Abstract
In the preceding paper, the authors isolated an ovicide and a larval growth inhibitor from the benzene soluble fraction of the methanol extract of leaves of Eupatorium japonicum and identified them as coumarin and a new guaianolide named euponin [3] respectively. More precise fractionation (Fig 1) guided by Drosophila test of the benz ene soluble fraction led to the isolation of two larval growth inhibitors A and B.
Larval growth inhibitor A [1] was identified as the oxid ation product of euponin [3] by manganese dioxide through the analysis of their mp, MS, UV, IR and 1H-NMR data. The structure of larval growth inhibitor B [2] was infered on the basis of spectral data and confirmed by chemical transformations shown in Fig.2.
Effects of [1], [2] and [3] on the development o f the fruitfly, Drosophila melanogaster were studied by administering them from the egg stage. The results are shown in Table 5. When the 1 st-instar larvae were introduced to the diet containing [2] they grew up normally to adults (Table 6). This indicates that like [3], [2] is not a feeding deterrent, and suggests that these sesquiterpene lactones inhibit the larval growth onyl when they are administered on the egg stage. The finding that a bioactive substance administered during embryonic stage has considerable influence on the growth or development in the succeeding stages would be important in understanding the defensive role of secondary substances of plants against herbivorous insects.
