Larval morphology and biology of two species oiAphodius ( Plagiogonus ) from the Iberian Peninsula ( Coleoptera : Scarabaeidae : Aphodiinae )

The larval morphology of Aphodius (Plagiogonus) nanus Fairmaire, I860 and A. (P.) arenarius (Olivier, 1789) are described and redescribed, respectively. The common characters of both species, and the specific diagnostic characters are provided and discussed. The most important morphological characters of the larvae of Plagiogonus Mulsant, 1842 are the longitudinal align­ ment of the anterior setae of the stipes, the spatulate form of the posterior-lateral setae of the glossae of the hypopharynx, the slight development of the anal lobe slit, the form of the epitorma of the epipharynx, the slight sclerotization of the pternotormae and the relative length of second antennal segment. A key to the larvae of both species of Plagiogonus is presented along with life history data and the preferred food of these species. This study shows that A. arenarius and A. nanus feeding habits are closer to saprophagy than to coprophagy.


INTRODUCTION
The entire larval development of Aphodius Illiger, 1798 typically takes place in dung.Most species oviposit single eggs in fresh dung and some species construct primitive nests in the soil under the dung (Cambefort, 1991;Bar bero & Palestrini, 1995).Other species have trophic habits that are closer to saprophagy than coprophagy and tend to lay eggs in the interface between the trophic resource (dry dung, accumulations of manure, decom posing leaves, etc.) and the soil.In this case, the larvae never enter the dung (Lumaret & Stiernet, 1984;Verdú et al., 1997;etc.).Some species lay small compact groups of eggs directly into the soil as is typical of some saprophagous Aphodiinae such as Eupariini and Psammodiini (Lumaret & Lavalette, 1996;pers. obs.).
Aphodius (Plagiogonus) arenarius (Olivier, 1789) is a relatively rare species, mostly occurring in cold areas of the Palaeartic (Baraud, 1977;Lumaret, 1978Lumaret, , 1990;;Verdú, 1998).It is widespread throughout Europe, the Caucasus, Kazakhstan and Turkestan.In the Iberian Pen insula, A. arenarius has only been collected in high mountains and at present its southernmost limit is North of the Province of Alicante, Spain (Verdú, 1998).Mar tynov (1998) describes its larval morphology but omits some relevant characters.In the Iberian Peninsula, Apho dius (Plagiogonus) nanus Fairmaire, 1860 is rarer than the former species and its biology, ecology and larval morphology are unknown.Its distribution ranges from North Africa to the Middle East.In Europe, A. nanus is only found in the southern half of the Iberian Peninsula (Báguena, 1967;Baraud, 1977;Verdú, 1998).

