The trade-off between immunity and product quality of Opisthoplatia orientalis (Blattodea: Blaberidae) under low temperatures

Abstract

Opisthoplatia orientalis Burmeister is a traditional medicinal insect in China that is mass-produced by entrepreneur farmers. However, low temperatures pose a serious threat to the survival and quality of this insect, causing economic losses to the farmers. This study aimed to test the hypothesis that low temperatures induce a trade-off between immunity and physical condition of O. orientalis. The phenoloxidase activity and hemocyte concentration of O. orientalis under 25°C and 5°C were measured by micro-determination and haemocytometre, respectively. The immunocompetence of the insect was also evaluated by inoculating it with Metarhizium anisopliae M11, an entomopathogenic fungus. The physical factors (protein content, fatty acid content and body weight) of O. orientalis were determined accordingly. The results showed that phenoloxidase activity and hemocyte concentration increased from 9.21 mOD/min and 122.30 hemocyte/ml to 3.64 mOD/min and 55.70 hemocyte/ml when temperature down-regulated from 25 to 5°C. However, the insects at 5°C had higher protein and fatty acid content, but lower body weight, than those at 25°C. Moreover, there was a significant negative correlation between immunity and protein or fatty acid content, indicating a trade-off between immunity and physical condition in O. orientalis under low temperatures. This study provides useful insights for improving the efficiency of insect breeding and enhancing the quality of this medicinal insect.