Ecological segregation of bark beetle (Coleoptera, Curculionidae, Scolytinae) infested Scots pine

Ecol Res (2016) 31: 135–144 DOI 10.1007/s11284-015-1322-y O R I GI N A L A R T IC L E Andrzej Borkowski • Iwona Skrzecz Ecological segregation of bark beetle (Coleoptera, Curculionidae, Scolytinae) infested Scots pine Received: 29 July 2015 / Accepted: 8 November 2015 / Published online: 19 November 2015  The Author(s) 2015. This article is published with open access at Springerlink.com Abstract Bark beetles infest several pine tree species, often creating major economic losses. Biotic interactions between Scolytinae populations inhabiting Pinus sylvestris were analyzed using a new sampling method involving a two dimensional division of tree space resources into units and sections. The goal was to evaluate the effects of the type of available reproduction material on insect infestation. The P. sylvestris stands in this study included an analysis of bark beetles colonizing dead trees and uninfested living trees (trap trees). Analyzed trees were harvested and their stems divided into ten equal units; each unit was halved into two sections (half of the stem circumference). The colonization of dead trees by insects was evaluated immediately after cutting for infested trees and 2 months after cutting for trap trees. The type of breeding material significantly affected the species composition of bark beetles infesting P. sylvestris. The dead trees were colonized mostly by Trypodendron lineatum and Tomicus minor, and to a lesser extent by Tomicus piniperda, which dominated in trap trees. Tomicus piniperda and T. lineatum preferred thicker stems; however, T. minor, Hylurgops palliatus and Pityogenes bidentatus preferred thinner ones. The application of the new sampling method helped to increase the accuracy of niche segregation among insect species. The results of niche segregation indicate bark beetles exhibited spatial specialization in the use of resources, mainly related to the moisture content of breeding material and the availability of food resources which is the main factor determining the coexistence of bark beetles in the same environment. A. Borkowski Department of Ecology and Environment Protection, Institute of Biology, Jan Kochanowski University, Swietokrzyska 15 Str., 25-406 Kielce, Poland I. Skrzecz (&) Department of Forest Protection, Forest Research Institute, Braci Lesnej 3 Str., Sekocin Stary, 05-090 Raszyn, Poland E-mail: Tel.: +48 22 7150541 Keywords Insects Æ Niche breadth and overlap Æ Pinus sylvestris Æ Resource partitioning Æ Tomicus spp. Introduction When trees are weakened by various abiotic, biotic and anthropogenic factors, forest stands and cut trees become an important breeding base for bark beetles (Scolytinae; Dyer and Chapman 1965; Wood 1982; Jakuš 1998a, b; Sauvard 2004; Foit 2010). When beetles attack a tree this triggers defense responses, and the level of the response depends on the degree of tree weakening (Lieutier 2004). Bark beetles have developed specific mechanisms of infestation allowing the identification and selection of trees suitable for infestation, a phenomenon known in the literature as behavioral avoidance. Therefore, the physiological condition of trees has a significant effect on the species composition of treeinfesting cambio- and xylophagous insects (Borden 1997). The infestation of standing trees is closely related to the so-called threshold of successful attack (Christiansen et al. 1987) which may be exceeded as a result of: (1) decrease in tree resistance, (2) increase in population density size, or (3) when both of these situations occur simultaneously. Because cut trees lack resistance to beetle attack, they are often used as natural traps for predicting and reducing the populations of bark beetles such as the common pine shoot beetle Tomicus piniperda (L.) that commonly attacks Pinus sylvestris (L). In Europe, traps used for monitoring the population size of this species are made of whole trees or tree trunks (Grégoire and Evans 2004). In Poland, trap trees are usually placed in forest stands that have already been damaged by primary pests or pathogenic fungi and in the forest stands located near sawmill timber yards (Szujecki 1987). The stored unbarked wood of P. sylvestris is a breeding site of T. piniperda and the lesser pine shoot beetle Tomicus minor Hart. After emerging, the beetles of both species migrate to adjacent forests, where they feed on the shoots of healthy pines causing 136 disturbances in crown development and, consequently, significant losses in volume increment (Ericsson et al. 1985; Långström and Hellqvist 1990, 1991; Långström et al. 1990; Czokajlo et al. 1997; Borkowski 2001). The presence of more than one species of bark beetle attacking a single weakened tree may have positive and negative effects on beetle populations such as a combined effect that helps the beetles to overcome tree resistance or to increase competitive interactions among the beetle species (Light et al. 1983; Wagner et al. 1985; Flamm et al. 1987; Rankin and Borden 1991; Schlyter and Anderbrant 1993). Although many studies have addressed the effects of biotic interactions on the populations of species from different taxonomic groups (e.g. Mysterud 2000; Julliard et al. 2006; Dolédec et al. 2008; Young 2008), only a few publications have been conducted related to bark beetles. A few studies describe the biotic interactions of insects from the subfamily Scolytinae in spruce Picea abies L. (Karst.) (Grünwald 1986) or in pine species such as P. sylvestris (Amezaga and Rodrı́guez 1998; Borkowski 2013), Pinus radiata (D. Don) (Amezaga and Rodrı́guez 1998), Pinus resinosa Ait. (Ayres et al. 2001) and Pinus taeda (L.) (Paine et al. 1981). This type of research is very labor-intensive. It requires debarking of entire trees and precisely counting egg galleries. However, knowledge related to the distribution and density of egg galleries in trunks is essential for the description of biocoenotic interactions between bark beetles and host plants as well as the related mechanisms explaining the coexistence of various bark beetle species in the same habitat. In practice, the selection of a sampling method should allow the separation of the niches of all bark beetle species in accordance with Gause’s principle (Krebs 2009). This rule states that two species with similar environmental requirements can coexist only when they use available resources in different ways. The conditions of such coexistence can be accurately described by applying a method employing a factor (niche breadth, sampling method) that allows precise niche segregation for all the examined bark beetle species. This method could help researchers determine the nature of biotic interactions between bark beetles, which can be used in the protection of forest against pest insects. The methods adopted in earlier studies using bark thickness as a factor related to niche segregation in bark beetles were not fully effective (Grünwald 1986; Amezaga and Rodrı́guez 1998). T (...truncated)