MATERIAL AND METHODS
This study was carried out at different localities in the Prov ince of Alicante, southeastern Spain.Pitfall traps (Mena et al., 1989) baited with cattle dung were used to monitor the activity of adults of A. arenarius from April 1992 to April 1993 at Font Roja Nature Park (UTM: 30SYH1481; 1,350 m a.s.l.; supramediterranean bioclimate) and from January 1995 to January 1996 at Sierra de Onil (UTM: 30SYH0380; 1,206 m a.s.l.; supramediterranean bioclimate).Portions of partially buried pieces of wood and pitfall traps baited with dog faeces were used to monitor the activity of adults of A. nanus from January 1996 to January 1997 at "El Garbinet" (UTM: 30SYH2049; 50 m a.s.l.; termomediterranean bioclimate).All pitfall traps were baited fortnightly.Larvae and adults of both species were also collected directly from different droppings, manure, cut wood, carrion, decomposing leaves, etc.
For the purpose of laboratory studies, a total of 10-20 adult specimens of each species were kept in cylindrical plastic breeding cages (20 cm high, 10 cm diameter) with moistened soil and crumbled dry rabbit dung.The lid had an opening (6 cm diameter) covered with gauze screen.A total of six breeding cages were kept in a climatic chamber maintained at 25 : 20°C (L : D), 80 : 85% RH (L : D), and a photoperiod of 15 : 9 (L : D).The breeding cages were examined and results recorded weekly.Throughout the study period complementary data were obtained in the field.
Voucher specimens are deposited in the Entomological Col lection of the Universidad de Alicante (CEUA), Alicante, Spain.The morphological terms of Ritcher (1966), Kim & Lumaret (1988) and Verdu & Galante (1997) were used to describe the larvae.
Thorax.Size of respiratory plate of prothoracic spi racle is 34.0 x 14.2 pm; with a maximum of 4 holes along any diameter (Fig. 10).
Abdomen.Ventral anal lobe with one shallow slit; external angles of dorsal anal lobe slightly extended to ventral anal lobe (Fig. 11).
Biology.A total of 82 adults were captured during the sampling periods.The adults of A. arenarius are active from the beginning of March until the middle of June (Fig. 25).Maximum activity is in March (42.7%).Oviposition occurs in March, preferably in rabbit latrines.First larvae occur in mid-March and larval development con tinues until June.The entire larval development takes The larva, during its development, does not create a permanent nest, but feeds in the interface between the soil and the dung.Generally, they tend to move horizontally and never enter the dung.Prior to pupation, the larva migrates down into the soil.
The adults of A. arenarius have been found in rabbit, human and cattle dung used as bait in pitfall traps.They have been also found inside the brood-balls of the geotrupid Thorectes intermedius (Costa), and the species may be facultatively kleptoparasitic.
Thorax.Size of the respiratory plate of prothoracic spiracle 47.5 x 9.5 p,m; with a maximum of 3 holes along any diameter (Fig. 22).
Abdomen.Ventral anal lobe with undifferentiated slit; external angles of dorsal anal lobe not extended to ventral anal lobe (Fig. 23).
Biology.A total of 33 adults were captured.The adults of this species are active in winter, particularly from mid-November to mid-March (Fig. 26).Maximum activity is in December (78.8%).Oviposition occurs in December and January, preferably under tree trunks where decom- For successful development in A. nanus and A. arenarius, the larvae need to be able to move freely in the inter face between the trophic resource and the soil.They never enter the dung.For pupation the larvae migrate down into the soil.
The adults of A. nanus have been found in various materials such as accumulations of manure, under cut wood, in dog faeces and under carrion.

Larval morphology
Plagiogonus larvae have many morphological charac ters, which can be used to separate the subgenera of Aphodius, such as the arrangement of the anterior setae on the stipes (Figs 6a and 18a), the spatulate form of the posterior-lateral setae on the glossae of the hypopharynx (Fig. 8b), and the development of the anal lobe slit (Figs 11 and 23).Other relevant taxonomic characters are the form of the epitorma of the epipharynx and the slight sclerotization of the pternotormae, especially the left one.
In addition, the second antennal segment is shorter than the first and third, being half the size of the first.This character was also observed by Martynov (1998) in A. arenarius.Finally, the posterior part of the right oncyli of the hypopharynx bears an isolated group of tegumental expansions, which have only been observed in Aphodius (Ammoecius) lusitanicus Erichson, 1848(Verdu & Gal ante, 1995).
The larva of A. nanus may be confused with that of Platytomus tibialis (F., 1798) because of its small size, presence in the same accumulations of manure and tem poral coincidence of larval development (pers.obs.).The characters of the larva of P. tibialis described and illus trated by Lumaret & Lavalette (1996) and those described here for A. nanus are sufficient for distinguishing both species.The presence of two upper anal lobes in P. tibi alis, instead of one in A. nanus, is a particularly suitable and easily accessible character.
The most relevant diagnostic characters of Plagiogonus species are summarized in the following key: -Ventral anal lobe without a slit (Fig. 23).First antennal seg ment 2.2 times the length of the second (Fig. 15).Respira tory plate strongly elongated, with a maximum of 3 holes along any diameter (Fig. 22).Glossae with a row of 9-11 posterior-lateral setae on each side (Fig. 20) .... A. nanus

Biology
The trophic habits of the subgenus Plagiogonus are not typical of Aphodius (Cambefort, 1991).The data obtained in this study show that A. arenarius and A. nanus have habits closer to saprophagy than to coprophagy.The dung exploited by these species tends to be dry or has a texture and chemical composition close to that of decomposing leaves, conditions often found in piles of manure and in rabbit dung (Verdu, 1998).Panin (1957) reports A. are narius exploiting the faecal pellets of Marmota bobac and Citellus sp.(Rodentia) inside their burrows.Machatschke (1969) and Dellacasa (1983) also record this species in piles of cattle, horse and sheep manure.Another Plagio gonus species, A. (P.) ramamiensis Stebnicka, 1981 was found in cut wood and ex-river debris (Stebnicka, 1989).