Comparative efficiency of two models of co2 traps in the collection of free-living stages of ixodides

Abstract

Traps using carbon dioxide (CO2) as a chemical attractant are known to be effective when capturing nymphs and adults of some free-living tick species such as Amblyomma cajennense and Amblyomma parvum. Despite the fact that the main source of CO2 is dry ice, the chemical trap which uses 20 % lactic acid (C3H6O3) and calcium carbonate (CaCO3) has been tested as an alternative source of CO2 whenever it is difficult to obtain dry ice. The objective of this paper was to test and compare the efficiency of these two models of traps during the study of population dynamics of A. cajennense and Amblyomma dubitatum in Coronel Pacheco, Minas Gerais, Brazil. Within the period comprising May 2006 to April 2008, eight CO2 traps, of which four were dry ice and four chemical, were put in the pasture every 14 days at preestablished areas over a 1.0-m2 white cotton flannel cloth with a capture dispositive which constituted of double-sided adhesive tapes fixed onto the four corners of the flannels. On every collection day, a cotton flannel without any chemical attractant was placed in the same area of the pasture to become an instrument to control the traps' capture efficiency. After 1 h, the white flannels were collected and placed in plastic bags for later identification and counting of the ticks. A total of 2,133 nymphs of Amblyomma sp., 328 adults of A. cajennense, and 292 adults of A. dubitatum were collected. Out of this total, the dry ice traps captured 1,087 nymphs (51 %), 188 A. cajennense (58.2 %), and 151 A. dubitatum (53 %), while the chemical traps captured 1,016 nymphs (47.6 %), 133 A. cajennense (41 %), and 133 A. dubitatum (46.5 %); 30 nymphs (1.4 %), 7 A. cajennense (0.8 %), and 8 A. dubitatum (0.5 %) were found on the control flannel. The capture potentials of ticks, nymphs, and adults, by the two models of traps tested, were statistically similar (p > 0.05). These results confirm the efficiency of the chemical trap enabling its use in areas of either difficult access or too distant from a dry ice supplier as is the case of forest areas where studies about ixodological fauna are generally carried out.