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.

The basis for resistance of Bradford callery pear, Pyrus calleryana Decaisne ‘Bradford,’ [Rosaceae] to the Japanese beetle, Popillia japonica Newman, was investigated. Chloroform‐dipping rendered leaves palatable, initially suggesting that deterrent waxes had been removed. However, extracts containing surface waxes were not deterrent. Subsequent experiments showed that increased palatability of solvent‐dipped leaves is associated with enzymatic tissue browning, characteristic of polyphenol oxidases, rather than simply release of phagostimulants from surface disruption of damaged leaves. Frozen and thawed leaves showed similar browning, becoming increasingly palatable for several hours after thawing. Palatability changes were temperature‐ and aerobic‐sensitive, further evidence that oxidizing enzymes are involved. Juice from leaves that had been frozen and thawed stimulated feeding on glass fiber disks, whereas fresh leaf juice did not. Survival and fecundity were much higher for beetles fed frozen and thawed or chloroform‐dipped Bradford pear leaves than for beetles fed normal leaves. We hypothesize that decompartmentalization of deterrent compounds, possibly phenolics, followed by enzymatic oxidation and altered leaf chemistry may explain the increased palatability of chloroform‐dipped or frozen and thawed Bradford pear tissue to P. japonica. This approach may be helpful in identifying specific compounds responsible for resistance of woody plants to generalist insects.

Ontogenetic changes in feeding behavior of armyworms, Pseudaletia unipucta (Haworth), were compared on tall fescue [Schedonorus arundinaceus (Schreb.) Dumort] cultivars with spiny-, intermediate-, or smoothedged leaf blades to clarify whether the edge spines deter caterpillars, in which case release of modified, smooth-edged forage grasses for improved livestock performance might aggravate armyworm damage to pastures. Edge biting, success initiating edge-feeding, and propensity to window-or edge-feed were observed for individual 2nd, 3rd, or 4th instars on grass leaf blades with intact margins. Early second instars bit smooth and spiny leaf edges with equal frequency but were unable to initiate edge-feeding. They fed on leaf edges after margins were cut away, but not when leaf juice was applied to intact edges, indicating the leaf margin is a barrier. Third and 4th instars mostly edge-fed on smooth leaves, but on the grasses with spiny margins they compensated for the difficulty of edge-feeding by prolonging their window-feeding. There was no developmental cost to window-feeding by 3rd instars, but 4th instars suffered reduced weight gain on spiny grass apparently because, unlike earlier instars, their mandibles are too large and not well shaped for efficient window-feeding between the parallel vascular bundles. Armyworms display behavioral plasticity in feeding mode in response to spiny-versus smooth-edged grasses. Greater use of smooth-bladed pasture grasses may result in proportionately more edge-feeding by armyworms but is unlikely to result in markedly greater pasture losses because this grass-feeding specialist so effectively exploits conventional tall fescue despite its structural characteristics.

Poor livestock performance on tall fescue is linked to infection by a fungal endophyte that enhances grass resistance to stress, including herbivory, while producing ergot alkaloids toxic to vertebrate grazers. Novel ‘safe’ endophyte/grass associations produce no ergot alkaloids yet retain stand persistence, but they could be more susceptible to insect outbreaks. We tested the hypothesis that grass‐feeding insects are more abundant in novel endophyte pastures compared with those containing common endophyte. Above‐ and below‐ground herbivores were sampled across two growing seasons in pastures containing common strain endophyte (KY31), novel endophytes (MaxQ or AR584) or endophyte free. We also sampled natural enemies as an indicator of possible tritrophic effects. With a few exceptions, numbers of predatory, chewing (grasshoppers, crickets, caterpillars) or sucking insects (leafhoppers, planthoppers) were similar in common and novel endophyte pastures. Contrary to our hypothesis, Aphrodes spp. leafhoppers were more abundant in KY31 than other pasture types in 2008; their nymphs also were more abundant in KY31 than in MaxQ in 2009. Adults (but not total numbers or nymphs) of another leafhopper, Psammotettix striatus, were less abundant in KY31 than other pasture types in 2009. Popillia japonica and Cyclocephala spp. grubs did not differ in density, weight or instar among the endophyte‐containing associations. In feeding assays, armyworm (Mythimna unipuncta) survival was higher on MaxQ and NE9301, and weight gain was higher on NE9301, suggesting armyworm outbreaks could be more severe on such grasses, but that result may not be attributable solely to alkaloids because common strain and endophyte‐free grasses did not differ in either parameter. Caterpillar abundance did not differ among pasture types in the field. Our results suggest that re‐seeding common strain endophytic pastures with livestock‐safe novel endophyte/grass associations to alleviate fescue toxicosis is unlikely to promote markedly higher populations of plant‐feeding insects.

Grass breeders are developing new forage‐type tall fescue [Schedonorus arundinaceus (Schreb.) Dumort = Lolium arundinaceum (Schreb.) Darbysh., formerly known as Festuca arundinacea Schreb.] cultivars with smoother texture, improved nutritive value, and reduced fiber for improved livestock performance. We tested if such grasses are also more susceptible to a grass‐feeding caterpillar. True armyworms, Pseudaletia unipuncta (Haworth), were reared from first instar to adult on grass clippings from thirteen fescue cultivars or accessions differing in texture (smooth vs. standard), ecotype (northern European vs. Mediterranean), use (pasture vs. turf‐type), or provenance to clarify how modifying the texture (edge spines, trichomes, or cellulose margin), thickness, tissue strength, and nutritive value (dry matter, fiber, ash, or N) of pasture grasses will affect their resistance. We also studied feeding site initiation and development of first instars on intact leaf blades when prevented from exploiting a cut leaf edge. Larvae performed equally well across all groups when reared with grass clippings, despite variation in leaf texture and nutritive value. On intact blades, however, leaf thickness and tissue strength were correlated with reduced feeding site initiation and larval development. Gregarious and window feeding may allow more efficient exploitation of common feeding sites on tougher leaves. True armyworm is adapted to feed on a range of structurally‐diverse grasses, so increased use of forage‐type tall fescue cultivars with smoother texture or reduced fiber is unlikely to worsen its damage to pastures.