VOLATILE INSECTICIDAL COMPOUNDS AND CHEMICAL VARIABILITY OF HAWAIIAN ZANTHOXYLUM (RUTACEAE) SPECIES

Hexane extracts from the leaves and pericarps of Zanthoxylum kauanse A. Gray, Z. dipetalum H. Mann, and Z. hawaiiense Hillebr. (all endemic to Hawaii) were tested for the presence of volatile insecticidal compounds using a fruit fly (Dacus dorsalis Hendel) egg bioassay. Leaves and pericarps from 80 trees were separately evaluated. Extracts of different individual plants differed in the level of toxicity. Twelve of the 47 Z. kauaense, one of the 12 Z. dipetalum, and none of the 21 Z. hawaiiense extracts prevented egg hatch. Fourteen compounds were identified including aliphatic alcohols and ketones, mono- and sesquiterpenoids, and phenylpropanoids. The presence of these compounds and their percentage composition varied at all levels of comparison: among species, among and within populations, and between tissues. Ovicidal extracts of Z. kauaense contained primarily 2-undecanone and 2-tridecanone. Anethole, estragole and caryophyllene were the dominant compounds of the single toxic extract of Z. dipetalum. This study demonstrates the importance of identifying intraspecific chemical variations in the evaluation of pesticidal activity of higher plants.