Biochemical Evidence for Resistance of Rootstocks to the Peachtree Borer and Species Separation of Peachtree Borer and Lesser Peachtree Borer (Lepidoptera: Sesiidae) on Peach Trees

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Abstract
Emergence of peachtree borer (PTB), Synanthedon exitiosa (Say), moths from infested ‘Siberian C’ rootstocks was greater and began earlier in the season than from ‘Lovell’ rootstocks. The cyanogenic glucoside prunasin was present in ‘Siberian C’ at a level about twice that of ‘Lovell’, but the amino acids, reducing sugars, and phenolic compounds were not apparently different between the two rootstocks on eight sampling dates. Injured areas on scaffold branches of peach trees where lesser peachtree borers (LPTB), Synanthedon pictipes (Grote & Robinson), attacked had lower levels of prunasin than adjacent healthy tissue. Feeding studies indicated that PTB larvae gained significantly more weight when raised on an artificial diet augmented with the cyanogenic glucoside amygdalin, whereas LPTB larvae did not; however, both species survived for at least 21 d on the diet. The enzyme that degrades amygdalin and prunasin, β-glucosidase, was present in extracts of PTB larvae only if the larvae were raised on the diet containing amygdalin. LPTB larvae extracts had at least a 10-fold higher activity of the enzyme. Both PTB and LPTB larvae obtained from infested peach trees had β-glucosidase activity, but only PTB larvae had β-cyanoalanine synthase enzyme activity. The significance of the data in relation to separation of species is discussed.