Aspects of the life cycle of Amblyomma parvum (Acari: Ixodidae) under natural conditions.

Monthly samplings of the rodent Galea musteloides (Caviidae) were carried out from January 2005 to December 2006 in Quilino, Córdoba Province, Argentina, to determine the seasonal distribution of immature stages of Amblyomma parvum. In the same locality, cattle and goats were also monthly examined to asses the seasonality of the females of this species. Engorged ticks collected on their natural hosts were maintained in the laboratory at 25 degrees C and 83-86% relative humidity to study biological parameters, and groups of larvae and nymphs were also maintained at three different photoperiods [12h light (L)-12h dark (D), 14 L-10 D, and 10 L-14 D]. Larvae were found from late summer to early winter with the peak in autumn, nymphs were collected from early winter to early spring with the peak in middle winter, and females were detected on cattle and goats during spring and summer, with the peak in early and middle summer. The pre-moult-period of engorged immature ticks exposed at different photoperiods in the laboratory show no indication of morphogenetic diapause, being the maximum period 16.4 days for larvae and 21.8 days for nymphs. The difference in the mean engorgement weight of nymphs moulting to females (6.2mg+/-1.8) and to males (2.1mg+/-0.1) was statistically significant (P<0.01), but the difference in the pre-moult period of the nymphs moulting to females (20.1 days+/-2.0) and to males (18 days+/-2.0) was not significant (P>0.01). The average weight of females was 206.1mg+/-23.6, the mean number of eggs laid was 1500.4+/-298.2, the average of pre-oviposition period was 6.5 days+/-0.8, and the minimum incubation period of eggs was 33.1 days+/-1.2. There was not significant correlation between the weight of females and the pre-oviposition period and between weight of immature stages and pre-moult period, but there was significant positive correlation between weight of females and number of eggs laid. A. parvum has a life cycle under natural conditions with one generation per year characterized by distinct seasonal peaks of activity for each parasitic stage, where adults are abundant in the hottest months and the immature stages prevail in the dry season. Apparently, this life cycle is not regulated via diapause. Additional studies on the life cycle of A. parvum in nature should be performed in other countries to confirm the results obtained in Argentina.