The Japanese beetle (JB), Popillia japonica, was first discovered in the United States in 1916 just across the river from Philadelphia, PA at a nursery near Riverton, NJ. It is believed that JB larvae came into the area with a shipment of iris bulbs from Japan sometime before 1912 when commodities entering the U.S. started being inspected. In its native Japan, this insect was much less of a pest than it was to become in its adopted home. There, it was replaced by other Popillia species to the south, and was common only on northern Honshu and Hokkaido Islands, where grasslands provided a favorable larval habitat. However, cooler temperatures at those latitudes restricted the beetle to a two year life cycle rather than the one year cycle found in most of its U.S. distribution. In addition, a well synchronized parasitic fly has played a major role in suppressing populations there. This combination of lack of larval habitat, cool temperatures, and an effective parasite continues to keep JB populations in check in Japan.
In contrast, the beetle flourished in the United States, and greatly expanded its range from the original New Jersey establishment. The combination of readily available food sources for adults, abundant, well watered, turf for larval development, warm summer temperatures, and the lack of a specific natural enemy has favored the buildup and spread of beetle populations. At this time, JB are well established in all states east of the Mississippi River with the exception of Mississippi and Florida. Localized populations exist in Minnesota, Iowa, Missouri, Kansas, and Nebraska. Recently, beetles have also been captured in Texas, Arkansas, Colorado, Utah, and Oklahoma. Isolated infestations have been eliminated from three sites in California, and two locations in Oregon, leaving the west coast beetle free.
There are many biological agents which have a suppressing effect on JB populations. In contrast to the days of organo-chlorine pesticides, no one factor can be expected to "solve" the JB problem. Instead, a concentrated effort is needed to integrate various components to obtain effective, sustainable beetle control.
Vertebrate Predators. Birds such as grackles, meadowlarks, starlings, cardinals, and catbirds have been reported as significant predators of JB adults. In addition, pheasants, chickens, ducks, geese, and guineas readily feed on the beetles. Starlings, grackles, crows, and gulls also devour large numbers of JB larvae. The damage to turf by foraging crows can be more serious than that caused by the JB larvae themselves. A similar situation exists with skunks, racoons, and moles as predators. They can remove large numbers of grubs from the field, but the damage they inflict to the grass is often an unacceptable tradeoff for turf managers. Although toads, shrews, and mice may feed on JB adults or larvae, they have not been noted as an important factor in beetle control.
Invertebrate Predators. Spiders, praying mantids, robber flies and soldier bugs have little effect on adult JB populations. The effects of ground beetles and ants as predators on eggs and larvae are more important. A ground beetle, introduced from Japan in 1920-21, failed to survive the winter and did not become established. Many native species of ground beetles and ants feed on the immature stages of JB, but their true value has been hard to quantify. Mechanical and/or chemical eliminations of these predators indicate that they can be an important component in JB suppression. Control measures with less negative impact on these natural predators will be more effective in the long run than those with higher or broader original toxicities. The value of ants is further complicated since they can be turf pests in their own right, and have been observed as predators on some JB parasitoids.
PARASITIC INSECTS (PARASITOIDS)
Considerable effort has been expended in the foreign exploration for parasitoids of the JB, and on their establishment here in the U.S. Although eight species of Diptera (flies) and 16 species of Hymenoptera (wasps) were introduced from the Far East, only three tachinid flies and two tiphiid wasps were known to become established. Today, two of these parasitoids, the winsome fly, Istocheta (=Hyperecteina) aldrichi, and the Spring Tiphia, Tiphia vernalis, are important biological agents in some locations.
The introduced tachinid I. aldrichi is now found thoughout Connecticut, Rhode Island, and much of New England. The parasitoid has not been recently recovered from warmer areas where it was released in the 1920s. Parasitization of 20% or more of JB populations has been observed. Attempts are being made to recolonize I. aldrichi. Adult beetles can be collected from infested areas by using standard Japanese beetle traps. Parasitized beetles can be removed from the trap captures, held for fly development, and taken to new areas for release. Despite its 60+ year association with the JB in New England, the fly is not as well synchronized with beetle populations as it is in Japan where it is the primary biological control agent, and it tends to emerge prior to the beetle. Recent observations indicate that the winsome fly has been recolonized from Connecticut to the mountains of North Carolina. This parasitoid is a good candidate for JB suppression in several of the North Central States (Minnesota, Wisconsin, and Michigan) where beetles have become established.
