Neonate larvae of the specialist herbivore Diabrotica virgifera virgifera do not exploit the defensive volatile (E)-β-caryophyllene in locating maize roots

Abstract

The behavior of the neonate larvae of the western corn rootworm (WCR) Diabrotica virgifera virgifera LeConte, a major pest of maize, was assessed in the presence of maize roots constitutively emitting (E)-bcaryophyllene (EbC). This root volatile has been shown to attract both second instar WCR and insect-killing nematodes, and may offer innovative alternatives in helping to manage WCR. Under greenhouse conditions, the maize inbred line HiII, lacking the ability to emit EbC, was planted 75 cm from the maize inbred line 201-L1, the HiII inbred genetically engineered to constitutively emit EbC. WCR eggs were infested in the center of the two lines and neonate attraction toward either root system was recorded after collecting WCR larvae established on the plants. Whereas marginally more larvae were found on EbCemitting plants, counts of recovered WCR neonates did not significantly differ between the two lines. This supports the postulate that CO 2 is the primary attractant for WCR neonate larvae. The chemical ecology of WCR larvae is discussed. A conceptual model of the foraging behavior of this pest is proposed, summarizing our current knowledge on chemically mediated interactions between WCR larvae and maize roots.

Navigating on a chemical radar: Usage of root exudates by foragingDiabrotica virgifera virgiferalarvae

“…As herein discussed, there have been several successful attempts to control WCR by disturbing its foraging behaviour, but results were sometimes inconsistent, possibly because knowledge built from second instar larvae was passed on WCR neonate, to which it might not yet apply. Indeed, the sensitivity towards chemical cues changes during larval development (Blaney, Schoonhoven, & Simmonds, 1986), so WCR neonates may respond to different cues or to the same cues at different concentration than older larval stages, as hypothesized in Hiltpold and Hibbard (2016).…”

“…Second instar larvae were also attracted towards ( E )‐β‐caryophyllene (Robert, Erb, et al., ), a volatile typically emitted by maize in response to rootivory and attracting entomopathogenic nematodes (Hiltpold, Toepfer, Kuhlmann, & Turlings, ; Rasmann et al., ; Turlings, Hiltpold, & Rasmann, ). However, in a more natural set‐up, neonate larvae did not exhibit positive chemotaxis to this compound (Hiltpold & Hibbard, ). In series of manipulative experiments, Robert, Erb, et al.…”

“…Most of the research described above has been conducted with late WCR instars, and CO 2 remains the only identified attractant used by neonates (Bernklau & Bjostad,b; Hiltpold & Hibbard, ). However, because CO 2 is so ubiquitous in the ground, it is likely that a specialist insect will rely on additional cues yet to be discovered as hypothesized by Hiltpold et al.…”

“…Second instar larvae were also attracted towards (E)β-caryophyllene , a volatile typically emitted by maize in response to rootivory and attracting entomopathogenic nematodes (Hiltpold, Toepfer, Kuhlmann, & Turlings, 2009;Rasmann et al, 2005;Turlings, Hiltpold, & Rasmann, 2012). However, in a more natural set-up, neonate larvae did not exhibit positive chemotaxis to this compound (Hiltpold & Hibbard, 2016). In series of manipulative experiments, demonstrated that second or third instar WCR larvae use ethylene, a gaseous phytohormone partially regulating root growth (Yang & Hoffman, 1984), as a cue to select suitable maize roots (Robert, Veyrat, et al, 2012).…”

“…Most of the research described above has been conducted with late WCR instars, and CO 2 remains the only identified attractant used by neonates (Bernklau & Bjostad, 1998b;Hiltpold & Hibbard, 2016).…”