Anne Nissinen

Effects of elevated carbon dioxide and ozone on volatile terpenoid emissions and multitrophic communication of transgenic insecticidal oilseed rape (Brassica napus)

Does transgenically incorporated insect resistance affect constitutive and herbivore-inducible terpenoid emissions and multitrophic communication under elevated atmospheric CO(2) or ozone (O(3))? This study aimed to clarify the possible interactions between allocation to direct defences (Bacillus thuringiensis (Bt) toxin production) and that to endogenous indirect defences under future climatic conditions. Terpenoid emissions were measured from vegetative-stage non-Bt and Bt Brassica napus grown in growth chambers under control or doubled CO(2), and control (filtered air) or 100 ppb O(3). The olfactometric orientation of Cotesia vestalis, an endoparasitoid of the herbivorous diamondback moth (Plutella xylostella), was assessed under the corresponding CO(2) and O(3) concentrations. The response of terpenoid emission to CO(2) or O(3) elevations was equivalent for Bt and non-Bt plants, but lower target herbivory reduced herbivore-inducible emissions from Bt plants. Elevated CO(2) increased emissions of most terpenoids, whereas O(3) reduced total terpenoid emissions. Cotesia vestalis orientated to host-damaged plants independent of plant type or CO(2) concentration. Under elevated O(3), host-damaged non-Bt plants attracted 75% of the parasitoids, but only 36.8% of parasitoids orientated to host-damaged Bt plants. Elevated O(3) has the potential to perturb specialized food-web communication in Bt crops.

Response of Plutella xylostella and its Parasitoid Cotesia plutellae to Volatile Compounds

The effects of limonene, a mixture of limonene + carvone (1:1, v/v), and methyl jasmonate (MeJA) on diamondback moth (DBM) (Plutella xylostella L.) oviposition, larval feeding, and the behavior of its larval parasitoid Cotesia plutellae (Kurdjumov) with cabbage (Brassica oleracea L. ssp. capitata, cvs. Rinda and Lennox) and broccoli (B. oleracea subsp. Italica cv Lucky) were tested. Limonene showed no deterrent effect on DBM when plants were sprayed with or exposed to limonene, although there was a cultivar difference. A mixture of limonene and carvone released from vermiculite showed a significant repellent effect, reducing the number of eggs laid on the cabbages. MeJA treatment reduced the relative growth rate (RGR) of larvae on cv Lennox leaves. In Y-tube olfactometer tests, C. plutellae preferred the odors of limonene and MeJA to filtered air. In cv Lennox, the parasitoid preferred DBM-damaged plants with limonene to such plants without limonene. C. plutellae females were repelled by the mixture of limonene + carvone. In both cultivars, exogenous MeJA induced the emission of the sesquiterpene (E,E)-α-farnesene, the homoterpene (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT), and green leaf volatile (Z)-3-hexenyl acetate + octanal. The attractive effect of limonene and MeJA predicts that these two compounds can be used in sustainable plant protection strategies in organic farming.

Constitutive and herbivore-inducible glucosinolate concentrations in oilseed rape (Brassica napus) leaves are not affected by Bt Cry1Ac insertion but change under elevated atmospheric CO2 and O3

Glucosinolates are plant secondary compounds involved in direct chemical defence by cruciferous plants against herbivores. The glucosinolate profile can be affected by abiotic and biotic environmental stimuli. We studied changes in glucosinolate patterns in leaves of non-transgenic oilseed rape (Brassica napus ssp. oleifera) under elevated atmospheric CO2 or ozone (O3) concentrations and compared them with those from transgenic for herbivore-resistance (Bacillus thuringiensis Cry1Ac endotoxin), to assess herbivory dynamics. Both elevated CO2 and O3 levels decreased indolic glucosinolate concentrations in transgenic and non-transgenic lines, whereas O3 specifically increased the concentration of an aromatic glucosinolate, 2-phenylethylglucosinolate. The herbivore-inducible indolic glucosinolate response was reduced in elevated O3 whereas elevated CO2 altered the induction dynamics of indolic and aliphatic glucosinolates. Herbivore-resistant Bt plants experienced minimal leaf damage after target herbivore Plutella xylostella feeding, but exhibited comparatively similar increase in glucosinolate concentrations after herbivory as non-transgenic plants, indicating that the endogenous glucosinolate defence was not severely compromised by transgenic modifications. The observed differences in constitutive and inducible glucosinolate concentrations of oilseed rape under elevated atmospheric CO2 and O3 might have implications for plant–herbivore interactions in Brassica crop-ecosystems in future climate scenarios.

Host location behavior of Cotesia plutellae Kurdjumov (Hymenoptera: Braconidae) in ambient and moderately elevated ozone in field conditions

In field O(3)-enrichment experiments increased herbivore densities have been reported, which could be due to negatively affected host location behavior of natural enemies. We addressed the impact of doubling background O(3) on the host location of the parasitoid Cotesia plutellae by conducting 24-h trials in an open-air O(3)-fumigation system during two consecutive years. Two circles (radii 1.40 and 4.00 m) of Plutella xylostella-infested potted cabbage plants were placed in the O(3) and ambient plots. Female wasps were released into each plot from the center, and observed 5 times over a 24-h period to assess their host location capability. Thereafter, plants were kept in laboratory conditions until larvae pupation to determine parasitism rates. No significant differences were detected between ambient and O(3)-enriched environments either in the number of wasps found in the field, or in the percentages of parasitized larvae. This suggests that moderately elevated O(3) will not affect the behavior of this parasitoid.

