@phdthesis{Gabel2024, author = {Gabel, Martin Sebastian}, title = {Behavioural resistance to \(Varroa\) \(destructor\) in the Western honeybee \(Apis\) \(mellifera\) - Mechanisms leading to decreased mite reproduction}, doi = {10.25972/OPUS-36053}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-360536}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2024}, abstract = {The Western Honeybee (Apis mellifera) is among the most versatile species in the world. Its adaptability is rooted in thousands of the differently specialized individuals acting jointly together. Thus, bees that are able to handle a certain task or condition well can back up other individuals less capable to do so on the colony level. Vice versa, the latter individuals might perform better in other situations. This evolutionary recipe for success ensures the survival of colonies despite challenging habitat conditions. In this context, the ectoparasitic mite Varroa destructor reflects the most pronounced biotic challenge to honeybees worldwide. Without proper treatment, infested colonies rapidly dwindle and ultimately die. Nevertheless, resistance behaviours against this parasite have evolved in some populations through natural selection, enabling colonies to survive untreated. In this, different behaviours appear to be adapted to the respective habitat conditions and may complement each other. Yet, the why and how of this behavioural response to the mite remains largely unknown. My thesis focuses on the biological background of Varroa-resistance traits in honeybees and presents important findings for the comprehension of this complex host-parasite interaction. Based on this, I draw implications for both, applied bee breeding and scientific investigations in the field of Varroa-resistance. Specifically, I focus on two traits commonly found in resistant and, to a lower degree, also mite-susceptible colonies: decreased mite reproduction and the uncapping and subsequent recapping of sealed brood cells. Examining failures in the reproductive success of mites as a primary mechanism of Varroa-resistance, I was able to link them to specific bee behaviours and external factors. Since mite reproduction and the brood rearing of bees are inevitably connected, I first investigated the effects of brood interruption on the reproductive success of mites. Brood interruption decreased the reproductive success of mites both immediately and in the long term. By examining the causes of reproductive failure, I could show that this was mainly due to an increased share of infertile mites. Furthermore, I proved that interruption in brood rearing significantly increased the expression of recapping behaviour. These findings consequently showed a dynamic modulation of mite reproduction and recapping, as well as a direct effect of brood interruption on both traits. To further elucidate the plasticity in the expression of both traits, I studied mite reproduction, recapping behaviour and infestation levels over the course of three years. The resulting extensive dataset unveiled a significant seasonal variation in mite reproduction and recapping. In addition, I show that recapping decreases the reproductive success of mites by increasing delayed developing female offspring and cells lacking male offspring. By establishing a novel picture-based brood investigation method, I could furthermore show that both the removal of brood cells and recapping activity specifically target brood ages in which mite offspring would be expected. Recapping, however, did not cause infertility of mites. Considering the findings of my first study, this points towards complementary mechanisms. This underlines the importance of increased recapping behaviour and decreased mite reproduction as resistance traits, while at the same time emphasising the challenges of reliable data acquisition. To pave the way for a practical application of these findings in breeding, we then investigated the heritability (i.e., the share of genotypic variation on the observed phenotypic variation) of the accounted traits. By elaborating comparable test protocols and compiling data from over 4,000 colonies, we could, for the first time, demonstrate that recapping of infested cells and decreased reproductive success of mites are heritable (and thus selectable) traits in managed honeybee populations. My thesis proves the importance of recapping and decreased mite reproduction as resistance traits and therefore valuable goals for breeding efforts. In this regard, I shed light on the underlying mechanisms of both traits, and present clear evidence for their interaction and heritability.}, subject = {Varroa destructor}, language = {en} } @article{WaeschkeHardgeHancocketal.2014, author = {W{\"a}schke, Nicole and Hardge, Kerstin and Hancock, Christine and Hilker, Monika and Obermaier, Elisabeth and Meiners, Torsten}, title = {Odour Environments: How Does Plant Diversity Affect Herbivore and Parasitoid Orientation?