The antifeedant activity of Wedelia chinensis Merr. against different instar larvae of rice leaffolder

Cnaphalocrocis medinalis Guenee

were determined by leaf dipping. The results showed that three parts of W. chinensis had strong antifeedant activity against the larvae of rice leaffolder

the antifeedant rate of the extracts from the stem

leaves or flowers extracts against the 2~5

nd

instar larvae of C. medinalis in 24 hours were about 80% (72.35%~91.11%)

not more than 60% (40.90%~56.95%)

100% respectively; All instar larvae had strong antifeedant activity on the methanol extracts from the stems

the antifeedant rate in 24 hours decreased as the increasing of the larval instar

for example

the antifeedant rate of the second instar larvae was up to（91.11 ± 3.85）%

and that of 5

th

insatr larvae was down to (72.35 ± 9.08)%; All instar larvae had weaker antifeedant activity on the methanol extracts from the leaves

the highest antifeedant rate in 24 hours was only (57.84 ± 3.68)%; All instar larvae were very sensitive to the methanol extracts from the flowers

the antifeedant rate in 24 hours reached 100%

no significantly differences among all instar larvae in the antifeedant rate in 24 hours or 48 hours ;the toxic effects of the extracts from stems or leaves on all instar larvae were not good

but the toxic effects of the extracts from flowers on younger larvae were better

for example

the mortality of the second instar larvae treated by the flower extracts in 48 hour was up to 72.7%

however the toxic effects on older larvae were dramatic declined

the mortality of the 4

th

or 5

th

instar larvae treated by the flower extracts in 48 hour was below 30%.