Strode, C. | bioRxiv Science

bioRxiv2022

Rapid evaporative ionisation mass spectrometry (REIMS): A potential and rapid tool for the identification of insecticide resistance in mosquito larvae.

Insecticide resistance is a significant challenge facing the successful control of mosquito vectors globally. Bioassays are currently the only method for phenotyping resistance. They require large numbers of mosquitoes for testing, the availability of a susceptible comparator strain and often insectary facilities. This study aimed to trial the novel use of rapid evaporative ionisation mass spectrometry (REIMS) for the identification of insecticide resistance in mosquitoes. No sample preparation is required for REIMS and analysis can be rapidly conducted within hours. Temephos resistant Aedes aegypti (Linnaeus) larvae from Cucuta, Colombia and temephos susceptible larvae from two origins (Bello, Colombia, and the lab reference strain New Orleans) were analysed using REIMS. We tested the ability of REIMS to differentiate three relevant variants: population source, lab versus field origin and response to insecticide. The classification of these data was undertaken using linear discriminant analysis (LDA) and random forest. Classification models built using REIMS data were able to differentiate between Ae. aegypti larvae from different populations with 82% ({+/-} 0.01) accuracy, between mosquitoes of field and lab origin with 89% ({+/-} 0.01) accuracy and between susceptible and resistant larvae with 85% ({+/-} 0.01) accuracy. LDA classifiers had higher efficiency than random forest with this data set. The high accuracy observed here identifies REIMS as a potential new tool for rapid identification of resistance in mosquitoes. We argue that REIMS and similar modern phenotyping alternatives should complement existing insecticide resistance management tools.

systems biology↗

bioRxiv2021

Expansive and diverse phenotypic landscape of field Aedes aegypti larvae with differential susceptibility to temephos: beyond metabolic detoxification

Arboviruses including dengue, Zika and chikungunya are amongst the most significant public health concerns worldwide and their control relies heavily on the use of insecticides to control the vector mosquito Aedes aegypti. The success of controlling these vector-pathogen systems is threatened by widespread insecticide resistance. The work presented here profiled the gene expression of the larvae from two field populations of Ae. aegypti with differential susceptibility to temephos. The contrasting phenotypes originated from two Colombian urban locations, Bello and Cucuta, that we have previously reported to have distinctive disease incidence, socioeconomics, and climate. The closeness of the geographical origin of the study populations was suspected to be highly influential in the profiling of the gene expression of resistance since the mosquitos resistance levels themselves are highly dependent upon environmental variables. We demonstrated that an exclusive field-to-lab (Ae. aegypti reference strain New Orleans) comparison generates an over estimation of differential gene expression (DGE) and that the inclusion of a geographically relevant field control, as used here, yields a more discrete, and likely, more specific set of genes. The composition of the obtained DGE profiles is varied, with commonly reported resistance associated genes such as detoxifying enzymes having only a small representation. We identify cuticle biosynthesis, ion exchange homeostasis, an extensive number of long non-coding RNAs, and chromatin modelling among the specifically and differentially expressed genes in field resistant Ae. aegypti larvae. It was also shown that temephos resistant larvae undertake further gene expression responses when temporarily exposed to this insecticide. The results from the sampling triangulation approach undertaken here contributes a discrete DGE profiling with reduced noise that permitted the observation of a greater gene diversity. This deeper gene granularity significantly increases the number of potential targets for the control of insecticide resistant mosquitoes and widens our knowledge base on the complex phenotypic network of the Ae. aegypti mosquito responses to insecticides. Author SummaryAedes aegypti mosquitoes are vectors for several significant human viruses including dengue, Zika and chikungunya. The lack of widely available vaccines and specific antiviral treatments for these viruses means that the principal method for reducing disease burden is through controlling the vector mosquitoes. Mosquito control relies heavily on the use of insecticides and successful vector control is threatened by widespread insecticide resistance in Ae. aegypti. Here, we examined changes in gene expression that occur in temephos resistant populations of Ae. aegypti from two field populations in Colombia. We compare gene expression in resistant larvae from Cucuta with susceptible larvae from Bello and a susceptible laboratory strain of Ae. aegypti (New Orleans). We also compare mosquitoes from Cucuta with and without temephos exposure. We report several differentially expressed genes beyond those usually reported in resistant mosquitoes. We also demonstrate the over estimation in differential gene expression that can occur when field resistant populations are compared against lab susceptible populations only. The identification of new mechanisms involved in the development of insecticide resistance is crucial to fully understanding how resistance occurs and how best it can be reduced.

genetics↗