Heavy metal pollution in freshwater ecosystems is a serious threat to aquatic organisms. Species of Megaloptera are important predators of aquatic invertebrates and have been widely used as bioindicators in assessing the quality of freshwater ecosystems. In this study, we determined the differential gene expression profile of Protohermes costalis (Walker) (Megaloptera: Corydalidae) in response to cadmium (Cd) exposure by using transcriptome analysis. A total of 60,627 unigenes were obtained in the transcriptomes of 150 mg/liter (PL), 1,000 mg/liter (PH) CdCl₂ treatment, and the no Cd control (PC). Differential expression gene (DEG) analysis by pairwise comparison identified 2,794 DEGs after filtering the noninsect genes and repetitive counts. 606 DEGs were shared in comparisons of PL versus PC and PH versus PC, with 165 DEGs consistently up-regulated and 441 down-regulated by both PL and PH. Six heat shock proteins (HSPs) in the HSP70 family were identified in P. costalis and PcosHSP68 was up-regulated by both PL and PH. Real-time quantitative polymerase chain reaction (RT-qPCR) confirmed that the expression levels of PcosHSP68 in PL and PH were higher than that of PC by 31 and 197%, respectively. These results showed that exposure to Cd altered the gene expression profiles of P. costalis and the transcriptome data presented in this study provide insight into future studying on molecular mechanisms of Cd toxicity to these insects.

Pesticides released into the environment are increasingly recognized as a global threat to freshwater ecosystems because of their adverse effects on non-target organisms, particularly aquatic insects and other arthropods. Superoxide dismutases (SODs) are important antioxidant enzymes that play a crucial role in protecting organisms from oxidative stress induced by harmful materials. In this study, we identified 2 cellular SODs (PxSOD1 and PxSOD2) in Protohermes xanthodes Navás (Megaloptera: Corydalidae), an freshwater predatory insect, and determined the oxidative stress induced in P. xanthodes larvae by sublethal exposure to chlorpyrifos (CPF). PxSOD1 and PxSOD2 are members of the cytoplasmic Cu/ZnSODs and mitochondrial MnSODs, respectively, and differ substantially in protein structure. Both PxSOD1 and PxSOD2 recombinant proteins demonstrated catalytic activity toward O2•− in the activity assays. After exposure to sublethal concentrations of CPF, malondialdehyde (MDA) content and SOD activities were increased in P. xanthodes larvae in a dose-dependent manner. PxSOD1 expression was decreased in the 0.42 and 4.2 μg/L CPF groups and increased in the 4.2 μg/L CPF group. PxSOD2 was upregulated by 0.42, 4.2, and 8.4 μg/L CPF treatments and the expression levels in the 4.2 and 8.4 μg/L CPF groups were significantly higher than that in the no CPF control. Our results suggest that sublethal concentrations of CPF can induce oxidative stress in P. xanthodes larvae, and the cellular SODs in P. xanthodes larvae may contribute to the protection against CPF-induced oxidative stress.

The courtship behavior of moths is closely related to the biosynthesis and release of sex pheromones. To understand the mechanisms of the reproductive behavior of the ghost moth Endoclita davidi, a host insect of Cordyceps xuefeng (Ophiocordyceps xuefengensis), this study examined the courtship behavior and the ultrastructure of the sex pheromone gland of E. davidi. Infrared photography was used to analyze the courtship behavior, while SEM, paraffin tissue sectioning, and TEM were employed to examine the sex pheromone glands on the hind tibia. The courtship behavior of E. davidi occurs during the scotophase, during which males vibrate their wings and unfold the hairpencils located on the hind tibiae to lure the female moths. The hairpencil’s surface features regular longitudinal ridges interspersed with multiple circular pits. Multiple small holes were evident on the slightly enlarged areas close to the ends of the hairpencils. These small holes, formed at the base of the circular pits, connect to the internal glandular duct within the hairpencil, which links to the tibia glandular canal. The epidermal layer of the hind tibiae contains numerous glandular canals and dense microvilli. The glandular cells, specialized from dermal cells, contain numerous mitochondria, rough endoplasmic reticulum, clear vesicles of varying sizes, and round lipid droplets. The sex pheromone glands of male E. davidi release pheromones through the hairpencils in the hind tibia. The courtship behavior and ultrastructure of the sex pheromone gland of the male E. davidi provide a basis for further understanding pheromone release and communication mechanisms.