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    • It has been well established that triazophos is

    2021-09-07

    It has been well established that triazophos is a classic resurgence-inducing insecticide favoring N. lugens population growth by fecundity stimulation, with enhanced contents of soluble sugar, crude fat, soluble protein content of fat body and ovary, glucose and trehalase activity but reduced trehalose content (Bao et al., 2009; Cheng et al., 2014; Ge et al., 2010; Ge et al., 2011a; Ge et al., 2017; Yin et al., 2001; Yu et al., 2012; Zhao et al., 2011), which were also observed in this study, e.g., the contents of soluble protein (Fig. 3), glucose (Fig. 4B) and soluble sugar (Fig. 5) surged following TZP spray, whereas the trehalose content (Fig. 4A) decreased as compared to untreated control. Trehalose and glucose contents are relatively stable and are negatively correlated in the hemolymph (Tang et al., 2010). Additionally, TZP stimulated a dramatic rise of Hex-1 transcript level by circa 1.6–4.9 fold compared to untreated control at 1–3 DPE (Fig. 2), consistent with our proteomic analysis that Hex-1 in the fat body of N. lugens adult females exposed to TZP at 3 DPE was significantly up-regulated (data not shown). Hexokinase plays an essential role in glucose utilization by cells, considered part of the glucose transport system because it maintains a high transmembrane gradient for free glucose (Ritov and Kelley, 2001). The insect hexokinase as a switch mediating the glucose matabolism or energy production during cold hardening, diapause, oogenesis and embryogenesis (Fraga et al., 2013; Lin and Xu, 2016; Muise and Storey, 2001; Vital et al., 2010). Trehalose is the primary hemolymph sugar of larvae, pupae and adult insects, catabolized by trehalase into glucose in muscle triclabendazole and mitochondria via glycolysis (Becker et al., 1996; Tompson, 2003; Wan et al., 2013), and serve multiple physiological roles in insect feeding regulation, sugar absorption, energy supply, chitin biosynthesis, and egg-laying (Shi et al., 2016; Shi et al., 2017; Yasugi et al., 2017). We also found the reciprocal alternations in concentration of trehalose and glucose in TZP + dsHex-1 treated females (Fig. 4), in line with the phenomenon observed in Spodoptera exigua RNAi-mutants (Chen et al., 2010b). Our data did not show noticeable difference compared to the TZP and TZP + dsGFP treatments post Hex-1 silencing (Fig. 4A), indicating the dispensable role of Hex-1 in trehalose metabolism and trehalase activity. Sugar metabolism is a fundamental biological event that correlates with lipid and protein metabolism (Heming, 2003). Sugar, lipid, and protein are requisite nutrients for a cascade of reproductive activities such as vitellogenin synthesis, oogenesis, egg-laying and posterior embryonic development (Heming, 2003; Wang, 2004). The present findings showed that TZP + dsHex-1 silencing led to reduced soluble sugar content of ovaries relative to TZP-treated group at 3 DPE (Fig. 5A). Accordingly, the protein accumulation of fat bodies and ovaries was largely reduced after dsHex-1 diet (Fig. 4). Nonetheless, in the fat body, there was no significant difference between them (Fig. 5B). We previously revealed that silencing PYK led to reduced sugar content of ovarian and fecundity in N. lugens females (Ge et al., 2017). Hence, Hex may also modulate insect growth and reproduction with interplay of the PYK activity, e.g., the PYK and Hex patterns of activity are positively correlated throughout embryogenesis, exerting a connected action in mosquito embryo development (Vital et al., 2010). This may also corroborate, at least in part, the decreased female fecundity following Hex-1 depletion (Fig. 6A). Fraga et al. (Fraga et al., 2013) analyzed several parameters related to fecundity in T. castaneum females injected with HexA1 dsRNA. First, egg laying of the Tc-HexA1 dsRNA injected females was drastically reduced to only 10% of the control. Accordingly, Tc-HexA1 RNAi also gave rise to abnormal ovary morphology and stopped embryonic. Our present data showed that the number of eggs laid by dsHex-1-treated females dropped markedly by 46.4% relative to the dsGFP-treated ones (Fig. 6B), supporting a pivotal role of this gene in N. lugens fecundity via glucose metabolism regulation (Fig. 4B).