Experimental and Applied Acarology 25: 751–755, 2001.© 2002 Kluwer Academic Publishers. Printed in the Netherlands.

Short Communication

Life-cycle of Suidasia medanensis (= pontifica)(Acari: Suidasiidae) under laboratory conditions in atropical environment

DILIA MERCADO, LEONARDO PUERTA∗ and LUIS CARABALLOInstituto de Investigaciones Inmunológicas, Universidad de Cartagena, Apartado Aéreo4610, Cartagena, Colombia

(Received 19 December 2000; accepted 16 November 2001)

Abstract. The life cycle of Suidasia medanensis (= pontifica) was studied under laboratoryconditions at 26◦C and 86% relative humidity. Freshly laid eggs were observed until theydeveloped into adults and the periods between stages were recorded. Production of eggs bymated females was monitored until they died. The eggs required an average of 12.6 ± 0.6 daysto develop into adults. Mean longevity of mated females and males was similar (48.6 ± 13 and49.1 ± 20 days, respectively). The conditions used in this study may be considered optimal forin vitro culture of S. medanensis.

Key words: Suidasia medanensis, Suidasia pontifica, Blomia tropicalis, domestic mites, miteculture, allergy

Introduction

Mite allergens are a common cause of respiratory allergy. Studies of mitefauna suggest that Blomia tropicalis and Dermatophagoides pteronyssinusare the most common domestic mite species in Cartagena, a Caribbean city inColombia. However, other genera such as Suidasia are also present in housedust of asthmatic patients in this tropical locale (Fernández-Caldas et al.,1993). Suidasia spp. are associated with the nests of vertebrates and insectsand with stored products (Hughes, 1976; Oconnor, 1982). The taxonomy ofthe family Suidasia is somewhat confused. Suidasia pontifica (Oudemans,1905) is probably a junior synonym of S. medanensis (Oudemans, 1924).However, since Oconnor (1982) and Hughes (1976) use the species namemedanensis in their important identification keys, we prefer to use this name.

Several species of this genus have been isolated from house dust intropical regions (Vargas and Mairena, 1991; Fernández-Caldas et al., 1993;

∗ Author for correspondence (Tel./Fax: 57-5-6698491; E-mail: lpuerta@red.net.co)

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Chew et al., 1997). The clinical relevance of S. medanensis was investigatedamongst an asthmatic population from Cartagena. It was found to be a sourceof sensitizing allergens in house dust (Caraballo et al., 1999). Informationabout the biology of domestic mites is important for understanding the pop-ulation dynamics of laboratory cultures and in mite control. The biology ofthe non-pyroglyphid mites, B. tropicalis and S. nesbitii, which are commonin tropical and subtropical regions, has been investigated by Mariana and Ho(1996) and Chmielewski (1991), respectively. In this work we studied theduration of the stages in the life cycle of S. medanensis, as well as fecundity,developmental time and longevity.

Materials and Methods

Mites were collected from dust from homes of asthmatic patients in Cart-agena, Colombia. Fifty milligram of dust from each sample were suspendedin 50% lactic acid. All mites present in each sample were collected with a fineneedle, placed in two drops of Hoyer’s medium on a microscope slide, thenidentified using identification keys and reference slides (Fernández-Caldaset al., 1993). The culture of S. medanensis was set up at 26◦C and 86% RHin the Mite Laboratory of The Institute of Immunological Research. Mitedevelopment was monitored in Petri dishes (3.5 cm diameter). Several disheswere placed together in boxes covered with plastic. Approximately 2 mg offood (tetramin fish food + yeast) were placed in each dish.

To define the life cycle duration, 35 freshly-oviposited eggs were placedin separate dishes and observed daily. The time of development of differentstages from egg to adult was recorded. In a separate experiment, fecundityand reproductive statistics were assessed. We started with 32 pairs of freshlyemerged adult males and females. Pairs were placed in separate dishes andeggs were counted and removed daily. At the end of the experiment, only in25 pairs data were complete and suitable for statistical analysis. Observationof female fecundity was continued even if the males died before the females;dead males were not replaced.

The time between the deposition of the first and last egg was defined as thereproductive period. During this period, each day that a female deposited eggswas counted and the sum of days was expressed as ‘egg-laying days’. Fecun-dity was the total number of eggs laid per female; the rate of reproduction wascalculated as the number of eggs laid per day by a female during the repro-ductive period. The pre-reproductive period started with the introduction ofnewly emerged females to males and ended with the deposition of the first egg.

