Gonads and gametogenesis in Chaetodactylus osmiae (Acariformes: Astigmata: Chaetodactylidae) a parasite of solitary bees

International audienceChaetodactylus osmiae (Dufour, 1839) is a mite parasitizing the solitary bee - Osmia rufa L.- used as a commercial pollinator. In this study we present the anatomy of female and male reproductive systems of this species as well as its gonadal structure and gametogenesis at the ultrastructural level. The reproductive systems are similar to those of other Astigmata. The ovaries are paired and each contains germ-line cells – a giant nutritive ovarian cell connected via funnel-type intercellular bridges to oogonia and previtellogenic oocytes. Germinal cells are embedded in several large somatic stroma cells. Remarkable numerous protrusions of the nutritive ovarian cell penetrate into the stroma cell cytoplasm. Conspicuous ER cisterns run close and parallel to the surface of the germinal cells. Oocytes entering vitellogenesis disassociate with the nutritive cell and a vitelline envelope composed of heterogeneous material appears on their surface. When vitellogenesis is completed, the oocytes are full of lipid droplets and two types of yolk spheres; the vitelline envelope transforms into a thin and homogeneous chorion.Paired testes are located on one side of the body, whereas the opposite side is filled by a male accessory gland. In testis, germinal cells are embedded in a few somatic stroma cells. The earliest spermatogonia form a compact germarium, whereas later stages are dispersed randomly within the testis. Spermatocytes are characterized by a superficial spongy layer, formation of mitochondrial derivatives, loss of nuclear envelope and condensation of chromatin in threads. A single electron-dense lamella appears during the spermatid stage, separating chromatin threads from a large spongy body surrounded by arcuate, double-membrane bounded cisterns. In spermatids, the superficial spongy layer is absent. The testicular central cell in the germarium and structures related to meiotic division were not observed in the testes. Spermatozoa are multiform cells (approx. 4x11µm) containing electron-dense lamella (ca. 45 nm thick) surrounded by mitochondrial derivatives which separate chromatin threads 45-50 nm thick from remnants of the spongy body i.e. arcuate cistern profiles. Spermatozoa deposited in female spermatheca are more electron dense; the electron-dense lamella is deeply folded several times, whereas chromatin threads are present in the center of the spermatozoon and are either flanked by lamella folds or located more peripherally under the plasmalemma. Remnants of the spongy body are not discernible

Domesticated bumblebee (Bombus terrestris L.) as source of parasites for wild bumblebee populations

Celem badań było wyjaśnienie czy importowane trzmiele Bombus terrestris, stosowane komercyjnie do zapylania upraw szklarniowych, stanowią rezerwuar pasożyta Nosema bombi i są źródłem zarażenia dziko występujących gatunków trzmieli. Sprawdzono również czy komercyjne gniazda trzmieli są zagrożeniem dla dzikich populacji trzmieli jako źródło roztoczy. Badania dotyczące wpływu trzmieli komercyjnych (B. terrestris) na lokalną faunę trzmieli przeprowadzono w Polsce południowej. Trzmiele pochodziły z trzech szklarni, pobliża tych szklarni oraz z trzech powierzchni kontrolnych oddalonych od szklarni o minimum 30 km. Sprawdzono częstość i poziom zarażenia trzmieli pasożytem N. bombi i przeanalizowano czynniki wpływające na zarażenie. Badania składu gatunkowego roztoczy w gniazdach trzmieli komercyjnych, przeprowadzono po okresie użytkowania gniazd w szklarni. Porównano liczebność roztoczy w gniazdach producenta holenderskiego i izraelskiego z dwóch szklarni w Polsce. Sprawdzono, czy komercyjne gniazda zawierają obce dla polskiej fauny gatunki roztoczy. Wszystkie przebadane gniazda komercyjnych trzmieli B. terrestris zawierały osobniki zarażone pasożytem N. bombi. Częstość zarażenia była najwyższa wśród trzmieli komercyjnych, niższa średnio o połowę u trzmieli z pobliża szklarni i najniższa u trzmieli z powierzchni kontrolnych. Podobny wzorzec wykryto dla poziomu zarażenia. Zatem obecność w szklarniach silnie zarażonych trzmieli komercyjnych wpływa istotnie na zarażenie pasożytem N. bombi dziko występujących gatunków, narażonych na kontakt z uciekającymi ze szklarni trzmielami. W lokalnych populacjach najczęściej i najbardziej zarażonym gatunkiem był trzmiel ziemny (B. terrestris), zarówno w pobliżu szklarni jak i na powierzchniach kontrolnych. Samce wszystkich lokalnych gatunków były zarażone częściej i na wyższym poziomie niż robotnice. Częstość i poziom zarażenia dziko występujących gatunków trzmieli wzrastały istotnie wraz z postępem sezonu. W komercyjnych gniazdach trzmieli pochodzących z dwóch szklarni i od dwóch producentów, stwierdzono siedem gatunków roztoczy należących do rodzin: Acaridae, Laelapidae oraz Parasitidae. Nie było wśród nich gatunków roztoczy obcych dla fauny Polski. Wszystkie były wcześniej odnotowywane w Europie na dziko występujących trzmielach lub w ich gniazdach. Tym samym nie stwierdzono by komercyjne gniazda trzmieli były źródłem roztoczy, które mogłyby stanowić zagrożenie dla lokalnych gatunków