}, series = {PlOS ONE}, volume = {9}, journal = {PlOS ONE}, number = {1}, issn = {1932-6203}, doi = {10.1371/journal.pone.0085152}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-117687}, pages = {e85152}, year = {2014}, abstract = {Plant diversity is known to affect success of host location by pest insects, but its effect on olfactory orientation of non-pest insect species has hardly been addressed. First, we tested in laboratory experiments the hypothesis that non-host plants, which increase odour complexity in habitats, affect the host location ability of herbivores and parasitoids. Furthermore, we recorded field data of plant diversity in addition to herbivore and parasitoid abundance at 77 grassland sites in three different regions in Germany in order to elucidate whether our laboratory results reflect the field situation. As a model system we used the herb Plantago lanceolata, the herbivorous weevil Mecinus pascuorum, and its larval parasitoid Mesopolobus incultus. The laboratory bioassays revealed that both the herbivorous weevil and its larval parasitoid can locate their host plant and host via olfactory cues even in the presence of non-host odour. In a newly established two-circle olfactometer, the weevils capability to detect host plant odour was not affected by odours from non-host plants. However, addition of non-host plant odours to host plant odour enhanced the weevils foraging activity. The parasitoid was attracted by a combination of host plant and host volatiles in both the absence and presence of non-host plant volatiles in a Y-tube olfactometer. In dual choice tests the parasitoid preferred the blend of host plant and host volatiles over its combination with non-host plant volatiles. In the field, no indication was found that high plant diversity disturbs host (plant) location by the weevil and its parasitoid. In contrast, plant diversity was positively correlated with weevil abundance, whereas parasitoid abundance was independent of plant diversity. Therefore, we conclude that weevils and parasitoids showed the sensory capacity to successfully cope with complex vegetation odours when searching for hosts.}, language = {en} } @article{MollRocesFederle2013, author = {Moll, Karin and Roces, Flavio and Federle, Walter}, title = {How Load-Carrying Ants Avoid Falling Over: Mechanical Stability during Foraging in Atta vollenweideri Grass-Cutting Ants}, series = {PLoS ONE}, volume = {8}, journal = {PLoS ONE}, number = {1}, doi = {10.1371/journal.pone.0052816}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-131211}, pages = {e52816}, year = {2013}, abstract = {Background: Foraging workers of grass-cutting ants (Atta vollenweideri) regularly carry grass fragments larger than their Fragment length has been shown to influence the ants' running speed and thereby the colony's food intake rate. We investigated whether and how grass-cutting ants maintain stability when carrying fragments of two different lengths but identical mass. Principal Findings: Ants carried all fragments in an upright, backwards-tilted position, but held long fragments more vertically than short ones. All carrying ants used an alternating tripod gait, where mechanical stability was increased by overlapping stance phases of consecutive steps. The overlap was greatest for ants carrying long fragments, resulting in more legs contacting the ground simultaneously. For all ants, the projection of the total centre of mass (ant and fragment) was often outside the supporting tripod, i.e. the three feet that would be in stance for a non-overlapping tripod gait. Stability was only achieved through additional legs in ground contact. Tripod stability (quantified as the minimum distance of the centre of mass to the edge of the supporting tripod) was significantly smaller for ants with long fragments. Here, tripod stability was lowest at the beginning of each step, when the center of mass was near the posterior margin of the supporting tripod. By contrast, tripod stability was lowest at the end of each step for ants carrying short fragments. Consistently, ants with long fragments mainly fell backwards, whereas ants carrying short fragments mainly fell forwards or to the side. Assuming that transporting ants adjust neither the fragment angle nor the gait, they would be less stable and more likely to fall over. Conclusions: In grass-cutting ants, the need to maintain static stability when carrying long grass fragments has led to multiple kinematic adjustments at the expense of a reduced material transport rate.}, language = {en} } @unpublished{Dandekar2007, author = {Dandekar, Thomas}, title = {Some general system properties of a living observer and the environment he explores}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-33537}, year = {2007}, abstract = {In a nice assay published in Nature in 1993 the physicist Richard God III started from a human observer and made a number of witty conclusions about our future prospects giving estimates for the existence of the Berlin Wall, the human race and all the rest of the universe. In the same spirit, we derive implications for "the meaning of life, the universe and all the rest" from few principles. Adams´ absurd answer "42" tells the lesson "garbage in / garbage out" - or suggests that the question is non calculable. We show that experience of "meaning" and to decide fundamental questions which can not be decided by formal systems imply central properties of life: Ever higher levels of internal representation of the world and an escalating tendency to become more complex. An observer, "collecting observations" and three measures for complexity are examined. A theory on living systems is derived focussing on their internal representation of information. Living systems are more complex than Kolmogorov complexity ("life is NOT simple") and overcome decision limits (G{\"o}del theorem) for formal systems as illustrated for cell cycle. Only a world with very fine tuned environments allows life. Such a world is itself rather complex and hence excessive large in its space of different states - a living observer has thus a high probability to reside in a complex and fine tuned universe.}, subject = {Komplex }, language = {en} }