Do exotic generalist predators alter host plant preference of a native willow beetle?

Abstract

1 Selection can favour herbivores that choose host plants benefitting their offspring either by enhancing growth rates or by increasing larval defences against native predators. For exotic predator species that feed on herbivores, their success with invading new habitats may depend upon overcoming defences used by native prey. Whether exotic predators can alter herbivore host choice has remained unexamined. Therefore, we compared the efficacy of larval defence by Chrysomela knabi (a native beetle species) that had fed on two native willow hosts: Salix sericea (a phenolic glycoside (PG)-rich species) and Salix eriocephala (a PG-poor species), when attacked by exotic generalist predators. In addition, the preference and performance of C. knabi on S. sericea and S. eriocephala was examined. 2 Chrysomela knabi preferred and performed better on S. sericea. In a common garden, adult C. knabi were nine-fold more common and oviposited five-fold more frequently on S. sericea than on S. eriocephala . In the laboratory, adult feeding preference on leaf discs and survival rates of larvae were both greater on S. sericea , and time to pupation was shorter. 3 Chrysomela knabi larvae produced significantly more salicylaldehyde when fed S. sericea leaves than when fed S. eriocephala leaves. Additionally, those larvae with greater salicylaldehyde had reduced predation by two exotic generalist predators, Harmonia axyridis larvae and juvenile Tenodera aridifolia sinensis . 4 The results obtained in the present study suggest that selection favoured the preference of C. knabi for PG-rich willow plants because larvae grew and survived better and that selection by common exotic generalist predators would reinforce this preference. HerbivoreChrysomela knabi are abundant at Milford, New York, where they feed and oviposit on the foliage of both willow species.Exotic generalist predators and a native beetle 177

Profiling phenolic glycosides in Populus deltoides and Populus grandidentata by leaf spray ionization tandem mass spectrometry

“…These secondary compounds function as defense chemicals against herbivores, including both insects and mammals. [7][8][9][10][11][12][13][14][15][16][17][18] Furthermore, they are found in high concentration among many species, being reported at up to 30% of dry plant mass in the case of Populus tremuloides. 8 In particular, the hydroxycyclohexen-on-oyl (HCH) functional group, present in salicortin, tremulacin, HCH salicortin, and lasiandrin, has been shown to confer considerable toxicity against herbivores.…”

“…18 However, some specialist herbivores, including the native willow beetle, preferentially feed on PGrich tissue in order to obtain PGs, which they chemically cleave and alter to salicylaldehyde to be used as a deterrent against generalist predators. 16,17 Thus, PGs mediate multiple trophic interactions (plant-herbivore and herbivore-predator), and, as a result, PGs are of great ecological interest.…”