Thermal constant estimation in tropical horse tick, Anocentor nitens (Acari:Ixodidae)

Experience has demonstrated that the exclusive use of acaricides as a control method against cattle ticks causes several problems, and is not totally effective. Other methods need to be added in order to achieve better and more profitable control of these parasites. Groups of 12 to 15 engorged ticks, bred on bovines, were individually incubated at six temperatures (T = 24, 26, 28, 30, 32, and 34 degrees C) and four relatives humidities (RH = 100, 80, 75.5, and 70%), creating 24 variants. The onset of oviposition and eclosion (emergence of larvae from eggs) was observed in all ticks, and preeclosion times (PET) were determined. A linear regression equation for the velocity of development with temperature as a function of the inverse of PET was calculated for each RH value. For each RH the minimum thermal threshold (MTT) was obtained by extrapolation and the effective temperature summation (ETS) calculated from the equation (incubation temperature--MTT) x PET. The four MTT values obtained were not significantly different; the mean value of MTT was 15.25 degrees C. The thermal constants did not prove to be not statistically different over the range of RH values employed in the experiments, the mean being 354.04 degrees C-day.