Protein in mosquito antennae detects insecticide, triggering defense response

Greg Howard
8th October, 2025

Protein in mosquito antennae detects insecticide, triggering defense response

This magnified image, captured with a laser-scanning microscope, uses a glowing dye to reveal a surge of the AcSAP1 protein in a mosquito after insecticide exposure, visualizing its chemical alarm system in action.

Image adapted from: Saini et al / CC BY (Source)

Key Findings

  • In India, research on Anopheles culicifacies mosquitoes revealed that Sensory Appendage Protein 1 (AcSAP1) is highly expressed during the night, coinciding with peak host-seeking activity
  • Reducing AcSAP1 levels delayed mosquitoes’ attraction to hosts, indicating this protein plays a key role in finding blood meals
  • Mosquitoes can detect the common insecticide deltamethrin, and exposure to it significantly increased AcSAP1 expression in olfactory tissues, legs, wings, and surprisingly, the eyes
Mosquitoes pose a significant global health threat, primarily due to their ability to transmit deadly diseases like malaria[2]. Anopheles mosquitoes are particularly dangerous vectors, responsible for the vast majority of malaria cases. Controlling mosquito populations is therefore crucial, but their adaptability and complex behaviors present ongoing challenges. A key aspect of these behaviors is their ability to locate hosts and avoid insecticides. Recent research from ICMR-National Institute of Malaria Research, AcSIR, and ICMR-National Institute of Virology[1] sheds light on the molecular mechanisms underpinning both of these vital functions, focusing on a family of proteins called Sensory Appendage Proteins (SAPs). Mosquitoes rely heavily on their sense of smell – olfaction – to find hosts[2]. However, the process isn't simply about detecting odorants; it involves a complex interplay of proteins that capture, transport, and interpret these chemical signals. The study investigated six different SAP members in Anopheles culicifacies, identifying AcSAP1 and AcSAP2 as the most prominent, being highly expressed in both olfactory tissues and legs. This suggests a broad role in chemical sensing beyond just the antennae. The researchers found that the expression levels of AcSAP1, and to a lesser extent AcSAP2, fluctuate throughout the day, following a circadian rhythm. Importantly, peak expression correlated directly with the times when female mosquitoes are most actively seeking hosts – at night. Silencing the AcSAP1 gene (effectively reducing its activity) resulted in a noticeable delay in the mosquitoes’ attraction to hosts, strongly suggesting that AcSAP1 plays a critical role in this behavior. This aligns with broader understanding of host preference behaviors across the Culicidae family, where mosquitoes exhibit behavioral plasticity and can learn to associate cues with positive or negative experiences[3]. Beyond host-seeking, the study revealed a surprising connection between SAPs and insecticide resistance. Using computer modeling, the researchers predicted that AcSAP1 had a strong affinity for deltamethrin, a common synthetic pyrethroid insecticide. Further experiments confirmed that SAPs could indeed detect this toxic chemical cue. Bioassays, using the standard WHO tube test method, demonstrated that mosquitoes were able to sense the presence of deltamethrin and exhibited changes in gene expression within their olfactory organs, wings, and legs. This finding is particularly significant because it suggests mosquitoes aren’t simply passively exposed to insecticides; they actively sense them. The research team also observed a substantial increase in AcSAP1 expression in the eyes of mosquitoes exposed to deltamethrin. This is a novel observation, indicating that SAPs may integrate visual and chemosensory cues, potentially allowing mosquitoes to combine sight and smell to better avoid insecticides. The role of soluble proteins in detecting chemical signals is well-established[4]. Odorant-Binding Proteins (OBPs) and Chemosensory Proteins (CSPs) are known to bind semiochemicals and activate chemoreceptors. While OBPs are found in vertebrates and insects, CSPs are more limited in their distribution within the arthropod world. The study expands on this understanding by highlighting the previously unappreciated role of SAPs in this process. The findings of demonstrate the multifaceted nature of SAPs, functioning in both host-seeking and insecticide avoidance. This dual role has significant implications for developing new strategies to control mosquito populations. By understanding how mosquitoes detect and respond to insecticides at the molecular level, researchers can potentially develop methods to disrupt these sensory pathways, making mosquitoes more vulnerable to control efforts. The study also builds on the growing knowledge of odorant reception in insects, where ORs, ODEs, and OBPs all contribute to the sensitivity of the olfactory system[5].

GeneticsBiochemAnimal Science

References

Main Study

1) Sensory appendage protein triggers alarm to pyrethroid in Indian malarial vector Anopheles culicifacies

Published 7th October, 2025

https://doi.org/10.1371/journal.pone.0333483

Related Studies

2) Olfaction in Anopheles mosquitoes.

https://doi.org/10.1093/chemse/bjab021

3) Olfaction, experience and neural mechanisms underlying mosquito host preference.

https://doi.org/10.1242/jeb.157131

4) Soluble proteins of chemical communication: an overview across arthropods.

https://doi.org/10.3389/fphys.2014.00320

5) Odorant reception in insects: roles of receptors, binding proteins, and degrading enzymes.

https://doi.org/10.1146/annurev-ento-120811-153635


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