none Exposing third instar larvae of the wasp Bracon hebetor to triethylamine (TEA) results in malformed antennae in eclosing adults. The purpose of this research was to examine the effects of TEA at the cellular level. Rate of growth of treated antennal buds (56-76 h) and mean size (76-96 h) were significantly reduced. Internal pH was elevated for 5 h after TEA exposure. Cell size remained constant except in treated buds from 76 to 96 h, when diameter was reduced. The mean mitotic index (MI) was reduced and a normal peak at 72-76 h was eliminated. Cell death (DI) increased. Increased DI and decreased MI from 0 to 5 hours after exposure are attributed to increased pH. TEA can form reactive alkylating intermediates, and loss of the MI peak 12 h after exposure accompanied by increased DI may be due to alkylation. It is concluded that the reduced number of segments is due to an overall reduction in total number of cells. Abnormal segmentation may involve alkylation induced somatic mutations.