Utilizing associational resistance for biocontrol: impacted by temperature, supported by indirect defence

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Earthworms Use Odor Cues to Locate and Feed on Microorganisms in Soil

Earthworms are key components of temperate soil ecosystems but key aspects of their ecology remain unexamined. Here we elucidate the role of olfactory cues in earthworm attraction to food sources and document specific chemical cues that attract Eisenia fetida to the soil fungi Geotrichum candidum. Fungi and other microorganisms are major sources of volatile emissions in soil ecosystems as well as primary food sources for earthworms, suggesting the likelihood that earthworms might profitably use olfactory cues to guide foraging behavior. Moreover, previous studies have documented earthworm movement toward microbial food sources. But, the specific olfactory cues responsible for earthworm attraction have not previously been identified. Using olfactometer assays combined with chemical analyses (GC-MS), we documented the attraction of E. fetida individuals to filtrate derived from G. candidum colonies and to two individual compounds tested in isolation: ethyl pentanoate and ethyl hexanoate. Attraction at a distance was observed when barriers prevented the worms from reaching the target stimuli, confirming the role of volatile cues. These findings enhance our understanding of the mechanisms underlying key trophic interactions in soil ecosystems and have potential implications for the extraction and collection of earthworms in vermiculture and other applied activities

Enemies in low places - insects avoid winter mortality and egg parasitism by modulating oviposition height

Oviposition site selection in insects is essential in terms of low egg mortality, high offspring survival and therefore a high reproductive output. Although oviposition height could be a crucial factor for the fitness of overwintering eggs, it has rarely been investigated. In this study the oviposition height of a polyphagous leaf beetle, Galeruca tanaceti Linnaeus in different habitats and at different times of the season was examined and its effect on egg clutch mortality was recorded. The leaf beetle occurs as an occasional pest on several agricultural plants. It deposits its eggs within herbaceous vegetation in autumn. Eggs are exposed to numerous biotic and abiotic mortality factors summarized as egg parasitism and winter mortality. Oviposition height of the leaf beetle was not uniform, but changed significantly with the structure of the habitat and during the season. Mean oviposition height per site (70.2±4.9 cm) was significantly higher than mean vegetation height (28.4±2.4 cm). Height of plants with egg clutches attached and oviposition height were significantly positively correlated. The results suggest that females try to oviposit as high as possible in the vegetation and on the plants selected. In accordance with this, the probability of egg parasitism and of winter egg clutch mortality significantly declined with increasing oviposition height. A preference of G. tanaceti for oviposition sites high up in the vegetation might therefore have evolved due to selection pressures by parasitoids and winter mortality

Volatile exchange between undamaged plants - a new mechanism affecting insect orientation in intercropping

Changes in plant volatile emission can be induced by exposure to volatiles from neighbouring insect-attacked plants.However, plants are also exposed to volatiles from unattacked neighbours, and the consequences of this have not beenexplored. We investigated whether volatile exchange between undamaged plants affects volatile emission and plant-insectinteraction. Consistently greater quantities of two terpenoids were found in the headspace of potato previously exposed tovolatiles from undamaged onion plants identified by mass spectrometry. Using live plants and synthetic blends mimickingexposed and unexposed potato, we tested the olfactory response of winged aphids, Myzus persicae. The altered potatovolatile profile deterred aphids in laboratory experiments. Further, we show that growing potato together with onion in thefield reduces the abundance of winged, host-seeking aphids. Our study broadens the ecological significance of thephenomenon; volatiles carry not only information on whether or not neighbouring plants are under attack, but alsoinformation on the emitter plants themselves. In this way responding plants could obtain information on whether theneighbouring plant is a competitive threat and can accordingly adjust their growth towards it. We interpret this as aresponse in the process of adaptation towards neighbouring plants. Furthermore, these physiological changes in theresponding plants have significant ecological impact, as behaviour of aphids was affected. Since herbivore host plants arepotentially under constant exposure to these volatiles, our study has major implications for the understanding of howmechanisms within plant communities affect insects. This knowledge could be used to improve plant protection andincrease scientific understanding of communication between plants and its impact on other organisms