Functional Characterization of Sugar Receptors in <i>Agasicles hygrophila</i> Larvae

Sugar perception is critical for insect feeding and host selection. <i>Agasicles hygrophila</i> is a monophagous natural enemy insect introduced for controlling the invasive weed <i>Alternanthera philoxeroides</i>, yet its molecular mechanism underlying sugar sensing remains unclear. In this study, eight sugar compounds, including the most abundant sucrose, were identified in <i>A. philoxeroides</i>. Sucrose and fructose elicited attractive larval responses, whereas ribose, glucose, galactose, and mannose were repellent. Supplying sucrose or fructose mitigated the feeding inhibition of ribose, galactose, and mannose, but only fructose alleviated the aversive effect of glucose. Larval maxillary palpi contained taste sensilla responsive to sucrose and fructose. Silencing sugar receptor <i>AhygGR4</i> reduced larval feeding preferences for galactose, glucose, and mannose, while knockdown of <i>AhygGR5</i> abolished feeding selectivity for sucrose, ribose, and galactose. This study elucidates the molecular basis of sugar sensation in <i>A. hygrophila</i> and provides valuable insights for assessing the ecological safety of the introduced biological control agents.