关键词: 粉蚧, 外来入侵物种, 猎物选择, 猎物转换, 捕食者-猎物互作, 密度依赖

Abstract: 【Aim】 The alien invasive species as prey may influence the foraging and predation behaviors of native generalist predators. This study aims to clarify the foraging and predation behaviors of the harlequin ladybird (Harmonia axyridis) on the alien cotton mealybug (Phenacoccus solenopsis) co-existing with a native bean aphid (Megoura japonica). 【Methods】 Two feeding treatments were previously applied to H. axyridis, in which H. axyridis ladybirds were fed with P. solenopsis and M. japonica, respectively, for more than three generations before the experiment and thus referred to as mealybug-fed and aphid-fed ladybirds, respectively. Vicia faba seedlings were provided as substrates, on which one prey combination patch on a leaf was set up and exposed to one individual of the 4th instar larva of H. axyridis that had been starved for 24 h, and the patch consisted of both the 3rd instar nymphs of P. solenopsis and the 3- or 4-day-old nymphs of M. japonica with mealybugs accounting for 5.6%-83.3% in total 20-30 individuals (specific numbers were determined at random). The ladybird larva was thereafter followed for 2 h to record its first attack of prey and the proportions of consumed mealybugs in the total number of prey, searching time in the total time, and prey-handling time in the total searching time. Regression models were applied to determine the probability of the first attack on mealybugs and other observed variables as a function of previously fed prey species and the proportion of available mealybugs in the patch. 【Results】 The 4th instar larva of H. axyridis increased the probability of making its first attack on mealybugs with the proportion of available mealybugs, increased by 77.2% for each 10% increase in the proportion of available mealybugs; however, this probability was not influenced by the species of previously fed prey. The relationship between the proportion of mealybugs in the total prey consumed by H. axyridis and the proportion of available mealybugs depended on the species of previously fed prey: the proportion of consumed mealybugs increased by 137% for the ladybird that was previously fed with mealybugs while by 60% as fed with aphids with each 10% increase in the proportion of available mealybugs. The proportion of searching time in the total foraging time of H. axyridis was influenced by the proportion of available mealybugs but not by the species of previously fed prey, being increased by 13% with each 10% increase in the proportion of available mealybugs and slightly reduced by 7% for the ladybird previously fed with mealybugs as opposed to that with aphids. The proportion of mealybughandling time among the total foraging time of H. axyridis was influenced by the proportion of available mealybugs but not by the species of previously fed prey, being increased by 41% for each 10% increase in the proportion of available mealybugs. 【Conclusion】 The results of this study suggest that H. axyridis may exercise a prey frequency-dependent predation on P. solenopsis coexisting with native aphids in a patch, and such dependence may become stronger if it has the experience of predation on the mealybug.

Key words: Phenacoccus solenopsis, alien invasive species, prey selection, prey switching, predator-prey interaction, density dependence