Entomologia Experimentalis et Applicata 101: 25–32, 2001. © 2001 Kluwer Academic Publishers. Printed in the Netherlands. 25 Potential for habituation to a neem-based feeding deterrent in Japanese beetles, Popillia japonica D.W. Held, T. Eaton & D.A. Potter University of Kentucky, Department of Entomology, S-225 Agric. Science Bldg. North, Lexington, KY 40546-0091, USA Accepted: August 2, 2001 Key words: Japanese beetle, habituation, Popillia japonica, neem, azadirachtin, polyphagy, Coleoptera, Scarabaei- dae Abstract We tested the potential for the Japanese beetle, Popillia japonica Newman, to habituate to a neem-based feeding deterrent applied to foliage of linden, Tilia cordata L., a preferred host for the adults. Female beetles’ consumption of control foliage versus foliage treated with either a low or high rate of neem insecticide, corresponding to 9 or 39 pm azadirachtin, respectively, was tested in a series of 4-h choice or no-choice tests over four successive days. In another experiment, females were conditioned for 22 h with either control foliage, leaves treated with the low rate, or a mixture of both treated and untreated leaves. Deterrence of either the low or high rate of neem to these beetles was then evaluated in choice tests with control foliage, as before. In choice tests, mean consumption of control foliage was always greater than for treated foliage, regardless of rate. There was, however, proportionately more feeding on foliage treated with the high rate upon successive exposures. In no-choice tests, beetles initially deterred by the low rate were not significantly deterred by that rate by the third and fourth days of the experiment. Finally, beetles conditioned by exposure to leaves treated with the low rate were not deterred by that rate in a subsequent choice test, although they were deterred by the higher rate. Despite these trends, we suggest that Japanese beetles’ polyphagy and mobility probably would reduce the likelihood for habituation to neem-based feeding deterrents in the field. Introduction Antifeedants that deter or suppress feeding by phy- tophagous insects have potential value for plant pro- tection (Chapman, 1974; Warthen, 1979; Prokopy & Lewis, 1993). These may be either extracts of plants that are resistant to the target pest (Metzger & Grant, 1932; Chapman, 1974), or commercially formu- lated secondary plant compounds such as azadirachtin (Schmutterer, 1990). The utility of antifeedants for pest management may be limited by high cost (Chap- man, 1974), lack of efficacy (Metzger & Grant, 1932; Witt et al., 1999), source variability (Ladd et al., 1978), and the possibility that pests may overcome them through experience-based changes such as ha- bituation (Bernays, 1983; Jermy, 1987; Prokopy & Lewis, 1993). Habituation, or the waning in response to a stim- ulus, is thought to be an adaptation that allows herbi- vores to exploit initially distasteful and rejected, but non-toxic hosts (Jermy et al., 1982; Jermy, 1987; Bernays & Chapman, 1994). This phenomenon can re- sult from repeated exposure through palpation, biting, or ingestion, to deterrent compounds present either as natural constituents of a non-host or applied as plant protectants (Szentesi & Bernays, 1984). The capacity for habituation may be greater in polyphagous than in oligophagous or monophagous species (Jermy et al., 1982; Bernays, 1983; Prokopy & Lewis, 1993). Methods by which antifeedants are deployed in pest management may also influence the rate and extent of habituation. Factors such as mixture heterogeneity and concentration of deterrent compounds, as well as host plant diversity, may decrease the potential for ha-