Abstract: The walnut aphid Chromaphis juglandicola (Kaltenbach) and the ladybeetle Hippodamia variegata (Goeze) are the main pest and dominant natural enemy in walnut orchards, respectively, in southern Xinjiang. In this study, the predatory function responses of the ladybeetle larvae (i.e., 1^st, 2^nd, 3^rd, and 4^th instars), female and male adults to the walnut aphid were investigated under laboratory conditions to assess the control potential of ladybeetle on walnut aphid. The results showed that the daily predation of ladybeetle larvae increased with the increasing larval instar. There were no significant differences between the daily predation amount of the ladybeetle female and male adults and the 4^th instar larvae under the condition of sufficient prey. When the prey density was low, however, the predatory ability of male adults was weaker. The predatory function responses of the 1^st to 4^th instar larvae, female and male adults of the ladybeetle to walnut aphid fitted well with the HollingⅡ model. The daily maximum predation of the 4^th instar larvae, female and male adults of the ladybeetle were much higher, 362.55, 297.19 and 377.24, respectively. This study suggests that ladybeetle is a promising biocontrol agent for walnut aphid and provides a scientific basis for the innovation of biological control technology of walnut aphid in southern Xinjiang.

Key words: walnut, aphid, ladybeetle, predatory function, biological control