Todd Parlo Wrote:
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> It may be interesting to find out how these researchers attained sap readings.
I was curious enough to track down one of the principles and pose the question.
Mr Potter wrote back:
"For our study (reprint attached), we did not extract sap. Rather, volatile compounds emitted by leaves were trapped and analyzed to compare the odors emitted by foliage of resistant versus susceptible varieties. The conclusion was that there is relatively little difference in volatile bouquets emitted by intact leaves of resistant versus susceptible cultivars. Later work showed that those cultivars do differ in palatability (acceptance or rejection) once the beetles land and taste the foliage – probably related to balance of feeding deterrents and stimulants (e.g., sugars). Once the leaves are damaged by Japanese beetles, they emit complex volatile blends that attract more beetles (like “sharks to a blood trail”)."
He also was kind enough to attach a pdf of the paper and I found the following passage:
"Recently, Spicer et al. (1995) reported marked differences in susceptibility of 42 crabapple cultivars (Malus spp.) to the Japanese beetle. Defoliation ranged from nearly 100% to less than 10% for cultivars grown at the same site. Sub-sequently, a number of physical and chemical variables of crabapple leaves were examined in an attempt to determine the factors involved in Japanese beetle discrimination between different cultivars (Potter and Spicer, unpublished results). Leaves of preferred cultivars generally contained higher levels of nitro-gen and
sugars and lower amounts of tannins…"
Since that seemed to be the paper that did have a sugar variable, and he was involved with it as well, I have written back asking if the methodology used then could be expounded upon. More if and when I get a reply.
If you are interested in the full text of the first paper, or are interested in the follow up which details the "sharks to a blood trail", pm me and I will email you a copy of either as Mr Potter forwarded a pdf of both.