A new insight into Cd exposure-induced hemocyte reduction in Lymantria dispar larvae: Involvement of the ROS-ATF6-ER stress-apoptosis pathway

Hemocytes are important targets for heavy metal-induced immunotoxicity in insects. This study aimed to investigate the mechanism by which cadmium (Cd) exposure affects the hemocyte count in Lymantria dispar larvae. The results showed that the number of larval hemocytes was significantly decreased under Cd exposure, accompanied by a significant increase in the apoptosis rate and the expression of Caspase-3. The endoplasmic reticulum (ER) of hemocytes in the Cd-treated group showed irregular swelling. Expression levels of ER stress indicator genes (CHOP, Bip1, Bip2, Bip3, and Bip4) were significantly higher in the Cd-treated group. Among the three pathways that potentially mediate ER stress, only the key genes in the ATF6 pathway (ATF6, S1P-1, S1P-2, and WFS1) exhibited differential responses to Cd exposure. Cd exposure significantly increased the levels of reactive oxygen species (ROS) and the expression of oxidative stress-related genes (CNCC, P38, and ATF2) in hemocytes. Studies using inhibitors confirmed that apoptosis mediated the decrease in hemocyte count, ER stress mediated apoptosis, ATF6 pathway mediated ER stress, and ROS or oxidative stress mediated ER stress through the activation of the ATF6 pathway. Taken together, the ROS-ATF6-ER stress-apoptosis pathway is responsible for the reduction in the hemocyte count of Cd-treated L. dispar larvae.

CncC-Keap1-P450s pathway is involved in the detoxification of emamectin benzoate in the spongy moth Lymantria dispar

The detoxification of insecticides in insects is dependent on the expression and activity of multiple detoxification enzymes. As an important modulator of detoxification enzymes, the CncC-Keap1 pathway was involved in the detoxification of various pesticides. However, whether the CncC-Keap1 pathway is involved in the detoxification of emamectin benzoate (EMB) is unclear. In this study, we cloned the LdCncC and LdKeap1 from spongy moths (Lymantria dispar). Our results showed that EMB exposure induced oxidative stress, and activated the CncC-Keap1 pathway at mRNA and protein levels. Removing ROS by N-acetylcysteine remarkably decreased H2O2 levels and restored the expression of LdCncC and LdKeap1. The silencing LdCncC, not LdKeap1, by dsRNA significantly decreased the cytochrome P450 activities, and increased the sensitivity of larvae to EMB. Besides, the expression of CYP6B7v1, CYP321A7 and CYP4S4v1 were significantly decreased after silencing LdCncC. Notably, the knockdown of CYP6B7v1, CYP321A7 or CYP4S4v1 significantly increased the mortality induced by EMB exposure. Therefore, we proposed that activation of CncC-Keap1 pathway induced by ROS increased the detoxification of EMB in spongy moths by regulating the expression of CYP6B7v1, CYP321A7 and CYP4S4v1. Our study strengthened the understanding of the detoxification of EMB from the perspective of CncC-Keap1-P450s pathway.

Host-specific growth responses of Larix kaempferi and Quercus acutissima to Asian gypsy moth defoliation in central Korea

As the risk of gypsy moth outbreaks that have detrimental effects on forest ecosystem in the Northern Hemisphere increase due to climate change, a quantitative evaluation of the impact of gypsy moth defoliation is needed to support the adaptive forest management. To evaluate the host-specific impact of gypsy moth defoliation, radial growth and annual carbon accumulation were compared for one severely defoliated (Larix kaempferi (Lamb.) Carrière) and one moderate defoliated (Quercus acutissima Carruth.) host, in defoliated and non-defoliated site using tree-ring analysis. Finally, the resilience indices of radial growth variables were calculated to assess the ability of sampled trees to withstand defoliation. Gypsy moth defoliation mainly decreased latewood width and caused reduction in annual carbon absorption more than 40% for both tree species. However, L. kaempferi, showed the reduced growth until the year following defoliation, while Q. acutissima, showed no lagged growth depression and rapid growth recover. The findings show how each species reacts differently to gypsy moth defoliation and highlight the need of managing forests in a way that takes resilient tree species into account.

Effect of fluorescent brighteners on the insecticidal activity of Bacillus thuringiensis var. kurstaki and LdMNPV on Lymantria dispar asiatica in Korea

Stilbene-based fluorescent brighteners (FBs) have been demonstrated to improve the insecticidal activities of entomopathogenic viruses; however, there is limited information regarding their effect on entomopathogenic bacteria. We conducted this study to investigate the effect of two FBs (FB 28 and FB 71) on the insecticidal activities of Bacillus thuringiensis var. kurstaki (Btk) and Lymantria dispar multiple nuclear polyhedrosis virus (LdMNPV) on Lymantria dispar asiatica. FB 28 and Btk combination at low concentration (1.6 × 102  IU/mL) increased the mortality, whereas FB 71 and Btk combination at intermediate and high concentrations (1.6 × 103 and 1.6 × 104  IU/mL) slightly reduced the mortality compared with that with Btk alone. The lethal time was also shorter with combinations of Btk and FB 28 than with FB 71. Both FB 28 and FB 71 increased the mortality in combination with LdMNPV at all concentrations (3 × 102 , 3 × 104 , and 3 × 106  polyhedral occlusion bodies/mL compared with that with LdMNPV alone. Our results suggest that FBs improve the insecticidal activities of Btk and LdMNPV, and their activities depend on their interactions with the midgut structures of the host insect species.

Chromosome-level genome assembly of the Asian spongy moths Lymantria dispar asiatica

The Asian spongy moth, Lymantria dispar asiatica, is one of the most devastating forestry defoliators. The absence of a high-quality genome limited the understanding of its adaptive evolution. Here, we conducted the first chromosome-level genome assembly of L. dispar asiatica using PacBio HIFI long reads, Hi-C sequencing reads and transcriptomic data. The total assembly size is 997.59 Mb, containing 32 chromosomes with a GC content of 38.91% and a scaffold N50 length of 35.42 Mb. The BUSCO assessment indicated a completeness estimate of 99.4% for this assembly. A total of 19,532 protein-coding genes was predicted. Our study provides a valuable genomics resource for studying the mechanisms of adaptive evolution and facilitate an efficient control of L. dispar asiatica.