The Spring Tiphia was first introduced into the U.S. in 1924, with almost 120,000 specimens shipped from China and Korea by 1933. Although the wasps were recovered from 11 eastern states in 1950, the availability of new pesticides after WWII seemed to eliminate interest in this parasitoid. Recent explorations indicate that T. vernalis are common in areas where JB has been established for many years (Ohio, North Carolina, New Jersey), and can even be found in areas with relatively new infestations (Tennessee, Indiana). Additional searches for this species, and the Fall Tiphia, T. popilliavora, need to be conducted to evaluate the distribution and potential of these parasitoids. Adult female T. vernalis can be collected as they respond to nectar sources, or search over turf for larvae. Historically, new colonies have been started with about 50 female wasps. Because this is a larval parasitoid, it is hard to evaluate the effectiveness of the wasps.
It is clear that habitat modification to provide adequate food sources for adults of these parasites is an important step in making them more effective control agents.
As with the predators and parasitoids, natural and introduced pathogens also play an important role in suppressing JB populations. It is important to take note of these pathogens when preparing beetle control plans. There are a number of protozoa that have been found in both adult and larval JB. None of these have been produced as biological control agents, and they mostly seem to stress host insects, but cause very little direct mortality. Although viral pathogens have been the primary component of scarab control programs in other parts of the word, no effective virus has been found for JB. Fungal pathogens are more commonly associated with both JB adult and larval mortality, but no commercially successful product is available. Tests are now being conducted to evaluate the potential of using adult beetles to disperse an entomopathogenic fungus into JB larvae in the field. Early indications are promising, but additional research is needed.
Milky disease, caused by a native U.S. bacterium Bacillus popilliae, is probably the most wide spread and effective natural control agent of JB larvae. More than 15,000 pounds of spore powder were produced by governmental agencies, and distributed in a colonization program in 16 eastern states and the District of Columbia between 1939 and 1951. The effort was considered highly successful in terms of suppression of the beetle in general. The bacteria were not intended to be used as a microbial insecticide to eliminate specific JB larvae, but to reduce peak populations on an area wide basis. Milky disease was the first registered microbial product, and is still available today. However, the high cost of the spore powder, the specificity of commercial products for JB larvae, the natural distribution of B. popilliae spores, emphasis on private rather than community protection, the availability of effective "safer" pesticides, and lack of success in field trials, have curtailed expanded use of milky disease products. Another bacterium, B. thuringiensis (BT), with activity against JB larvae has been discovered. Although field tests have been promising, commercial development of a BT based product has been put on hold.
Entomopathogenic nematodes in the families Steinernematidae and Heterorhabditidae have been found naturally parasitizing JB larvae. Species in these two families have been commercialized for control of a number of cryptic and soil-inhabiting insects. Several strains of Heterorhabditis species and Steinernema glaseri have been effective against JB larvae in field trials and are available to home owners and turf managers. These organisms are living biological agents and require precautions to maintain their viability throughout the procurement and application process. Additional research and extension efforts are needed to make these nematodes most effective in beetle suppression programs.
Attractants and traps exist for capturing both male and female JB. Commercially available attractants consist of the JB sex attractant or pheromone (Japonilure) and a food-type or floral lure (phenethyl propionate: eugenol: geraniol; 3:7:3). Although Japonilure attracts only males when used alone, it can increase the captures of both males and females when used in combination with the floral lure. Attractant traps have proven particularly useful in finding and delineating JB populations. Although home-owners are usually very pleased with the numbers of beetles which can be captured in these traps, plants in the immediate area of traps can sustain increased damage from beetles before they are captured, and even removing millions of beetles probably doesn't significantly reduce populations.
Predators, parasitoids, and insect pathogens all play a role in reducing the numbers of Japanese beetle in the U.S. Researchers are continuing to explore how these natural enemies can be better utilized for improved biological control of this important pest.
- Michael Klein, USDA-ARS Japanese Beetle Lab, Wooster, OH
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