Mushroom-like synnemata of the entomopathogenic fungi, Isaria cicadae Miq.（Ascomycota: Hypocreales）, appeared gregariously on the ground of a Fraxinus japonica plantation, Takizawa City, Iwate, Japan, situated 170-km from the known geographic range of the fungi. The synnemata that grew inside the emergence trap for collecting the defoliators in the plantation grew 1.5-times more prominently than those on the outside, which lead to the present discovery. The micro-climate inside the trap was 23.7% darker, 2.8°C milder in the daily temperature changes, and 4.7% moister than that on the outside, which would promote the growth in height. The synnemata emerged uniformly throughout the plantation at a density of 8.86, 4.57, and 1.44/m² in 2016, 2017, and 2020, respectively. A total of 125 specimens of the hosts dug out from the soil were all the last instar larvae of Meimuna opalifera（Walker）（Hemiptera: Cicadidae）. The number of cicadas killed by the fungi on the plantation of 389 m² was 3448, 1779, and 564 in 2016, 2017, and 2020, respectively. However, only 2, 5, and 6 cicadas survived in these respective years. The density increased and the catastrophic mortalities of the cicadas were found to be restricted to this plantation.

Dithiocarbamate fungicides, such as mancozeb and maneb, are sprayed on Satsuma mandarin trees 3 or 4 times during the summer to control major diseases, but laboratory experiments using these chemicals have shown negative effects on phytoseiid mites. Here we evaluated the effects of mancozeb and four alternative fungicides—kresoxim-methyl, dithianone, oxine-copper, and copper hydroxide with calcium carbonate—on the occurrences of phytoseiid mites and their prey Panonychus citri（McGregor）（Acari: Tetranychidae）in neonicotinoid-treated Satsuma mandarin fields. As expected from laboratory findings, mancozeb application reduced the overall population of phytoseiid mites, which was mainly composed of Amblyseius eharai Amitai and Swirski（Acari: Phytoseiidae）, and increased the P. citri density. In contrast, the four alternative fungicides did not adversely affect the phytoseiid mite population, and three of these treatments—kresoxim-methyl, dithianone, and oxine-copper—did not increase the P. citri density. From these results, we encourage careful selection of fungicides when the native natural enemy A. eharai is used for the control of P. citri.