In general, the feeding habits of Rhaphidophoridae cave crickets are considered to be omnivorous–saprophagous (Chopard 1938). Early observations on the genus Dolichopoda Bolivar, 1880 indicated the exploitation of vegetable matter and arthropod remains (Monti 1902). A similar diet has also been described for other Rhaphidophoridae (Macropathinae), such as species of the Australian genera Gymnoplectron Hutton, 1897, Pallidoplectron Richards, 1958, Micropathus Richards, 1964 and Pallidotettix Richards, 1964 (Richards 1962, 1968, 1970), Spelaeiacris tabulae Peringuey, 1916 from Wynberg cave, Capetown, SouthAfrica (Carchini et al. 1991) and of the Patagonian species Heteromallus cavicola Ander, 1932 (Di Russo et al. 1996). Furthermore, other data indicating a omnivorous diet are available for some species of the North American genera Hadenoecus Scudder, 1863 and Ceuthophilus Provancher, 1876 (Hubbel and Norton 1978, Lavoie et al. 2007).

An example of predatory habits was reported by Chopard (1959) for Rhaphidophora oophaga Chopard, 1959, of which some individuals were observed to eat eggs of the Black-nest Swiftlet Collocalia maxima Hume, 1878 in the Subis cave, Sarawak, Malaysia.

In a more recent study, conducted on some Italian populations of the genus Dolichopoda, the trophic niche has been quantitatively described (De Pasquale et al. 1995). In this case, differences in the exploitation of resources in relation to the age of the cave, climatic stability of the habitat, type and amount of trophic resources and the diversity of the biotic community were established. Concerning species and populations of the genus Troglophilus Krauss, 1879, very little is known about their feeding habits. Early, fragmentary observations suggested an omnivorous diet for Troglophilus (Remy 1931, Avesani et al. 2009). Semi-quantitative analysis confirming this type of diet are available only for some populations of Troglophilus cavicola (Kollar, 1833) from Slovenian cave habitats (Novak and Kustor 1983).

The present study is part of a more extensive research project investigating the population ecology of the Italian species of Troglophilus cave crickets (Di Russo et al. 2008). In particular, the results on trophic resource exploitation of two populations belonging to Troglophilus cavicola and Troglophilus andreinii Capra, 1927 are reported and discussed in relation to their population ecology.

The genus Troglophilus has a wide east-mediterranean distribution, with 15 species occurring from Austria and Italian pre-Alps to the Balkan-Anatolian region (Eades et al. 2013). The large number of species present in the latter area suggests a primary centre of dispersal located in the eastern paleo-Mediterranean (Ruffo 1955). Recently, some studies on the population ecology of Troglophilus have been carried out, but information on this topic is very fragmentary and insufficient. In particular, these studies, conducted on some populations of Troglophilus cavicola and Troglophilus neglectus Krauss, 1879 from Slovenia caves, allowed for only a partial description of their life cycle as completed in two years. Furthermore, the occurrence of two seasonal ecophases was established: one hypogean in winter and one epigean in summer. According to these observations, the crickets use the caves only as winter shelter, and defect the caves in summer to feed and to reproduce in the epigean habitat (Novak and Kustor 1983; Pehani et al. 1997). Beginning in 2000, similar studies were also carried out in some Italian populations of Troglophilus cavicola and Troglophilus neglectus from the Lessini Mountains (Latella et al. 2002; Avesani et al. 2009) and of Troglophilus andreinii from Apulia (Di Russo and Rampini 2005). In these studies, strong summer reductions of population sizes in caves were reported, confirming the existence of the two ecophases in the Italian populations just as in those from Slovenia. However, although summer population reductions occur in Troglophilus andreinii, these appear to be less marked and involve a very short time span.

