Biology subjects

Theepan, V.

Publications and source records attributed to Theepan, V..

2 recordsLinked to original sources

bioRxiv2020

Integration of plant primary and secondary metabolites as fitness-relevant foraging cues for a specialist herbivore

Plants produce complex mixtures of primary and secondary metabolites. Herbivores use these metabolites as behavioral cues to increase their fitness. However, how herbivores integrate different metabolite classes into fitness-relevant foraging decisions in planta is poorly understood. We developed a molecular manipulative approach to modulate the availability of sugars and benzoxazinoid secondary metabolites as foraging cues for a specialist maize herbivore, the western corn rootworm. By disrupting sugar perception in the western corn rootworm and benzoxazinoid production in maize, we show that sugars and benzoxazinoids act as distinct and dynamically integrated mediators of short-distance host finding and acceptance. While sugars improve the capacity of rootworm larvae to find a host plant and to distinguish post-embryonic from less nutritious embryonic roots, benzoxazinoids are specifically required for the latter. Host acceptance in the form of root damage is increased by benzoxazinoids and sugars in an additive manner. This pattern is driven by increasing damage to post-embryonic roots in the presence of benzoxazinoids and sugars. Benzoxazinoid- and sugar-mediated foraging directly improves western corn rootworm growth and survival. Interestingly, western corn rootworm larvae retain a substantial fraction of their capacity to feed and survive on maize plants even when both classes of chemical cues are almost completely absent. This study unravels fine-grained differentiation and integration of primary and secondary metabolites into herbivore foraging and documents how the capacity to compensate for the lack of important chemical cues enables a specialist herbivore to survive within unpredictable metabolic landscapes.

animal behavior and cognition↗

bioRxiv2020

Plant-derived CO2 mediates long-distance host location and quality assessment by a root herbivore

Insect herbivores can use volatile and visual cues to locate and select suitable host plants from a distance. The importance of CO2, arguable the most conserved volatile marker of metabolic activity, is not well understood in this context, even though many herbivores are known to respond to minute differences in CO2 concentrations. To address this gap of knowledge, we manipulated CO2 perception of the larvae of the western corn rootworm (Diabrotica virgifera virgifera; WCR) through RNA interference and studied how CO2 perception impacts their interaction with their host plant, maize (Zea mays). We show that the expression of a putative Group 2 carbon dioxide receptor, DvvGr2, is specifically required for dose-dependent larval responses to CO2 in the ppm range. Silencing DvvGr2 has no effect on the ability of WCR larvae to locate host plants at short distance (<9 cm), but impairs host location at greater distances. Using soil arenas and olfactometer experiments in combination with DvvGr2 silencing and CO2 scrubbing, we demonstrate that WCR larvae use CO2 as a long-range host plant finding cue, but employ other volatiles for short-range host location. We furthermore show that the larvae use CO2 as a fitness-relevant long-distance indicator of plant nutritional status: Maize plants that are well-fertilized emit more CO2 from their roots and are better hosts for WCR than plants that are nutrient-deficient, and the capacity of WCR larvae to distinguish between these plants depends exclusively on their capacity to perceive CO2 through DvvGr2. This study unravels how CO2 can mediate plant-herbivore interactions by serving as a distance-dependent host location and quality assessment cue.

ecology↗