insects are accorded much less importance in the pitch canker disease cycle in the southeastern United States (Blakeslee & Oak 1979). Several bark beetle and weevil species are associated with F. circinatum in the Basque region of Spain (Romon et al 2007). In this study, there was no difference in genetic diversity of F. circinatum isolates associated with insects versus other isolates from Collections 1 and 2.…”

“…This species accounts for almost 60 % of the forested area in Bizkaia, a province within the Basque Country (Gonzalez-Ariasa et al 2006). The presence of pitch canker in the Basque Country and its association with bark beetles is a serious concern to its forest industry (Romon et al 2007). The objective of this study was to characterise the genetic diversity of F. circinatum in the Basque Country using mating type assays, VCG tests, DNA-based polymorphic markers, and amplified fragment length polymorphism (AFLP) analyses.…”

Sydowia polyspora Dominates Fungal Communities Carried by Two Tomicus Species in Pine Plantations Threatened by Fusarium circinatum

“…In spite of this, F. circinatum was not present in collected insects either from this infected plot or from plot B. The most plausible explanation for this absence could be the previously reported low phoresy rate of T. piniperda [11,49], even in infected pine stands (4% according to Bezos et al [12]). There is not much information on phoretic capacity of T. destruens, although it might be expected to be similar to its sister species.…”

“…; Dolichopodidae) have been identified as carriers of PPCD fungus in the USA, as summarized by Brockerhoff et al [9]. In Spain, all identified carriers of F. circinatum belong to Curculionidae, including seven species of Scolytinae, one Molytinae and one Entiminae [10,11].…”

Bark Beetles Control in Forests of Northern Spain

“…Fungal taxa underlined indicate high percentage of isolation with the corresponding insect within a row. Fungal species with an upper symbol are present in the Basque Country, as follows: Saprophytic species (*), facultative pathogens (**) and strictly pathogens (***)(Adapted from Kirisits, 2004;Romón et al, 2007aRomón et al, , 2007b.…”