Quantitative Resistance Traits and Suitability of Woody Plant Species for a Polyphagous Scarab, <I>Popillia japonica</I> Newman

Abstract

The Japanese beetle, Popillia japonica Newman, has an unusually broad host range among deciduous woody plants, yet it feeds only sparingly, or not at all, on certain species in the field. We evaluated beetles' preference, survival over time and fecundity on eight woody plant species historically rated as susceptible or resistant and, after verifying those ratings, tested whether resistance is correlated with so-called quantitative defense traits including leaf toughness, low nutrient content (water, nitrogen, and sugars), and relatively high amounts of tannins or saponins, traditionally associated with such plants. We further tested whether species unsuitable for Japanese beetles are also rejected by fall webworms, Hyphantria cunea (Drury) (Lepidoptera: Arctiidae), the expected outcome if the aforementioned traits serve as broad-based defenses against generalists. Choice tests supported historical resistance ratings for the selected species: tuliptree, lilac, dogwood, and Bradford callery pear were rejected by Japanese beetles, whereas sassafras, cherry plum, Virginia creeper, and littleleaf linden were readily eaten. Rejected species also were unsuitable for survival over time, or egg-laying, indicating beetles' inability to overcome the resistance factors through habituation, compensatory feeding, or detoxification. None of the aforementioned leaf traits was consistently higher or lower in the resistant or susceptible plants, and plant species rejected by Japanese beetles often were not rejected by fall webworms. Specialized secondary chemistry, not quantitative defenses, likely determines the Japanese beetle's dietary range among deciduous woody plant species it may encounter.

Japanese Beetle and Other Coleoptera Feeding on Grapevines in Eastern North America

“…Some host plants favor higher JB reproduction than others (Ladd 1987 ) , and the suitability of host plants appears to be dictated by secondary chemistry rather than quantitative traits, such as digestibility-reducing materials (Keathley and Potter 2008 ) . Feeding causes the release of volatile plant compounds, which lead to the attraction of even more beetles (Loughrin et al 1996 ) .…”

Arthropod Management in Vineyards:

“…Japanese beetle is highly polyphagous, feeding on more than 300 species representing 79 different plant families, with Vitaceae among the most preferred (Potter and Held 2002 ) . Some host plants favor higher JB reproduction than others (Ladd 1987 ) , and the suitability of host plants appears to be dictated by secondary chemistry rather than quantitative traits, such as digestibility-reducing materials (Keathley and Potter 2008 ) . Feeding causes the release of volatile plant compounds, which lead to the attraction of even more beetles (Loughrin et al 1996 ) .…”

Ecosystem consequences of selective feeding of an insect herbivore: palatability-decomposability relationship revisited

“…Tannins are common as anti-herbivore defensive substrates in a diverse group of woody plants (Feeny, 1970;Barbosa & Krischik, 1987). However, there is increasing evidence that tannins are not always a feeding deterrent against insect herbivores (Ayres et al, 1997;Forkner et al, 2004;Keathley & Potter, 2008). In particular, they have little or no effect on host selection of generalist insect herbivores, such as L. dispar and Popillia japonica Newman (Barbosa & Krischik, 1987;Keathley & Potter, 2008).…”

“…However, there is increasing evidence that tannins are not always a feeding deterrent against insect herbivores (Ayres et al, 1997;Forkner et al, 2004;Keathley & Potter, 2008). In particular, they have little or no effect on host selection of generalist insect herbivores, such as L. dispar and Popillia japonica Newman (Barbosa & Krischik, 1987;Keathley & Potter, 2008). In contrast, alkaloids have a strong feeding deterrence for the host plant selection of L. dispar larvae (e.g.…”

“…In most of the previous studies investigating the relationship between leaf palatability and litter decomposability, leaf palatability was determined by feeding experiments using slugs or crickets (Grime et al, 1996;Schädler et al, 2003;Pálková & Leps, 2008;Kurokawa et al, 2010), which are suitable test organisms as generalist herbivores in determining leaf palatability. However, the leaf palatability derived from those herbivores would not always be applicable to other insect herbivores, because leaf palatability would depend on the identity of insect species as a result of species-specific feeding adaptation to host plants (Keathley & Potter, 2008). Hence, a positive correlation between leaf palatability and litter decomposability may not always be expected in all plant-insect systems (Kurokawa & Nakashizuka, 2008).…”