Abstract: 【Aim】 This study aims to investigate intra-guild predation in aphidophagous predaceous insects and their control effects of the cotton aphid, Aphis gossypii, in Xinjiang, West China. 【Methods】 We conducted experiments in greenhouse to examine intraguild predation between the seven-spotted ladybird beetle, Coccinella septempunctata, and the green lacewing, Chrysopa pallens,by pairing them at different life stages on potted cotton seedlings in the absence of the prey aphid A. gossypii. In addition, we manipulated the two predators at larval and adult stages as pairing treatments to investigate their effects on A. gossypii density on potted cotton seedlings. 【Results】 In the absence of aphids, intraguild predation between two predators on cotton plants for 24 h showed the following results. In pairing treatments of two predators at comparable life stages, no intraguild predation occurred at adult stage; Ch. pallens survived more than C. septempunctata at the 1st larval instar; but C. septempunctata survived more than Ch. pallens at the last larval instars. In pairing treatments involved with eggs, the eggs were preyed on in all pairings except that C. septempunctata eggs were not preyed on by Ch. pallens adults. In pairing treatments including pupae, the pupae were not preyed on except that C. septempunctata pupae were preyed on by the last instar larvae ofCh. pallens. In pairing treatments between larvae and adults, C. septempunctata adults preyed on the 1st instar larvae of Ch. pallens, but not on the last instar larvae, and no intraguild predation occurred between Ch. pallens adults and the 1st instar or 4th instar larvae of C. septempunctata. In pairing treatments between different instar larvae, the last instar larvae of Ch. pallens preyed on the 1st instar larvae of C. septempunctata  but its 1st instar larvae was preyed on by the 4th instar larvae of C. septempunctata. Experiments to examine effects on A. gossypii density of the two predator pairings showed that whereas two predator larvae each alone decreased A. gossypii density, pairing treatments between Ch. pallens larvae and either C. septempunctata larvae or adults increased the aphid density, but pairing treatments between Ch. pallens  adults and either C. septempunctata larvae or adults caused the decrease of aphid density. 【Conclusion】 The results suggest that intraguild predation occurs between Ch. pallens and C. septempunctata, but their combined effects on aphid density may depend on Ch. pallens life stages involved, decreasing aphid density at the adult stage but increasing it at the larval stage.

Key words: Chrysopa pallens, Coccinella septempunctata, Aphis gossypii, predator-prey interaction, intra9guild predation, aphidophagous guilds