Feeding Behavior Analyses Reveal Nicotine Selectively Inhibits Sap Ingestion in Crapemyrtle Bark Scale (Acanthococcus lagerstroemiae), an Invasive Insect in the U.S.1

Crapemyrtle bark scale (CMBS; Acanthococcus lagerstroemiae Kuwana) is an invasive pest that primarily infests crapemyrtles ( Lagerstroemia spp.), along with a few other economically important plants in the U.S. Current management practices predominantly rely on neonicotinoid insecticides, which are structurally similar to nicotine and act as agonists at nicotinic acetylcholine receptors (nAChRs), disrupting insect nervous systems. However, the specific impact of these insecticides on CMBS herbivory performance remains unclear. This study combines pectinolytic enzyme detection and electrical penetration graph (EPG) techniques to investigate nicotine’s impact on CMBS salivation and ingestion. CMBS feeding assays were conducted on agarose plates containing various concentrations of pectin and nicotine. The enzyme detection experiments revealed CMBS salivation involves pectinesterase and polygalacturonase secretion, unaffected by nicotine. Consistent with these findings, EPG analysis confirmed salivation (waveform E1) occurred in nicotine-containing agarose. Unexpectedly, phloem sap ingestion (waveform E2) was absent when nicotine was added to the agarose, indicating selective inhibition of CMBS ingestion. These findings suggest nAChRs specifically regulate sap ingestion in CMBS, but not salivation and other feeding behaviors. These insights into nicotine and neonicotinoid insecticide action on CMBS could inform precision insecticide application in IPM programs, potentially enhancing control efficacy while reducing environmental impact. Species used in this study: Crapemyrtle bark scale ( Acanthococcus lagerstroemiae Kuwana). Chemicals used in this study: Agarose (Bio-Rad Laboratories), pectin (MP Biomedicals), nicotine (Sigma-Aldrich), sucrose (Domino Foods Inc.), glutamine (Thermo Fisher Scientific), ruthenium red (Enzo Life Sciences Inc.).