Species diversity and niche separation of cocoon parasitoids in different forest types with endemic populations of their host, the Common Pine Sawfly Diprion pini (Hymenoptera: Diprionidae)

Abstract

Abstract. Species diversity and potential impact of cocoon parasitoids on the abundance of the common pine sawfly, Diprion pini L. (Hymenoptera: Diprionidae), were explored in different forest habitats, with endemic sawfly populations, by the regular exposure of laboratory reared sawfly cocoons. Different cocoon spinning sites of the sawfly were simulated by exposing cocoons at several strata (soil, litter, trunk and stem of pine trees) in a forest. In more fertile, mixed spruce/pine-forests, parasitism on exposed cocoons was lower than in typical outbreak stands with a lower vegetational diversity. The parasitoid communities comprised of up to nine parasitoid species, which showed temporal and spatial niche separation. The ichneumonid Pleolophus basizonus Grav. (Hymenoptera: Phygadeuontinae) occured throughout the season at all strata as well as in all forest types. The ichneumonid Gelis cursitans F. (Hymenoptera: Phygadeuontinae) was only found in pine forests with sparsely developed ground vegetation, parasitizing exposed cocoons in the upper story in spring. The torymids Monodontomerus dentipes Dalm. (Hymenoptera: Torymidae) and M. minor Ratz.(Hymenoptera: Torymidae) were present in all forest types, but parasitized commonly only cocoons in the upper story in summer. Apparently, these generalists can quickly respond to increased densities of upper story exposed "summer" cocoons and thus limit the population growth of the pine sawfly due to the development of a second generation.

Generalist predation on forest tent caterpillar varies with forest stand composition: an experimental study across multiple life stages

“…Although the natural enemies hypothesis was originally motivated by observations from agricultural systems, observations of reduced forest pest damage in more diverse forest stands has advanced its consideration in forest systems (e.g. For other forest defoliators, such as the spruce budworm, Choristoneura fumiferana Clemens (Lepidoptera: Tortricidae), and autumnal moth, Epirrita autumnata Borkhausen (Lepidoptera: Geometridae), predation and parasitism, especially by generalists, are higher in more diverse forest stands (Cappuccino et al, 1998;Quayle et al, 2003;Riihimäki et al, 2005), although the response by specialist parasitoids may be opposite (Herz & Heitland, 2005). For other forest defoliators, such as the spruce budworm, Choristoneura fumiferana Clemens (Lepidoptera: Tortricidae), and autumnal moth, Epirrita autumnata Borkhausen (Lepidoptera: Geometridae), predation and parasitism, especially by generalists, are higher in more diverse forest stands (Cappuccino et al, 1998;Quayle et al, 2003;Riihimäki et al, 2005), although the response by specialist parasitoids may be opposite (Herz & Heitland, 2005).…”

“…Jactel et al, 2005;Koricheva et al, 2006;Jactel & Brockerhoff, 2007). For other forest defoliators, such as the spruce budworm, Choristoneura fumiferana Clemens (Lepidoptera: Tortricidae), and autumnal moth, Epirrita autumnata Borkhausen (Lepidoptera: Geometridae), predation and parasitism, especially by generalists, are higher in more diverse forest stands (Cappuccino et al, 1998;Quayle et al, 2003;Riihimäki et al, 2005), although the response by specialist parasitoids may be opposite (Herz & Heitland, 2005). Forest stand diversity may therefore alter the interactions between FTC and its natural enemies, with potential implications for the dynamics of FTC populations in the mixedwood boreal forest.…”

Influence of soil and topography on defoliation intensity during an extended outbreak of the common pine sawfly (Diprion pini L.)

“…For example, Scots pine (Pinus sylvestris L.) needle N contents increase with soil N contents (Björkman et al 1991, Raitio 1999, which have also been shown to affect the contents of secondary defense compounds (Björkman et al 1991, Kainulainen et al 1996. In addition, predators and parasitoids of defoliators have been shown to be affected by site fertility (Hanski & Parviainen 1985, Herz & Heitland 2005.…”

Spatial niche partitioning of two saproxylic sibling species (Coleoptera, Cetoniidae, genus Gnorimus)

“…Our study was focused on: (i) collecting data about distribution, abundance and detectability of chafer beetles within the study area, also in the light of the used sampling method (airtraps), and (ii) on investigating ecological factors associated to spatial niche partitioning between the two species. Spatial niche partitioning was explored in several studies on insects (Wassmer, ; Herz and Heitland, ; Friberg et al ., ,b; Gilbert et al ., ), and in some cases has been considered as a key evolutionary phenomenon responsible for adaptive speciation (Friberg et al ., ).…”