Identification and biocontrol of Planococcus citri Risso (Hemiptera: Pseudococcidae), a new pest of licorice (Glycyrrhiza uralensis Fisch.) using cuticle-degrading enzymes of Bacillus velezensis CE 100

Licorice is a valuable medicinal and industrial crop, but is highly prone to pest damage, especially to polyphagous sap-sucking mealybugs (Hemiptera) insect pests. This study reports for the first the identification citrus mealybugs as insect pests of tremendous economic importance in licorice production. The insect pests collected were identified as Planococcus citri based on analysis of the morphological features and DNA barcode sequencing of mitochondrial Cytochrome Oxidase subunit I (COI) gene. Due to the hazardous effects of chemical insecticides, this study investigated the entomopathogenic potential Bacillus velezensis CE 100 against P. citri . The bacterium produced cuticle-degrading enzymes: lipase, chitinase and protease in a pattern corresponding with cell growth. The maximum lipase, chitinase and protease activity was 32.7 unit/mL, 96.5 unit/mL and 35.7 unit/mL, respectively, which corresponded to the highest cell growth of 25.6 × 10 7 colony-forming units, observed after 6 days of incubation. Treatment of P. citri with bacterial culture caused the hydrolysis of the cuticular wax layer, chitin laminae and structural proteins of P. citri , resulting in 80.0 % mortality within 6 h after treatment. The control and PB media treatment did not cause insect mortality. The scanning electron microscopy analysis of the treated insects revealed severe cuticle degradation, with deep cracks extending from the epicuticle to the procuticle, and the erosion of the wax layer and broken setae. This study identified P. citri as an insect pest of economic importance in licorice cultivation, for the first time in the world. It also demonstrates the biopesticides potential of B. velezensis CE 100 against P. citri, through the lipolytic, chitinolytic and proteolytic activities, which could enhance licorice production and quality.