An investigation of the influence of Trichoderma virens (hypocreales: hypocreaceae) on reticulitermes virginicus (isoptera: rhinotermitidae) feeding, with an evaluation of the use of labral morphology for identification of reticulitermes from Texas

Abstract

Subterranean termites encounter numerous kinds of fungi during foraging and feeding activities. Nearly nine decades of research have exposed only a small fraction of the termitefungal interactions that exist in nature. The first portion of research presented here focused on how feeding behaviors of Reticulitermes virginicus (Banks) were affected by the fungus Trichoderma virens (Miller, Giddens & Foster) von Arx. Tests were performed with 'P' (GLT+) and 'Q'(GLT-) strains of T. virens. Both strains were applied to filter paper and wood disks cut from southern yellow pine and Sentricon® monitoring devices. The first bioassay assessed the termites' feeding responses to fungal extracts removed from liquid media on days 2 through 7, and again on day 15. Only the GLT+ extracts from days 6 and 7 inhibited termite feeding significantly from the controls (16% and 54% less area loss, respectively). Response to wood covered by live T. virens mycelia was tested in the second bioassay. No significant differences in termite consumption were seen between fungal strains, but both substantially reduced the area loss due to termite feeding of treated wood by an average of 35%. A vacuum impregnation system was used to inoculate wood disks with fungal homogenate in the third bioassay. The wood treated with either GLT+ or GLT- homogenates did not have significant differences in area loss due to termite feeding. Overall, these results reiterated the plasticity that exists with termitefungal relationships. The second research topic addressed the applicability of labrum-based identification techniques to Reticulitermes Holmgren in Texas. Soldier labral morphology of four species, R. flavipes (Kollar), R. hageni (Banks), R. tibialis Banks, and R. virginicus (Banks), was evaluated as a character to separate species. Length and width measurements of five soldier labra were taken from each of the eight collection sites. These results were then judged against molecular analysis of the mtDNA 16S rRNA gene. Findings showed that labral shape was an unreliable diagnostic characteristic when comparing all species. A combination of length and length-towidth ratio successfully segregated all four Reticulitermes species. Comparison of a morphology-based dendogram to the phylogenetic analysis revealed a shared pattern between phenotypic and genotypic variations.