Identification of Differentially Expressed Genes In Deltamethrin-Resistant Culex pipiens quinquefasciatus

Binding characteristics of pheromone-binding protein 1 in Glyphodes pyloalis to organophosphorus insecticides: Insights from computational and experimental approaches

Glyphodes pyloalis (Lepidoptera: Pyralidae) is one of the major pests in mulberry production in China, which has developed resistance to various insecticides. Chemoreception is one of the most crucial physiological tactics in insects, playing a pivotal role in recognizing chemical stimuli in the environment, including noxious stimuli such as insecticides. Herein, we obtained recombinant pheromone-binding protein 1 (GpylPBP1) that exhibited antennae-biased expression in G. pyloalis. Ligand-binding assays indicated that GpylPBP1 had the binding affinities to two organophosphorus insecticides, with a higher binding affinity to chlorpyrifos than to phoxim. Computational simulations showed that a mass of nonpolar amino acid residues formed the binding pocket of GpylPBP1 and contributed to the hydrophobic interactions in the bindings of GpylPBP1 to both insecticides. Furthermore, the binding affinities of three GpylPBP1 mutants (F12A, I52A, and F118A) to both insecticides were all significantly reduced compared to those of the GpylPBP1-wild type, suggesting that Phe12, Ile52, and Phe118 residues were crucial binding sites and played crucial roles in the bindings of GpylPBP1 to both insecticides. Our findings can be instrumental in elucidating the effects of insecticides on olfactory recognition in moths and facilitating the development of novel pest management strategies using PBPs as targets based on insect olfaction.

Clock genes regulate mating activity rhythms in the vector mosquitoes, Aedes albopictus and Culex quinquefasciatus

BACKGROUND

Endogenous circadian rhythms result from genetically-encoded molecular clocks, whose components and downstream output factors cooperate to generate cyclic changes in activity. Mating is an important activity of mosquitoes, however, the key aspects of mating rhythm patterns and their regulatory mechanisms in two vector mosquito species, Aedes albopictus and Culex quinquefasciatus, remain unclear.

METHODOLOGY/PRINCIPAL FINDINGS

We determined and compared the diel mating activity rhythms of these two mosquito species and discovered that Ae. albopictus had mating peaks in the light/dark transition periods (ZT0-3 and ZT9-12), while Cx. quinquefasciatus only had a mating peak at ZT12-15. Knockouts of the clock (clk) orthologous genes (Aalclk and Cxqclk) resulted in phase delay or phase reversal of the mating peaks in Ae. albopictus and Cx. quinquefasciatus, respectively. In addition, the temporal expression pattern of the desaturase orthologous genes, desat1, in both mosquito species was also different in respective wild-type strains and showed phase changes similar to the mating rhythms in clk mutant strains. Inhibition of desat1 expression resulted in decreased mating activity in male mosquitoes of both species but not females. In addition, desat1 regulated cuticular hydrocarbons' synthesis in both species. Silencing desat1 in male Ae. albopictus resulted in decreases of nonadecane and tricosane, which promoted mating, with concomitant increases of heptacosane, which inhibited mating. Silencing desat1 in male Cx. quinquefasciatus also resulted in decreases of tricosane, which promoted mating.

CONCLUSIONS/SIGNIFICANCE

These results suggest that Aalclk and Cxqclk have significant roles in the mating activity rhythms in both Ae. albopictus and Cx. quinquefasciatus by regulating the temporal expression of the desat1 gene under LD cycles, which affects sex pheromone synthesis and mating. This work provides insights into the molecular regulatory mechanism of distinct mating rhythm of Ae. albopictus and Cx. quinquefasciatus and may provide a basis for the control of these two important vector mosquitoes.

