Abstract
ABSTRACTTrehalose plays an important role in energy storage, metabolism, and protection from extreme environmental conditions in insects. Trehalose is the main blood sugar in insects, and it can be rapidly used as an energy source in times of need. To elucidate the mechanisms of the starvation response, we observed the effects of starvation on trehalose and glycogen, trehalase activity, and the relative gene expression of genes in the trehalose and glycogen metabolic pathways in the invasive beetle Harmonia axyridis. Our results show that trehalose levels and the activities of two types of trehalases decreased significantly in the first 8 h of starvation, while the relative expression of HaTreh1-1 increased. While trehalose remained nearly constant at a relatively high level from 8 to 24 h, glycogen levels decreased significantly from 8 h to 24 h of starvation. Likewise, glycogen phosphorylase (HaGP) expression was significantly higher at 12 to 24 h starvation than the first 8 h, while the expression of glycogen synthase (HaGS) was relatively stable. Furthermore, trehalose decreased significantly from 24 h starvation to 72 h starvation, while trehalase activities and the relative expression of some HaTreh genes generally increased toward the end of the starvation period. The expression of trehalose-6-phosphate synthase (HaTPS) increased significantly, supporting the increase in trehalose synthesis. These results show that trehalose plays a key role in the energy provided during the starvation process through the molecular and biochemical regulation of trehalose and glycogen metabolism.
Highlights
The beetle Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) is native to Asia but has been intentionally introduced to many countries as a biological control agent of pest insects (Roy et al, 2016)
The results showed that the highest level of trehalose content observed [98.21±11.31 mg trehalose/g protein] was at 0 h starvation (F7, 16=22.74, P
The results show that soluble trehalase decreased significantly from 28.06±3.79 mg trehalose/g protein/min at 0 h to 7.41±0.889 mg trehalose/g protein/ min at 8 h, and leveled off at approximately 5.51±0.21 mg trehalose/g protein/min from 8 h to 24 h, followed by a significant increase to 17.26±6.54 mg trehalose/g protein/min at 48 h starvation and 17.76± 1.05 mg trehalose/g protein/min at 72 h starvation (F7, 16=15.92, P
Summary
The beetle Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) is native to Asia but has been intentionally introduced to many countries as a biological control agent of pest insects (Roy et al, 2016). In addition to dramatically increased numbers in countries where it was introduced, H. axyridis has spread to many countries where it was not intentionally released Is H. axyridis notoriously invasive in Europe (Adriaens et al, 2008; Brown et al, 2008a,b), it has been reported that the global spread of H. axyridis has been a rapid process (Brown et al, 2011) This beetle is considered to be an important natural enemy of insect pests (Zappalà et al, 2013; Mirande et al, 2015), and is a focus of pest control strategies in both agriculture and forestry in Asian countries, including China (Tang et al, 2014). The hardiness of H. axyridis in relation to cold is an important characteristic and has been widely studied with respect to biological control applications and aspects of invasiveness (Bazzocchi et al, 2004; Berkvens et al, 2010; Pervez and Omkar, 2006; van Lenteren et al, 2008)
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