Sylvie Derridj

Plant growth stages in the interspecific oviposition preference of the european corn borer and relations with chemicals present on the leaf surfaces

The oviposition preference of the European Corn Borer Ostrinia nubilalis Hbn. Lepidoptera pyralidae was studied in relation to phenological stages of different plant species (Zea mays L., Helianthus annuus L., Phaseolus vulgaris L.). The experiments were done in greenhouses in binary choices. The results show that the plant phenological stages were more important than the plant species in the insect oviposition preference. When the choice was given between two plant species throughout their growth, the preference varied in relation to the development of each species. The relative differences in fructose amounts found on the leaf surfaces (phylloplane) were highly correlated with the insect oviposition preference. Amounts of proline, glucose and sucrose may accentuate this previous effect.

Incidence of apple fruit and leaf surface metabolites on Cydia pomonella oviposition

Water soluble metabolites identified from surfaces of apple tree fruit and leaf stimulate oviposition in Cydia pomonella L. The effects of two artificial blends of primary metabolites representing fruit and leaf surfaces, respectively, and of components within the blends were examined on egg‐laying after two time periods: 3 min and 25 min of darkness. An artificial mixture of six metabolites, viz., three sugar alcohols (sorbitol, quebrachitol, and myo‐inositol) and three sugars (glucose, fructose, and sucrose) did stimulate egg‐laying. Fructose, sorbitol, and myo‐inositol are important components of the stimulatory blend. Contact durations may induce variations in egg‐laying responses. After 3 min of darkness, there were no differences in numbers of females laying eggs nor in the numbers of eggs laid on cloths treated with the complete blends and the controls. There were, however, clear effects of groups of compounds and of individual compounds. Reduced blends without sugars and sugar alcohols were in many cases significantly less stimulatory than the complete blends and the controls. After 25 min of darkness, the proportions of females laying eggs as well as the numbers of eggs were higher after treatment with the complete blends than on the controls. The proportions of females laying eggs on cloths treated with the reduced blends were rather similar to the controls, whereas there were still significant effects on the numbers of eggs laid after treatment with reduced blends derived from fruits but not from leaves.

Increase of European corn borer (Ostrinia nubilalis) oviposition induced by a treatment of maize plants with maleic hydrazide: Role of leaf carbohydrate content

Earlier experiments seemed to indicate a positive correlation between the choice of the oviposition site of Ostrinia nubilalis Hbn. on maize (Zea mays L.) leaves and their carbohydrate content. In the present study a growth regulator, maleic hydrazide (M.H.), is used to increase the soluble carbohydrate content of the plants. It seems that the insect prefers to oviposit on the treated plants which display higher carbohydrate contents. On the other hand the distribution of the egg‐masses on the leaf blade is also modified. Plant height has no influence on these choices.

Nutrients on the Leaf Surface

The leaf surface constitutes the interface between the external environment and the plant tissues. It is limited by a thin layer (about 1.0 µm), the cuticle, composed of non soluble lipid polymers (the cutin) in which soluble lipid waxes are embedded. The function of the cuticle is to protect the leaf from external (biotic and abiotic) aggressions and to regulate the passage of water from the plant to its environment (Schonherr, 1976), of inorganic ions (Ferrandon and Chamel, 1989), and organic solutes (Tukey, 1970; Mengel et al., 1990) coming from tissues and particularly from the extracellular matrix and intercellular air spaces (apoplast). Under natural conditions many factors may cause injury to leaf surfaces: indirectly such as physiological disorders, nutrient and moisture deficiencies, adverse temperatures, poor aeration, deficient light and leaching and directly such as invasion of micro-organisms, attack by insects, wind and air pollution, (Tukey, 1963).

Leaf epicuticular lipids of Prunus laurocerasus: importance of extraction methods

Abstract Compounds of four chemical classes (alkanes, primary alcohols, free fatty acids and polar lipids) were isolated, identified and quantified for the first time from the epicuticular waxes of Prunus laurocerasus leaves. Alkanes were the major class and constituted 80% of the wax. Using chloroform, more wax was removed from leaves after dipping for 210 sec than by rinsing for the same length of time. Duration of solvent contact also had an effect on the composition of the soluble cuticular lipids extracted. Alkanes and primary alcohols were extracted earlier than fatty acids and, whatever the class of compounds, short chain-length homologues (C 16 C 25 ) needed more time to be extracted from the cuticle than longer ones (C 26 C 35 ).

