Interactions between Formosan Subterranean Termites, Brown Rot Fungus (Gloeophyllum trabeum) and Some of the Fungi Present on the Termite Integument and Gut
Although the brown rot fungus, Gloeophyllum trabeum (Pers.:Fr.) Murrill, has been shown to be attractive and beneficial to subterranean termites, including Coptotermes formosanus Shiraki, to date no research has been conducted to determine if the association is mutualistic. We first set out to determine if the fungus could be spread by termites. This would represent an obvious benefit to the fungus. We found that C. formosanus does not spread G. trabeum. Unexpectedly, Formosan subterranean termites were found to suppress the growth of G. trabeum. To further investigate this finding, Formosan subterranean termite workers were released into Petri dishes with wood chips inoculated with G. trabeum. To serve as controls, an equal number of Petri dishes received all components as above but without termites. Growth of G. trabeum was measured on the 6th day of incubation and a significant suppression of fungus growth was observed in treatments with termites. In follow up studies G. trabeum inoculated wood chips were placed on to potato dextrose yeast agar medium and measured for G. trabeum growth after 7 days. G. trabeum did not grow but, many green-spored fungi were predominant in all the cultures. We hypothesized that these green-spored fungi may be carried on or in the body of C. formosanus and were the cause of the observed G. trabeum suppression. Dual culture tests of fungi isolated from the external surface of Formosan subterranean termites showed that several isolates were parasites and/or antagonists and effectively controlled the growth of G. trabeum. These fungi included Aspergillus flavus Link, Trichoderma harzianum Rifai, Trichoderma virens (Miller et al.), Trichoderma asperellum Samuels, Lieckfeldt & Nirenberg and Trichoderma ghanense Y. Doi, Y. Abe & J. Sugiyama. In the intestinal tracts of C. formosanus a different complex of fungi were present, some of which were antagonistic to G. trabeum. Aspergillus flavus, Hypocrea virens Chavarri, Samuels and Steward, T. asperellum, along with Penicillium janthinellum Biourge and Cladosporium cladosporioides (Fres.) de Vries were the fungi isolated from the guts. A. flavus was commonly isolated from external surface and gut of laboratory maintained termite colonies when compared to freshly collected field termite colonies. When these fungi were tested against C. formosanus, only A. flavus was found to be toxic to termites. Our study is the first to show that fungi present on the termite exoskeleton control the growth of a competing cellulose consumer, G. trabeum.
Advisor:Michael Stout; Gregg Henderson; Roger Laine
School:Louisiana State University in Shreveport
School Location:USA - Louisiana
Source Type:Master's Thesis
Date of Publication:09/20/2006