Research Article Selection of Oviposition Sites by Libelloides
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Hindawi Publishing Corporation Journal of Insects Volume 2014, Article ID 542489, 10 pages http://dx.doi.org/10.1155/2014/542489 Research Article Selection of Oviposition Sites by Libelloides coccajus (Denis & Schiffermüller, 1775) (Neuroptera: Ascalaphidae), North of the Alps: Implications for Nature Conservation Markus Müller,1 Jürg Schlegel,2 and Bertil O. Krüsi2 1 SKK Landschaftsarchitekten, Lindenplatz 5, 5430 Wettingen, Switzerland 2 Institute of Natural Resource Sciences, ZHAW Zurich University of Applied Sciences, Gruental,8820W¨ adenswil,¨ Switzerland Correspondence should be addressed to Markus Muller;¨ [email protected] Received 27 November 2013; Accepted 18 February 2014; Published 27 March 2014 Academic Editor: Jose´ A. Martinez-Ibarra Copyright © 2014 Markus Muller¨ et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (1) The survival of peripheral populations is often threatened, especially in a changing environment. Furthermore, such populations frequently show adaptations to local conditions which, in turn, may enhance the ability of a species to adapt to changing environmental conditions. In conservation biology, peripheral populations are therefore of particular interest. (2) In northern Switzerland and southern Germany, Libelloides coccajus is an example of such a peripheral species. (3) Assuming that suitable oviposition sites are crucial to its long-term survival, we compared oviposition sites and adjacent control plots with regard to structure and composition of the vegetation. (4) Vegetation structure at and around oviposition sites seems to follow fairly stringent rules leading to at least two benefits for the egg clutches: (i) reduced risk of contact with adjacent plants, avoiding delayed drying after rainfall or morning dew and (ii) reduced shading and therefore higher temperatures. (5) Furthermore, the study showed that it is possible to successfully create secondary habitats for L. coccajus, as shown by a road verge in one of our study areas. It is likely that other artificial habitats such as abandoned gravel pits and quarries may also provide suitable habitats. 1. Introduction foundinopenforests,onrockyscrees,andinmeadowswith quite dense vegetation that never becomes dry [7]. North Peripheral populations are of particular interest in conser- of the Alps, the climate is substantially colder and in the vation biology. As species in peripheral populations tend summer months wetter than in the Mediterranean region, to live under suboptimal conditions [1], these populations so that thermophilic species such as L. coccajus can survive often show adaptations to local conditions and therefore can only on exceptionally warm and dry sites which are mostly enhance the species’ ability to adapt to a changing environ- isolated [8, 9]. Such a shift in habitat preferences is widely ment [2–4]. Guo et al. [5] also point out that monitoring known for several plant species (e.g., [10, 11]) as well as for marginal populations can improve the understanding of various insect species [12–14]. It follows that global warming crucial site factors and, in consequence, enhance the chances [15] might enhance habitat suitability for L. coccajus on sites of correctly predicting future developments. Accordingly, with microclimatic conditions which up to now have been peripheral populations are of great significance for conserva- suboptimal, as has been shown for various species [16, 17]. tion biology [2, 6]. On the other hand, any change in the size and/or number In northern Switzerland and southern Germany, the- of such habitat islands, for example, due to changes in land highly thermophilic Libelloides coccajus (Denis and Schif- use, may present a fatal threat and risk of local extinction. fermuller,¨ 1775) (Neuroptera: Ascalaphidae) is an example There is evidence that over the past 70 years L. coccajus has of a peripheral species. L. coccajus has its core distribution substantially declined north of the Alps [18–20], but no long- around the Mediterranean coast, where this species can be term monitoring of populations of L. coccajus, north of the 2 Journal of Insects Alps, is currently available. On the Red List of endangered animals in Switzerland [21], L. coccajus is categorized as “endangered” in northern Switzerland as well as on the Red Lists for Bavaria and Baden-Wurttemberg,¨ Germany [22, 23]. To date, knowledge of the autecology of L. coccajus is fragmentary [7, 8, 24]. Focusing on the habitat requirements of adult L. coccajus, north of the Alps, Gonseth [24] described the habitat of L. coccajus intheCantonofNeuchatelˆ as extensively used, south-facing grassy