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ON THE LEGUMINOUS HOST PLANTS OF SEED PREDATOR WEEVILS (COLEOPTERA: APIONIDAE, CURCULIONIDAE) IN HUNGARY

PODLUSSÁNY, A.(1), JERMY, T.(2) and Á. SZENTESI (3)
Hungarian Natural History Museum, H-1431 Budapest, P.O.Box 137, Hungary Plant Protection Institute, Hungarian Academy of Sciences H-l525 Budapest, P.O.Box 102, Hungary,  Loránd Eötvös University, Faculty of Natural Sciences, Department of Systematic Zoology & Ecology, H-1518 Budapest, Hungary, P.O.Box 120, 

Fruit bearing shoots of 139 leguminous species (cca 86% of known species of Leguminosae in Hungary) were collected at 148 sites all over the country since 1978. Only 54 species (38.8%) were found to host altogether 43 weevil species. The rearing method largely reduced the prob-ability of getting adult weevils that may have used a plant only as an adult food source or only as refuge. This strongly increased the reliability of the host plant data obtained. The host plant range showed great differences within and between weevil genera. From the 54 plant species found as hosts, 29 and 11 (altogether 74.1 %) harboured only one and two weevil species, re-spectively. The resource exploitation rate turned out very low at the plant species level.
Key words: Apionini, Tychiini, Leguminosae, specialisation, resource use


INTRODUCTION

In the course of research programmes aiming to reveal the seed predator in-sects associated especially with wild leguminous species of the Hungarian flora, species of Apionidae and Curculionidae were reared from fruits collected all over the country. This enabled us to get reliable data on the host plant affiliations of weevils. As COLONNELLI and OSELLA (1998) pointed out, the literature contains data on genuine host species on which larval development takes place as well as data on refuge plants which are used only as food, as shelter, and for transport by the adults. Consequently, the reliability of earlier host plant data is often question-able. A further factor of uncertainty is the frequent change in the taxonomy of wee-vil species. Therefore, below we refer only to recent literature data that support our findings. We deliberately do not mention reports on host plants that differ from ours, because we do not want to repeat possibly dubious data already published.
I    n the following we discuss the main characteristics of the host plant ranges comparing the data within and between weevil genera taking into consideration also the higher taxa (tribes) of the family of Leguminosae.


METHOD

Short shoots bearing ripe or almost ripe pods or flower heads, in a few instances only pods, were collected throughout Hungary since 1978. Sampling was focused mostly on wild legume species of natural or semi-natural habitats. Cultivated legume species were sampled only occasionally. The samples were put separately in paper bags and were transferred in the laboratory into glass jars covered with linen. The repeated handling of the plant material before placing it into the jars largely reduced, though did not exclude totally, the possibility that adults using the plants only as food or ref-uge remained in the sample. Furthermore, this rearing method did not prevent us obtaining adults that developed as larvae in the short shoots of the samples. The larvae of most species pupated and devel-oped to adults in the collected plant material. Those that emerged as fully grown larvae were put into separate glass jars with steamed soil for pupation. Unfortunately, the mortality of these larvae was high. All emerging adults were collected and preserved for identification. The jars were kept at room temperature until autumn, afterwards they were transferred to an open air insectary for over-wintering. The jars were repeatedly checked for emerging insects for at least one year.
    The taxonomy of the weevil species dealt with below is based primarily on the works of CALDARA (1990), DIECKMANN (1977,1988), EHRET (1990), ENDRODI (1971), and GYORFFY (1956). We use the names of the plant tribes according to the publications of the Royal Botanical Gardens, Kew (POLHILL & RAVEN 1981), while the plant species names correspond to those in the work by TUTIN et al. (1978) with the exception of Vicia angustifolia that is regarded below as a separate spe-cies while according to TUTIN et al. it is only a subspecies of Vicia sativa.


RESULTS AND DISCUSSION

The biology of several weevil species, especially those developing in wild plants, is still very poorly known. Most literature sources are restricted to data on the collection of adults on certain plant species without rearing them from the plants, so the biology of the larvae remained unknown. As our rearing method did not exclude totally to get also adults that may have developed as larvae in the shoots or buds, in Table 1 we have marked with * those species for which seed predation can only be supposed by analogy of closely related species, though has not been proved yet.
    The biology of the larvae of Exapion corniculatum was unknown earlier (DIECKMANN 1977). PODLUSSANY (1981) found, however, that the larva devel-oped to adult within a single seed of Lembotropis nigricans. All Tychius spp. are most likely seed predators as, according to CALDARA (1990), no other types of lar-val feeding has been observed in this genus so far.
    We collected samples at 148 sites (Table 2) from 139 species and subspecies of Leguminosae equalling roughly 86% of all known legume taxa of the Hungarian flora. Interestingly, only 54 species (38.8% of all sampled species) (Table 3) turned out to harbour weevils representing 43 species (Table 1). The host plant af-filiation of weevil species found can be characterised as follows.