Statview 4.5 was used for statistical analysis. Student’s t-test (95% con-fidence limits) was used for comparing longevities of mated mites.

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Table 1. Duration of developmental stages and reproductive statistics for females ofS. medanensis at 26◦C and 85% RH

Stage Number Duration (days)

Mean ± SD Range

Egg 35 4.3 ± 0.5 4–5

Larva 25 1.9 ± 0.3 1–2

Protonymph 23 2.1 ± 0.4 2–3

Tritonymph 20 2.1 ± 0.4 2–3

Egg-adult 20 12.6 ± 0.6 11–13

Pre-reproductive period 25 2.5 ± 0.8 2–4

Reproductive period 25 20 ± 5.6 10–36

Post-reproductive period 25 27.2 ± 14.3 2–52

Results

Eggs required an average of 12.6 days to develop into adults. Twenty of the 35eggs observed (57%) became adult. Mortality at the larval and protonymphstages was 8 and 13%, respectively. There was no mortality at the tritonymphstage. Duration of egg stage was approximately 35% of total developmenttime, followed by larval (15.4%), protonymphal and tritonymphal stages,each accounting for 17.1% (Table 1). Resting larvae, resting protonymphaland resting tritonymphal stages were also observed, each one with durationof approximately 1 day.

The pre-reproductive period lasted 2.5 days, and the reproductive period20 days. Fecundity ranged from 62 to 177 eggs (mean ± standard deviation:111.6 ± 30). The number of egg-laying days ranged from 9 to 24 (16.8 ± 4.8)and the rate of reproduction from 2.7 to 8.4 eggs/day (6 ± 1.7).

Mated females and males lived 48.6 ± 13.6 (range 18–64) and 49.1 ± 20(range 15–75) days, respectively. No significant difference in the longevity ofmated mites was found (p = 0.89). Fourteen of the mated females (56%) diedbefore the males.

Discussion

The development of S. medanensis from egg to adult (12.6 days) was fasterthan those reported for B. tropicalis (22.9 days) and D. pteronyssinus (23.6days); whereas the pre-reproductive periods for all three species were sim-ilar (Van Bronswijk and Sinha, 1971; Mariana et al., 1996). The egg-adultperiod of S. medanensis is close to the 14.4 days reported for S. nesbitti,

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but the fecundity of S. medanensis (111.6 eggs) was lower than that of S.nesbitii (172.9 eggs) under similar laboratory conditions (Chmielewski, 1991).S. medanensis shows a longer reproductive period and higher fecundity thanB. tropicalis (Mariana et al., 1996) at similar temperature, but higher RH. Themean number of eggs deposited by S. medanensis per day is also comparableto data indicating that D. farinae can lay five eggs in 24 h (Sánchez andFernández-Caldas, 1994).

Our findings seem to contradict the epidemiological data from house dustsamples which show that the prevalence of S. medanensis is lower than thatof B. tropicalis and D. pteronyssinus (Vargas and Mairena, 1991; Fernández-Caldas et al., 1993; Mariana and Ho, 1996; Chew et al., 1997). Accordingto the fast development of S. medanensis in the laboratory, the occurrenceof this species in house dust should be more abundant than reported in thesestudies. However, reproduction and development of house dust mites in thelaboratory do not always reflect their dynamics in the domestic environment(Hart, 1998). Colloff (1987) found differences in the development and mor-tality of eggs between laboratory and wild populations of D. pteronyssinusreared under fluctuating conditions of temperature and humidity.

Temperature, RH and food availability are the most important environ-mental factors that influence the biology and growth of dust mites. Thesefactors determine where they live, how large the populations become and howthey fluctuate seasonally. B. tropicalis is abundant in tropical and subtropicalareas, predominantly in regions of high mean annual temperatures and hu-midity (Vargas and Mairena, 1991; Fernández-Caldas et al., 1993; Marianaand Ho, 1996; Chew et al., 1997); whereas D. pteronyssinus has a broaddistribution that appears to be less constrained by microclimates. This canbe explained by the better maintenance of the body water balance within thePyroglyphidae, which makes pyroglyphid mites more adapted to the periodicmicroclimatic fluctuations in homes. However, it is more difficult to explainwhy S. medanensis has lower prevalence than B. tropicalis in house dust in thetropics and additional studies should be conducted to explain this difference.

Acknowledgment

This study was supported by COLCIENCIAS, Grant 1 107-04-887-98.

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