Cymbopogon citratus essential oil-induced ultrastructural & morphological changes in the midgut, cuticle & Haller’s organ of the tick Haemaphysalis longicornis (Acari: Ixodidae)

Haemaphysalis longicornis Neumann is a widely distributed species known for its capacity to transmit pathogens of medical, public health, and veterinary importance. Due to the environmental contamination caused by synthetic acaricides, plant essential oils have emerged as a promising alternative to manage tick infestation. This study evaluated the ultrastructural and morphological changes induced by Cymbopogon citratus Stapf (lemongrass) essential oil on adult H. longicornis tick. The concentrations of lemongrass essential oil used for the treatment via the adult immersion test were from 10 to 40 mg/mL. The most significant alterations 24 h post-exposure include the proliferation of lysosomes, reduction in the number of the rough endoplasmic reticulum, disorganization of the microvilli, the disappearance of lipid droplets and hematin granules, and cytoplasmic vacuolization (midgut); a thinner endocuticle and epicuticle, the deletion of the subdivision’s demarcation of the procuticle, disfiguration of the lamellar arrangements of the exocuticle, and cytoplasmic vacuolization of the epithelial cells (integument); cracks on the sensilla sockets, the detachment of one or two sensilla in the anterior pit, and partial disfiguration of part of the slit’s edge (Haller’s organ). These results reflect the acaricidal properties of the essential oil and could be an alternative means of tick control.

Neurophysiological and Behavioral Responses of Ixodes scapularis to host odors

ABSTRACTThe black-legged tick, Ixodes scapularis (Ixodida, Ixodidae), is one of the major disease vectors in the United States and due to multiple human impact factors, such as decreasing forest size for land development and climate change, it has expanded its range and established across the United States. Throughout the life cycle, ticks locate hosts for their blood-meal and although the ecologies of this tick and their hosts have been studied in depth, the sensory physiology behind host location largely remains unexplored. Here we report establishing a robust paradigm to isolate and identify odors from the natural milieu for I. scapularis. We performed single sensillum recordings (SSR) from the olfactory sensilla on the tick tarsi, and used the SSR system as biological detector to isolate natural compounds that elicited biological activity. The SSR setup was further tested in tandem with gas chromatography (GC) wherein the ticks’ olfactory sensillum activity served as a biological detector. The GC-SSR recordings from the wall pore sensilla in the Haller’s organ, and further identification of the biologically active deer glad constituents by GC-mass spectrometry (GC-MS) revealed methyl substituted phenols as strong chemostimuli, as compared to ethyl or propyl substitutions. Strongest electrophysiological activity was elicited by meta-cresol followed by para-cresol. Ethyl- and propylphenols with any of the three, ortho, meta or para substitutions, did not induce any neurophysiological activity. Finally, a behavioral analysis in a dual-choice olfactometer of all these phenols at three different doses revealed no significant behavioral response, except for p-cresol at −3 dilution Overall, this study contributes to our understanding of I. scapularis tick’s neurophysiology and provides a robust platform to isolate and identify natural attractants and repellents.

Ticks Home in on Body Heat: A New Understanding of Ectoparasite Host-Seeking and Repellent Action

Ticks are second only to mosquitoes as vectors of disease to humans and animals. Commercial insect repellents reduce or prevent potentially infectious tick bites by disrupting tick host-seeking behavior. Tick host-seeking is mainly ascribed to the Haller’s organ, a complex sensory structure on the tick foreleg that detects odors, carbon dioxide and heat 4–7, but these host-seeking mechanisms and the mechanism of their disruption by repellents are not well understood1,2. There is anecdotal evidence that ticks and other ectoparasites are attracted to heat, but it has never been demonstrated that they use radiant heat to detect hosts at a distance. In fact, previous attempts to do this have concluded that radiant heat is not used by ticks. Here we show that Amblyomma americanum and Dermacentor variabilis ticks can sense and home in on a human from several meters away, guided by radiant heat sensed by the Haller’s organ, and specifically the capsule, a covered spherical pit organ. An aperture in the capsule cover confers directionality and highly reflective interior surfaces of the capsule provide high sensitivity. Low concentrations of the insect repellents DEET, picaridin, 2-undecanone, citronellal and nootkatone eliminate thermotaxis without affecting olfactory-stimulated host-seeking behavior. Our results demonstrate that the tick Haller’s organ capsule is a radiant heat sensor used in host-finding and that repellents disrupt this sense at concentrations that do not disrupt olfaction. We anticipate this discovery to significantly aid insect repellent research and development of innovative strategies for protection against ectoparasites and vector-borne disease.