The larval mite Endotrombicula pillersi (Acarina: Trombiculidae) as a species-specific parasite of a West African savannah frog (Phrynobatrachus francisci).

INTRODUCTION

Chigger mites are uncommon parasites of amphibians. Only in a few parasitological inventories, especially of anurans in North America, is infestation of frogs with chigger mites mentioned (Brandt, 1936; Kuntz, 1941; Murphy, 1965; Campbell, 1968; Duszynski and Jones, 1973; Shoemaker and Clark, 1975; McAllister et al., 1995). Chigger mites were not found in many long-term parasitological inventories of amphibians (Markov and Rogoza, 1955; Lees, 1962; Plasota, 1969; Kozak, 1969; Frandsen, 1974; Spieler, 1990). In infested frogs, the prevalence of larval mites differed considerably among host species as well as localities. The reason for this variability is unknown. Similarly, little is known about the long-term development of infestation intensities in individual hosts and the dynamics of the prevalence within one population (Welbourn and Loomis, 1975). We checked the 34 anuran species that occur in Comoe National Park, Ivory Coast (Rodel, 1996) for infestation with chigger mites and investigated the prevalence and intensity of infestation as well as the pathological effects of these parasites. We also looked for changes in the number and location of parasites in individually marked frogs, the progress of infestation within a frog population in the course of the reproductive period and the differences in prevalence between local populations of frogs during 3 y.

The mite species we found was determined as Endotrombicula pillersi (Sambon, 1928) (originally described in the genus Schongastia by Sambon (1928) and reclassified by Radford, 1954a [ILLUSTRATION FOR FIGURE 1 OMITTED]. Our classification was confirmed by A. Hoffmann, Laboratory of Acarology of the Facultad de Ciencias (Biologia), University of Mexico. The genus Endotrombicula Ewing, 1931 includes four species: E. penetrans Ewing, 1931 from the East African frog Phrynobatrachus minutus (Boulenger, 1895), E. pillersi from the West African frog P natalensis (Smith, 1849), E. madagascariensis (Sambon, 1928) from the Madagascarian frog Mantidactylus luteus Methuen and Hewitt, 1913 and E. bufonica Radford, 1954 from the South Arabian Bufo orientalis Werner, 1895. Ewing (1931) emphasized that the genus Endotrombicula is closely related to the genus Hannemania Oudemans, 1911 which includes 27 species that infest frogs and toads of the New World (Radford, 1954b; Gould, 1956; Hoffmann, 1969, 1990; de Alzuet and Mauri, 1987). Most ecological and histological studies deal with chigger mites on frogs infested by the mite genus Hannemania, thus we took this genus as a reference organism for our study of E. pillersi.

The life cycle of Endotrombicula pillersi is unknown. However, it may resemble that of the closely related species Hannemania dunni Sambon, 1928 and H. hegeneri Hyland, 1956 which were investigated in detail by Hyland (1950, 1961). The free-living adults lay eggs on the bottom of small crevices. Larvae hatch and penetrate the skin of frogs if they encounter a host. This endoparasitic stage is encapsulated by host tissue. The chigger's mouthparts (gnathosoma) may pierce this layer, presumably to feed on lymph or lysed tissue of the host. If the frog dies without being eaten by a predator, the larvae leave the capsule and develop into the free-living adult trombiculid mites which feed on eggs of small arthropods, especially collembolans.

METHODS

This study was conducted in the Guinea savannah of the Comoe National Park (8[degrees]5[minutes]-9[degrees]6[minutes]N, 3[degrees]1[minute]-4[degrees]4[minutes]W) in the northeastern part of the Ivory Coast (West Africa). This savannah type is characterised by distinct rainy and dry seasons (Poilecot, 1991). To date, we found individuals of 34 anuran species (Table 1) in the national park (Rodel, 1996) and checked them for the occurrence of small red excrescences which indicate infestation by chigger mites. We captured frogs with a net or …