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

Abstract

During host plant selection and particularly after alighting on a plant, chemical cues from the plant surface influence an insect's 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.

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

“…Accidental collection of internal leaf fluids such as sap was prevented by sealing the petiole after harvesting with melted (40 C) paraffin. Metabolites were dissolved and removed from leaves by spraying with ultra-pure water as per Fiala et al (1990) and concentrations of sugars, polyols and malic acid quantified as per the technique given in Lombarkia and Derridj (2008).…”

“…Typically, sugars act as phagostimulants, while the influence of amino acids is more variable, but includes action as phagostimulants (Chapman 2003;Schoonhoven et al 2005). Primary metabolites can also influence oviposition behaviour (Derridj et al 1989;Lombarkia and Derridj 2008). Lombarkia and Derridj (2008) found that variations in the proportional representation of fructose, sorbitol and myo-inositol could explain differences in oviposition by Cydia pomonella (L.) (Lepidoptera: Tortricidae) on resistant and susceptible apple cultivars.…”

“…Primary metabolites can also influence oviposition behaviour (Derridj et al 1989;Lombarkia and Derridj 2008). Lombarkia and Derridj (2008) found that variations in the proportional representation of fructose, sorbitol and myo-inositol could explain differences in oviposition by Cydia pomonella (L.) (Lepidoptera: Tortricidae) on resistant and susceptible apple cultivars. Epicuticular waxes can also act as insect feeding and oviposition stimulants -as well as deterrents (Eigenbrode and Espelie 1995;Schoonhoven et al 2005).…”

Foliar application of microdoses of sucrose to reduce codling moth Cydia pomonella L. (Lepidoptera: Tortricidae) damage to apple trees

“…The quantities and proportions of the blend compounds can vary with the organ, stage of development and variety. The exogenous foliar application of sucrose and D‐fructose can induce resistance by antixenosis to insect egg laying . Actually, these foliar applications of microdoses of sucrose (10 −3 %) or D‐fructose (10 −4 %) induced changes in the composition of the water‐soluble metabolome at the bourse shoot leaf surfaces that are usually preferred for egg laying.…”

Excised Leaf Bioassay: Phenotypic Expression of Natural Resistance in Apple against the Obliquebanded Leafroller

“…For example, the putative gene, Cob1, in 'Prima' confers resistance to the brownheaded leafrollers in New Zealand [43]. Sugar metabolites on the surface of apple foliage of 'Golden Delicious' influenced codling moth oviposition in France [44]. Research in Switzerland identified QTLs of 'Discovery' that are associated with codling moth susceptibility [45], which also appear to be a function of fruit quality [46] [47].…”