Ophiostomatoid Fungal Infection and Insect Diversity in a Mature Loblolly Pine Stand
Type of DegreeMaster's Thesis
Forestry and Wildlife Science
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Root-feeding beetles and weevils are known vectors of ophiostomatoid fungi, such as Leptographium and Grosmannia, that have been associated with a phenomenon called Southern Pine Decline in the Southeastern United States. One of these fungi, species name Leptographium terebrantis, has a well-known effect on pine seedlings, but the effect on mature, field-grown trees and associated insect populations is still to be determined. This study examined changes in insect diversity one year pre- and post-inoculation of mature loblolly pine trees with varying levels of a L. terebrantis isolate, giving special attention to monitoring insects of concern. Three different insect traps of two types – pitfall and airborne – were used during the twenty-five month study. Insects were collected every two weeks, identified to family where possible, and further sorted to morphospecies. Of 9,748 insects collected, we identified 16 orders, 149 families, and a total of 676 morphospecies. Of these, less than ten individuals were each Hylastes, Hylobiini, and Ips species of concern. We collected over 60 individual ambrosia beetles in nine species. However, all but one had six or less individual beetles. Only one species, the invasive Xylosandrus germanus, had a total of 44 individuals. Ground-based pitfall traps were more efficient at capturing Hylobiini weevils, but airborne panel traps caught overwhelmingly more ambrosia beetles. Insect diversity did not vary with treatment, but instead showed seasonal variation between the two years. A drought that occurred at the end of the first year may be a possible explanation for this. Antifreeze-based pitfall traps were marginally significant between treatments for the year they were out. Additional monitoring may provide a greater understanding of inoculum load on insect diversity. Methods of ophiostomatoid fungal identification have initially relied on manual and molecular methods. These often require growing fungal cultures that can take weeks to develop. Other options, including using near-infrared light waves to size features on bark beetles, including fungal spores, have just become a potential avenue to investigate. Our study addressed the possibility of identifying fungal species with these light waves on the surface of a beetle. We used spores from three fungal species: Grosmannina alacris, Leptographium procerum, and a Graphium species. Hylastes salebrosus beetles were collected from neighboring wildlife areas, sterilized before use, and rolled in corresponding fungal cultures to mimic vectoring of spores. Prepared beetles were then transported to CytoViva, Inc., for imaging. To help identify regions of the beetle’s surface where spores could be found, we devised a code to be used with ImageJ and called it “FFT map” after basing it on the fast fourier transform algorithm. After consulting wavelengths of associate species, we could set thresholds to identify areas that match reflecting spores. Of 52 fungal spores identified and measured for size, we found an average mean spore size of 3.15 µm, 3 µm, and 2.31 µm for G. alacris, L. procerum, and the Graphium species, respectively. We showed that two of our three species can be identified with hyperspectral interferometry. Though our map eliminated much of the beetle’s surface that did not contain spores, narrowing our search scope and quickening identification, additional automation could provide a simple, optical tool for identifying spore loads on insects. This process was made more challenging by the presence of setae and other beetle surfaces that cause interference.