Facet-Dependent Lethality of a Contact Insecticide Crystal

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