TOXICITY OF ACORUS-CALAMUS RHIZOME POWDER FROM EASTERN NEPAL TO SITOPHILUS-GRANARIUS (L.) AND SITOPHILUS-ORYZAE (L.) (COLEOPTERA, CURCULIONIDAE)

Powders prepared from sweetflag Acorus calamus rhizomes collected at b oth high (1700 m) and low (900 m) altitude in Eastern Nepal were admir ed with wheat at concentrations in the range 0.05-2% w/w and the wheat infested with Sitophilus oryzae or S. granarius adults. Following a 7 day incubation, the mortality of both species was significantly lower at 20 degrees C than at 30 degrees C, and the material collected from high altitude was slightly less toxic than that from low altitude. Th e moisture content of the wheat (14 or 17%) and the part of the rhizom e used to prepare the powder (young or mature growth) had no apparent effect on the toxicity of the preparation. Sitophilus granarius (L.) a dults were more tolerant of the material than S. oryzae (L.), while th e converse was true for larvae developing in treated grain. An admixtu re rate of approximately 2% why admired rhizome powder was required to give complete kill of adults of both species following 7 days exposur e at 20 degrees C, while a concentration of 1% w/w either prevented th e emergence of adults or killed them rapidly following emergence when wheat containing eggs of either species was incubated for 7-8 weeks at 30 degrees C. The beta-asarone content of the rhizome powders was det ermined by GC-MS as 6.4 and 4.7% w/w (mature section of rhizomes colle cted at high and low altitudes, respectively) and 3.6 and 4.0% w/w (yo ung sections of rhizomes collected at high and low altitudes, respecti vely). It is anticipated that, under field conditions and in the tempe rature range 20-30 degrees C, the initial residue of approximately 130 0 mg/kg beta-asarone required to disinfest wheat containing these weev il species would decline rapidly due to evaporation. (C) 1997 Elsevier Science Ltd.