RELATIVE SUSCEPTIBILITY OF WOODY LANDSCAPE PLANTS TO JAPANESE BEETLE (COLEOPTERA: SCARABAEIDAE)

Journal of Arboriculture, Nov 2004 by Held, David W

Abstract. The Japanese beetle (Popillia japonica Newman) was introduced to a New Jersey nursery in 1916 and continues to spread across the United States and Canada. Adults attack foliage, flowers, and fruit of more than 300 species of plants; however, some plants are notably resistant. This paper summarizes data on plant susceptibility of woody plants to Japanese beetles collected from observations and controlled experiments. Resistance to Japanese beetle has been documented among species of maples (Acer) and birch (Betula) and among cultivars of crabapple (Malus), crapemyrtle (Lagerstroemia), and linden (Tilia). Production of certain plant odors, presence of secondary compounds in leaves, and leaf pubescence are factors affecting resistance to this insect. Host plant resistance is the most sustainable means of managing feeding damage or plant losses resulting from Japanese beetle adults. When suitable, incorporating Japanese beetle-resistant plants into new landscapes can reduce or eliminate the expense of replacing damaged plants or frequent insecticide applications.

Key Words. Popillia japonica; Japanese beetle; integrated pest management; host plant resistance.

The Japanese beeile (Popillia japonica Newman) is one of the most damaging pests of urban landscapes in the eastern United States. Yearly costs for management and mitigation of damage are estimated at US$500 million (USDA/APHIS 2002). This scarab was introduced in 1916 to the eastern United States in infested nursery stock (Fleming 1972). At that time, entomologists were unaware of the pernicious nature of this species as evidenced from this quote, "While inspecting a nursery in southern New Jersey during August 1916, our attention was attracted by a scarabaeid feeding on the lips of Crataegus. ... Inasmuch as it was assumed to be a southern species, no particular attention to it was paid at that time" (Dickerson and Weiss 1918). In the presence of abundant grass and pasture land, and the apparent absence of natural enemies, the Japanese beetle flourished. Currently, this immigrant species partially infests or is established in all stales east of the Mississippi River except Florida, and its range extends north into Canada (NAPIS 2003).

Adult Japanese beetles are broadly oval, 8 to 11 mm (aboul 0.5 in.) long, metallic green in color and have coppery-brown wing covers. Larvae are typical white grubs, C-shaped and cream colored, with three pairs of legs and a light-brown head capsule (Fleming 1972). Japanese beetle has a 1-year life cycle, spending most of its life underground as a grub. A small grub, about 1.5 mm (0.06 in.) long, emerges from an egg laid 3 to 5 cm (1 to 2 in.) deep into moist soil, typically under turfgrass. Females alternate between periods of feeding and mating on host plants and oviposition. During her lifetime, a female will have 12 or more egg-laying bouts and produce 40 to 60 eggs. Once hatched, grubs feed on roots and will reach full size, about 32 mm (1.25 in.) long, by late summer (Fleming 1972). Management of grubs is accomplished with soil insecticides applied preventively (e.g., Merit or Mach2) before egg hatch, or curatively (e.g., Dylox or Sevin) after small grubs are present. Presence of grubs or grub damage may be associated with nearby plants infested with adults; however, females will disperse to find a suitable site for oviposition (Fleming 1972; Potter and Held 2002).

Japanese beetle adults are active from June through August in most of its geographic range. These beetles are day active and mate and feed concurrently on host plants. They can defoliate more than 300 species of woody and herbaceous plants in 79 plant families (Fleming 1972; Potter and Held 2002). Because of their mobility and gregarious habits, swarms of Japanese beetle continually infest and defoliate new plants during the growing season. These factors can complicate control of adults, especially when using short-residual insecticides such as pyrethroids. Certain systemic products delivered through soil or trunk injection are available for control of Japanese beetles on mature, established street and residential trees; however, that treatment may not be an option for newly installed landscape plantings.

Use of insecticides to manage Japanese beetle can be reduced if resistant plants are substituted for more susceptible ones in commercial and residential landscapes. Observations and controlled experiments indicate that certain plant species, and even cultivars of the same species, vary in susceptibility. For example, moderate or complete resistance to Japanese beetle feeding is documented for most evergreens, certain crabapples (Malus), lindens (Tilia), maples (Acer), birch (Betula), and crapemyrtles (Lagerstroemia) (Fleming 1972; Ranney and Walgenbach 1992; Spicer et al. 1995; Potter et al. 1998; Miller and Ware 1999; Pettis et al. 2004). There is no resistance to Japanese beetle among species or cultivars of rose (Rosa) (Potter et al. 1998; Held and Potter 2004).