Abstract
Harmonia axyridis is an important predatory insect and widely used in biological control of agricultural and forestry pests. Trehalose is directly involved in the energy storage of the H. axyridis and in the oxidative function of various physiological activities thereby providing an energy source for its growth and development. The aim of this study was to explore the potential function of membrane-bound-like trehalase (TRE2-like) and membrane-bound trehalase (TRE2) genes in H. axyridis by RNAi. In addition, the activity of soluble and membrane-bound trehalase and the expression of genes related to trehalose and glycogen metabolism were determined in the larvae injected with dsTRE2-like or dsTRE2. The results showed that wing abnormality and mortality appeared in adults, as well as the activity of soluble trehalase and glycogen contents increased when interfering with TRE2-like gene. However, the activity of membrane-bound trehalase, trehalose and glucose contents in the larvae decreased. The expression of glycogen synthase (GS) and glycogen phosphorylase (GP) genes were decreased after RNAi in the ecdysis stage. The expression of chitin synthase gene A (CHSA), chitin synthase gene B (CHSB), and trehalose-6-phosphate synthase genes (TPS) were decreased significantly after RNAi, especially in the ecdysis stage. These results indicated that RNA interference is capable of knocking down gene expression of TRE2-like and TRE2, thereby disrupting trehalose metabolism which affects the chitin synthesis pathway in turn and also leads to developmental defects, such as wing deformities. This study could provide some theoretical guidance for the function of TRE2 gene in other insects.
Highlights
Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) is an important natural enemy of aphids and other pests (Nakayama et al, 2010; Wu et al, 2016; Adachi-Hagimori et al, 2019)
As TRE genes are known to be vital to insect growth and development (Zhang et al, 2019a), the present study investigated the functions of TRE2-like and TRE2 genes in H. axyridis using RNAi via the injection of double-stranded RNA corresponding to conserved TRE2-like and TRE2 genes structure
Similar findings were observed in the present study, wherein we found that silencing TRE2-like and TRE2 genes seriously affected the whole nymph development process of H. axyridis leading to the inhibition of the growth of nymph or pupa, especially in the molting stage and further phenotypic abnormality and decreased survival rates (Figure 1)
Summary
Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) is an important natural enemy of aphids and other pests (Nakayama et al, 2010; Wu et al, 2016; Adachi-Hagimori et al, 2019). The typical breeding strategy of H. axyridis involves multiple mating and increasing its population (Awad et al, 2017; Du et al, 2019). When faced with various natural threats, H. axyridis adapts with different strategies, such as gathering in winter to protect against cold (Durieux et al, 2015) and releasing harmful exudates to expel natural enemies (Schmidtberg et al, 2019). As an immediate source of energy, trehalose plays a vital role in the energy storage of the H. axyridis, in the oxidative function of various physiological activities, and in the growth and development Trehalose is widely distributed in different tissues and expressed in various development stages of insects, and mainly synthesized in the fat body of insects and released into the hemolymph rapidly (Thompson, 2003)
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