Previous phylogenetic investigations on the mayfly Baetis rhodani Pictet from several European countries, excluding Italy, strongly suggested the presence of cryptic species. Our paper reports a DNA-taxonomy phylogenetic analysis of B. rhodani with additional populations coming from Italian and UK sites, and aims to identify potential cryptic species with a coalescent-based method (GMYC model) and to understand the mechanisms of local coexistence of cryptic species. Twenty-five haplotypes of Italian samples and five haplotypes of UK samples were identified and added to a large European dataset. A total of 11 potential cryptic species have been recognised, and three of them co-occured in one Italian area. Such cryptic species seem to be phylogenetically over-dispersed on the tree and temporally segregated, and the seasonal substitution pattern of cryptic species could explain the apparently widespread distribution of the B. rhodani complex and its ability to adapt to different temperatures and food resources, justifying some of the differences observed in the relationship between water temperature, growth rates and phenology documented from field studies.

The present investigation tests through friction experiments the attachment ability of adults of the southern green stink bug Nezara viridula L. (Heteroptera: Pentatomidae), a polyphagous insect representing a cosmopolitan pest, on different host plant species characterized by smooth, hairy and waxy surfaces. Surfaces of different tested plants have been studied in Cryo-Scanning Electron Microscope (Cryo-SEM). The load cell force transducer was used to evaluate the potential damage to the insect attachment devices induced by walking on the different leaf surfaces. In case of the plant Phaseolus vulgaris, where insects showed a strong reduction in their adhesion ability during and after walking on the leaf, the damage to the insect by two cultivars with different morphological features and the insect ability to recover after 24 h has been evaluated. The ability to recover notwithstanding the damage to attachment devices, shown by Cryo-SEM investigations, together with the strong attachment forces produced on various plant leaves, characterized by different morphological features, is in agreement with the great adaptability and ecological plasticity of this widely-spread bug species. The present study, increasing our knowledge on the mechanical interaction of this species with different host plant species, can help to develop new strategies to control this insect pest.

 AbstractGaino, E. and Rebora, M. 2000. Synthesis and function of the fibrous layers covering the eggs of Siphlonurus lacustris (Ephemeroptera, Siphlonuridae). -Acta Zoologica (Stockholm) 82 : 41-48Ultrastructural analysis (transmission and electron scanning microscopy) of the eggs of the mayfly Siphlonurus lacustris (Eaton) showed that they are wrapped in a thick coat composed of a network of tightly entwined filaments. Groups of twisted filaments form slightly uplifted buttons that are scattered on the coat surface. After experimentally induced egg deposition, egg-water interaction promotes marked cohesion of the eggs and their firm adhesion to the substrate. Egg masses include numerous gametes; the covering of those located close to the substrate greatly extends to anchor the whole mass. Eggs removed from the coat reveal a slightly punctuated smooth chorion and tagenoform micropyles (three to five). The coat increases egg size by about 20%. The lack of female reproductive accessory glands in Ephemeroptera transfers the synthesis of the adhesive coats to the follicle cells, which are typically competent for insect egg shell deposition (vitelline envelope and chorionic layers). This covering results from electron-dense granules that give rise to filaments progressively organized to form superimposed layers variously orientated around the egg. In addition to egg adhesion to the substrate, a trophic function and protection from shear stress are postulated for this covering.

The present paper characterizes the attachment ability of males and females of Nezara viridula (Heteroptera: Pentatomidae) on artificial surfaces (smooth hydrophilic, smooth hydrophobic, different surface roughness) and on both leaf surfaces of the typical host plant species Vicia faba, using a centrifugal force tester and a traction force experiments set up. N. viridula is a serious crop pest in the world and shows attachment devices different from the so far investigated Heteroptera, with a tarsus characterized by distal smooth flexible pulvilli combined with claws and proximal ventral hairy pad. Notwithstanding the different body mass between the sexes, no difference was found between friction forces generated by females and males. Friction force was higher on hydrophilic surfaces than on hydrophobic ones and was lower on both sides of V. faba leaf compared with both hydrophilic and hydrophobic artificial smooth surfaces. On the surfaces with different roughness, the friction force values varied significantly, with the higher attachment ability on the surface with very high asperity size followed by the smooth surface. The lowest attachment was on the surfaces with intermediate asperity sizes. These results could be related to the specific combination of attachment devices of N. viridula.

Based on analyses with cryo-scanning and transmission electron microscopy, the present study reports on the morphology and ultrastructure of the attachment structures of the green stinkbug Nezara viridula L. (Heteroptera: Pentatomidae), a cosmopolitan pest of different crops in most areas of the world. In addition, the presence and distribution of large proportions of the elastic protein resilin in these structures was revealed by confocal laser scanning microscopy. The attachment structures of each leg comprise two sclerotised claws, a pair of smooth flexible pulvilli and a hairy adhesive pad located at the ventral side of the basitarsus. No sexual dimorphism is evident. Contact areas of resting individuals on a smooth surface show that N. viridula creates contact to the substrate with the ventral surface of (a) the distal portions of the pulvilli, (b) the setae of the hairy adhesive pad, (c) the two paraempodia representing mechanosensory setae, and (d) the tips of the claws. Each pulvillus is a sac-like structure formed by complex cuticular layers that vary in their structure and resilin content. The dorsal side consists of sclerotised chitinous material, while the ventral cuticle consists mainly of resilin and shows a very thin epicuticle and a thick exocuticle. The setae of the hairy adhesive pad are pointed and socketed. They exhibit a pronounced longitudinal gradient in the material composition, with large proportions of resilin being present in the setal tips. In most of these setae, especially in those of the distal-most part of the pad, also a transverse gradient in the material composition is visible.

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The tarsal attachment devices of the southern green stink bug Nezara viridula, a cosmopolitan pest of different crops, encompass a pair of claws, distal pretarsal smooth pulvilli, and a proximal hairy pad on the ventral basitarsus. To evaluate the role of these attachment devices in generating attachment, behavioural experiments testing locomotion of insects with ablated pulvilli, shaved hairs and cut-off claws were performed. Using traction force experiments, insect attachment performance was evaluated on artificial substrates characterised by different roughness and on two substrates with different surface energies in the air and under water. To examine the contact area of attachment devices during resting, pulling and inverted walking, intact insects and those without claws were video-recorded using a high-speed camera. The present data reveal a great involvement of pulvilli in insect attachment on all the tested surfaces, while the hairy pad seems to have a role in producing friction forces only on smooth surfaces and on surfaces with intermediate roughness. The hairy pad was revealed to be important in adhesion to hydrophobic substrates under water, a function that could be relevant for N. viridula insects in consideration that many plant leaves tend to have hydrophobic surfaces and may be often covered by water film.

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