A β-carotene-amended artificial diet increases larval survival and be applicable in mass rearing of Harmonia axyridis

Abstract

Artificial diets that devoid of insect components have been widely developed for predatory insects, but often yield disappointing results. Carotenoids play vital roles in insects and generally must be acquired from diet, but their supplementation in insect artificial diets has been rarely concerned. Here, we tried to evaluate the function and application prospect of carotenoids in artificial diet of Harmonia axyridis. Firstly, the physical form of component pork liver in artificial diet was improved using fine powder to replace the homogenate, and the survival of infant larvae was greatly increased. Then, four β-carotene-amended artificial diets were developed (0, 0.3, 3 and 30 μg/g (β-carotene/pork liver powder), indicated as AD-A, AD-B, AD-C and AD-D respectively) to evaluate their feeding efficiency for H. axyridis, and the aphid Myzus persicae was used as control. The larval survival on AD-D was equal to that on aphids, and was significantly higher than those on other artificial diets. However, H. axyridis feeding on artificial diets, whichever of the concentration of β-carotene, had significantly longer pre-imaginal development time and obtained smaller newly emerged adults than those on M. persicae. Overall, AD-D showed to be the optimal diet. Finally, the performance of AD-D-fed H. axyridis was evaluated on the target pest M. persicae. Compared to aphid-fed lady beetles, the fourth instar larvae raised with AD-D had similar number of aphid consumption and both showed preference for non-parasitized aphid than newly parasitized by Aphidius gifuensis; the adults produced fewer eggs but had undifferentiated pre-ovipostion period and egg hatch rate.In conclusion, supplementation of β-carotene could increase the efficiency of artificial diet. On M. persicae, H. axyridis developed from AD-D had outstanding performance which was applicable for releasing in biological control. Our results highlight the importance of carotenoids in artificial diet and might provide a new approach for developing artificial diets.