In its introduced southern hemisphere range, Sirex noctilio causes considerable mortality in non-native pine forests. In its native Eurasian range however, S. noctilio is of little concern perhaps due to interactions with a well-developed community of pine-inhabiting insects and their associated microorganisms. If such interactions occur, they may limit the woodwasp’s impact in its newly introduced range in North America. My research addresses two broad questions: 1) Does S. noctilio share its habitat with other insects and if so, with whom? 2) Is there evidence that co-habitants affect S. noctilio, and if so how might such interactions occur?
Field studies undertaken to describe the woodwasp’s host-attack ecology in Pinus sylvestris showed S. noctilio activity occurred between mid-July and late August, and other phloem- and woodborers sometimes entered the tree after the woodwasp. Tree mortality occurred from two weeks to several months after initial woodwasp symptoms. Suppressed or intermediate trees, those with ≤ 25% residual foliage, or those with stem injury or previous woodwasp symptoms were most likely to have symptoms of woodwasp attack.
A second field study conducted to identify associated insect species in S. noctilio-infested Pinus sp. showed the wasp was sometimes found alone, but usually shared the tree with other phloem- or woodboring insects, most commonly the curculionids Tomicus piniperda, Pissodes nemorensis and Ips grandicollis and the cerambycid Monochamus carolinensis. I found no indication that wasps were absent when beetles were present, but there was evidence that woodwasps were less abundant, but larger, when beetles were present.
Experiments showed that indirect interactions can occur between the two insect groups via fungal associates of one or both. In the laboratory, the woodwasp symbiont was outcompeted by two beetle-associated fungi, Leptographium wingfieldii and Ophiostoma minus, over a range of temperatures. Under field conditions the woodwasp was able to detect and avoid ovipositing in P. sylvestris inoculated with L. wingfieldii, but its oviposition was unaffected by O. minus.
My results show that insects co-habiting pine with S. noctilio have potential to exert a measure of biological control on the woodwasp and may help to limit its impact in North America.
| Identifer | oai:union.ndltd.org:TORONTO/oai:tspace.library.utoronto.ca:1807/29855 |
| Date | 31 August 2011 |
| Creators | Ryan, Kathleen |
| Contributors | Smith, Sandy, de Groot, Peter |
| Source Sets | University of Toronto |
| Language | en_ca |
| Detected Language | English |
| Type | Thesis |
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