The southern pine beetle (Dendroctonus frontalis) (SPB) is the most damaging beetle pest of pine trees in the southern United States, causing large losses in loblolly pine plantations and natural ecosystems. SPB is associated with three fungal species, two mutualistic and one antagonistic. Ceratocystiopsis ranaculosus and Entomocorticium sp. A, the mutualistic species, serve as a nutritional source for developing larvae, whereas the antagonistic one, Ophiostoma minus, competes for the substrate with SPB larvae, and is also antagonistic to the other two mutualistic fungi. While direct competition for space might be one of the reasons why O. minus hinders these two fungal species, other mechanisms might also be involved. We hypothesize that O. minus induces a defense response in the host plant that is more detrimental to the mutualistic fungi than to itself. In fact, the mutualistic species, unlike O. minus, are not pathogens and hence have not evolved to withstand tree defense responses. Objectives of this study are the following: (i) to determine which compounds are induced in loblolly pine after the inoculation of the three fungal species, and (ii) in vitro testing of the previously identified compounds to determine their toxicity against each of the fungal species. Results of this work will assist in elucidating the interactions within the complex SPB system, as well as clarifying what defensive chemical traits of loblolly pine are important in fungal arrest.