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  • Author or Editor: James F. Walgenbach x
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Japanese beetles (JB), Popillia japonica Newman, are destructive, highly polyphagous herbivores that show a general preference for Rosaceous plants. Choice and nochoice feeding assays were conducted to determine the level of resistance among 10 taxa of Malus spp. Mill. Under no-choice conditions, M. baccata (L.) Borkh. `Jackii', M. × `Hargozam' Harvest Gold and M. transitoria (Balatin) Schneider `Schmitcutleaf' Golden Raindrops were highly resistant, with <2 cm2 leaf area consumed in 24 hours. M. × `Radiant' was highly susceptible, with 7.6 cm2 consumed, and the remaining six cultivars were intermediate. Under choice conditions, eight taxa were resistant with <10% defoliation, M. × `Red Splendor' was intermediate with 26%, and M. × `Radiant' was susceptible with 73% defoliation. Feeding responses to eight individual phenolics were tested in artificial diets over a range from 0 to 100 mm. Phloridzin, phloretin, naringenin, and catechin were all feeding deterrents, whereas quercetin and rutin were feeding stimulants. Chlorogenic acid stimulated feeding at low concentrations and deterred feeding at higher concentrations (i.e., a peak response). Kaempferol had no effect. Analysis of endogenous foliar phenolics showed considerable variation in concentrations among taxa. Stepwise multiple regression analysis identified phloridzin as the only endogenous phenolic that was significantly related to resistance under both choice and no-choice feeding conditions.

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Feeding intensity of adult Japanese beetle (Popillia japonica Newm.) was compared among 27 taxa of Prunus host plants during 24-hour no-choice feeding trials conducted on individual leaves. Fecal dry mass per beetle, a measure of feeding intensity, varied from 0 mg·d-1 for Prunus padus L. to 20.4 mg·d-1 for P. sargentii Rehd. and P. tomentosa Thunb. Prunus padus, P. laurocerasus L., P. mahaleb L., P. serotina Ehrh., P. virginiana L., P. americana Marsh., P. ×yedoensis Matsum., and P. besseyi Bailey were resistant based on feeding intensities of <4.3 mg·d-1 (levels not significantly different from zero). Feeding intensity decreased exponentially as endogenous foliar cyanide potential increased. Evaluation of the cyanogenic glucoside prunasin in artificial diets showed a similar relationship with feeding being reduced by 50% (ED50) at 4.9 mmol·kg-1 in the diet. Prunus mahaleb was highly resistant to Japanese beetles despite having low cyanide potential. Two coumarin compounds known to exist in P. mahaleb, herniarin and coumarin, were tested in artificial diets and were effective feeding deterrents with ED50 values of 5.9 and 2.5 mmol·kg-1 in the diet, respectively. This research demonstrated a wide range of host plant resistance to feeding by adult Japanese beetles and further indicates that prunasin, herniarin, and coumarin are important factors in host plant resistance to this pest.

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