slopes at low altitudes (up to 1,200 m a.s.l.), often interspersed with rocks and shrubs, and adjacent to forests. InBavaria,severalstudiesregardingtheecologyofL. coc- cajus were carried out between 1995 and 2003 on five spatially very close and partially connected populations [9, 25–27]. Most of the habitats observed in Bavaria mainly correspond to the habitat description of Gonseth [24]. The authors’ results Figure 1: Male owlfly resting in the vegetation (21.05.2010/SKK). indicate that oviposition sites of L. coccajus are highly specific, and therefore small-scale habitat improvements may be a valuable conservation measure. Wolf [27]concludedthat (vegetation height, vegetation cover, floristic compo- oviposition sites of L. coccajus are primarily characterized sition, or indicator values) by comparison of known by (i) low vegetation cover and (ii) full exposure to the oviposition sites and adjacent control plots? sun during the day. In addition, L. coccajus seems to prefer comparatively flat microsites on the upper part of a slope. The The knowledge acquired will hopefully lead to a deeper eggs are deposited exclusively on living or dead plant stems understanding of the oviposition site selection behaviour [27] between 10 and 30 cm above the soil surface [25]. of L. coccajus and therefore help to improve conservation Based on this rather limited knowledge, several questions strategies. In particular, we are hoping to gain detailed infor- about the autecology of L. coccajus arise. Wolf ’s description of mation on how to create suitable oviposition sites without oviposition sites [27]as“patchesofmoreorlessopenground” jeopardizing the floristic quality of the surrounding habitat, suggests a considerable degree of variability. Several poten- forexample,byopeningnewgatewaysforinvasiveneophytes. tially important aspects in oviposition site selection remain unclear including (i) whether there is a maximum vegetation cover which should not be exceeded, (ii) if there are other 2. Material and Methods relevant structural parameters, (iii) which dimension is most appropriate for the characterization of oviposition micro- 2.1. Study Area. Fieldwork was conducted in 2010 on four habitats, (iv) whether floristic composition is important, and different populations of L. coccajus,threeinnorthernSwitzer- (v) how an optimal oviposition substrate (plant stem) can landandonejustacrosstheborderinthesouthernmostpart be characterized. Regarding the behaviour of L. coccajus,it of Germany. The four study areas were located within 25 km of one another, and the two closest were separated by 12 km would be of great interest to know whether females search ∘ ∘ for oviposition sites using primarily visual, thermal, or other (center approx. 47.35 N, 8.37 W). They were situated between stimuli. There is also a need for further research on larval 360 and 620 m a.s.l., with a mean annual precipitation (1986– ecology (habitat, food sources, and development) and on 2010) of between 986 and 1,080 mm (data by MeteoSwiss, population dynamics, especially as the dispersal potential of 2010). Based on the preliminary study carried out by Fischer the imagines remains largely unknown. [19], the main oviposition areas of the four populations were As small-scale vegetation structure was found to be a alreadyfairlywellknown(Table1). crucial element of habitat quality for many insect species (e.g., [28–30]), we focused our study on the small-scale 2.2. Study Species. Libelloides coccajus is a medium-sized vegetation structure of oviposition sites. The general goal was owlfly with a wingspan of 42–45 mm. On both forewings to elucidate the sizes of the oviposition microhabitat and the and hindwings, it has large yellow spots and black veins related requirements of L. coccajus in northern Switzerland. (Figure 1). It feeds on small flying insects [7]. North of the In particular, we addressed the following questions. Alps, flying adults may be observed between May and the (I) Do small-scale vegetation cover and vegetation height mid-June, with a tendency towards earlier activity in warmer vary significantly among circular areas of different years [9]. The maximum life span is approximately 50 days radii around the oviposition sites of L. coccajus? [9]. In northern Switzerland, L. coccajus occurs up to 1,200 m a.s.l. [24]. It undergoes a complete metamorphosis, but there (II)Basedonthevariationinsmall-scalevegetation is little data concerning its larval habitat and its presumably structure around oviposition sites, which dimension biennial larval development [7, 9, 18, 24, 25]. According to is appropriate for characterizing the sites? Tauber et al. [31], Ascalaphidae larvae live either epigeally (III) Can we characterize the oviposition