TOXICITY OF DIFLUBENZURON IN LARVAE OF GYPSY-MOTH (LEPIDOPTERA, LYMANTRIIDAE) - EFFECTS OF HOST-PLANT

Larvae of gypsy moth, Lymantria dispar (L.), reared on Douglas-fir, Ps eudotsuga menziesii (Mirb.) Franco, were significantly more tolerant o f both topically and orally administered diflubenzuron than were those raised on white alder (Alnus rhombifolia Nutt.). Topical administrati on resulted in an LD50 of 8.96 mug/g larva for larvae reared on Dougla s-fir and 3.58 mug/g larva for larvae reared on alder. The LC50s obtai ned with orally administered diflubenzuron were 0.38 ppm for larvae re ared on Douglas-fir and 0.07 ppm for larvae reared on alder. Topically treated females reared on either host and orally treated females rear ed on alder required significantly longer to pupate than did controls, but developmental periods of males reared on alder and both sexes rea red on Douglas-fir were unaffected by oral treatment. Pupal weights we re not affected by treatment in either sex, whether larvae were reared on Douglas-fir or alder.