The life cycle of Amblyomma neumanniRibaga, 1902 (Acari: Ixodidae) in the

laboratory

D.H. Aguirrea*, A.E. Vinabala and A.A. Guglielmoneb

a Instituto Nacional de Tecnologıa Agropecuaria, Estacion Experimental Agropecuaria Salta,CC 228, CP 4400 Salta, Argentina

b Instituto Nacional de Tecnologıa Agropecuaria, Estacion Experimental Agropecuaria Rafaela,CC 22, CP 2300 Rafaela (Santa Fe), Argentina

(Received 12 June 1998; accepted 19 July 1998)

ABSTRACT

A colony of Amblyomma neumanni was started with engorged females collected from cattle in theprovince of Salta (24° 51'S, 65° 33'W), Argentina. The larvae and nymphs were fed on rabbitsand the adults on calves. The non-parasitic stages were maintained in darkness at 27 6 1°C and83–86% RH. The life cycle (pre-feeding period not tested) had a mean duration of 205.7 days.The mean time (days) for the different phases of the cycle were as follows: feeding of females8.8, pre-oviposition 23.8, oviposition 41.4, minimum egg incubation 76.1, feeding of larvae 8.5,pre-moult to nymphs 16.4, feeding of nymphs 7.9 and pre-moult to adults 22.8. The meanrecovery rates of larvae, nymphs and females were 83.8, 85.6 and 89.3%, respectively. Thenymphs moulting to females were heavier (8.1 6 2.34 mg) than those moulting to males(6.0 6 2.34 mg; p , 0.01), but their range of engorgement weight showed overlap (2.3–16.2versus 2.2–12.8 mg, respectively). Two gynandromorphs were detected between the nymphs. Acomparison of biological parameters of A. neumanni with other American Amblyomma speciesfrom mammals is presented.Exp Appl Acarol 23: 159–164 © 1999 Kluwer Academic Publishers

Key words: Life cycle, Amblyomma neumanni, ticks, laboratory.

INTRODUCTION

Amblyomma neumanni Ribaga (1902) is found between 24 and 32°S and 60 and66°W in the Argentinian phytogeographical Chaco Domain where it parasitizesseveral hosts, including man and domestic animals (Guglielmone and Hadani,1981; Bulman and D’Agostino, 1983; Mangold et al., 1985; Lombardero et al.,1996). This tick species has also been found in Uruguay (Vogelsang, 1928) andColombia (Lopez and Parra, 1985). The taxonomy of A. neumanni was studied byGuglielmone and Hadani (1985), whereas Estrada-Pena et al. (1993) described theimmature stages of this tick species.

* To whom correspondence should be addressed at: Tel: 54 87 902081; Fax: 54 87 902214;e-mail: saproani@inta.gov.ar

Experimental & Applied Acarology, 23 (1999) 159–164

0168–8162 © 1999 Kluwer Academic Publishers

Natural infestation of cattle by A. neumanni showed that all stages were moreabundant in late autumn–early winter (May–July), being absent during summer(January–March), corresponding to a triennial life cycle regulated via diapause(Guglielmone and Hadani, 1982; Guglielmone et al., 1990). Forested habitatsfavour higher cattle infestations than deforested ones (Mangold et al., 1994).

Lombardero et al. (1996) reported deleterious effects in cattle severely infestedby A. neumanni, while Gaido et al. (1995) transmitted Anaplasma marginale tocattle using experimentally infected specimens of this tick species. Amblyommaneumanni is the ixodid species most frequently found parasitizing humans in north-western Argentina (Guglielmone et al., 1991a). This article refers to the develop-ment of A. neumanni from specimens fed in the laboratory.

MATERIAL AND METHODS

A colony of A. neumanni was started with 25 (14 partially engorged) femalesobtained from cattle at El Encon (24° 51'S, 65° 33'W), province of Salta, Argentina.Larvae and nymphs were fed on seven adult rabbits with no previous exposure totick infestation, as described by Guglielmone et al. (1991b). Four rabbits wereinfested with 150, 189, 147 and 263 larvae, respectively, while another three wereinfested with 100, 103 and 370 nymphs each. After four failed attempts withrabbits, adult ticks were fed on two calves. One calf was infested with sevenfemales and seven males and a second one with 14 females and 16 males.Considering the absence of parasitic stages during the summer no infestations weredone during this season. The ticks were 15–150 (larvae), 20–80 (nymphs) and 20(adults) days old when allowed to feed.

Engorged ticks were collected daily and each individual weighed with theexception of the engorged larvae which were weighed in groups of ten. Thereafterthey were maintained in darkness at 27 6 1°C and 83–86% RH and their develop-ment followed daily as described previously (Guglielmone et al., 1991b), includingmeasuring the reproductive efficiency index (REI 5 number of eggs laid/weight ofthe females in mg) (Drummond and Whetstone, 1970).

The t-test was used to determine differences between the means of the biologicalparameters of larvae and nymphs.

RESULTS

The recovery rate, moulting success, engorgement weight and feeding and pre-moult periods of the larvae and male and female nymphs are shown in Table 1. Therange of engorgement weight (2.2–12.8 mg) of the nymphs moulting to malesshowed overlap with the engorgement weight of the female nymphs (2.3–16.2 mg),indicating that this parameter cannot be used to predict the sex with accuracy. Two

160 D.H. AGUIRRE ET AL.

gynandromorphs were detected amongst the nymphs fed on the third rabbit(n 5 344).

