It is Japanese beetle time again—adults have already been detected in central Illinois. However, this is earlier than “usual.” I know many of you are wondering (as you do each year) why roses appear to be so susceptible to adult Japanese beetle feeding. Japanese beetle adults feed on both the flowers and leaves of roses, unlike other hosts. Research has demonstrated that natural sugar content and the presence of odoriferous compounds are important factors in determining susceptibility to attack by Japanese beetle adults. Roses contain a number of volatile chemicals, including eugenol and geraniol, that are very attractive to Japanese beetles. In fact, both chemicals have been the primary compounds used in mixtures for Japanese beetle lures. As Japanese beetle adults feed on roses, these chemicals are released, attracting more beetles to the area, which increases the likelihood of extensive feeding damage.
Several additional factors influence how attractive roses are to Japanese beetle adults: 1) roses in full sun tend to be favored more than those in wooded or shaded areas; 2) Japanese beetle adults seem to prefer and feed more extensively on white and yellow-colored rose flowers than apricot, orange, pink, mauve, and red; and 3) leaves fed upon by Japanese beetle adults produce odors or volatiles (as mentioned above) that attract other adult beetles. Other factors that may also affect susceptibility are rose height, fragrance, flower size, petal count, and number of blooms.