ORIGINAL PAPER In vitro efficacy of plant extracts and synthesized substances on Rhipicephalus (Boophilus) Microplus (Acari: Ixodidae) Ana Carolina de Souza Chagas & Luiz Daniel de Barros & Fernando Cotinguiba & Maysa Furlan & Rodrigo Giglioti & Márcia Cristina de Sena Oliveira & Humberto Ribeiro Bizzo Received: 30 April 2011 /Accepted: 6 June 2011 # Springer-Verlag 2011 Abstract Herbal drugs have been widely evaluated as an alternative method of parasite control, aiming to slow development of resistance and obtain low-cost biodegrad- able parasiticides. This study evaluated the in vitro efficacy on Rhipicephalus (Boophilus) microplus of extracts from Carapa guianensis seed oil, Cymbopogon martinii and Cymbopogon schoenanthus leaf essential oil, and Piper tuberculatum leaf crude extract and similar synthesized substances. In the immersion test, engorged females were evaluated in five dilutions ranging from 10% to 0.030625% concentration. In the larval test on impregnated filter paper, the concentration ranged from 10% to 0.02%. The treat- ments and controls were done in three replicates. Chemical analysis of the oils was performed by gas chromatography. The main compounds were oleic acid (46.8%) for C. guianensis and geraniol for C. martinii (81.4%), and C. schoenanthus (62.5%). The isolated and synthesized sub- stances showed no significant effect on larvae and adult. C. martinii and P . tuberculatum showed the best efficacy on the engorged females. The LC 50 and LC 90 were 2.93% and 6.66% and 3.76% and 25.03%, respectively. In the larval test, the LC 50 and LC 90 obtained for C. martinii, P . tuberculatum, and C. schoenanthus were 0.47% and 0.63%, 0.41% and 0.79%, 0.57% and 0.96%, respectively. The fact that geraniol is present in greater quantities in C. martinii explains its higher activity in relation to C. shoenanthus. It is necessary to validate the in vivo use of safe and effective phytoparasiticidal substances. Efforts should be focused on developing formulations that enhance the efficacy in vivo and lengthen the residual period. Introduction Rhipicephalus (Boophilus) microplus (Canestrini 1887) is commonly known as cattle tick because of its specificity for this host, although it can occasionally parasitize other species such as sheep, horses, buffalos, and dogs (Serra-Freire and Mello 2006). It is found in tropical and subtropical latitudes between 32° N and 32° S, in Asia, Australia, Africa, North and South America (Kessler and Schenck 1998). In Brazil, 80% of cattle herds are infected with this tick, causing economic losses estimated at 2 billion dollars a year. The injury caused to animals involves weight loss, decreased milk production, blood spoliation and hide damage, besides transmission of pathogens, especially those related to tick fever (Anaplasma marginale, Babesia bovis, and Babesia bigemina). Ticks also cause indirect losses from the costs for their control, involving the purchase of drugs and treatment equipment, beyond additional labor (Grisi et al. 2002; Leal et al. 2003). To reduce these losses, producers mainly use commercial acaricides, but the indiscriminate use of chemicals without adequate technical support leads to the development of A. C. de Souza Chagas (*) : M. C. de Sena Oliveira Embrapa Pecuária Sudeste, São Carlos, São Paulo, Brazil e-mail: carolina@cppse.embrapa.br L. D. de Barros : R. Giglioti Universidade Estadual Paulista Júlio de Mesquita Filho, Jaboticabal, São Paulo, Brazil F. Cotinguiba : M. Furlan Universidade Estadual Paulista Júlio de Mesquita Filho, Araraquara, São Paulo, Brazil H. R. Bizzo Embrapa Agroindústria de Alimentos, Rio de Janeiro, Rio de Janeiro, Brazil Parasitol Res DOI 10.1007/s00436-011-2488-z