Integrated pest management (IPM) programmes often look for more specific ways to control pests. Biological control agents, such as the bacterium, Bacillus thuringiensis Berliner, and the fungus, Beauveria bassiana (Balsamo) Vuillemin, can control insects with minimal disturbance to the environment because of their host specificity and short half-lives. Often these agents alone cannot prevent yield loss or are too expensive. This study looked at the in vitro combination of these agents and photoactive dyes, especially phloxine B (red dye D&C 28), a Food and Drug Administration approved dye, with the intent to provide better insect control. Photoactive dyes are being tested for the control of many pest insects. Phloxine B and related xanthene dyes, eosin y, fluorescein and rose bengal inhibited the growth of both B. thuringiensis and B. bassiana . Phloxine B was the most inhibitory and fluorescein the least inhibitory dye for both microbes. The magnitude of inhibition increased with increasing concentration...