Sustainable Suppression of Japanese Beetle Populations

The Japanese beetle, Popillia japonica Newman, is a highly destructive insect pest. Damage caused by the feeding larva (grubs) and adults result in the loss of hundreds of millions of dollars to the agricultural and ornamental plant industry in the eastern United States annually. Introduced accidentally into the United States in about 1916 near Trenton, New Jersey, the beetle has spread throughout most of the eastern United States, with several outbreak areas well ahead of the main front. Though western states have been successful in eradicating introduced populations of the beetle in the past, and it is not yet widely established in the midwest, it still presents a major quarantine threat to many of these areas, as well as to many countries outside the United States.

The Spring Tiphia, Tiphia vernalis Rohwer

The purpose of this guidesheet is to help persons and agencies interested in sustainably suppressing populations of the Japanese beetle to establish the spring Tiphia and optimize the wasps’ reproductive potential for maximum control through the use of habitat modification by planting known food plants that the wasps favor.

The spring Tiphia was originally identified as a significant biological control agent of the Japanese beetle in Japan and Korea in the early 1920s. Between 1925-1927 the wasp was released in the northeastern US, and became quickly established as a natural enemy of Japanese beetle populations there. Although it will not eradicate the beetle from an area, the spring Tiphia can help keep populations of the beetle low enough to lessen damage to plants and to minimize the potential of accidentally transporting and thus spreading the beetle. The spring Tiphia is especially effective in suppressing outbreak populations of Japanese beetles. In areas with appropriate food plants, the wasp parasitizes an increasing percentage of grub population, thus causing these populations to be diminished over a period of several years.

The suppression of Japanese beetle populations by the spring Tiphia in outbreak areas ahead of, and along the advancing beetle front can minimize the amount of feeding damage caused and also slow the spread of the beetle. Also, by suppressing beetle populations in sensitive areas, such as around airports, parks, and plant nurseries, we can lessen the probability of accidentally transporting and introducing the Japanese beetle to uninfested areas. These natural enemies can be safely used to sustainably suppress populations of the Japanese beetle, especially in environmentally sensitive areas such as those near waterways or in state and federal parks. Once established, the natural enemies remain in the area for as long as the Japanese beetle is present, keeping beetle populations sustainably lower than they would be in their absence.

Description of Tiphia vernalis

The spring Tiphia wasp looks very similar to a winged black carpenter ant. The female wasp is heavily set and built for digging in the ground in search of Japanese beetle grubs. Its size can range from ½ to ¾ of an inch long. The male wasp, which spends its adult life flying in search of female wasps, is more slender and is normally only ³/8 of an inch long. It has a tiny hook at the end of its abdomen that is used when mating with the female. The female wasp possesses a stinger and, if handled roughly, can give a mild sting, similar to a sweat bee. However, it is not aggressive towards humans and will not normally sting people.

The spring Tiphia wasp was originally released in New Jersey and Pennsylvania from 1925 to 1927. It established readily, and redistribution efforts by the USDA from 1927 through 1953 led to the release of the wasp in Maryland, New York, Delaware, Connecticut, Massachusetts, Rhode Island, West Virginia, Virginia, Ohio, North Carolina, New Hampshire, District of Columbia and Vermont.

Recent survey work by USDA APHIS (Animal Plant Health Inspection Service) has shown the spring Tiphia is widely distributed over many parts of the eastern United States. Researchers have found the wasp as far west as Indiana and Tennessee.

Life History of Tiphia vernalis

The spring Tiphia normally emerges when bridal wreath spirea are in bloom. After a brief period of feeding and mating, the female wasp begins to hunt for Japanese beetle grubs to parasitize. The female wasp is able to detect the presence of grubs in an area probably by scent, and burrows into the ground in search of a grub. Once she finds a grub in its earthen cell, a brief struggle ensues. The female wasp stings the grub, causing a temporary paralysis that lasts about 30 minutes. She then prepares an area on the underside of the now paralyzed grub between the thorax and abdomen to receive a single egg. She rasps the area with the tip of her abdomen and kneads it with her mandibles, then attaches an egg to this softened spot. By wearing away the membrane of the grub and making it thinner, the wasp larva, which hatches about 7 days later, has little problem piercing the skin of the grub in order to feed. The female wasp can normally parasitize 1 to 2 grubs daily in this manner, and can lay a total of between 40 and 70 eggs over her lifespan of 30 to 40 days.

