Immature stages and nest construction inSynapsis yunnanus(Coleoptera: Scarabaeidae)

Abstract

In this paper we describe and illustrate the nesting behaviour, egg and larvae of all three instars of Synapsis yunnanus Arrow 1933. Two nests of S. yunnanus were observed in Northern Yunnan, China. The nest is subterranean and paracoprid, with female present in the nest chamber after oviposition. The brood ball is covered with a compacted layer of soil, and the egg chamber is proximal, situated in dung. Six brood balls were found in each nest. Larvae are compared with the only other species known in larval stage, S. tmolus (Fischer von Waldheim 1821). We identify differences between individual larval instars of S. yunnanus and provide an identifi cation key to individual instars. Shape of anal plate of L3 found shortly after ecdysis is different from the plate of older larvae and therefore its value as differential character is limited. We also discuss the function of egg-bursters and the course of hatching, functions of the stipital "pars stridens" and of the raster on abdominal sternum X, and problems with the assessment of the generic diagnosis of Synapsis Bates 1868 larvae. Résumé. Stades immatures et nidifi cation de Synapsis yunnanus (Coleoptera : Scarabaeidae).Dans cet article, nous décrivons et illustrons la nidifi cation, l'oeuf et 3 stades larvaires de Synapsis yunnanus Arrow 1933. Deux nids de S. yunnanus ont été observés au nord du Yunnan, Chine. Le nid est souterrain et paracopride, avec la présence de la femelle dans la cavité après l'oviposition. La boulette du couvain est couverte d'une couche de terre compacte, la chambre de l'oeuf est proximale dans la bouse. Six boulettes ont été trouvées dans chaque nid. Les larves sont comparées avec la seule autre espèce connue au stade larvaire, S. tmolus (Fischer von Waldheim 1821). Nous indiquons les différences entre les différents stades larvaires de S. yunnanus et nous donnons une clé d'identifi cation des stades. La forme de la plaque anale du L3 trouvée juste après l'éclosion est différente de celle des larves plus vieilles et de ce fait, sa qualité diagnostique est limitée. Nous discutons aussi la fonction des "eggs bursters" et le déroulement de l'éclosion, les fonctions des "pars stridens" stipitales et du peigne du tergite abdominal X, ainsi que les caractéristiques génériques diagnostiques des larves de Synapsis Bates 1868.

Morphology of immature stages of Paraegidium costalimai (Coleoptera: Scarabaeidae: Orphninae) and remarks on egg-busters in Scarabaeidae first‑instar larvae

“…These have been called hatching spines, oviruptors, or egg-busters (Hayes, 1929). With the aid of muscular contractions, the egg-busters assist the embryo to break the chorion during the hatching process (Vitner & Král, 2009). Besides the function of egg-busters, some authors showed that the structure is also useful to identify some first-instar Coleoptera larvae (e.g., Scarabaeidae, Emden, 1941;Šípek et al, 2008).…”

“…Gardner (1935) found egg-busters in Rutelinae (Anomala polita Blanchard, 1851) and Cetoniinae (Heterorrhina elegans (Fabricius, 1781) and Oxycetonia albopunctata (Fabricius, 1798)), but Fidler (1936) did not find this structure in Melolonthinae (Amphimallon solstitialis (Linnaeus, 1758), Melolontha melolontha (Linnaeus, 1758), and Serica brunnea (Linnaeus, 1758)). Vitner & Král (2009) in a study of immatures of Synapsis yunnanus Arrow, 1933 (Scarabaeinae) suggested that egg-busters may not always be responsible for the initial fracture of chorion and that these sclerites possibly have a supportive function. The authors noted that the egg-busters probably serve as mechanoreceptors, since the sclerotized insertions of setae of the egg-busters keep them in a constant position relative to the chorion.…”

“…The shape of egg busters in other scarab beetles can be different from the above-mentioned. The egg-buster of the dung beetle Synapsis yunnanus (Scarabaeinae, described by Vitner & Král, 2009) has three conical projections backward directed, each projection bearing one robust subdistal seta. However, the egg-busters of P. costalimai are composed of a backward directed spine and other two small conic upward-directed projection, and a separated sclerite bearing projections.…”