Interactions between glucosinolate- and myrosinase-containing plants and the sawfly Athalia rosae

Abstract

Several insects have specialised on using Brassicaceae as host plants. Therefore, they evolved metabolic pathways to cope with the defensive glucosinolate-myrosinase system of their diet. Larvae of the turnip sawfly, Athalia rosae L. (Hymenoptera: Tenthredinidae), incorporate various glucosinolates from their hosts into their haemolymph. The ability to sequester these metabolites makes A. rosae a useful model system to study mechanisms of glucosinolate metabolism in this species compared to other specialists, and to study effects of sawfly feeding on levels of glucosinolates and their hydrolysing enzymes in plants. The levels of plant metabolites might in turn directly affect the performance of the insect. On the one hand, costs for glucosinolate uptake and avoidance of myrosinase activity were postulated. On the other hand, sequestration of glucosinolates can be part of the insect's defence against several predators. Here, the findings on glucosinolate metabolic pathways are compared between different herbivores and the sawfly. The impact of different glucosinolate levels and myrosinase activities on the performance of A. rosae is discussed. Furthermore, effects of feeding by A. rosae larvae on the chemical composition and enzyme activities of various Brassicaceae species are summarised. Induction patterns vary not only between different plant species and cultivars but also due to the inducing agent. Finally, the plant-herbivore interactions are discussed with regard to the sawflies' defence abilities against different carnivore guilds.

Plant chemistry and insect sequestration

“…The uptake is most likely mediated by a transporter in these species, as GLSs are rather polar and can therefore not passively diffuse through the gut membrane (Müller and Wittstock 2005). Furthermore, the hydrolysis of GLSs by plant enzymes must be somehow circumvented, either by a highly efficient transport of GLSs or by some form of inhibition of myrosinases (Müller 2009). …”

“…Larvae of the turnip sawfly, Athalia rosae (Tenthredinidae), also sequester GLSs from their host plants within the Brassicaceae and store them in their haemolymph (Müller 2009). GLSs taken up by the larvae are retained through metamorphosis into the adult stage.…”

“…Not all GLSs are sequestered with the same efficiency. Indole GLSs were only detectable in larvae that fed on plants with very high concentrations of this GLS group (Müller 2009) and could not be detected in adults (Müller, personal observation). In contrast, aliphatic and aromatic GLSs are sequestered highly effectively (Müller et al 2001).…”

Unraveling molecular mechanisms underlying plant defense in response to dual insect attack : studying density-dependent effects

“…Herbivore-induced changes in plant chemistry may prolong herbivore development and consequently extend the exposure period of the herbivore to its enemies (Benrey and Denno, 1997). Moreover, some specialist herbivores are able to sequester plant secondary metabolites and exploit these defenses for their own protection from natural enemies (Kazana et al, 2007;Müller, 2009) (Figure 2). Herbivore-induced plants may also influence immune responses of herbivores to parasitoids (Bukovinszky et al, 2009).…”

Plant responses to multiple herbivory : phenotypic changes and their ecological consequences

“…Herbivore-induced changes in plant chemistry may prolong herbivore development and consequently extend the exposure period of the herbivore to its enemies (Benrey and Denno, 1997). Moreover, some specialist herbivores are able to sequester plant secondary metabolites and exploit these defenses for their own protection from natural enemies (Kazana et al, 2007;Müller, 2009) (Fig 2). Herbivore-induced plants may also influence immune responses of herbivores to parasitoids (Bukovinszky et al, 2009).…”