Browsing by Subject "Hemiptera"

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Intraspecific microbiome dynamics across the life cycle of the milkweed bug Oncopeltus fasciatus
(2026) Larner, Will; Thölke da Silva Grego, Nádia; Panfilio, Kristen A.
The microbiome is an important part of the complete nutritional and genomic profile of insects. The species-rich insect order Hemiptera (aphids, cicadas and true bugs) is highly diverse for mode of microbiome acquisition, with the conundrum that species in the seed-feeding subfamily Lygaeinae have lost obvious anatomy for housing bacteria, either in bacteriocytes or midgut crypts. Here, we characterize the microbiome of the milkweed bug Oncopeltus fasciatus as a tractable lygaeinid, using 16S rRNA gene sequencing. We assess how bacterial taxa vary between the sexes and across life history stages in a controlled environment, focusing on maternal-to-embryo transmission and distinguishing egg-stage constituents that are superficial or internal (transovarially transmitted). Among a core microbiome of 28 genera, the egg stage shows the greatest diversity, with a particular expansion of the family Comamonadaceae. We also analyse inter-individual variability in nymphs and adults and validate structured, stage-specific detection of seed material. Comparative analysis identifies Rhizobium as a notable microbiome constituent in seed-feeding Hemiptera, which we had previously shown to lack nitrogen metabolism components in the genome. Overall, we provide a nuanced assessment of bacterial abundance dynamics between individuals and across the life cycle and discuss the implications for acquisition and potential relevance as nutritional endosymbionts. This will underpin comparative investigations in seed-feeding bugs and future work in O. fasciatus on tissue-specific and diet-specific microbiome profiles, including in natural populations.
The production of melezitose in honeydew and its impact on honey bees (Apis mellifera L.)
(2021) Seeburger, Victoria; Hasselmann, Martin
Honeydew honey is a honey type which is of high economic importance in Europe. Phloem sap feeding insects of the order Hemiptera (true bugs) excrete honeydew, the key component of honeydew honey. Beekeepers move their hives between forest regions so that their bees can process the honeydew into honey. In case of high osmolality in the phloem sap of the hemipterans’ host trees, they counteract osmotic pressure by osmoregulation and produce oligosaccharides such as melezitose. Melezitose-rich honeydew honey is a major issue for beekeepers; it crystallises and obstructs the combs, leading to an economical loss. Nevertheless, precise analyses of the conditions of the occurrence of melezitose have not been realised. Furthermore, it is not known which impacts the trisaccharide has on honey bee health and the honeydew flow disease documented in beekeepers’ journals can have one explanation in the nutrition on melezitose. In order to determine influence factors for the emergence of melezitose, more than 600 honeydew droplets from defined honeydew producer species were collected under different environmental conditions (hemipteran species (host tree specific), natural area, air temperature, relative humidity, altitude, time of the year and of the day) between 2016 and 2019. The sugar spectra were analysed by high performance anion exchange chromatography with pulsed amperometric detection. To obtain the impact of melezitose on honey bee health, additional feeding experiments with daily evaluation of food uptake, gut-body weight ratio and mortality have been realised between 2017 and 2019. Additionally, comprehensive 16S rRNA Illumina sequencing of the gut microbial community has been performed. Remarkable differences could be found in the amount of melezitose between honeydew samples collected from different honeydew producer species and according to different environmental conditions. Air temperature increases and decreases in relative humidity increased the melezitose production in honeydew by the observed seven hemipteran species. Both, scale insect species on Picea abies and aphid species on Abies alba produced significantly less honeydew containing melezitose than aphid species on Picea abies. Additionally, honeydew with increased melezitose content was significantly more frequent collected in natural areas with limited water reservoir capacities, at higher altitudes and years with low precipitation. All results lead to the conclusion that hemipteran species produce more melezitose when the host trees have less access to water, increasing the osmolality of the phloem sap and indirectly enhancing the osmoregulation with producing melezitose by hemipteran species. Bees fed with melezitose showed increased food uptake and higher gut-body weight ratio than the control groups. Furthermore, melezitose feeding caused disease symptoms such as swollen abdomen, abdomen tipping and impaired movement and a significantly higher mortality than in control groups. Gut microbiota analyses indicated a shift of the bacterial species Lactobacillus Firm-4 and Lactobacillus kunkeei in favour of Lactobacillus Firm-5 in melezitose fed bees. This PhD project provides the important knowledge about the indicators that point out an enhanced melezitose production. This is a valuable contribution to design a warning system for beekeepers that will help to prevent harmful nutrition for honey bees or crystallised honey in the future by timely removal of bee colonies from local regions at risk. Additionally, feeding experiments point out the high effort that is required for the degradation process of the large-molecule melezitose. This effort might lead to a higher uptake of food, heavier guts, shorter lifespan and a higher susceptibility to intestinal diseases. Finally, an evidence was presented that the lactic acid bacteria of the gut microbiota are significantly involved in the digestion of melezitose.