Insects are some of the best plant physiologists on the planet. Five native insects that come from different feeding guilds and attack different tissues at different developmental stages have revealed traits that are essential for N. attenuata’s survival in nature. By eliciting and responding to different plant traits, these sentinel insects provide essential high throughput screening services for traits that would be onerous to screen for under field conditions. We are able to identify 22 herbivore taxa and use the elicitors of some of these taxa to activate plant responses in a highly coordinated manner. Synchronized elicitations are ideal for mQTL and eQTL imputations and the screens can be readily conducted at several times during the growing seasons and be targeted to particular plant tissues such as stems, flowers, leaves of particular age classes. These elements are valuable in examining herbivore-order effects and distinguish tolerance/resistance responses.

Manduca spp.

Manduca sexta. D. Kessler
Manduca spp. damage on leaf of N. attenuata. D. Kessler

The tobacco and tomato hornworms (M. sexta and M. quinquemaculata: Lepidoptera: Sphingidae) have evolved an unprecedented capacity to detoxify the signature defense metabolite of the genus, Nicotiana, namely: nicotine. These nicotine-adapted larvae excrete the vast majority of the nicotine they ingest with their food, but also co-opt a small fraction for their own defense.

Manduca larvae are found on N. attenuata plants because the adult moths oviposit while nectaring at the plant’s flowers. Hence, this insect plays dual roles in the lives of N. attenuata plants, as a devastating herbivore during the larval stages and as an important pollinator as an adult.

Empoasca spp.

Empoasca spp. D. Kessler
Empoasca damage on N. attenuate leaf. D. Kessler

These piercing-sucking leafhoppers (Hemiptera: Cicadellidae) “eavesdrop” on the jasmonate (JA)-mediated signaling capacities of their host plants, preferentially selecting those hosts that are deficient in jasmonate accumulation. Given that JA signaling mediates the vast majority of N. attenuata’s defense responses, it is particularly intriguing that this natural phenotyping “bloodhound” specifically targets JA signaling, apparently independently of the major downstream defense metabolites that are known to be regulated by JA signaling.

Tupiocoris notatus

These free-living mirid (Heteroptera: Miridae) herbivores manipulate N. attenuata’s cytokinin (CK) signaling, and in the process have lifted a page from the playbook of endophytic insects.  Endophytic insects, because they are embedded within plant tissues and cannot easily move to other tissues, have instead evolved the ability to modify their hosts’ physiology to create metabolic “sinks” in the very tissues they infest. They do this in part by manipulating cytokinin signaling, which can transform a “source”, a plant organ that normally produces sugars – like a mature leaf – into a “sink”, where sugars are stored or consumed, as in fruits and young leaves. Mirids produce their own cytokinins, transferring these phytohormones to plants during feeding to increase food quality and minimize the activation of senescence processes that are part of a plant’s generalized defense response.

Trichobaris mucorea

Trichobaris mucoria on Solanum nigrum. D. Kessler
Trichobaris mucoria on N. attenuata. R.Halitschke, 2017
T. mucorea emerging from N. attenuata. D.Kessler
Evidence of T. mucorea occupation in N. attenuata.

The adult females of this weevil (Coleoptera: Curculionidae) oviposit eggs into basal parts of elongating stems, early in the growing seasons as plants transition from vegetative to reproductive growth. The hatched neonate weevils burrow into stems to feed on the pith of elongating stems, all without damaging the plant’s vasculature. These weevils manage to complete their life cycles with few negative consequences for their hostplant’s fitness, and adults emerge after overwintering in completely senescent stems, to mate and oviposit on a next generation of plant.

Larvae move up and down the stem, eliciting the production of phenolic and alkaloidal defenses in the pith, eating fresh pith as the stems grow, and consuming their own frass in the process. The larvae’s coprophagic behavior is likely important for the larvae’s ability to complete all 4 instars and pupate into an adult while only feeding on the limited amount of pith available in plant stems.

Geocorus spp.

Geochoris spp. 'big-eyed-bug'. D. Kessler

G. pallens and G. punctipes (Hemiptera: Geocoridae) can be found on N. attenuata or neighboring plant species throughout N. attenuata’s habitat in the Great Basin Desert. The adults and larvae are acutely responsive to the volatiles emitted from N. attenuata after herbivory, learning to associate the release of particular mono-, sesqui-terpenes and green leaf volatiles with the presence of feeding herbivores (their prey), and use the information in these complex volatile bouquets to optimize their hunting behavior and thereby mediating an important indirect defense for the plant.