Novel Approaches for control of Rhipicephalus (Boophilus) microplus

Abstract

We review recent progress for control of Rhipicephalus (Boophilus) microplus and R. (B.) annulatus. Outbreak infestations in the U.S. have reached alarming levels, due to increased populations of deer and other ungulates serving as alternative hosts. GIS mapping of infestations and deer habitat aids in utilizing methods and equipment designed for acaricide treatment of wild ungulates. Investigations include deer immunology, tick molecular genetics, acaricide resistance, and host-parasite interactions with deer or cattle, ticks, and pathogens. Acaricide resistance is widespread in Mexico and U.S. dipping vats depend on organophosphate (OP) inhibition of acetylcholinesterase (AChE). Three cDNAs putatively encoding acetylcholinesterases (AChE, E.C. 3.1.1.7) in R. (B.) microplus were expressed in the baculovirus system and exhibited Km values for acetylthiocholine of approx. 5, 50, or 90 µM, for rBmAChE1, rBmAChE2, and rBmAChE3, respectively. The rBmAChEs exhibited substrate preference for acetylthiocholine over butyrylthiocholine, and inhibition by eserine, paraoxon, and the AChE-specific inhibitor, BW284C51, confirming biochemical identification as AChEs. Expression of specific mutations from OP-resistant strains exhibited decreased sensitivity of rBmAChE1 and rBmAChE3 to OP inhibition. Each of the BmAChEs was expressed in synganglion as indicated by qRT-PCR. Multiple transcripts from individual ticks for each of the BmAChEs suggested alternative splicing or gene duplication. Quantitative real time PCR with genomic DNA supported the gene duplication hypothesis. Long dsRNA specific for BmAChE1, BmAChE2, and BmAChE3 was introduced by microinjection of unfed adult females and subsequent gene silencing was monitored by qRT-PCR and phenotypic effects. Specific physiological roles for BmAChE1, BmAChE2, and BmAChE3 remain to be elucidated.