Host Plant Odors Represent Immiscible Information Entities - Blend Composition and Concentration Matter in Hawkmoths

<div><p>Host plant choice is of vital importance for egg laying herbivorous insects that do not exhibit brood care. Several aspects, including palatability, nutritional quality and predation risk, have been found to modulate host preference. Olfactory cues are thought to enable host location. However, experimental data on odor features that allow choosing among alternative hosts while still in flight are not available. It has previously been shown that <i>M. sexta</i> females prefer <i>Datura wrightii</i> compared to <i>Nicotiana attenuata</i>. The bouquet of the latter is more intense and contains compounds typically emitted by plants after feeding-damage to attract the herbivore’s enemies. In this wind tunnel study, we offered female gravid hawkmoths (<i>Manduca sexta</i>) odors from these two ecologically relevant, attractive, non-flowering host species. <i>M. sexta</i> females preferred surrogate leaves scented with vegetative odors form both host species to unscented control leaves. Given a choice between species, females preferred the odor bouquet emitted by <i>D. wrightii</i> to that of <i>N. attenuata</i>. Harmonizing, i.e. adjusting, volatile intensity to similar levels did not abolish but significantly weakened this preference. Superimposing, i.e. mixing, the highly attractive headspaces of both species, however, abolished discrimination between scented and non-scented surrogate leaves. Beyond ascertaining the role of blend composition in host plant choice, our results raise the following hypotheses. (i) The odor of a host species is perceived as a discrete odor ‘Gestalt’, and its core properties are lost upon mixing two attractive scents (ii). Stimulus intensity is a secondary feature affecting olfactory-based host choice (iii). Constitutively smelling like a plant that is attracting herbivore enemies may be part of a plant’s strategy to avoid herbivory where alternative hosts are available to the herbivore.</p> </div

Effects of host blend composition and intensity on host choice in <i>M. sexta</i>.

<p>(A) Choice experiments with gravid <i>M. sexta</i> females were performed in a wind tunnel. Plants were placed in glass boxes outside the wind tunnel where they could not be seen by the moths. Pumps delivered plant headspace to two surrogate leaves serving as visual stimuli inside the wind tunnel. Two host plants, <i>D. wrightii</i> and <i>N. attenuata</i>, were tested (I) against a clean air control, (II) with their plant headspaces mixed together 1:1 against a clean air control, (III) against a conspecific plant whose headspace was diluted with clean air, and (IV) against each other, with <i>N. attenuata</i> headspace either not manipulated or diluted with clean air. Plant headspace and clean air were mixed in a 1:4 (vol/vol) ratio resulting in a 5-fold dilution. (B) The percentage of first choices made in the corresponding experiments. Sample size is given next to each experiment. Asterisks denote significant differences between sources (Binomial Test, *** p<0.001; ** p<0.01; *p<0.05). (C) Boxplots depict preference indices calculated from the number of contacts to each source. Values close to 1/-1 represent a high preference for one source; 0 means no preference. The black line delineates the median; color distribution within the box represents the percentage of contacts to each source. Asterisks above the boxes denote indices significantly different from 0 (Wilcoxon Signed Ranks Test, *** p<0.001; ** p<0.01; * p<0.05). Preference indices resulting from experiments in which the plant headspace of both species is offered superimposed or separately against clean air differed significantly (Kruskal-Wallis Test, p<0.0001, and Dunn’s post hoc test, ** p<0.01, * p<0.05). Furthermore, preference indices derived from interspecific choice experiments were significantly different from each other (Mann-Whitney U Test, p<0.05).</p

Supplementary Figure S1. from Baculovirus entry into the central nervous system of <i>Spodoptera exigua</i> caterpillars is independent of the viral protein tyrosine phosphatase

Resemblance between banded perinuclear structure observed in our study (A) and previous experiments in Sf9 cells (B), and a 3D construction of the p10 cage like structure (C). (A) represents the banded AcMNPV-eGFP:VP39 perinuclear structure superficially located on brain in vivo in present study (magenta channel TO-PRO-3 nuclei/dsDNA staining, green channel AcMNPV-eGFP:VP39), (B) represents AcMNPV-eGFP:VP39-infected Sf9 cells from Mu et al. (2014) (blue channel Hoechst staining of nuclei, green channel same AcMNPV-eGFP:VP39 construct as in (A), and (C) represents a 3D reconstruction of an AcMNPV-infected TN-368 cell at 3 dpi from Graves et al. (2019), showing the P10 cage like structure (Zeiss LSM 510 Meta scannings were processed with LSM 5 image Browser). All scalebars 10 µm

Supplementary Table S1. from Baculovirus entry into the central nervous system of <i>Spodoptera exigua</i> caterpillars is independent of the viral protein tyrosine phosphatase

Primer names and sequences for the utilised primers