Plant‐mediated interactions among above‐ground and below‐ground life stages of a root‐feeding weevil

1. Interactions among herbivores mediated by plant responses to herbivore injury may have large impacts on herbivore population densities. Responses may persist for weeks after injury and may affect not only the initial (inducing) herbivore, but also herbivores that are spatially or temporally separated from the initial attacker. 2. In many plant–insect interactions, multiple life stages of the insect may be associated with the same plant, and these various stages may interact indirectly with one another via induced responses. The rice water weevil (RWW), Lissorhoptrus oryzophilus, a serious global pest of rice, is one such insect. A series of experiments were performed with root‐feeding larvae and leaf‐feeding adults of the RWW using three conventional rice varieties. 3. The first objective of this study was to test whether RWW adult feeding on rice leaves resulted in altered oviposition by subsequent adults. The hypothesis for the first objective was that RWW adult feeding would decrease plant suitability, resulting in reduced oviposition by subsequent adults. 4. The second objective was to test whether injury by RWW larvae to rice roots resulted in altered oviposition by subsequent adults. The hypothesis for the second objective was that below‐ground RWW larval feeding would decrease plant suitability of rice to above‐ground RWW adults, resulting in decreased oviposition. 5. Results provided inconsistent support for the first hypothesis, indicating that responses differed among combinations of variety and injury level. Conversely, consistent support for the second hypothesis was found, indicating that larval feeding on roots decreased suitability of rice plants for oviposition. Prior injury to rice leaves by RWW adults inconsistently reduced numbers of first instars emerging from plants. These effects on oviposition were dependent on variety and level of injury. Injury to rice roots by RWW larvae reduced numbers of first instars that emerged from plants after subsequent exposure to adult females in all three experiments. This study demonstrates that adult and larval RWW may interact indirectly via changes in the shared host plant, although interactions were neither as pronounced nor as consistent as anticipated.