Resistance of apple trees to Cydia pomonella egg-laying due to leaf surface metabolites

During host plant selection and particularly after alighting on a plant, chemical cues from the plant surface influence an insects acceptance of the plant and, subsequently, its egg‐laying behaviour. Primary metabolites in the phylloplane may be more important than hitherto known. We have shown that soluble carbohydrates, such as glucose, fructose, and sucrose, and sugar alcohols, such as sorbitol, quebrachitol, and myo‐inositol, can be detected by insects after contacting the plant and that they positively influence egg‐laying of the codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae), on apple trees. We addressed the question whether a lack of these substances could also explain apple tree resistance to C. pomonella in terms of reduced egg‐laying. Leaf surface washings were collected in an apple orchard by spraying water on the resistant cultivar X65‐11 and on the susceptible cultivar P5R50A4. The washings were tested on a nylon cloth on isolated females under no‐choice conditions. The washings were analysed and synthetic blends, each consisting of the six metabolites in the proportions established in the leaf surface washings of both cultivars, were then tested for their effect on egg‐laying of C. pomonella. Dose–response egg‐laying tests were carried out on substrates impregnated with the X65‐11 leaf surface blend at 1, 100, 1 000, and 10 000 times the natural dose. Egg‐laying behaviour in the bioassays with leaf surface washings of both cultivars closely resembled egg‐laying in the orchard. Washings of P5R50A4 stimulated egg‐laying to a greater extent than those of X65‐11 and the water control. Synthetic blends reduced substrate acceptance and egg‐laying, compared to the washings of X65‐11. Ratios between components within the blend are responsible for this resistance. In conclusion, quantities and ratios of the six primary metabolites found on the leaf surface may influence host preference of C. pomonella as well as their egg‐laying behaviour, thus they may play a role in the trees’ resistance to the codling moth.

Species-specific composition of free amino acids on the leaf surface of fourSenecio species.

The specificity of the chemical composition of the leaf surface of fourSenecio species was studied in order to understand the host selection ofTyria jacobaeae, a monophagous moth that hasSenecio jacobaea as its principal host plant. Pyrrolizidine alkaloids characteristic forSenecio species were not detected in water and sulfuric acid extracts of the leaf surface ofSenecio jacobaea. Water extracts of the leaf surfaces ofS. jacobaea, S. vulgaris, S. viscosus, andS. sylvaticus contained low concentrations of free amino acids. The proportions of these amino acids were very different from those inside the leaf tissues. In a discriminant analysis, the four species could be completely separated on the basis of the relative proportions of amino acids on the leaf surface.

Statistical Analysis of Insect Preference in Two-Choice Experiments

Many studies of insect behavior in relation to chemicals from different plants require the use of statistical tests for determining whether attraction, repulsion, or neutrality is significant. In this paper, we propose a simple and efficient nonparametric statistical procedure for testing hypotheses about insect preference in two-choice experiments with individual insects. Three criteria are provided in order to detect the following alternatives to neutrality: (i) general attraction (or repulsion) in a sample population, (ii) strong variability of the individual responses, and (iii) slight but similar behavioral effects. Illustrations are given from two-choice experiments concerning the European corn borer (Ostrinia nubilalisHbn.) females oviposition behavior.

Epicuticular waxes and plant primary metabolites on the surfaces of juvenile Eucalyptus globulus and E. nitens (Myrtaceae) leaves

Our knowledge of the composition of the waxes on the surfaces of Eucalyptus leaves is growing but that of plant primary metabolites has been completely overlooked. The diffusion of primary metabolites above the cuticle exposes them to a variety of herbivorous taxa and has the potential to influence their responses to that plant. Juvenile leaves of two families of Eucalyptus globulus Labill. ssp. globulus and two families of E. nitens (Deane & Maiden) Maiden had 11 out of 16 of the epicuticular waxes that were detected in common. However, two phenylethyl esters (waxes) were only detected on leaves of one family of E. globulus and two benzyl esters (waxes) were not detected or were uncommon in samples from E. nitens. Wax compounds were generally found in samples from both leaf surfaces but a few were only detected in samples from particular sides. Species and families of eucalypt did not differ significantly in the concentrations of free sugars, polyols, malic acid or γ-aminobutyric acid (GABA) (all plant primary metabolites) collected from the surfaces of leaves. However, concentrations of all these metabolites were usually higher in collections from the upper surfaces of leaves. High wax abundance, especially on the lower surfaces of E. globulus leaves, is suspected to have hindered dissolution of all the primary metabolites quantified. Several free amino acids exhibited significant species-level differences in concentrations, namely the aromatic, amide and sulfur-containing amino acids as well as proline; family-level differences in amino acid concentrations were not significant. Australian and overseas evidence showing that differences in waxes and primary metabolites can be influential in plant susceptibility to herbivorous taxa is considered with respect to the threats posed by the autumn gum moth and Mycosphaerella leaf spot fungi.

Composition en métabolites primaires de la surface foliaire du poireau: étude comparative, incidence sur la sélection de la plante-hôte pour pondre par un insecte

Summary Chemical analyses of leek leachates show a large variety of metabolites as already observed on different plant species (corn, sunflower, tansy ragwort), especially free amino acids (21) and soluble carbohydrates. Leek leachates i) permit leek discrimination from other plant species by free amino acids proportions, ii) show caracteristic unknown ninhydrine positive substances and iii) higher levels of fructose, glucose and sucrose than leachates from young maize plant. These last substances, known to be active in the oviposition site preference of the generalist lepidoptera Ostrinia nubilalis Hbn., are still active in the host oviposition preference between leek and young corn plant. However, the highest number of eggs masses laid on leek leaves come off, and first instar larvae do not feed.