MITSUO KUWADA and TAKESHI HORIE: Effects on silkworm larvae attractiveness of mulberry leaves grown at different fertilizer application rates The objectives of this paper were to clarify the effects of chemical fertilizer application rates on mulberry leaves' attractiveness to silkworm larvae and to identify substances associated with this attractiveness. In the first experiment, mulberry (cv. Kairyonezumigaeshi)leaves from fertilized (30, 20, and 20 kg/10a in N, P2O5 and K2O, respectively) and

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... unfertilized for more than 3 years were oppositely placed at a 20 cm distance, and in between them 6 silkworm larvae of the 3rd to 5th instars were released to observe to which leaves they were attracted. The experiments were repeated for more than 2 times for each spring and late-autumn seasons for two years. The unfertilized leaves attracted more silkworm than the fertilized leaves by 6.6 and 52 times in the spring and late-autumn seasons, respectively. In the second experiment, silkworm attracting tests similar to that of the first experiment were conducted for the leaves from pot-grown mulberries with no chemical fertilizer (NF), no nitrogen (NO), standard nitrogen (N2; 2.0 g N/pot) and half the standard nitrogen (N1) applications at 2 g 1(20 and 1.5 g P2O5 per pot applications. The percentage of silkworm larvae attracted to NF, NO, N1, N2 leaves were 63, 24, 7 and 7%, respectively. The measurements of leaves by the GC/MS method indicated that the NF, NO and N1 leaves contained phenetyl alcohol by 9, 4 and 2 times more than the N2 leaves, respectively, which agreed with the silkworm's attractiveness. The above results suggest that leaves from unfertilized and no N application mulberry plants are more favored by silkworm larvae, and that phenetyl alcohol is a possible attractant to respond to fertilizer application rates.