Plant trichomes constitute a first line of defence against insect herbivores. The pre- and post-ingestive defensive functions of glandular trichomes are well documented and include direct toxicity, adhesion, antinutrition and defence gene induction. By contrast, the defensive functions of non-glandular trichomes are less well characterized, although these structures are thought to serve as physical barriers that impede herbivore feeding and movement. We experimentally varied the density of stellate non-glandular trichomes in several ways to explore their pre- and post-ingestive effects on herbivores. Larvae ofManduca sexta(Sphingidae) initiated feeding faster and gained more weight onSolanum carolinense(Solanaceae) leaves having lower trichome densities (or experimentally removed trichomes) than on leaves having higher trichome densities. Adding trichomes to artificial diet also deterred feeding and adversely affected caterpillar growth relative to controls. Scanning electron and light microscopy revealed that the ingestion of stellate trichomes byM. sextacaterpillars caused extensive damage to the peritrophic membrane, a gut lining that is essential to digestion and pathogen isolation. These findings suggest that, in addition to acting as a physical barrier to deter feeding, trichomes can inhibit caterpillar growth and development via post-ingestive effects.

Significance: Biodiversity is driven by complex associations among species, but ecologists often look only at competitive or facilitative interactions either independently or only for few species at a time. Using a large dataset of mountain ecosystems encompassing more than 2,000 species across the globe, we analyze the prevalence and importance of both positive and negative associations among plants. Our findings indicate that facilitation and competition between plant species must be studied together in order to explain biodiversity change.

Significance: Malaria elimination efforts are hindered by the prevalence of asymptomatic infections, which frequently go undetected and untreated. Consequently, there is a pressing need for improved diagnostic screening methods. Based on extensive collections of skin odors from human populations in Kenya, we report broad and consistent effects of malaria infection on human volatile emissions. Furthermore, we found that predictive models based on machine learning algorithms reliably determined infection status based on volatile biomarkers and, critically, identified asymptomatic infections with 100% sensitivity, even in the case of low-level infections not detectable by microscopy. These findings suggest that volatile biomarkers have significant potential for the development of robust, noninvasive screening methods for detecting symptomatic and asymptomatic malaria infections under field conditions.

It is increasingly clear that plants perceive and respond to olfactory cues. Yet, knowledge about the specificity and sensitivity of such perception remains limited. We previously documented priming of anti-herbivore defenses in tall goldenrod plants (Solidago altissima) by volatile emissions from a specialist herbivore, the goldenrod gall fly (Eurosta solidaginis). Here, we explore the specific chemical cues mediating this interaction. We report that E,S-conophthorin, the most abundant component of the emission of male flies, elicits a priming response equivalent to that observed for the overall blend. Furthermore, while the strength of priming is dose dependent, plants respond even to very low concentrations of E,S-conophthorin relative to typical fly emissions. Evaluation of other blend components yields results consistent with the hypothesis that priming in this interaction is mediated by a single compound. These findings provide insights into the perceptual capabilities underlying plant defense priming in response to olfactory cues.

Leaf trichomes play well-established roles in defense against insect herbivores, both as a physical barrier that impedes herbivore movement and by mediating chemical defenses. However, little work has examined how different trichome types influence herbivory by herbivores at different stages of development. We examined whether caterpillar instar and trichome type (glandular or non-glandular) affected the ability of the specialist herbivore caterpillar Manduca sexta to initiate feeding on 11 Solanaceous species exhibiting variation in the density and type of leaf trichomes. Our results suggest that non-glandular trichomes are far more effective than glandular trichomes in deterring the initiation of feeding by first- and second-instar caterpillars. Meanwhile, neither glandular nor non-glandular trichomes significantly affected the ability of third-instar caterpillars to commence feeding. These findings suggest that while non-glandular trichomes deter feeding initiation by early instar caterpillars, the contribution of both trichomes on later instars may depend on effects after feeding initiation.

Symbiotic rhizobia induce many changes in legumes that could affect aboveground interactions with herbivores. We explored how changing the intensity of Bradyrhizobium japonicum, as modulated by soil nitrogen (N) levels, influenced the interaction between soybean (Glycine max) and herbivores of different feeding guilds. When we employed a range of fertilizer applications to manipulate soil N, plants primarily dependent on rhizobia for N exhibited increased root nodulation and higher levels of foliar ureides than plants given N fertilizer; yet all treatments maintained similar total N levels. Soybean podworm (Helicoverpa zea) larvae grew best on plants with the highest levels of rhizobia but, somewhat surprisingly, preferred to feed on high-N-fertilized plants when given a choice. Induction of the defense signaling compound jasmonic acid (JA) by H. zea feeding damage was highest in plants primarily dependent on rhizobia. Differences in rhizobial dependency on soybean did not appear to affect interactions with the phloem-feeding soybean aphid (Aphis glycines). Overall, our results suggest that rhizobia association can affect plant nutritional quality and the induction of defense signaling pathways and that these effects may influence herbivore feeding preferences and performance—though such effects may vary considerably for different classes of herbivores.