Journal of Chemical Ecology, Vol. 28, No. 6, June 2002 (  C 2002) MICROBE INHIBITION BY Tribolium FLOUR BEETLES VARIES WITH BEETLE SPECIES, STRAIN, SEX, AND MICROBE GROUP HOLLY R. PRENDEVILLE and LORI STEVENS ∗ Department of Biology University of Vermont Burlington, Vermont 05405 (Received October 27, 2000; accepted February 12, 2002) Abstract—Tribolium flour beetles produce defensive compounds, including quinones, putatively aimed at deterring predators and inhibiting microbes. Here we examine how effective the defensive secretions of Tribolium confusum and T. castaneum are at inhibiting growth of various microbes and how this varies with species, geographic strain, and sex of the beetles. We explore differences at both the kingdom and species level of common flour microbes in their suscep- tibility to defensive compounds. Beetle species and strains vary in their ability to inhibit microbial growth. In addition, microbes vary in their sensitivity to the beetles’ defense compounds. The capability to suppress microbial growth is likely under stabilizing selection with optimum quinone production varying among populations and may be dependent on several environmental factors in- cluding temperature, humidity, and predators. Key Words—Tribolium confusum, Tribolium castaneum, microbe inhibtion, defense compounds, benzoquinones, Coleoptera, Tenebrionidae, beetle-microbe interactions. INTRODUCTION Flour beetles, genus Tribolium, are an agricultural pest commonly found in flour silos (Sokoloff, 1974). Their habitat is rich in microbial competitors such as bacte- ria, yeast, and fungi (Abramson et al., 1980; Borjesson et al., 1989; Yezerski et al., 2000). Presumably, to both inhibit microbe growth and deter predators (Dettner, 1993; Eisner et al., 1998), Tribolium produce and store defensive secretions in the form of a foul-smelling yellow fluid. The secretion of T. confusum consists of ∗ To whom correspondence should be addressed. E-mail: Lori.Stevens@uvm.edu 1183 0098-0331/02/0600-1183/0 C  2002 Plenum Publishing Corporation