Differing acceptance of familiar and unfamiliar plant species by an oligophagous beetle

Abstract

The mustard leaf beetle, Phaedon cochleariae (F.) (Coleoptera: Chrysomelidae), is specialized to feed and develop on various species within the Brassicaceae. In this study, we investigated the acceptance of several host plant species (Brassica rapa L. and Sinapis alba L.), commonly used by the beetle (familiar plants), and of various unfamiliar plants, including systematically and chemically related [Bunias orientalis L. (Brassicaceae) and Tropaeolum majus L. (Tropaeolaceae), both Brassicales], as well as unrelated non‐host plant species [Plantago lanceolata L. (Plantaginaceae); Lamiales]. Emphasis was laid on the acceptance of the neophyte B. orientalis, and on underlying cues responsible for the acceptance of the various species. Behavioural responses to plant volatiles were studied using a static four‐chamber olfactometer. Stimulants and deterrents were investigated by bioassay‐guided solid phase extraction and semi‐preparative high performance liquid chromatography. A difference in acceptance of plant species was found: odours and polar compounds of all Brassicales evoked attraction and feeding stimulation, respectively, in Ph. cochleariae. Glucosinolates and their volatile hydrolysis products could be the main compounds that are involved in attraction of the beetles. In contrast, Ph. cochleariae did not respond to odours of the non‐host P. lanceolata, and some fractions of this plant had feeding‐deterrent effects, due to the presence of iridoid glycosides, among others. Although adult females accepted the neophyte B. orientalis for oviposition, neonate larvae did not survive on it. The flavonoid‐containing fraction of this plant was deterrent, whereas a similar fraction had been shown to cause some feeding stimulation when derived from S. alba. Differences in qualitative and quantitative composition of related metabolites lead to differentiated plant acceptance, proving the complexity of plant cues and of insect responses that determine host acceptance behaviour. The possibility of a diet breadth enlargement to B. orientalis and the role of Ph. cochleariae as a putative native biocontrol agent of this invasive plant are discussed.

Relevance of visual and olfactory cues for host location in the mustard leaf beetle Phaedon cochleariae

“…Differences between sexes can also be demonstrated in response to olfactory cues. Odour in various Brassicaceae species including nonhost plants is reported to be highly effective in that P. cochleariae spend more time in air containing these volatiles in a four-chamber olfactometer than in clean control air, with females responding more strongly to odour than males (Kühnle & Müller, 2009). In the present study, both males and females respond to odour of N. officinale when tested in the stem arena, whereas only females show a preference for the main volatile compound 2-phenylethyl isothiocyanate.…”

“…Members of the Brassicaceae contain glucosinolates as characteristic metabolites, which are readily hydrolysed to volatile isothiocyanates (Halkier & Gershenzon, 2006). Beetles of P. cochleariae show different preferences for different Brassicaceae species (Kühnle & Müller, 2009) and are partly stimulated by glucosinolates and their hydrolysis products (Tanton, 1977a; Reifenrath & Müller, 2008). Furthermore, the age of leaf tissue is an important determinant of host suitability for larval performance of this species (Reifenrath & Müller, 2009).…”

Variation in plant defences among populations of a range‐expanding plant: consequences for trophic interactions

“…The plant has been present in non-native ecosystems for more than a century, but began a rapid expansion in the 1980s (Steinlein et al, 1996). Previous studies have shown that B. orientalis is of poor quality for the development of brassicaceous specialist herbivores from local populations in Germany and the Netherlands (Travers-Martin & M€ uller, 2008;K€ uhnle & M€ uller, 2009;Harvey et al, 2010a;Fortuna et al, 2012). By contrast, a Dutch population of a generalist herbivore, the cabbage moth Mamestra brassicae (Lepidoptera: Noctuidae), readily feeds on introduced populations of the plant and achieves high fitness on it (Harvey et al, 2010a;Harvey & Gols, 2011).…”

Uncovering different parameters influencing florivory in a specialist herbivore

“…The other two chambers contained filter papers only. It has been demonstrated that insects are able to detect and respond to volatiles of different plant material under these circumstances (Kühnle & Müller, 2009). A gauze covering the cylinder served as the walking arena, on which a larva was placed in the centre.…”