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, Pseudotsuga menziesii (Mirb.) Franco, were significantly more tolerant of both topically and orally administered diflubenzuron than were those raised on white alder (Alnus rhombifolia Nutt.). Topical administration resulted in an LD50 of 8.96 mug/g larva for larvae reared on Douglas-fir and 3.58 mug/g larva for larvae reared on alder. The LC50s obtained with orally administered diflubenzuron were 0.38 ppm for larvae reared on Douglas-fir and 0.07 ppm for larvae reared on alder. Topically treated females reared on either host and orally treated females reared on alder required significantly longer to pupate than did controls, but developmental periods of males reared on alder and both sexes reared on Douglas-fir were unaffected by oral treatment. Pupal weights were not affected by treatment in either sex, whether larvae were reared on Douglas-fir or alder.