In this paper, the results of the experiment concerning insect agent in carrying the spermatia of Gymnosporangium Haraeanum and fertilizing the fungus were reported. These can be summarized as follows:<br>1. The nectar, secreted from the pustules on pear leaves, contains reducing sugar, and is sweetish to the taste, but has no distinct odor.<br>2. Under field conditions, by preventing the free access of the insects to the pustules on pear leaves with cheesecloth covering, the formation of aecia was reduced to half, as compared to those infections which were not covered.<br>3. It was proved experimentally that the insects, Eristalis cerealis FABRICIUS, Musca domestica LINNAEUS, Calliphora erythrocephala MEIGEN and Iridomyrmcx itoi FOREL, mix the nectars of separate monosporidial pustules and thus cause the production of aecial stage of the fungus.<br>4. In the fields in the city of Hukuoka, the insects, mentioned below, have visited the pustules on pear leaves and brought about the spermatia from one pustule to another. They are Musca domestica LINNAEUS, Sarcophaga melanura MEIGEN, Calliphora erythroephala MEIGEN, Ophyra calcogaster WIEDEMANN, Chortophila cinerella FALLÉN, Eristalis cerealis FABRICIUS, Syrphus corolla FABRICIUS, S. ribesii LINNAEUS, S. baltcatus DE GEER, Formica fusca japonica MOTSCHULSKY, Paratrechina flavipes SMITH, Iridomyrmex itoi FOREL, Pristomyrmex japonicus FOREL, Lasius fuliginosus LATREILLE, Camponotus herculeanus japonicus MAYR, Bassus laetatorius FABRICIUS, Arge nigrinodosa MOTSCHULSKY, Rhaphidopalpa femoralis MOTSCHULSKY, and Anthrenus verbaci LINNAEUS. Among them flies visited the pustules most frequently and ants were second.<br>5. Duration of excretion of the nectar from sterile pustules was longer than that of fertilized ones.