Experimental approaches to unravel proximate mechanisms of parasitoid searching and patch leaving behaviour

Animals exploit complex environments in an optimal way, often with limited brain capacities. Interestingly, it is largely unknown, how they do so. This thesis comprises five studies investigating proximate mechanisms modulating the searching behaviour of parasitoid wasps. These organisms serve as excellent organisms for such questions due to their tight link of searching success and fitness. While the first study assumed a simple motor response to serve as a heuristic, yet effective, mechanism, the remaining studies focussed on the role of octopamine [OA] and dopamine [DA]. Both substances being essential in the assessment of reward and aversive stimuli, respectively. Neither the assumed motor response could be met nor did OA or DA reveal any consistent effects with respect to the assessment of rewards and costs. DA slightly impacted the movement pattern. Treatment with OA revealed numerous effects, in total indicating an influence on stress level. Both is in line with studies on other species. Yet, although OA significantly influences searching behaviour, the underlying mechanism is considerably more complex than initially assumed. Last, it was shown that a generalisation on the basis of a few studies and stimuli with respect to the role of OA in the integration of rewards is a simplification

Plant-based natural product chemistry for integrated pest management of Drosophila suzukii

Since the first reports of damage by Drosophila suzukii, the spotted-wing Drosophila (SWD), over a decade ago in Europe, widespread efforts have been made to understand both the ecology and the evolution of this insect pest, especially due to its phylogenetic proximity to one of the original model organisms, D. melanogaster. In addition, researchers have sought to find economically viable solutions for the monitoring and management of this agricultural pest, which has now swept across much of Europe, North America and Asia. In a new direction of study, we present an investigation of plant-based chemistry, where we search for natural compounds that are structurally similar to known olfactory cues from parasitoid wasps that in turn are welldescribed ovipositional avoidance cues for many Drosophila species. Here we test 11 plant species across two plant genera, Nepeta and Actinidia, and while we find iridoid compounds in both, only those odorants from Actinidia are noted to be detected by the insect antenna, and in addition, found to be behaviorally active. Moreover, the Actinidia extracts resulted in oviposition avoidance when they were added to fruit samples in the laboratory. Thus we propose the possible efficacy of these plants or their extracted chemistry as a novel means for establishing a cost-effective integrated pest management strategy towards the control of this pest fly

Collective Defense of Aphis nerii and Uroleucon hypochoeridis (Homoptera, Aphididae) against Natural Enemies

The prevalent way aphids accomplish colony defense against natural enemies is a mutualistic relationship with ants or the occurrence of a specialised soldier caste typcial for eusocial aphids, or even both. Despite a group-living life style of those aphid species lacking these defense lines, communal defense against natural predators has not yet been observed there. Individuals of Aphis nerii (Oleander aphid) and Uroleucon hypochoeridis, an aphid species feeding on Hypochoeris radicata (hairy cat's ear), show a behavioral response to visual stimulation in the form of spinning or twitching, which is often accompanied by coordinated kicks executed with hind legs. Interestingly, this behaviour is highly synchronized among members of a colony and repetitive visual stimulation caused strong habituation. Observations of natural aphid colonies revealed that a collective twitching and kicking response (CTKR) was frequently evoked during oviposition attempts of the parasitoid wasp Aphidius colemani and during attacks of aphidophagous larvae. CTKR effectively interrupted oviposition attempts of this parasitoid wasp and even repelled this parasitoid from colonies after evoking consecutive CTKRs. In contrast, solitary feeding A. nerii individuals were not able to successfully repel this parasitoid wasp. In addition, CTKR was also evoked through gentle substrate vibrations. Laser vibrometry of the substrate revealed twitching-associated vibrations that form a train of sharp acceleration peaks in the course of a CTKR. This suggests that visual signals in combination with twitching-related substrate vibrations may play an important role in synchronising defense among members of a colony. In both aphid species collective defense in encounters with different natural enemies was executed in a stereotypical way and was similar to CTKR evoked through visual stimulation. This cooperative defense behavior provides an example of a surprising sociality that can be found in some aphid species that are not expected to be social at all

