Molnar, B. P. | bioRxiv Science

bioRxiv2022

The push-pull intercrop Desmodium does not repel, but intercepts and kills pests

Over two decades ago, scientists developed a push-pull intercropping strategy that received critical acclaim for synergizing food security with ecosystem resilience in smallholder farming. The strategy suppresses Lepidopteran pests in maize through a combination of a repellent intercrop (push), commonly Desmodium spp., and an attractive, dead-end border crop (pull). Key is the intercrops constitutive release of volatiles that repel herbivores. Surprisingly, however, we found that Desmodium does not constitutively release volatiles, and only minimally upon herbivory. Further, in oviposition choice settings, Spodoptera frugiperda, a devastating invasive pest, was not repelled by Desmodium volatiles. In search of an alternative mechanism, we found that neonate larvae strongly preferred Desmodium over maize. However, their development stagnated and none survived. In addition, larvae were frequently seen impaled and immobilized by the dense network of silica-fortified, non-glandular trichomes. Thus, entirely different from repelling adult moths, Desmodium intercepts and decimates dispersing offspring. As a hallmark of sustainable pest control, maize-Desmodium intercropping has inspired countless efforts trying to emulate a stimulo-deterrent diversion in other cropping systems. However, detailed knowledge of the actual mechanisms is required to rationally improve the strategy, and translate the concept into other cropping systems.

ecology↗

bioRxiv2018

Trace impurities in test stimuli can seriously compromise chemosensory studies

The discovery of olfactory receptors and major technological advances have greatly accelerated our understanding of chemosensory mechanisms. However, some of this rapid progress may be compromised by inadequate knowledge or characterization of the purity of chemical stimuli used to challenge olfactory or other chemoreceptors when mapping their response profiles. Here, we provide strong evidence that the presence of trace impurities in test stimuli can completely obscure true ligand-receptor relationships. DmOR7a, an olfactory receptor of the vinegar fly (Drosophila melanogaster) has been reported to respond to several long-chain aliphatic ligands such as a putative Drosophila pheromone1, the pheromone of the silkworm moth Bombyx mori2, and a common fatty acid, linoleic acid3. By contrast, we show that DmOR7a responds with high sensitivity to volatile impurities and degradation products present in minute quantities in authentic standards of those compounds, but not to the standards themselves. Responses to impurities can easily go unnoticed due to two main factors. First, the sensitivity of receptors to key ligands may be greater than that of analytical chemistry instruments used to check sample purity. Second, the concentration of highly volatile impurities in an odour puff may be orders of magnitude higher than the main component of a sample, due to the large differences in vapour pressures between the impurities and the main component. Issues concerning impurities are not limited to studies on olfaction that use odour puffs to characterize receptor-ligand interactions, but may affect all studies on chemosensation, from molecular biology and in-silico predictions to behaviour. Purity, which is crucial in receptor-ligand studies, is always implied, but rarely checked rigorously. To avoid misinterpretations, a proper account of all compounds present in test stimuli and an unequivocal confirmation of ligand affinity should accompany chemosensory studies.

neuroscience↗