Isamu Nakayama

The induction of an imperfect supernumerary larval moult by juvenile hormone analogues in Manduca sexta

Abstract A newly synthesized juvenile hormone analogue 2-[1-methyl-2-(4-phenoxyphenoxy) ethoxylpyridine (S-31183) was found to be about 320 times more active than methoprene in the Manduca black larval assay. It was 32 times more active in causing a supernumerary larval moult when applied to day-2 5th-instar Manduca larvae. At low doses, the treated day-2 larvae wandered after a dose-dependent delay and subsequently formed pupae or larval-pupal intermediates. At higher doses, the larvae ecdysed to supernumerary larvae, all showing head-capsule slippage on day 7, irrespective of dose. Prothoracicotropic hormone (PTTH) release in the larvae given 0.01 μg S-31183 was delayed by 2 days, whereas that in larvae given 10 μg was delayed by about 3 days. In the latter case, the concentration of S-31183 in the haemolymph was still high at the time of PTTH release. These results suggest that prolonged exposure to an excess of juvenile hormone analogue can cause the brain to revert to a larval type of PTTH release.

Chemistry, Absolute Structures and Biological Aspect of the Most Active Isomers of Fenvalerate and Other Recent Pyrethroids

Abstract A number of stereoisomers of recent pyrethroids having an α-cyano-3-phenoxybenzyl moiety, i.e., fenvalerate, Cypermethrin and fenpropanate could be optionally synthesized from (+)- or (-)-3-phenoxy-mandelic acid and their absolute configurations were determined to be S to the benzylic asymmetric carbon atoms of the most active isomers. Toxicity ratios of the S-isomers to the R-isomers to house fly were generally larger than those to mosquito larva. Relative toxicity of fenvalerate As (S-acid, R-alcohol) to Aα was enhanced in accordance with exposure period of mosquito larva on dipping or tobacco cutworm on dry leaf residue. The late emerging toxicity of the As appears to result from in vivo activation as evidenced by biological assays involving hemolymph exchange and ligature on larvae of cabbage armyworm. Feeding deterrent nature of As was also discussed.