This study is based on the analysis of 225 faecal and gut content samples collected periodically from August 2004 to October 2005. In Troglophilus cavicola we analysed 76 samples (56 feculae and 20 guts) from Covoli di Velo cave in the Lessini Mountains (Grotta Inferiore dei covoli di Velo 44 V/VR, altitude 878 m a.s.l., Velo Veronese, Verona). For Troglophilus andreinii, an endemic species of Apulia, we analysed 149 samples (98 faeces and 51 guts) from Tranese cave [Grotta della Masseria Tranese 486 Pu/BA, altitude 330 m a.s.l., Contrada Tranese, Putignano, Bari]. Sub-samples from individuals of different sex and developmental stages (adult, nymphs and young) were analyzed. In particular for Troglophilus cavicola, we utilized 24 adults, 26 nymphs and 26 young instars, while for Troglophilus andreinii 52 adults, 47 nymphs and 50 young instars have been used. The distinction in these three age classes is based on the maturation of sexual characters for the adults and the hind tibia lenght for the other two classes (Nymph = hind tibia included between 15 and 21 mm; Young instar = hind tibia < 15 mm). Fresh faeces were collected from individuals put in a plastic box separately for 24 hours without any food supply. Gut samples were obtained by dissection of fresh individuals. Both faecal and gut pellets were conserved in alchool 70%. The comparison among gut and faecal samples does not reveal any differences in their content, permitting us to pool data obtained by these two types of source.

Feacal and gut contents were spread in Euparal on 24×24 mm slides and examined with an optical microscope (Leica M.Z.12.5). The material analysed was classified into three categories: green vegetables, vegetable fibres and arthropod remains. In order to obtain quantitative estimates, we used a 576 mm² grid and the food items scored were recorded as proportion of the total area observed. The niche breadth was cumulatively evaluated, for each periodical sub-sample, by the Gini-Simpson index (Gini 1912):

B = 1- ∑p_i²

where p_i = the proportion of the ith item in the faecal or in the gut content.

The overlap in the resource exploitation among age and sex sub-samples was investigated by the Morisita index (1959) as modified by Horn (1966):

M_o = 2 ∑ p_ij p_ik / ∑ p²_ij +∑p²_ik

where p_ij and p_ik are the proportions of ith item utilization by the jth and kth populations.

The examined specimens and slides are deposited in the collections of the Museo Civico di Storia Naturale of Verona and of the Dipartimento di Biologia e Biotecnologie “Charles Darwin”, Università degli Studi di Roma “Sapienza.

Remarkable differences in exploitation of these resources can be observed comparing the diet of the two populations herein studied. In particular, in the Troglophilus cavicola population we observed a diet mainly based on arthropod remains (69%). This finding is chiefly due to the exploitation inside the cave of this type of resource in winter during the strictly hypogean ecophase. In this case, individuals at Covoli di Velo were forced into the cave by the hard climate typical of pre-alpine winter. The large amount of arthropods in this unfavourable winter period can be related to the high availability of this resource inside the Covoli di Velo, where a complex cave biocenosis is present (Caoduro et al. 1994, Zorzin et al. 2000). By contrast, in the Troglophilus andreinii population, located in southern Italy, the abundance of vegetable matter (green and fibres) appears constant throughout the year suggesting a continuous exploitation of vegetables outside the cave habitats. In the Tranese cave, due to the typical dry climate of the Mediterranean regions, all phases of the life cycle are completed in the hypogean habitat, as suggested by the observations of mating and hatching of eggs in the cave, with crickets moving outside the cave only for daily food. This result is in agreement with the reduction in the Tranese population of a strict division of the population phenology in two ecophases as shown by the occurrence in summer of a remarkable number of individuals in the cave.

The analysis of niche breadth seems to confirm this result: lower values of Gini-Simpson index in Troglophilus cavicola indicating a dominance of a single type of resource (arthropods), are observed only in winter; in the same period, the Tranese population shows an higher value of this index, suggesting a diet more balanced among the available resources outside and inside the cave.

On the whole, as described for other Rhaphidophoridae species (Di Russo and Sbordoni 1998), we can confirm for Troglophilus populations an omnivorous diet based on vegetable matter and arthropod remains.

The study of overlap resource exploitation seems to indicate a separation of diet among young instars and the other age classes of the populations (nymphs and adults). This finding is confirmed by the Morisita–Horn index and is more evident in the Troglophilus cavicola populations. As found in the Italian Dolichopoda populations (De Pasquale et al. 1995), differences in niche during the life cycle can affect population dynamics and reduce competition for food among individuals of different ages (Polis 1984, Ebenman 1987). Differences in diet between males and females have been observed only in the Tranese population. In this case, the increase of female niche breadth in autumn is related to the exploitation of a consistent percentage of arthropod remains. This period of the year corresponds to the time of reproduction of the population (Di Russo et al. 2008); therefore, as found in other arthropods (Coll and Guershon 2002), increasing the animal component in the diet could be interpreted as a protein requirement for maturation of eggs.