Odorant Binding Protein C17 Contributes to the Response to Artemisia vulgaris Oil in Tribolium castaneum

The red flour beetle, Tribolium castaneum (T. castaneum), generates great financial losses to the grain storage and food processing industries. Previous studies have shown that essential oil (EO) from Artemisia vulgaris (A. vulgaris) has strong contact toxicity to larvae of the beetle, and odorant-binding proteins (OBPs) contribute to the defense of larvae against A. vulgaris. However, the functions of OBPs in insects defending against plant oil is still not clear. Here, expression of one OBP gene, TcOBPC17, was significantly induced 12–72 h after EO exposure. Furthermore, compared to the control group, RNA interference (RNAi) against TcOBPC17 resulted in a higher mortality rate after EO treatment, which suggests that TcOBPC17 involves in the defense against EO and induces a declining sensitivity to EO. In addition, the tissue expression profile analysis revealed that the expression of TcOBPC17 was more abundant in the metabolic detoxification organs of the head, fat body, epidermis, and hemolymph than in other larval tissue. The expression profile of developmental stages showed that TcOBPC17 had a higher level in early and late adult stages than in other developmental stages. Taken together, these results suggest that TcOBPC17 could participate in the sequestration process of exogenous toxicants in T. castaneum larvae.

Deltamethrin interacts with Culex quinquefasciatus odorant-binding protein: a novel potential resistance mechanism

BACKGROUND

Odorant-binding proteins (OBPs) play important roles in many physiological processes of mosquitoes. Previous high-throughput sequencing studies have revealed that some OBPs of Culex quinquefasciatus might be involved in the development of resistance to insecticides.

METHODS

Based on the results of sequencing analyses, the OBP28 gene was selected for evaluation in this study. Three laboratory strains of Cx. quinquefasciatus [susceptible strain (SS), deltamethrin-resistant strain 1 (HN) and deltamethrin-resistant strain 2 (RR)] were first examined by using the Centers for Disease Control and Prevention bottle bioassay, after which the expression level of the OBP28 gene in the susceptible and deltamethrin-resistant strains was determined by real-time quantitative polymerase chain reaction. The OBP28 gene in deltamethrin-resistant strain RR was silenced using RNA interference technology. The expression level of OBP28 and the resistance level were tested in the silenced strain and control strain after microinjection of double-stranded RNA for a 48-h interference period. Four field-collected strains (henceforth 'field strains') of Cx. quinquefasciatus were also examined for their resistance to deltamethrin and levels of OBP28 expression. Finally, a correlation analysis between deltamethrin resistance and gene expression was carried out for all seven strains, i.e. the four field strains and the three laboratory strains.

RESULTS

In the bioassay, the mortality of SS, HN and RR was 100%, 21.33% and 1.67%, respectively. The relative expression levels of OBP28 in strains HN and RR were 6.30- and 6.86-fold higher, respectively, than that of strain SS. After silencing of the OBP28 gene, the mortality of strain RR was 72.20% and that of the control strain 26.32%. The mortality of strain RR increased significantly after interference compared to that of the control strain. There was a negative correlation between OBP28 gene expression and mortality in adult mosquitoes after exposure to deltamethrin.

CONCLUSIONS

To our knowledge, this study shows for the first time a correlation between the expression of a gene coding for OBP and insecticide resistance in mosquitoes. The potential resistance mechanism that was elucidated provides a new target gene for the surveillance of resistance in mosquitoes.

Odorant-Binding Proteins Contribute to the Defense of the Red Flour Beetle, Tribolium castaneum, Against Essential Oil of Artemisia vulgaris

The function of odorant-binding proteins (OBPs) in insect chemodetection has been extensively studied. However, the role of OBPs in the defense of insects against exogenous toxic substances remains elusive. The red flour beetle, Tribolium castaneum, a major pest of stored grains, causes serious economic losses for the agricultural grain and food processing industries. Here, biochemical analysis showed that essential oil (EO) from Artemisia vulgaris, a traditional Chinese medicine, has a strong contact killing effect against larvae of the red flour beetle. Furthermore, one OBP gene, TcOBPC11, was significantly induced after exposure to EO. RNA interference (RNAi) against TcOBPC11 led to higher mortality compared with the controls after EO treatment, suggesting that this OBP gene is associated with defense of the beetle against EO and leads to a decrease in sensitivity to the EO. Tissue expression profiling showed that expression of TcOBPC11 was higher in the fat body, Malpighian tubule, and hemolymph than in other larval tissues, and was mainly expressed in epidermis, fat body, and antennae from the early adult. The developmental expression profile revealed that expression of TcOBPC11 was higher in late larval stages and adult stages than in other developmental stages. These data indicate that TcOBPC11 may be involved in sequestration of exogenous toxicants in the larvae of T. castaneum. Our results provide a theoretical basis for the degradation mechanism of exogenous toxicants and identify potential novel targets for controlling the beetle.