Selecting Areas for Release of Tiphia vernalis

The spring Tiphia wasp needs three factors for a successful release. They are: 1) An area that contains an abundant supply of its host, (which is the 3rd instar Japanese beetle or Oriental beetle [Anomala orientalis Waterhouse]); 2) Adequate food plants to enable the wasp to realize its reproductive potential; and 3) High and low ground to ensure continuance of the grub population in both wet and dry years. Studies by USDA researchers found that percentage of parasitization was greater for more dense grub populations: 57% for 6 grubs per square foot; 31% for 2 grubs per square foot; and less than 20% for one grub per square foot. However, the authors have found that these percentages could be increased by planting or having additional food plants in the areas where beetle grubs consistently occur, such as golf courses, parks and the areas surrounding airports.

The potential release area can be surveyed to determine how many Japanese beetle grubs per square foot are present. By doing some preliminary survey work, you will be able to select an area that has the most grubs, which will give you the best chance for establishment of the spring Tiphia. Grid off the potential area being considered for release. If you have a large area, such as a golf course or a park, you will want to make several sample sites to determine which has the most grubs. Each potential survey area can be gridded into a 30 foot by 30 foot square grid. Each section in the grid is a 10 foot by 10 foot piece, for a total of 9 ten foot square areas. The overall grid pattern looks like a tic-tac-toe drawing. Take one soil sample from each of the nine squares. Each soil sample should be 1 foot square and 6 to 8 inches deep. Count all the grubs in each soil sample. By looking at the raster pattern on the rear of each grub, you can determine if the grub is a Japanese beetle grub. Do this sampling pattern for each area under consideration for release of the Tiphia wasp.

Food Plants for Adult Tiphia vernalis

USDA researchers found that, in the northeastern U.S., adult spring Tiphia wasps feed primarily on the honeydew exuded from aphids, scale insects, and leafhoppers. The adult wasps were found feeding on the shaded foliage of maple, elm, cherry, tulip and pine trees, and some broad-leafed shrubs. The wasp will also feed on the nectar of blossoms, such as forsythia, and on the extra-floral nectaries of peonies. However, as the wasps were later redistributed into other parts of the eastern and southern US, the potential exists for them to utilize other plants for food. Research by the author (RCM) while with the North Carolina Department of Agriculture (NCDA) found that Tiphia adults used blooming tulip poplar trees, Liriodendron tulipifera as a food and mating site. Researchers in China have used the knowledge of food plants to increase the rates of Tiphia parasitization of white grubs to an average of 85%. Thus, the potential for using food plants to increase the rates of parasitization of the Japanese beetle by the spring Tiphia is great and should be utilized whenever possible.

Food Plants Known to be Utilized by Adult Tiphia vernalis:

Tulip Poplar	Liriodendron tulipifera
Choke Cherry	Prunus virginiana
Norway Maple	Acer platanoides
American Elm	Ulmus americana
Forsythia	Forsythia x intermedia
Firethorn	Pyracantha coccinea
Pine trees	Pinus spp.

Determining Tiphia vernalis Parasitization Rates

In order to determine the parasitization rate of the spring Tiphia on the Japanese beetle, soil sampling must be done in a manner similar to that described above. Between 25 and 40 soil samples are normally taken. The timing of the survey work for parasitization rates is of utmost importance. The survey must occur between the time that the spring Tiphia has ceased its egg laying activities, and before the Japanese beetles begin to emerge as adults. Normally, this is a 7 to 10 day period, and usually occurs in early June in North Carolina. Due to the brevity of this period, only a certain amount of sampling can occur each year.

By digging up Japanese beetle grubs and pupae, you can examine each one to determine if the spring Tiphia has been active. You may find grubs, grubs with Tiphia larvae attached, Tiphia cocoons, or Japanese beetle pupae. The number of grubs and pupae that have no sign of spring Tiphia attack are compared to the number of parasitized grubs and Tiphia cocoons found in a particular area. This number will give an indication of the relative amount of parasitization of a particular population of the Japanese beetle.

Another indication of the relative effectiveness of the spring Tiphia is the large numbers of adult wasps seen flying on sunny days. Each wasp seen has developed at the expense of a Japanese beetle grub. Large numbers of these wasps flying about suggests that the parasites may be of much greater benefit than is usually thought. Wasps can be sampled non-destructively by spraying foliage with sugar water and counting the wasps attracted to the bush in a fixed interval.

Obtaining Spring Tiphia Wasps for Release

If you are interested in obtaining spring Tiphia wasps for release, please contact Richard McDonald.