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Hymenopteran endoparasitoids that develop inside their lepidopteran host may exert a multitude of interactions with their host until they are able to emerge successfully from a developmentally arrested host that finally dies. Parasitoid interferences comprise physiological and biochemical modifications in the host endocrine and immune system which in turn affect host growth and development (reviewed in Edwards & Weaver, 2001). We use the gypsy moth, Lymantria dispar (Lep., Lymantriidae) and the endoparasitic, polydnavirus (PDV)-carrying braconid wasp Glyptapanteles liparidis (Hym., Braconidae) as a model system to study the endocrine changes associated with parasitism. Following wasp oviposition into young gypsy moth larvae, the parasitoids develop through two endoparasitic instars, and then emerge as newly molted third instars from a host that dies in the larval stage. In previous studies we have already described the endocrine changes in parasitized gypsy moth larvae which show an increase in juvenile hormone (JH) titers, a shift from JH II to JH III as the dominant homologue, and a prominent decrease in the JH degrading enzymes (Schopf & al., 1996; Schafellner & al., 2004). Here, we investigated the possible mechanisms that account for the JH elevating effects such as (i) stimulated host corpora allata activity, (ii) reduced activity of the JH metabolic enzymes such as JH esterase, and (iii) synthesis and release of JH by the parasitoid larvae.
Rising atmospheric CO2 is regarded as the main driver of global warming (Crowley, 2000). While temperature changes directly affect plants and animals (Root et al., 2003; Parmesan, 2006), the effects of CO2 on herbivores are mediated through changes in nutrient quality. Elevated concentrations of atmospheric CO2 are likely to increase photosynthetic activity and thus provide more C-based compounds which may alter plant chemical profiles and plant–herbivore–natural enemy interactions. There are several scenarios how insects will react when confronted with a different food quality. A nutrient poor diet, induced by nitrogen dilution, may result in compensatory feeding with either no adverse effects on insect performance or with negative effects on insect growth due to low digestibility of plant structural compounds (e.g. lignin) or toxic effects of secondary metabolites (e.g. tannins). Here we present data from on-tree feeding trials with larvae of the generalist herbivore Lymantria dispar and one of its natural enemies, the hymenopteran endoparasitoid Glyptapanteles liparidis, studied in 2005. The experiments were conducted at the Swiss free-air CO2 enrichment (FACE) site near Basel, in an approximately 80-100-yr-old, mixed-species forest. The data link changes in foliar chemistry of three tree species (Quercus petraea, Fagus sylvatica, Carpinus betulus) exposed to 540 ppm CO2 with herbivore and parasitoid performance.