RATE OF PENETRATION AND RESIDUAL TOXICOKINETICS OF CARBARYL ON SOUTHERN PINE-BEETLE AND SPRUCE BEETLE (COLEOPTERA, SCOLYTIDAE)

Carbaryl-naphthyl-1-C-14 (1-naphthyl methylcarbamate) was topically ap plied in acetone to the prothorax of adult southern pine beetle, Dendr octonus frontalis Zimmermann, and spruce beetle, D. rufipennis (Kirby) . The rate of penetration of carbaryl into both species is best descri bed by an open, two-compartment model. The residual toxicokinetics mod el was established to compare tile biphasic rate of penetration of car baryl within these beetles. The estimated exoskeleton residual half-li fe of the slow phase (phase II) for the southern pine beetle was 90 h or 13 times that of tile spruce beetle (7 h). At 8 h, the accumulation of radioactivity internally for the spruce beetle was almost double t he amount for the southern pine beetle. The amount of methanolic unext ractable compounds was similar for both beetle species; unextractable compounds increased as incubation times increased. LD(50) levels for c arbaryl indicated that the spruce beetle was more susceptible to carba ryl than the southern pine beetle. This information and results of the toxicity tests suggest that decreased exoskeletal penetration may be one of the major mechanisms of southern pine beetle tolerance to carba ryl.