Coniocleonus nigrosuturatus (Goeze, 1777)

Stejskal, Robert, Trnka, Filip & Skuhrovec, JiĜí, 2014, Biology and morphology of immature stages of Coniocleonus nigrosuturatus (Coleoptera: Curculionidae: Lixinae), Acta Entomologica Musei Nationalis Pragae 54 (1), pp. 337-354 : 348-350

Biology of Coniocleonus nigrosuturatus

Habitat. Based on our observations, C. nigrosuturatus prefers dry, sunny places in grassland habitats with sparse vegetation, bare ground and patchily growing host plants. The weevil often inhabits road margins, pastures and dykes along rivers and requires a special habitat structure originating from a proper disturbation regime. Heterogeneous patches of properly disturbed sites occur for instance due to vehicle traf¿c ( Figs 5E–F ) or the grazing of domestic animals ( Fig. 5D ). The adults avoid places with compact and overgrown vegetation, where we suppose the soil is not suf¿ciently warm for larval development. Regarding bedrock, the weevil is quite flexible, occurring on a wide range of substrata, such as limestone and various sediments (sand, sandy gravel and loess).

Adult behaviour. The weevils are diurnal and can be very agile during sunny weather, however, during cold weather, they remain motionless. We usually observed adults ( Fig. 5A ) on the ground or on host plants, where they spend most of their time sitting on the top or underside of the host plant rosette ( Fig. 5B ). An attacked plant was usually occupied by 1–4 beetles. The adults were not observed in flight but are fully winged ( ANGELOV 1963). Specimens examined by us for this character (in total 3 specimens from Hungary, Romania and Slovakia) were all macropterous. Adults can be observed from March onwards, with peak activity from mid-April to mid-May. Single adults can be observed at the end of summer or during autumn (August/October). We also observed beetles mating on the host plants. A mating male tightly embraces the female and repeatedly stimulates her with his mid-legs by knocking very rapidly on her metathorax.

Host plant. Both adults and larvae were observed feeding exclusively on Common Stork’sbill ( Erodium cicutarium (L.) L’Hér.) ( Geraniaceae , Figs 5B–C ). Adults feed on leaves, whereas larval development occurs underground on the stem base. We also tested feeding on thyme ( Thymus sp. ), which was mentioned as a host plant by several authors ( KLEINE 1910, FLEISCHER 1927 –1930, FREMUTH 1982, TER- MINASIAN 1988, ARZANOV 2006). The adults completely avoided feeding on thyme, both in the laboratory and in the ¿eld, and we thus consider thyme solely as an occasional refuge plant. Other plant species were not tested. Based on our observations and experiments, Coniocleonus nigrosuturatus hence appears to be most likely monophagous, feeding exclusively on Erodium cicutarium .

Life cycle. Coniocleonus nigrosuturatus is a univoltine species. We did not ¿nd the site of egg deposition, but we suppose that females lay eggs in the soil near the root neck. Mature larvae live ectophagously near the host plant root and construct a vertical tunnel in the soil up to several centimeters long. The larval tunnel, which has a circular to oval shape in cross section with diameter of 4–5 mm, opens onto the soil surface, where the larvae feed externally on the stem base (Figs. 14D–F). We have not observed younger instar larvae, but we suppose that they most likely also live ectophagously, like the mature larvae. Their development insi- de roots/stems could be excluded because we did not ¿nd any elongated tunnels inside the plants despite exhaustive searching. No feeding marks were found on roots. At an attacked plant, a single larva was usually observed; however, sometimes up to 3 larvae were found. The host plant infestation rate may reach 50–75% according to our estimation. We observed higher larval feeding activity during the morning hours (before 10 a.m.), in the evening (after 7 p. m.) and in cloudy weather. During midday under warm and sunny conditions, larvae hid deeper in the tunnels. From the beginning of July, larvae pupate in oval, closed earthen cells, 25–30 mm long and 10–15 mm wide ( Fig. 4B ), located several centimeters below the soil surface under the host plant. The inner diameter of the earthen cell is approximately 5 mm, and its inner length is approximately 20 mm. The only reared adult emerged in the laboratory at the end of July. Further details of the life cycle were not observed. However, we suppose that a part of the population overwinters in the pupation cells, and some adults leave the cells at the end of summer, resulting in the records of adults in August to October ( DIECKMANN 1983, Stejskal & Trnka, unpubl.). Most likely, the weevils then spend some time feeding on the host plants and look for suitable shelters to overwinter in later.

Rearing of the larvae. In general, rearing of the larvae proved very dif¿cult. We observed high larval mortality particularly due to the drying or decay of host plants. Only three larvae (of 25) pupated in the laboratory, of which one dried out, and another one was destroyed accidentally while examined. A fresh, not fully coloured adult was found in the earthen cell on July 22 nd. After emergence, it remained in its pupation cell for at least a few days. The reared beetle was kept alive for observation but died on August 13 th. The rearing of larvae on specially prepared host plants (technique 2 as described in Material and methods) was more succesfull because it prevented predation of the weevil larvae by carabid larvae taken accidentally from the ¿eld with the host plants.

Figures

Fig. 5. Adult, host plant and habitats of Coniocleonus nigrosuturatus (Goeze, 1777).A – adult beetle; B – host plant Erodium cicutarium (L.) L’Hér.; C – an excavated host plant with larval feeding marks; D–E: habitats in Romania (Sfânta Elena); F – habitat in Slovakia (KolíĖany).

Fig. 4. Immature stages and feeding marks of Coniocleonus nigrosuturatus (Goeze, 1777). A – mature larva; B – earthen cell with mature larva; C – pupa (removed from the earthen cell); D – opening of larval tunnel in the soil; E – opening of the larval tunnel and feeding marks; F – detail of larval feeding marks.