Ecological aspects of four species of ticks found on cattle in Salta, northwest Argentina.

The seasonal activity of Amblyomma cajennense, Amblyomma neumanni, Amblyomma parvum and Boophilus microplus on cattle was studied in a ranch located in the northern part of the phytogeographical district of the Chaco Serrano where the habitat had suffered minimal human disturbance. The female ticks on one side of 10-25 cows were counted at intervals of 20-50 days from 29 October 1985 to 5 November 1986. The percentage of cattle parasitized with larvae and nymphs of Amblyomma was recorded, along with the proportion corresponding to the different species. Collection of ticks from the ground cover vegetation in areas with and without forest was performed using the dragging technique. B. microplus was found all year round; peaks of abundance were observed in May (55 females per cow/2) and November 1986 (71 females per cow/2). The peak in November was unexpected and possibly due to a higher stocking rate around watering places and poor nutrition at the end of the dry season. A. cajennense appears to produce a generation a year. Larvae were more abundant from June to August, nymphs from August to November and females from November (34 per cow/2) to January (15 per cow/2). A. neumanni showed a cycle corresponding to a generation every 3 years regulated via diapause that involves, at least, all the summer months. The peak of abundance for larvae, nymphs and females occurred in late autumn-early winter. The highest number of females (44 per cow/2) was recorded in June.(ABSTRACT TRUNCATED AT 250 WORDS)