Biological Control Agents of Multiflora Rose, Rosa multiflora Thunbergh

1. RRD and Phyllocoptes fructiphilus. Symptoms of RRD in multiflora rose include a red or purplish vein mosaic (this symptom is diagnostic), bright red lateral shoots, dwarfed foliage, and premature development of lateral buds producing many compact lateral branches forming "witches' brooms" (Amrine and Hindal 1988). Symptoms on ornamental roses include a yellow mosaic pattern on leaves, greatly increased thorniness of stems, wrinkled foliage, and witches' brooms; however, the bright red lateral shoots and vein mosaic seen in multiflora rose do not usually occur. Rose rosette disease is transmitted by the eriophyid mite, Phyllocoptes fructiphilus, which develops in high numbers on shoots of RRD-infected multiflora roses. Many eriophyid mites are dispersed in air currents, and we believe that P. fructiphilus may also be disseminated in this manner. However, the spread of RRD the past two years has been slower than expected, suggesting that there may be a requirement for phoretic transport of P. fructiphilus by an unidentified insect that feeds on roses. We currently are conducting research on this possibility in West Virginia and neighboring states. Also, several predators of P. fructiphilus have appeared in West Virginia: a thrips (unidentified), a small cecidomyiid fly (unidentified), and several species of mites in the families Phytoseidae, Tydaeidae, and Anystidae. The combined activities of these predators and a parasitic fungus may have reduced field populations of the vector, thus slowing the observed spread of RRD.

In early spring, the mites move from wintering sites (clumps of overwintering foliage, under loose bark, old bud scales, etc.) onto developing shoots to lay eggs; females live about 30 days and lay about one egg per day. Eggs hatch in 3 to 4 days and the development of each immature stage (protonymph and deutonymph) requires about two days. Thus in warm weather, one generation may be produced per week. Development is continuous throughout the season until weather turns cold in the fall.

In May 1987, Amrine et al. (1990) began a long-term study at Clifty Falls State Park in Madison, Indiana. The site was heavily infested with both healthy and RRD-symptomatic multiflora roses. A total of 180 multiflora rose plants were marked and visited monthly during the growing season for the next five years. The initial average density was 1,200 plants per acre and, at the beginning of the study, 30% of plants were symptomatic and 1% had been killed by RRD. The infection increased each year and leveled off at 94% in September 1991 with a mortality of 88%. The average longevity of infected plants was 22.4 months (range = 3 to 48 months).

Mite populations were 14 times larger on symptomatic plants compared to healthy plants in 1987 and 1988. Mite populations were low and sporadic in April and gradually increased to peak populations by September in most years. At peak populations, nearly all RRD-symptomatic plants were infested with mites. The average number of mites per symptomatic shoot in September of each year (1987-1990) was 112, 30, 112, and 6.6 respectively. The low average number in 1988 (30) resulted from severe drought that caused death of mites on desiccated foliage; the mites rebounded to an average of 72 per shoot by October 1988. The very low average numbers in September 1990 (6.6), and during the entire year resulted from unusually cold weather in December 1989 (-31°C = -24°F), which killed nearly all aboveground RRD-symptomatic canes and thus killed most of the overwintering mites.

Overall, RRD will have a very significant impact on multiflora rose, potentially reducing numbers by 93% throughout the eastern United States.

2. The rose seed chalcid, Megastigmus aculeatus var. nigroflavus, was reported from New Jersey in 1917. It was causing heavy mortality of multiflora rose seed imported from Japan for rootstock for ornamental roses (Weiss 1917). Later, Milliron (1949) reported that the rose seed chalcid "now appears to be well established in parts of the Atlantic Seaboard." Scott (1965) found large numbers of the rose seed chalcid at the Patuxent National Wildlife Refuge near Washington, D.C., with infestation rates around 95% percent. Mays and Kok (1988) reported a survey for the chalcid in multiflora rose seed in Virginia during 1985 and 1986 and found average infestation rates of 26.5% (range of 2-59%) and 23.9% (range of 2-52%), respectively, in 50 of 51 counties surveyed. Hindal and Wong (1988) found the chalcid in West Virginia and mentioned its potential for biocontrol.

Amrine (unpublished) surveyed multiflora rose seed (dissecting all seed from each of 20 rose hips per sample) from 67 sites (in 21/55 counties) in West Virginia in 1984-1985 and found an average of 49.7% (range = 0-100%) of seed infested with the torymid. A survey of 16 sites from Maryland, Missouri, Oklahoma, Pennsylvania, Tennessee, Texas, and Virginia had an average seed infestation of 46.7 % (range = 0-95%). In the samples dissected, the hips had an average of 5.75 (range = 1-21) full-size seeds. Amrine found that the chalcid oviposits in the developing receptacle just after petalfall in June. The wasp takes a position along the shriveled stamens, inserts her ovipositor from a single point, and guides it into each of the developing ovules (Fig. ). A typical oviposition required 45 minutes to complete.

Larvae develop in the ovules during July and August consuming the contents of the seeds and killing them. They reach full size by late September and then enter diapause. During the winter, larvae begin to die when exposed to temperatures below -20°C (-5°F), suffering 20-80% mortality when temperatures fall below -26°C (-16°F) for extended periods. Amrine (unpublished) found that chalcids in rose hips close to the ground and in other protected sites survived low temperatures better than those hips on upper canes exposed to ambient low temperatures. By late May the larvae transform to pupae. At about petal fall (this occurs about the third week of June in West Virginia), adult wasps eclose within the seed and begin to chew their way out of the seed and the hip, leaving neat round exit holes.

