First Evidence of the Implication of Cuticular Based Mechanisms in Aedes Aegypti Populations Resistant To Pyrethroids and DDT in Cameroon

Pyrethroid resistance is now expanding in the two main arboviruses vectors Aedes aegypti and Aedes albopictus from Cameroon. Although recent studies suggested the implication of target site (kdr) resistance and overexpression of detoxification enzymes as key mechanisms, the implication of additional mechanisms such as cuticular resistance has not been investigated. The present study assesses the possible implication of cuticle in Aedes species resistance to pyrethroids. High cuticular hydrocarbon (CHC) content was detected in Ae. aegypti populations from Douala and Yaoundé. The difference (38% increase) between the Douala and susceptible populations was found to be statistically significant.The study confirms the implication of cuticular-based mechanisms in resistant to pyrethroids and DDT Aedes aegypti mosquitoes from Cameroon.

Hormetic response and transcriptome profiling reveal the mechanism underlying metabolic and cuticular resistance to host-specific terpenoid defences in an emerging insect pest, Pagiophloeus tsushimanus (Coleoptera: Curculionidae)

The resistance mechanisms evolved by insects to overcome host-plant allelochemicals are a key consideration in pest management. Camphor oil (EO) and its main component (i.e., D-camphor) form a specific terpenoid-defensive system in camphor trees, Cinnamomum camphora. However, an emerging insect pest, Pagiophloeus tsushimanus, has recently caused serious damage to this intractable plant species and is largely elusive. Here, we used feeding bioassays and RNA-seq to investigate the mechanism underlying the resistance of the beetle to host-specific terpenoid defences. First, a hormetic response in both larval weight and developmental time, which is a highly generalized dose-response phenomenon in toxicology but occurs infrequently in the context of insect-plant interactions, was observed in terpenoid-feeding individuals. Then, comparative transcriptome analysis between terpenoid-feeding and control groups indicated that both CYP450-mediated metabolic resistance and CP-mediated cuticular resistance were jointly employed to cope with terpenoid-induced stress. In addition, a small portion of genes involved in the glucose transport pathway were upregulated at the low D-camphor dose, suggesting that an extra intake of glucose used for larval growth may contribute to a hormetic response. These findings suggested that the dual terpenoid resistance mechanisms in this specialist are an essential precondition for the hormetic response in larval growth, ultimately contributing to the widespread successful colonization of host camphor trees. Overall, our study will open new avenues for understanding insect-plant coevolutionary adaptation and developing durable pest control strategies.

Transcription factor FTZ-F1 regulates mosquito cuticular protein CPLCG5 conferring resistance to pyrethroids in Culex pipiens pallens

Background Culex pipiens pallens poses a serious threat to human health because of its widespread distribution, high carrier capacity for several arboviruses, frequent human-biting, and growth in urban environments. Pyrethroid insecticides have been mainly used to control adult Cx. pipiens pallens during outbreaks of mosquito-borne diseases. Unfortunately, mosquitoes have developed resistance, rendering the insecticides ineffective. Cuticular resistance is the primary mechanism of pyrethroid resistance. Previously, we revealed that cuticular protein of low complexity CPLCG5 is a major cuticular protein associated with deltamethrin resistance in Cx. pipiens pallens, which is enriched in the cuticle of mosquitoes’ legs and participates in pyrethroid resistance by forming a rigid matrix. However, the regulatory mechanisms of its transcription remain unknown. Results First, qRT-PCR analysis revealed that the expression of FTZ-F1 (encoding Fushi tarazu-Factor 1) was ~ 1.8-fold higher in the deltamethrin-resistant (DR) than deltamethrin-susceptible (DS) strains at 24 h post-eclosion (PE) and ~ 2.2-fold higher in the DR strain than in the DS strain at 48 h PE. CPLCG5 and FTZ-F1 were co-expressed in the legs, indicating that they might play an essential role in the legs. Dual luciferase reporter assays and EMSA (electrophoretic mobility shift experiments) revealed that FTZ-F1 regulates the transcription of CPLCG5 by binding to the FTZ-F1 response element (− 870/− 864). Lastly, knockdown of FTZ-F1 not only affected CPLCG5 expression but also altered the cuticle thickness and structure of the legs, increasing the susceptibility of the mosquitoes to deltamethrin in vivo. Conclusions The results revealed that FTZ-F1 regulates the expression of CPLCG5 by binding to the CPLCG5 promoter region, altering cuticle thickness and structure, and increasing the susceptibility of mosquitoes to deltamethrin in vivo. This study revealed part of the mechanism of cuticular resistance, providing a deeper understanding of insecticide resistance.

Needle browning and death in Pinus pumila in the alpine region of central Japan were not related to mechanical damage of cuticle and cuticle thickness

The browning and death of needles of evergreen conifers in alpine regions occur mainly in early spring at the point where the shoot protrudes from the snowpack. They are thought to be caused by excessive transpiration due to mechanical damage to the cuticle or to a thinner cuticle. However, there are a few studies that do not necessarily agree with this idea. We assessed needle browning and death in Pinus pumila (Pallas) Regel. in the alpine region of Japan in relation to mechanical damage to the cuticle, cuticular resistance, and cuticle thickness. Mechanical damage was not observed on needle cuticles of Pinus pumila browning in a natural environment. The color of needles with artificially abraded cuticles changed from green to brown in the abraded part. However, the brown color at the abraded part differed from the brown of a browning needle in its natural environment. There was no correlation between cuticular resistance and cuticle thickness. Needle browning and death in P. pumila were not related to mechanical damage of the cuticle or to cuticle thickness but might be due to changes in the quality and structure of the cuticle and other stresses.

Review and parameterisation of bi-directional ammonia exchange between vegetation and the atmosphere

Current deposition schemes used in atmospheric chemical transport models do not generally account for bi-directional exchange of ammonia (NH3). Bi-directional exchange schemes, which have so far been applied at the plot scale, can be included in transport models, but need to be parameterised with appropriate values of the ground layer compensation point (χg), stomatal compensation point (χs) and cuticular resistance (Rw). We review existing measurements of χg, χs as well as Rw and compile a comprehensive dataset from which we then propose generalised parameterisations. χs is related to Γs, the non-dimensional ratio of [NH4+]apo and [H+]apo in the apoplast, through the temperature dependence of the combined Henry and dissociation equilibrium. The meta-analysis suggests that the nitrogen (N) input is the main driver of the apoplastic and bulk leaf concentrations of ammonium (NH4 apo