Novel Methods of Hematophagous Arthropod Control


Ticks are important vectors of human and animal diseases. One protective measure against ticks is the use of personal arthropod repellents. Here, the history and efficacy of tick repellents, discovery of new repellents, and areas in need of attention such as assay methodology, repellent formulation, and the lack of information about the physiology of repellency are reviewed. Studies were conducted to examine the efficacy of the repellent BioUD with the active ingredient 7.75% 2-undecanone, originally derived from wild tomato plants. BioUD was compared with 7 and 15% deet using arm-in-cage studies against the mosquitoes Aedes aegypti and Ae. albopictus. No differences were found in mean repellency over 6 h after application between BioUD versus 7 and 15% deet for Ae albopictus. For Ae. aegypti, no differences were found over the same time period for 7% deet. Compared to 15% deet, BioUD was less repellent over the 6-h test period. Human subject field trials were conducted in North Carolina and Ontario comparing the repellency of BioUD to products containing 25 and 30% deet. BioUD provided the same repellency or was more efficacious than 25 and 30% deet, respectively. Repellent efficacy of BioUD and 98.1% deet against ticks was examined in the laboratory using a choice test between repellent-treated and control filter paper surfaces for Amblyomma americanum, Dermacentor variabilis and Ixodes scapularis. BioUD provided greater repellency against A. americanum and I. scapularis than deet. No difference was found between BioUD and deet against D. variabilis. In head-to-head assays between BioUD and deet, undiluted and 50% dilutions of BioUD were more repellent than undiluted deet against all three species. A 25% dilution of BioUD was more repellent than deet against A. americanum while no differences were found between a 25% dilution of BioUD and deet against D. variabilis and I. scapularis. Based on regression analysis, the concentration of BioUD required for equivalent repellency to 98.1% deet was 39.5% for D. variabilis and 29.7% for I. scapularis. A log-probit model could not be constructed for A. americanum from the dosages tested. Repellency of BioUD was compared to five repellents against A. americanum and D. variabilis in two-choice bioassays on treated versus untreated cotton cheesecloth. Overall mean percentage repellency against both species was greatest for and did not differ significantly between BioUD and products containing 98.1% deet, 19.6% IR3535, and 30% oil of lemon eucalyptus. Products containing 5 and 15% Picaridin and 0.5% permethrin were also repellent compared to untreated controls but to a lesser degree than BioUD. The four most active repellents were directly compared in head-to-head bioassays. BioUD provided significantly greater overall mean percentage repellency than IR3535 for A. americanum and D. variabilis. BioUD was significantly more repellent than oil of lemon eucalyptus for A. americanum but did not differ significantly in repellency against D. variabilis. No statistically significant difference in overall mean percentage repellency was found between BioUD and deet for A. americanum or D. variabilis. Laboratory trials were also conducted to determine the repellent activity of BioUD against D. variabilis on human skin. BioUD repelled ticks at least 2.5 h after application to human skin. Characterization of the expressed genes in the tick central nervous system could lead to a greater understanding of the control of development and reproduction at the molecular level. A transcriptome to the female D. variabilis synganglion identified 21,119 unique putative gene sequences, of which 7,379 had significant matches to the GenBank nonredundant database. Microarray analysis comparing synganglia from unfed, partially fed, and mated replete females revealed that 121 of these genes were differentially regulated.



microarray, transcriptome, synganglia, ticks, BioUD, deet, repellents, mosquitoes