Facet-Dependent\nLethality of a Contact Insecticide\nCrystal

The\nactivity of crystalline contact insecticides relies on the\nextraction of surface molecules by insect tarsi upon contact. Most\ncrystals are inherently anisotropic, and surface molecules on symmetry\nindependent faces are expected to have different free energies. The\nfacet-dependent bioavailability and associated efficacy of insect\nlethality have not been investigated, however. We discriminate the\nbioactivity of various facets of single crystals of DDT (1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane),\na well-known contact insecticide. Our findings reveal facet-dependent\nlethality differences of nearly 75% among four crystallographically\nunique facets. Furthermore, computations reveal that the respective\nlethalities of the facets are strongly correlated with the detachment\nenergies of molecules from the crystal surfaces. This facet-dependent\nlethality suggests a pathway to enhance the efficacy of known contact\ninsecticides through crystal habit control.