Effects of nitrogen deposition on tree growth and soil nutrients in boreal Scots pine stands

The aim of the study is to analyse effects of nitrogen deposition on tree growth and soil nutrients in boreal Scots pine stands. We describe a model ‘Forest Element Fluxes’ (FEF) which is based on theories of carbon and nutrient metabolism of trees, decomposition of soil organic matter (SOM), and solution chemistry in forest soil. The main idea is that element fluxes and regularities in tree structure determine soil development and stand growth. Tree roots, microbes which immobilise nitrogen (N) or nitrify NH4+, and cation exchange sites compete for inorganic N. Hydrological balance and chemical reactions, for example cation-exchange reactions and bicarbonate equilibrium, determine the leaching of N, H+, Al, Ca, Mg and K to surface waters. Observed leaching of N to brooks after clear-cutting was used to calibrate immobilisation of nitrogen. The model behaviour was tested by comparing the model outputs to stand growth at sites of different fertility. The model generated the stemwood production at the different sites, and the increase in nitrogen leaching after clear-cut. The analysis suggests that increase in nitrogen deposition has increased tree growth by 12%, but it is evident that other nutrients will become crucial with the present nitrogen deposition. The present accumulation of nitrogen in forest soil will lead to major changes in forest growth, nutrient availability and nitrogen leaching.

Short feeding period of carrot psyllid (Trioza apicalis) females at early growth stages of carrot reduces yield and causes leaf discolouration

Overwintered adult carrot psyllids [Trioza apicalis Förster (Homoptera: Psylloidea: Triozidae)] damage carrot [(Daucus carota ssp. sativum L.) (Apiaceae)] seedlings by phloem feeding on the leaves. The aim of this study was to investigate the carrot root and shoot growth in relation to carrot psyllid density during early growth stages. One, two, or three carrot psyllids were allowed to feed on carrot seedlings for 3 days. Leaf damage was measured at the 8‐leaf stage, and root, leaf fresh weight, and number of true leaves were measured at harvest. Both the age of the carrot seedling at infestation and the psyllid density had a significant effect on leaf damage at the 8‐leaf stage: seedlings damaged at the cotyledon stage exhibited more leaf damage than seedlings damaged at the 1‐leaf stage. A higher psyllid density significantly reduced the carrot root weight at harvest. The significant interaction of psyllid density with seedling age indicates that differently aged carrot seedlings responded differently to feeding: one psyllid feeding for 3 days at the cotyledon stage caused a significant yield loss, whereas three psyllids were needed to cause the same impact at the 1‐leaf stage. Carrot leaf weight at harvest was not reduced by carrot psyllid feeding: leaves recovered from the damage but roots did not. Our results confirm the farmers’ observations that a trap replacement period of 1 week for carrot psyllid monitoring is too long, especially at the cotyledon stage. Severe leaf discolouration on damaged carrots was observed at harvest. The possible reasons for this discolouration, such as toxin excreted in psyllid saliva or plant pathogenic mycoplasma infection, are discussed.

Essential oil composition in leaves of carrot varieties and preference of specialist and generalist sucking insect herbivores

1  The carrot psyllid Trioza apicalis and Lygus rugulipennis can cause serious damage to cultivated carrots, especially at the seedling stage. The essential oil composition in leaves of several carrot varieties was studied in relation to oviposition acceptance by sucking insect herbivores that have different feeding strategies. Of the insect species studied, T. apicalis is a carrot specialist, T. anthrisci is an Apiaceae specialist, and L. rugulipennis is a generalist. 2  The oil composition differed significantly between leaves from different carrot varieties (Flakkeer 2, Nantura, Parano, Napoli, Panther, Splendid, Nantes 3 Express). 3  There were no differences in the mean numbers of eggs laid by T. apicalis or T. anthrisci on different varieties, but L. rugulipennis laid fewer eggs on the Panther variety than on Nantes 3 Express. 4  There was a negative linear correlation between limonene concentration and number of eggs laid by T. apicalis, confirming that limonene is a repellent to the carrot psyllid. Results suggest that only particular compounds influence the preference of the carrot psyllid, and these compounds may not be the main components in the essential oil of carrots. 5  A positive correlation was found between myrcene concentration and number of eggs laid by T. anthrisci. Essential oil composition did not explain egg‐laying preference of L. rugulipennis. 6  The results indicate that essential oil composition of carrot varieties affects host preference of Apiaceae specialists more than that of generalists.

Elevated atmospheric ozone increases concentration of insecticidal Bacillus thuringiensis (Bt) Cry1Ac protein in Bt Brassica napus and reduces feeding of a Bt target herbivore on the non-transgenic parent

Sustained cultivation of Bacillus thuringiensis (Bt) transgenic crops requires stable transgene expression under variable abiotic conditions. We studied the interactions of Bt toxin production and chronic ozone exposure in Bt cry1Ac-transgenic oilseed rape and found that the insect resistance trait is robust under ozone elevations. Bt Cry1Ac concentrations were higher in the leaves of Bt oilseed rape grown under elevated ozone compared to control treatment, measured either per leaf fresh weight or per total soluble protein of leaves. The mean relative growth rate of a Bt target herbivore, Plutella xylostella L. larvae was negative on Bt plants in all ozone treatments. On the non-transgenic plants, larval feeding damage was reduced under elevated ozone. Our results indicate the need for monitoring fluctuations in Bt toxin concentrations to reveal the potential of ozone exposure for altering dosing of Bt proteins to target and non-target herbivores in field environments experiencing increasing ozone pollution.