Monophagy or at least a very narrow specialisation has been found with the following species (considering only cases when at least 4 plant samples from at least 3 locations were collected): Exapion difficile on Genista tinctoria (9 samples from 8 locations), E. fuscirostre on Cytisus scoparius (8 samples from 7 locations), Oxystoma craccae on Vicia hirsuta (7 samples from 6 locations), Tychius schnei-den on Anthyllis vulneraria ssp. polyphylla (9 samples from 7 locations), T. squamulatus on Lotus corniculatus (12 samples from 11 locations). According to DIECKMANN (1977) Protapion gracilipes is monophagous on Trifolium medium. This has been supported strongly by our data (11 samples from 11 locations).
It is important to note that all Exapion spp. were reared exclusively from gen-era belonging to one plant tribe: Genisteae (altogether 56 samples from 28 loca-tions).
    The species of Protapion are strongly specialised to Trifolium spp. Namely, 8 from the 10 species emerged exclusively from Trifolium spp. (56 samples from 34 locations). The exceptions are as follows: P. ononidis occurred on Ononis spp. (15 samples from 15 locations); P. apricans occurred, as well as on Trifolium spp. (14 samples from 12 locations), also on Ononis spinosa and Vicia tetrasperma (1 sample each). That means that Protapion spp. use mostly plant species of the tribe Trifolieae.
    A less narrow specialisation prevails in the genus Oxystoma, though Vicia spp. occur most often among the host plants followed by Lathyrus spp. In detail, O. cerdo, O. craccae (not found in Vicia craccal), O. dimidiatum, O. ochropus, and O. pomonae occurred only in Vicia spp. (71 samples from 23 locations). O. subu-latum occurred, as well as on Lathyrus pratensis (25 samples from 21 locations), also on Lotus corniculatus and on Astragalus glycyphyllos (1 sample each). Thus, Oxystoma species were associated mostly with species of Vicieae, but sporadically also with species of Galegeae and Loteae.
    A relatively broad host plant range (5 genera of 3 tribes) characterised Ischnopterapion loti, although it was mostly found in Lotus spp. (59 samples from 37 locations) while it was present in only one sample each of Dorycnium penta-phyllum, Lathyrus pratensis, Medicagofalcata and in two samples of V. tetrasperma.
    The species of Tychius showed a most variable host affiliation. Unfortu-nately, most species were found only in a few samples, therefore in most cases fur-ther investigation is necessary to get a better picture of host affiliation in this genus. Taking into consideration only species that were reared from at least 4 sam-ples from at least 3 locations, there seems a decisive specialisation in T. picirostris to Trifolium spp. (6 samples from 5 locations) while Medicago falcata is represented only by one sample and, as mentioned before, in T. schneideri to Anthyllis vulneraria ssp. polyphylla (9 samples from 7 locations). On the other hand, several species use plant species of quite far related plant genera such as T. flavus (3 genera of 2 tribes) and T quinquepunctatus (4 genera of 2 tribes).
    In conclusion, the host plant specialisation of the seed predator weevil spe-cies shows a very variable picture from possible monophagy or at least ecological monophagy (FOX & MORROW 1981) to narrow oligophagy and to a broader host range such as in Ischnopterapion loti: species of 5 plant genera belonging to 3 tribes.
    Besides the host plant species listed in Table 1 we have reared the following weevil species from plant species that seem "unusual" as they contradict both the majority of our rearing data and the available literature data. They need further in-vestigation the more so as we have reared only one adult of each species from these plants: Oxystoma cerdo from Chamaecytisus supinus, Protapion ruficrus from Tri-folium ochroleucon and Tychius quinquepunctatus from Astragalus glycyphyllos.
    As for the number of curculionid species per plant species (Table 3), it is re-markable that among the 54 plant species found as hosts, 29 and 11 species (i.e., 53.7 + 20.4 = 74.1%) were infested only by one and two weevil species, respec-tively, while the maximum of 6 species occurred only in Lotus corniculatus. Fur-thermore, in about two-third of the host plant species, weevils emerged from less than half of all samples collected. Considering also the fact that seed predator wee-vils occurred only in 38.8% of the sampled leguminous species, it can be con-cluded that the rate of resource exploitation by these insects is quite low at the plant species level.

TABLE 1-3

Acknowledgements - This work was supported by the Bakony Program of the Hungarian Nat-ural History Museum and by the National Scientific Research Fund (OTKA T1436 and Tl 3300). The authors are deeply thankful to Prof. A. HORANSZKY (Budapest) for checking the identification of the plant species and to Dr D. REAVEY (Chichester, UK) for improving the English of the text.


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