Date of Graduation

12-2012

Document Type

Thesis

Degree Name

Master of Science in Entomology (MS)

Degree Level

Graduate

Department

Entomology

Advisor

Fred M. Stephen

Committee Member

Terry Kirkpatrick

Second Committee Member

Don Steinkraus

Third Committee Member

Ashley Dowling

Abstract

Sirex (Hymenoptera: Siricidae) woodwasps develop within xylem of host conifers. Sirex females drill through the bark, phloem and into xylem tissues where they deposit eggs along with a symbiotic Amylostereum fungus. The presence of Amylostereum is necessary for successful development of Sirex immatures as the larvae are unable to derive adequate nutrition from xylem in the absence of the fungus. The Eurasian woodwasp, Sirex noctilio F., was discovered in northeastern North America in 2004. Sirex noctilio has caused significant economic damage in Pinus radiata D. Don plantations of the southern hemisphere, but is of little economic significance in its native range. It is unknown how S. noctilio will impact pine forests in the southeastern United States. The presence of associated subcortical insects in S. noctilio's native range and their absence in the southern hemisphere has led researchers to speculate that these associate species may inhibit S. noctilio population expansion. I investigated interactions between a native woodwasp, S. nigricornis F., and its associated subcortical insect-complex with the goal of understanding how woodwasp populations are impacted by these interactions. The objectives of my research were to: 1) identify the relative timing of host colonization between S. noctilio and its associated species; 2) investigate how tornado disturbance affects the relative abundance of S. nigricornis; and 3) determine if associated insects affect oviposition behavior and survival of Sirex. The most common insect inhabitants of downed pine trees are subcortical beetles (e.g. Cerambycidae and Scolytidae) which normally colonized host substrate before S. nigricornis. Sirex nigricornis abundance was similar at high and low levels of host material while more beetles were trapped in areas with more host material. Sirex nigricornis females drilled into host material with similar frequency regardless of the presence of associated beetles. There was evidence of less S. nigricornis oviposition on beetle-colonized as opposed to non-colonized bolts. Sirex nigricornis mortality estimates were higher on beetle-colonized than non-colonized bolts. These results suggest that Sirex are negatively affected by the presence of associated insects.

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