Cascading effects of N input on tritrophic (plant–aphid–parasitoid) interactions

Abstract

Because N is frequently the most limiting mineral macronutrient for plants in terrestrial ecosystems, modulating N input may have ecological consequences through trophic levels. Thus, in agro‐ecosystems, the success of natural enemies may depend not only from their herbivorous hosts but also from the host plant whose qualities may be modulated by N input. We manipulated foliar N concentrations by providing to Camelina sativa plants three different nitrogen rates (control, optimal, and excessive). We examined how the altered host‐plant nutritional quality influenced the performances of two aphid species, the generalist green peach aphid, Myzus persicae, and the specialist cabbage aphid, Brevicoryne brassicae, and their common parasitoid Diaeretiella rapae. Both N inputs led to increased N concentrations in the plants but induced contrasted concentrations within aphid bodies depending on the species. Compared to the control, plant biomass increased when receiving the optimal N treatment but decreased under the excessive treatment. Performances of M. persicae improved under the optimal treatment compared to the control and excessive treatments whereas B. brassicae parameters declined following the excessive N treatment. In no‐choice trials, emergence rates of D. rapae developing in M. persicae were higher on both optimum and excessive N treatments, whereas they remained stable whatever the treatment when developing in B. brassicae. Size of emerging D. rapae females was positively affected by the treatment only when it developed in M. persicae on the excessive N treatment. This work showed that contrary to an optimal N treatment, when N was delivered in excess, plant suitability was reduced and consequently affected negatively aphid parameters. Surprisingly, these negative effects resulted in no or positive consequences on parasitoid parameters, suggesting a buffered effect at the third trophic level. Host N content, host suitability, and dietary specialization appear to be major factors explaining the functioning of our studied system.

Tri-trophic interactions among nitrogen-fertilized tomato cultivars, the tomato fruit worm, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) and the ectoparasitoid, Habrobracon hebetor (Say) (Hymenoptera: Braconidae)

“…The larval period of the parasitoid was significantly affected by N levels on different The means followed by different capital letters in the rows and small letters in the columns for every stage refer to the significant differences (P ≤ 5%) n0 no fertilization, n− standard fertilization minus 30%, ns standard fertilization, n+ standard fertilization plus 30% treatments (P < 0.05), and the application of fertilizers improved the developmental rate of the parasitoid. These results are consistent with the findings of Chesnais et al (2016). The total pre-adult period ranged from 10.14 ± 0.09 to 12.83 ± 0.11 days, which was significantly different among treatments by increasing N levels, except P cultivar (P < 0.05).…”

Host plant nitrogen enrichment has both positive and negative effects on the larval growth of a specialist butterfly

“…Hence, there is probably a threshold beyond which the benefits of eating nitrogen‐enriched food decrease, and further nitrogen enrichment may result in digestion costs (Stockhoff, ; Fischer & Fiedler, ). This hypothesis is supported by population‐level studies showing that high nitrogen levels are typically associated with declines in population size (Weiss, ), and studies focusing on communities which found a decline in species diversity in nitrogen‐rich areas (Öckinger et al ., ; Feest et al ., ), these effects being dependent on how phytophagous insects adjust their feeding behaviour and growth to these new conditions (Payne et al ., ; Chesnais et al ., ).…”

How the use of nitrogen fertiliser may switch plant suitability for aphids: the case of Miscanthus, a promising biomass crop, and the aphid pest Rhopalosiphum maidis

“…Consistent with our assumption about M. sacchariflorus , R. maidis aphids weight was significantly greater in treated (+N) plants and their feeding behaviour seemed to be positively affected. Indeed, we recorded a significantly shorter duration of stylet derailment (F), a phase generally considered as an indicator of plant resistance . The phloem sap intake duration was similar for both treatments, although phloem quality was probably better in treated plants, as indicated by their smaller leaf C:N ratio.…”

“…Indeed, we recorded a significantly shorter duration of stylet derailment (F), a phase generally considered as an indicator of plant resistance. 26 The phloem sap intake duration was similar for both treatments, although phloem quality was probably better in treated plants, as indicated by their smaller leaf C:N ratio. This could explain why R. maidis weight was so remarkably greater.…”

“…For each treatment and species, plant sprouts were individualised and weighed using an electronic balance (Mettler Toledo ML204, maximum 220 g, d = 0.1 mg), then placed in the freezer at −80 ∘ C for later use in C and N content measurements as described in previous works. 26 For M. sacchariflorus, 12 plants were weighed for the − N treatment, and seven for the + N treatment. Eleven plants of M. × giganteus were weighed for the − N treatment, and ten plants for the + N treatment.…”