Dispersal studies by Shaffer and Amrine (Shaffer 1987) indicated that the seed chalcid has poor abilities to fly to newly established rose plantings. Apparently, most dispersal is by movement of infested seed by birds, which would explain the apparently low colonization of rose seed in Virginia (24-26%) and West Virginia (49%). The millions of multiflora roses planted in the eastern United States were set out as rooted cuttings--they were not planted from seeds; thus no chalcids were disseminated. Therefore, the chalcid has had a monumental "catchup" job to find and colonize all the potential rose sites. We believe that the chalcid will eventually find and utilize 90% or more of the multiflora rose seed in the eastern United States and act as a powerful biological control for the weed, helping to reduce its rate of spread to a low level. But, we believe this process will be slow, perhaps in 20 or more years.

Recent research shows good potential for management of the seed chalcid. Two 100-foot rows of multiflora roses, each containing 50 plants, were set out as rooted cuttings in 1988 at WVU. The plants first bloomed in 1989 and produced abundant seed in 1990 and 1991. They were assayed in November 1991 for populations of Megastigmus aculeatus; each sample consisted of 20 hips collected at random, and each seed was cut to reveal presence of larvae. Overall, each hip had an average of 6.9 developed seeds. The average infestation of 12 samples in November 1991 was 3.15% (range of 0-14%). For comparison with multiflora roses growing nearby, three plants within 500 m of the plot were examined and the infestation was 74.1% (range of 64.1-79.4%).

Two sets of about 10 panicles each (ca. 50 hips per panicle, 7 seeds per hip) were placed on the ground, under the roses, at opposite ends of the rows in December 1991; infestation of the seed in the panicles was 79.3%. In December 1992, 21 samples of hips were collected from the rows and the average infestation was 77.5 % (range of 57.3-92.9%). Thus the infestation increased from 3.15% in fall 1991 to 77.5% in fall 1992, showing a great reduction in the number of viable seed being spread by birds from the source plants. The average infestation of nine multiflora roses within 500 m of the study site was 86.9% (range of 55.6 to 100%); we expect the chalcid infestation of the seed in the study plot to approach 90% in fall 1993.

3. The rose stem girdler. Amrine and Stasny found several sites in Ohio, Indiana, and West Virginia where the rose stem girdler, Agrilus aurichalceus aurichalceus (Coleoptera: Buprestidae), was fairly abundant and provided some degree of control of multiflora rose. At sites along I-71 in Ohio (Fayette County), near Woodsfield (Monroe County Ohio), and in a pasture near Morgantown, West Virginia, upwards of 12% of canes were found attacked by the girdler in 1988-1989, often with two or three larvae girdling each cane. All tissue distal to the girdle was killed including developing rose hips and seeds.

The overwintering borers, still in the previous season's girdled canes, pupate in April and emerge as adults in May. The adults are small (1/4"), golden to bronze-colored metallic beetles that can be found on sunlit multiflora rose foliage in the mornings. They find new shoots in May and June and oviposit just under the bark. The larvae hatch and begin burrowing under the bark, spiraling outward from the oviposition site. The initial burrowing does not kill the cane, but by late July the infested stems begin to wilt and by August or September, they die and appear as brown "flags" on rose bushes. Since no infested site has been found in which more than 12% of canes were affected and large numbers of larvae were found parasitized, we believe that this insect will have only minor importance as a biocontrol agent of multiflora rose.

References

Amrine, J. W., Jr. and D.F. Hindal. 1988. Rose rosette: a fatal disease of multiflora rose. Circular 147, August, 1988. West Virginia University. Agr. and For. Exp. Stn., Morgantown, WV.

Amrine, J. W., Jr., D. F. Hindal, R. Williams, J. Appel, T. Stasny, and A. Kassar. 1990. Rose rosette as a biocontrol of multiflora rose. Proc. Southern Weed Sci. Soc. 43: 316-319.

Hindal, D. F., J. W. Amrine, R. L. Williams, and T. A. Stasny. 1988. Rose rosette disease on multiflora rose (Rosa multiflora) in Indiana and Kentucky. Weed Technol. 2: 442-444.

Hindal, D. F. and S. M. Wong. 1988. Potential biocontrol of multiflora rose, Rosa multiflora. Weed Technology. 2: 122-131.

Mays, W. T. and L.-K. Kok. 1988. Seed wasp on multiflora rose, Rosa multiflora, in Virginia. Weed Technol. 2: 265-268.

Milliron, M. E. 1949. Taxonomic and biological investigations in the genus Megastigmus. Am. Midl. Nat. 41: 257-420.

Scott, R.F. 1965. Problems of multiflora rose spread and control. Trans. 30th North American Wildlife and Nat. Reserv. Conf. 30: 360-378.

Shaffer, D. F. 1987. A study of the biocontrol of Rosa multiflora Thunb. utilizing the rose-seed chalcid wasp Megastigmus aculeatus var. nigroflavus Hoffmeyer (Hymenoptera: Torymidae) in West Virginia. M. S. Thesis, West Virginia Univ., Morgantown. 72pp.

Weiss, H. B. 1917. Megastigmus aculeatus Swed., introduced into New Jersey from Japan. J. Econ. Entomol. 10: 448.