Abstract
Insect antennae are sophisticated sensory organs, usually covered with sensory structures responsible for the detection of relevant signals of different modalities coming from the environment. Despite the relevance of the head louse Pediculus humanus capitis as a human parasite, the role of its antennal sensory system in the highly dependent relation established with their hosts has been barely studied. In this work, we present a functional description of the antennae of these hematophagous insects by applying different approaches, including scanning electron microscopy (SEM), anterograde antennal fluorescent backfills, and behavioral experiments with intact or differentially antennectomized lice. Results constitute a first approach to identify and describe the head louse antennal sensilla and to determine the role of the antenna in host recognition. SEM images allowed us to identify a total of 35–40 sensilla belonging to seven different morphological types that according to their external architecture are candidates to bear mechano-, thermo-, hygro-, or chemo-receptor functions. The anterograde backfills revealed a direct neural pathway to the ipsilateral antennal lobe, which includes 8–10 glomerular-like diffuse structures. In the two-choice behavioral experiments, intact lice chose scalp chemicals and warm surfaces (i.e., 32°C) and avoided wet substrates. Behavioral preferences disappeared after ablation of the different flagellomeres of their antenna, allowing us to discuss about the location and function of the different identified sensilla. This is the first study that integrates morphological and behavioral aspects of the sensory machinery of head lice involved in host perception.
Highlights
Lice are members of the order Phthiraptera, which contains nearly 5,000 species of wingless insects
This work constitutes the first approach in the functional study of the role of the antennae of head lice in the detection and perception of environmental and/or host-related stimuli
As it happens with most animals that develop parasitic lifestyles, a relatively simple and closely host-tuned sensory system was found in P. humanus capitis
Summary
Lice are members of the order Phthiraptera, which contains nearly 5,000 species of wingless insects. The antennae of insects are the main peripheral sensory organs involved in the detection of external cues relevant to their lives, such as host odors, sexual pheromones, or refuge signals, among other. Along their surfaces, a variable number of sensilla adapted to assess different modalities of stimuli are present. The architecture of the sensory machinery of a given species is strongly tuned to maximize the communication with their environment, for what the functional study of their sensory structures gives the opportunity to speculate about the natural habits and preferences of the individuals
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