Evidence of female sex pheromones and characterization of the cuticular lipids of unfed, adult male versus female blacklegged ticks, Ixodes scapularis
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Copulation in Ixodes scapularis involves physical contact between the male and female (on or off the host), male mounting of the female, insertion/maintenance of the male chelicerae in the female genital pore (initiates spermatophore production), and the transfer of the spermatophore by the male into the female genital pore. Bioassays determined that male mounting behavior/chelicerae insertion required direct contact with the female likely requiring non-volatile chemical cues with no evidence of a female volatile sex pheromone to attract males. Unfed virgin adult females and replete mated adult females elicited the highest rates of male chelicerae insertion with part fed virgin adult females exhibiting a much lower response. Whole body surface hexane extracts of unfed virgin adult females and males, separately analyzed by GC–MS, identified a number of novel tick surface associated compounds: fatty alcohols (1-hexadecanol and 1-heptanol), a fatty amide (erucylamid), aromatic hydrocarbons, a short chain alkene (1-heptene), and a carboxylic acid ester (5β-androstane). These compounds are discussed in terms of their potential role in female–male communication. The two most abundant fatty acid esters found were butyl palmitate and butyl stearate present in ratios that were sex specific. Only 6 n-saturated hydrocarbons were identified in I. scapularis ranging from 10 to 18 carbons.
KeywordsTicks Pheromones Chemical communication Reproduction Cuticle Cuticular lipids Blacklegged tick Ixodes scapularis Lyme disease
This work was funded by grants to RMR and DES from NIH (1R21AI096268) and NSF (IOS-0949194) and from support to RMR from the NCSU Ag. Research Station. ALC was also supported in part by a Graduate Student Teaching Assistantship from the Department of Entomology at North Carolina State University.
Compliance with ethical standards
Conflicts of interest
The authors have no conflicts of interest in the publication of the results reported in this paper.
Students conducting research on this project have received training in a Graduate School approved ethics course at NC State University, which complies to the NSF standards.
Human and animal rights
No human subjects were used in the research reported in this paper. All use of animals in this study was carried out in strict accordance with the recommendations in the Guide for the Care and Use of Laboratory Animals of the National Institutes of Health. The protocols were approved by the Old Dominion University Institutional Animal Care and Use Committee (#10-018 and #10-032) and are on file at the Office of Research, Old Dominion University, Norfolk, Virginia. Tranquilizers (Acepromazine) were administered to the animals prior to handling to minimize anxiety and/or discomfort. No animal work was conducted at NC State University.
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