Linear and non-linear effects of goldenrod invasions on native pollinator and plant populations

The increased introduction of non-native species to habitats is a characteristic of globalisation. The impact of invading species on communities may be either linearly or non-linearly related to the invaders’ abundance in a habitat. However, non-linear relationships with a threshold point at which the community can no longer tolerate the invasive species without loss of ecosystem functions remains poorly studied. We selected 31 wet meadow sites that encompassed the entire coverage spectrum of invasive goldenrods, and surveyed the abundance and diversity of pollinating insects (bees, butterflies and hover flies) and native plants. The species richness of native plants decreased linearly with goldenrod cover, whereas the abundance and species richness of bees and butterflies decreased non-linearly with increasing goldenrod cover. However, no statistically significant changes across goldenrod cover were noted for the abundance and species richness of hover flies. Because of the non-linear response, goldenrod had no visible impact on bees and butterflies until it reached cover in a habitat of about 50% and 30–40%, respectively. Moreover, changes driven by goldenrod in the plant and pollinator communities were related to species loss rather than species replacement. We demonstrated that the impact of goldenrod cover on a habitat is not instantaneous. Habit management aimed at preventing the invasion process and alleviating its impact should take into account that, for the non-linear relationships, the negative impact can appear rapidly after crossing the threshold point

Greenhouse bumblebees (Bombus terrestris) spread their genes into the wild

Bumblebees (Bombus spp.) are commonly used for greenhouse pollination of tomatoes and other crop plants. The colonies used for this purpose are provided by commercial bumblebee breeders, which by now operate at a professional company level. As a result of this practice commercially bred bumblebee colonies are transported and used over large distances and national borders, introducing subspecies into non-endemic regions. The question whether and to what extends gene flow between such managed greenhouse and wild bumblebee populations exists, so far has not been addressed. Here we used samples from three greenhouses in Poland and the surrounding populations to address this question. Using microsatellite DNA data we found strong genetic introgression from the sampled greenhouse populations into the adjacent populations. Depending on the analysed population, the number of individuals assigned to the greenhouse populations ranged from 0.08 to 0.47. We also found that more distant populations were much less affected by genetic introgression from the greenhouses

Mite species inhabiting commercial bumblebee (Bombus terrestris) nests in Polish greenhouses

Nests of social insects are usually inhabited by various mite species that feed on pollen, other micro-arthropods or are parasitic. Well-known negative effects of worldwide economic importance are caused by mites parasitizing honeybee colonies. Lately, attention has focused on the endoparasitic mite Locustacarus buchneri that has been found in commercial bumblebees. However, little is known of other mites associated with commercial bumblebee nests. Transportation of commercial bumblebee colonies with unwanted residents may introduce foreign mite species to new localities. In this study, we assessed the prevalence and species composition of mites associated with commercial bumblebee nests and determined if the mites are foreign species for Poland and for Europe. The study was conducted on 37 commercial bumblebee nests from two companies (Dutch and Israeli), originating from two greenhouses in southern Poland, and on 20 commercial bumblebee colonies obtained directly from suppliers. The species composition and abundance of mites inhabiting commercial bumblebee nests were determined. Seven mite species from three families were found in nests after greenhouse exploitation. The predominant mite species was Tyrophagus putrescentiae (Acaridae) that was a 100-fold more numerous than representatives of the family Laelapidae (Hypoaspis marginepilosa, H. hyatti, H. bombicolens). Representatives of Parasitidae (Parasitellus fucorum, P. crinitus, P. ignotus) were least numerous. All identified mite species are common throughout Europe, foreign species were not found. Mites were not detected in nests obtained directly from suppliers. We conclude that probably bumblebee nests are invaded by local mite species during greenhouse exploitation

Mite fauna (Parasitiformes: Gamasida) associated with nests of selected species of native bumblebees (Hymenoptera: Apidae: Bombus spp.)

Bumblebee nests are annual microhabitats that can be attractive for various microarthropods including mites. Bumblebee nests ensure a stable microclimate, food and possibility to spread to new habitat with adult bumblebees.The fauna of Gamasida mites inhabiting wild bumblebee nests is almost unknown - mite species associated with wild bumblebees have been described only based on phoretic forms collected from foraging individuals. This study was conducted on three bumblebee nests of three different bumblebee species: Bombus hortorum (Linnaeus, 1761), Bombus ruderarius (Muller, 1776) and Bombus pascuorum (Scopoli, 1763). The mite species composition and abundance were determined from a total of 355 mites. Nine mite species was Leiodinychus orbicularis (C.L. Koch, 1839) (Trematuridae). The second most numerous was Dinychus woelkei Hirschmann & Zirngiebl-Nicol, 1969 (Dinychidae). Representatives of families Laelapidae and Parasitidae were least numerous. Most of the identified mite species were at the deutonymphal developmental stage