All females allowed to feed on the first calf were recovered as engorged ones and11 engorged females were recovered from the 14 females fed on the second calf.Fifteen (83.3%) of these engorged female ticks laid eggs masses and hatching wasobserved in 14 (93.3%) of them. The feeding period, engorgement weight, pre-oviposition and minimum egg incubation periods, egg hatching and REI obtainedfrom engorged females are presented in Table 2. The mean and extreme values tocomplete one life cycle of A. neumanni (pre-feeding period not tested) are shown inTable 3.

DISCUSSION

The comparison of the life cycle of A. neumanni with the cycle of other Am-blyomma species (Amblyomma cajennense, Amblyomma parvum and Amblyomma

TABLE 1

Certain biological parameters (mean ± SD) of larvae and nymphs of A. neumanni fed on rabbits

Larvae

Nymphs

Males and females Malesa Females

Recover rate (%) 83.8 ± 12.98 85.6 ± 16.30Number of rabbits infested 4 3

Moulting succes (%) 77.0 ± 20.27 93.5 ± 5.67Number of rabbits infested 4 3

Engorgement weight (mg) 0.72 ± 0.207 6.0 ± 2.34a 8.1 ± 2.34b

n 510 195 272Feeding period (days) 8.50 ± 1.62 7.8 ± 0.37a 7.9 ± 0.53a

n 633 195 272Pre-moult period (days) 16.4 ± 2.55 22.9 ± 3.05a 22.8 ± 2.74a

n 520 195 272

a Numbers not sharing the same letter are significantly different (p , 0.01).

TABLE 2

Certain biological parameters (mean ± SD) of engorged females of A. neumanni fedon calves

n Mean SD

Feeding period (days) 18 8.8 3.05Engorgement weight (mg) 18 390.5 166.42Pre-oviposition period (days) 15 23.8 16.50Minimum incubation period of the eggs (days) 14 76.1 11.38Egg hatching success (%) 4 8.9 5.63REI 4 7.1 2.89

161THE LIFE CYCLE OF A. NEUMANNI IN THE LABORATORY

pseudoparvum) from the same phytogeographical domain, reared under similarconditions (Guglielmone et al., 1991b, 1992; Mangold and Guglielmone, 1993)showed that A. neumanni needed almost twice the time to complete it. The maindifference was due to the long pre-oviposition, oviposition and minimum egg pre-hatch periods. Another difference from those tick species is that the rabbit was notan appropriate host for feeding adults of A. neumanni. On the other hand, the rabbitbehaved as a proper host for A. neumanni nymphs and, in particular, for the larvaejudged by a recovery rate higher than 80%. Previous studies (Guglielmone et al.,1991b, 1992; Mangold and Guglielmone, 1993) with the larvae of Amblyommaspecies of the Chaco Domain fed on rabbits never reached 50% of recovery rate.

The feeding and pre-moult periods of male and female nymphs were almostidentical. As in most ixodids (Guglielmone and Moorehouse, 1985), female nymphswere significantly heavier than male nymphs. However, sexes cannot be separatedwith accuracy by using this parameter due to overlap in the engorgement weights.In this sense A. neumanni is similar to A. cajennense (Guglielmone et al., 1992)and different from several American Amblyomma species such as Amblyommainornatum (Gladney et al., 1977), Amblyomma americanum (Koch, 1981), A. par-vum (Guglielmone et al., 1991b) and A. pseudoparvum (Mangold and Guglielmone,1993). The feeding period of A. neumanni larvae was longer than the correspondingnymphal period. This is uncommon for ixodids, but again similar to the findingswith an Argentinian colony of A. cajennense maintained on rabbits (Guglielmoneet al., 1992). The female engorgement weight was intermediate to the range foundin other American Amblyomma species from mammals reared in the laboratory: 211mg for A. pseudoparvum (Mangold and Guglielmone, 1993) to 919 mg forAmblyomma maculatum (Drummond and Whetstone, 1970).

Field studies showed that A. neumanni is a tick species with summer diapause (arare event for ixodids) and probably a triennial life cycle, as suggested by the

TABLE 3

The mean, minimum and maximum duration of the life cycle of A. neumanni (pre-feeding period not evaluated) at 27 ± 1°C and 83–86% RH in darkness

Developmental period

Duration(days)

Mean Minimum Maximum

Feeding of females 8.8 4 13Pre-oviposition 23.8 12 67Oviposition 41.4 30 51Incubation of the eggs 76.1 53 86Feeding of larvae 8.5 4 15Pre-moult to nymphs 16.4 13 33Feeding of nymphs 7.9 7 14Pre-moult to adults 22.8 17 44

Total 205.7 140 323

162 D.H. AGUIRRE ET AL.

coincidence of the onset of parasitic activity of the larvae, nymphs and adults(Guglielmone and Hadani, 1982; Guglielmone et al., 1990). These aspects of thebiology of A. neumanni were not elucidated upon. Nevertheless, the long pre-oviposition and minimum egg developmental periods (the longest found for anAmerican Amblyomma from mammals reared in laboratory conditions similar to thepresent study) as well as the low egg hatching are indications of morphogeneticdiapause and delayed oogenesis and embryogenesis, respectively, as defined byBelozerov (1982). The delayed embryogenesis may be an important aspect in thelife cycle of A. neumanni. However, more field and laboratory studies are needed tounderstand this biological feature of that tick species properly, since Lombardero etal. (1996) reported a minimum egg hatch period of 28 days with engorged femalescollected from naturally infested cattle.

Finally, the finding of two gynandromorphs is an interesting phenomenon. Asdiscussed by Vinabal et al. (1994) it appears that the frequency of this anomaly ishigher in A. neumanni than in other Ixodidae.

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