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Drubbing Grubs, Naturally
September 1, 2009 By: Ana Legrand TurfGrass TrendsTiphia parasitic wasps take on Japanese and Oriental Beetle grubs
The Japanese beetle, Popillia japonica, was first detected in Riverton, N.J., in 1916. It's believed this insect was accidentally introduced in infested nursery stock from Japan. Since then it has expanded its range, continuing to be a pest of ornamentals and turfgrass.
In 2008, surveys were completed to determine the extent of spring Tiphia parasitism on Japanese and Oriental beetle grubs. Collections were made at 12 sites that included public parks and golf courses in Connecticut.
Tiphia has been known as a parasitic wasp for decades. During the 1920s and early 1930s, U.S. Department of Agriculture entomologists imported Tiphia vernalis Rohwer (Hymenoptera: Tiphiidae) from Korea as a biological control agent against the Japanese beetle. C.P. Clausen and J.L. King, who spent several years in Japan and other parts of Asia searching for natural enemies of the Japanese beetle, led the effort.
 Tiphia wasps feed on extrafloral nectar from Peony Big Ben. (PHOTOS COURTESY: ANA LEGRAND) |
T. vernalis, also known as the spring Tiphia, is a parasitic wasp that attacks Japanese and Oriental beetle grubs. The small insect is not harmful to people, and it's not known to attack any native beetle species (Ladd and McCabe 1966). With its help, populations of Japanese beetles are reduced in number from what potentially could be more severe infestations.
The USDA has made numerous wasp releases throughout the Northeast.T. vernalis was released in most of Connecticut's counties between 1936 and 1949. But since 1950, little information was available on the status of this wasp in the Northeast, and it was considered to be rare. However, a survey in Connecticut indicated that spring Tiphia wasps were widely distributed in the state (Ramoutar and Legrand 2007). Populations of the spring Tiphia have also been documented in Kentucky, Missouri, Ohio and Tennessee.
 The parasitic larva securely attaches itself outside the host and feeds on the grub. (PHOTOS COURTESY: ANA LEGRAND) |
Spring Tiphia females are about a half-inch long and the males are about three-eighths of an inch long. These shiny black wasps are solitary. They don't live in nests or swarms, and they have only one generation per year. Male wasps emerge first and females emerge three to four days later. In Connecticut, spring Tiphia wasps are active from the first week of May to mid-June with a peak in numbers observed around the last week of May. Adult wasps feed on honeydew produced by insects like aphids, and they are seen on the foliage of maple and cherry. Tulip trees are reported as being one of their preferred plants for seeking honeydew.
After mating, female wasps burrow into the soil discreetly and search for grubs. When a grub is found, the wasp stings it and paralyzes it momentarily while the wasp attaches one egg on the ventral groove between the third thoracic and first abdominal segments. When the wasp egg hatches, the resulting parasitic larva begins feeding on the grub. The parasitic larva securely attaches itself outside the host and feeds on the grub until the host grub dies.
 The full-grown larva spins a silken cocoon.(PHOTOS COURTESY: ANA LEGRAND) |
The parasitic larva grows rapidly and the full-grown larva spins a papery, water-resistant, silken cocoon. Within the cocoon, it completes its development and transforms into an adult wasp. It passes the winter in this stage within the cocoon until the next spring when wasps emerge to start the cycle again.
Tiphia females live for about a month and may lay 40 to 50 eggs on as many different grubs. The female wasps seek out the Japanese beetle grubs in May to early June when the grubs are feeding before pupation.
 Parasitism Chart |
Samples at the 12 sites were taken throughout June. Larvae collected during the survey were from European chafers, Asiatic garden beetles, Japanese and Oriental beetles. As expected, only the Japanese and Oriental beetle larvae were parasitized by the spring Tiphia. Previous research had shown the range of parasitism rates of this parasitoid to be 19 percent to 61 percent on Japanese beetle grubs (King and Parker 1950). In our survey, we found a range of 61 percent to 100 percent parasitism on the Japanese beetle grubs (see table). In addition, the spring Tiphia is also inflicting mortality on Oriental beetle populations with a parasitism rate ranging from 7 percent to 33 percent in low-density Oriental beetle populations. Reding and Klein (2001) found in an Ohio nursery the rate of T. vernalis parasitism on Oriental beetles ranged from 6 percent to 23 percent.
On average, parasitism of Oriental beetle was less than that found on Japanese beetle larvae, and we will continue work to determine possible reasons for this. Nevertheless, the spring Tiphia can be a significant source of mortality for the Japanese beetle, and it should be integrated with other management tactics.
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