Identification and Biocontrol of Mindarus japonicus Takahashi, a New Pest of Abies koreana E.H.Wilson Using Bacillus velezensis CE 100

Abstract

Subalpine conifers such as Abies koreana E.H.Wilson (Korean fir) play a significant ecological role but are increasingly endangered due to the effects of climate change, including the high prevalence of insect pests. This study identified for the first time, a notorious aphid pest on newly developed needles and twigs of A. koreana, causing leaf curling, clustering, and stunted growth. The pest was identified as Mindarus japonicus Takahashi based on the morphological features and molecular analysis of mitochondrial barcode region. Due to restrictions on the use of chemical pesticides in forest environments, this study investigated the aphicidal effectiveness of Bacillus velezensis CE 100 as a prospective biocontrol strategy against M. japonicus. During growth, B. velezensis CE 100 produced cuticle-degrading enzymes: lipase, protease, and chitinase in the bacterial broth culture to a peak activity of 148.74, 45.12, and 77.08 units/mL, respectively. Treatment with the bacterial broth of B. velezensis CE 100 caused 75.00% mortality after 48 h. The crude enzyme fraction showed specific enzyme activity of 9398.66, 716.21, and 508.00 units/mg protein for lipase, protease, and chitinase, respectively, and caused 87.50% aphid mortality. Ultrastructural analysis using scanning and transmission electron microscopy revealed that both treatments caused extensive damage to the epicuticle, including cracking and pore formation, collapsed, and disorientation of the internal cuticle layers. The findings demonstrate the prospect of applying B. velezensis CE 100 as an eco-friendly strategy in the management of M. japonicus, a newly identified pest of A. koreana, to enhance the conservation of subalpine conifers.