DIGITALNA ARHIVA ŠUMARSKOG LISTA
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| ŠUMARSKI LIST 3-4/2021 str. 45 <-- 45 --> PDF |
enucleator, L. bischoffi, P. conwagana). Other specimens were mostly parasitoid wasps in different stages, which, with the exception of E. urozonus pupae, remained unidentified. L. enucleator, found only in native narrow-leaved ash seeds in this research, is the most common and widespread species of the Palearctic Lignyodes (Clark and Lodos 1981), present in the most part of the Europe on ash seeds and seeds of Ligustrum vulgare L. and Syringa vulgaris L. (Dieckman 1970, Mazur 2002, Arndt and Hielscher 2007, Nakladal 2011, Bacal et al. 2013, Caldara 2013, Delbol 2013). Proportion of seeds infested by L. enucleator in the present study was only 4.64% altogether, which could be a consequence of its preference towards trees that are well exposed to the sun, mostly in rural and urban biotopes (Gosik et al. 2017), and avoidance of trees growing in riparian forests, where its larvae and pupae overwintering in the soil could be inundated and killed during spring floods (Kania et al. 2001; Gosik et al. 2001). The fact that analysed seeds were collected in regularly flooded narrow-leaved ash forest stands is the most probable cause for low rate of L. enucleator presence in seeds. Therefore, it is plausible to conclude that this weevil does not represent danger to the seed health status and reproduction rate of narrow-leaved ash in its natural habitat in Croatia. In the present study, L. bischoffi was found only in the seeds of introduced green ash. In Europe this weevil is so far confirmed in Austria, Hungary, Moldova, Poland, Russia, Slovakia, Switzerland and Ukraine, most frequently on the North American species such as F. americana L., F. nigra Marsh and F. pennsylvanica, but also on F. ornus L., F. lanceolata Borkh., F. oxyxarpa Will., and F. excelsior (Dieckmann 1974, Clark 1980, Caldara 2013, Bacal et al. 2013, Arzanov 2013, Gosik et al. 2017). This is the first official report of L. bischoffi in Croatia. Although the proportion of seeds infested by living larvae was only 2.1% in this study, in every seed where wasp larva was found there was a dead larva of the weevil as well; and since the ash seeds were collected at the beginning of November, some larvae had already left the seeds, leaving an exit hole. Combining those findings, the actual proportion of infested seeds was around 16%, but was significantly decreased by the present parasitoids. The fact that L. bischoffi prefers urban areas and trees surrounded by grassy areas well exposed to the sun |