Visual Attention in Jumping Spiders

The different ways that animals extract and analyze visual information from their environment is of interest to sensory ecologists. Jumping spiders, well-known for visually guided mating and hunting behavior, are an interesting model for the study of visual attention because they quickly and efficiently integrate information from eight eyes with a small brain. Stimuli in front of the spider are examined by two functionally and morphologically distinct pairs of forward-facing eyes. The principal eyes discern fine details and have small retinas and thus a small visual field. However, their position at the back of moveable tubes within the cephalothorax expands this visual field. The anterolateral eyes, one of the three pairs of secondary eyes, have lower spatial acuity and a larger visual field that overlaps with that of the principal eyes. They act as motion detectors, directing the principal eyes to objects appearing in their visual field. In Chapter 1, using a salticid-specific eyetracker, I explore how characteristics of a stimulus influence whether the secondary eyes redirect the gaze of the principal eyes from a principal stimulus to a new stimulus appearing in the visual field. I found that spiders suppressed redirection of the principal eyes when engaged by a salient stimulus, and redirected to moving peripheral stimuli more frequently than to stationary peripheral stimuli. The principal eyes are also known to engage in a complex behavior called “scanning,” involving both dorsoventral and rotational movement. One hypothesis regarding scanning’s function is that it helps spiders identify important lines and angles in stimuli. However, scanning routines are not well understood. In Chapter 2, I measured scanning behaviors when spiders were watching quickly moving versus still or slowly moving images. I found that spiders spent more time overall looking at still or slowly moving images, and that stimulus speed does not appear to affect rotational movement of the retinas. Overall, I conclude that motion in an appearing stimulus elicits the attention of the principal eyes, but it remains unclear how and whether scanning functions in the extraction of detail from moving stimuli

Host plant constancy in ovipositing Manduca sexta

Many pollinating insects exhibit flower constancy, i.e. they target flower species they have already experienced and fed from. While the insects might profit from reduced handling costs when revisiting similar flowers, flower constancy, in addition, is of benefit for the plants as it guarantees pollen transfer to conspecifics. Here we investigate whether the previous experience of an insect can also result in oviposition constancy, i.e. whether ovipositing on a given plant species will drive future oviposition preference in a female insect. We show that female hawkmoths (Manduca sexta), after having oviposited on a given plant species only once, indeed will prefer this plant in future oviposition choices. As oviposition preference is even affected 24 h after the moth has oviposited on a given plant, long term memory seems to be involved in this oviposition constancy. Our data furthermore suggest that, as shown for flower constancy, ovipositing moths increase their handling efficiency by targeting those host plants they have already experienced

The olfactory coreceptor IR8a governs larval feces-mediated competition avoidance in a hawkmoth

Finding a suitable oviposition site is a challenging task for a gravid female moth. At the same time, it is of paramount importance considering the limited capability of most caterpillars to relocate to alternative host plants. The hawkmoth, Manduca sexta, oviposits on solanaceous plants. Larvae hatching on a plant that is already attacked by conspecific caterpillars face food competition. Here, we show that feces from conspecific caterpillars are sufficient to deter a female M. sexta from ovipositing on a plant. Furthermore, we not only identify the responsible compound in the feces but also localize the population of sensory neurons that governs the female’s avoidance. Hence, our work increases the understanding of how animals cope with a competitive environment

Exploring diverse molecular processes in two genome sequenced hymenopteran model systems : Nasonia vitripennis-(non)host interactions and honeybee fertility

Two genome sequenced hymenopteran species were investigated in this PhD thesis. The main part of this work was performed on the parasitoid wasp Nasonia vitripennis. Nasonia vitripennis venom was extensively studied and revealed some of its possible functions in both natural hosts and non-host cell lines, which was found to target specific pathways. Some of these are involved in immunity and stress resulting in cytotoxic effects such as apoptosis, which is in accordance with the available literature. Two protease families, metallo-and serine proteases, present in the venom were found to exert these cytotoxic effects of which the latter is involved in apoptosis in Sf21 cells. Furthermore, merging of the obtained results suggest that also other venom components of non-protein nature are present in the venom. The second part of this thesis, supports the notion that there is an overlap in the molecular pathways involved in both caste differentiation and worker reproduction. Here, EGFR was found to play a key role in honeybee worker ovary activation

Learning-based oviposition constancy in insects

The search for resources occupies a major part of the time and energy budget of many insects. In this context, many insects display constancy behavior, in which they learn to return to the same, predictably rewarding resource repeatedly. Flower constancy is one such behavior, where nectar-feeding insects restrict foraging visits to a few plant species, sometimes overlooking potentially better-rewarding plants. This phenomenon is well documented in multiple species and is believed to be an optimal strategy to maximize benefits, while minimizing energy and time expenditure. Oviposition constancy is a similar behavior, where insects, dependent on previous experience, restrict their visits to a few types of potential oviposition sites. In contrast to flower constancy, the prevalence of oviposition constancy and the rationale behind this behavior are relatively unknown. An improved understanding of oviposition constancy can act as a lens into the evolutionary history of local insect adaptations, it can help gauge the impact of climate change on insect plant interactions, and it can aid the design of crop-pest management strategies. In this review, we discuss the potential benefits of oviposition constancy in insects and the extent of plasticity occurring in host-plant choice for oviposition