Causes of black turfgrass ataenius and aphodius outbreaks
on golf courses

Pesticide use may increase ataenius numbers by reducing predator populations.

David Smitley, Ph.D., and Terrance Davis

Rough habitat

Ataenius and aphodius are very similar in appearance. Ataenius adults and larvae are at least four times as abundant in fairways as in roughs. Experiments have eliminated differences in grass species and irrigation as potential causes of ataenius outbreaks in fairways. Pesticides may reduce predator populations, thereby increasing populations of ataenius. Further research is necessary to determine the influence of other factors on ataenius outbreaks.

Infestations of ataenius larvae may build to high levels in fariways, sometimes exceeding 500 per square foot.

The black turfgrass ataenius (Ataenius spretulus) is present in turf throughout most of the United States and Canada (9), but populations are so low in home lawns that ataenius rarely causes damage.

Ataenius was first reported as a turf pest in 1932 in Minnesota, where large numbers of ataenius larvae were found in damaged portions of a golf course green (2). Over the next 35 years, ataenius damage to turf was not mentioned in scientific journals (9). But after 1970, ataenius was regularly reported as a sometimes serious pest of golf course fairways in most of the Midwest and Northeast United States and Ontario (1,4,11-13).

Because ataenius overwinters as an adult (5), researchers were able to collect adults from September through March from the top 5 centimeters of soil along the edge of golf course woodlots, where populations were as great as 264 adults per square meter (13).

On golf courses in Ohio, ataenius completes two generations per year. Eggs are deposited in May, and in June larvae reach a peak density that may surpass 500 larvae per 0.1 m² (5,13). A second generation of adults emerges in July. Eggs can be found again in July and August, and larvae reach a second peak of activity in August. Nearly all of the larvae pupate by early October (13).

Ataenius completes at least two generations per year in regions south of central Ohio, and one generation per year, sometimes followed by a partial second generation, in areas north of central Ohio (8,10,13).

Aphodius granarius, a native of Europe, is widely distributed in the United States, but has only recently been known to damage golf course fairways and greens in Colorado, Michigan and Ontario (3,6,7,9).

Although aphodius adults and larvae look very much alike, examination under a microscope shows that adult aphodius can be distinguished from ataenius by the hind tibia, and the larvae can be distinguished from each other by the pattern of hairs on the underside of the last abdominal segment (9).

In Michigan, larvae of the two species do not occur at the same time (7). Aphodius adults become active in May, and larvae are present in June; whereas ataenius adults become active in late May, and the larvae are present in July and early August (7,8). Based on spring and fall peaks of adult activity in Ontario and Ohio (6,9), aphodius was believed to have two generations per year, but only one generation of larvae was observed in Michigan (7).

Michigan research
At the request of golf course superintendents in Michigan, we began investigating ataenius in 1992. We started with the question, "Why do ataenius larvae cause damage at some golf courses, while they are scarce at other golf courses and in home lawns?"

Ataenius and aphodius larvae may damage fairways, tees or greens by eating all the roots, leaving turf plants water stressed, starved and susceptible
to disease.

We started our investigation with three golf courses in the Detroit area: Franklin Hills Country Club, Orchard Lake Country Club and Oakland Hills Country Club. At one golf course ataenius was most abundant; at another aphodius was most abundant; and at another aphodius and ataenius were equally abundant. At all three courses, ataenius and aphodius larvae were five- to 10-fold more abundant in fairways than in adjacent roughs (8).

The observed difference in grub activity between the fairway and the rough raised more questions. Because irrigation coverage was similar in our fairway and rough plots at all three courses, it was not considered a factor.

One of the students working on the project noticed that we caught more ground beetles and rove beetles in the rough. These beetles are known to be predators of other insects. Are rove beetles and ground beetles important predators of ataenius? What else could explain why ataenius larvae are much more abundant in the fairway? Other factors that may differ between the fairway and the rough are pesticide use, grass species composition, milky spore disease of ataenius, fertility and mowing practices.

We decided to determine the distribution of ataenius larvae, rove beetles and ground beetles in the fairway and rough within 10 meters (30 feet) of the fairway/rough border. In 1995, we sampled a fairway where no insecticides had been used for two years at Spring Lake Country Club in western Michigan.

Pitfall traps were placed along replicated transects running into the fairway and rough, and a golf course cup-cutter was used to remove soil cores along the same transects for counting ataenius larvae. A total of 112 pitfall traps were changed weekly from early May to early July. We captured 341 aphodius, 1,131 ataenius, 4,703 ants, 2,693 ground beetles and 2,304 rove beetles in pitfall traps.

Ataenius adults were again more abundant in the fairway, and the numbers of predatory insects captured in pitfall traps declined sharply when crossing from the rough into the fairway. As the numbers of predators caught in pitfall traps increased, the number of ataenius adults decreased, suggesting that rove beetles, ground beetles and ants are important predators. Where irrigation coverage thinned out -- some 15-20 feet into the rough from the fairway border -- the number of predators began to decrease.

The adult black turfgrass ataenius is 4 to 5 millimeters long (3/8 inch). The aphodius beetle is so similar that it cannot be distinguished from ataenius without a microscope.

In 1996 a similar experiment was conducted at Cattails Golf Club in South Lyon, Mich., where both the fairways and roughs are perennial ryegrass. No pesticides had ever been used on the fairway where our plots were located. Pitfall traps were placed in lines running from the fairway into the rough in a design similar to the one used at Spring Lake in 1995.

The types of insects found in pitfall traps was similar to those found at Spring Lake, but the number of rove beetles and ground beetles was only one-third of the number found at Cattails GC, demonstrating that predator activity may vary considerably from one golf course to another. Even with the same grass species in the fairway and rough and no history of pesticide use in the fairway, we still found two to three times as many predators in the rough as in the fairway and five times as many ataenius adults and larvae in the fairway.

Conclusions from Michigan research
Ataenius adults and larvae are at least four times as abundant in golf course fairways as in roughs.

Rove beetles, ground beetles and ants are two to 10 times as abundant in roughs.

The abundance of ataenius adults and larvae is inversely correlated to the abundance of surface predators.

Experiments at Cattails GC have eliminated grass species and irrigation as potential causes of outbreaks of ataenius in fairways.

Rove beetles are members of the family Staphylinidae (2,900 species in North America). The adults and larvae of many species are predators of other insects. The adults roam the soil surface while the larvae
live underground.

Even when pesticides are not used in the fairway, predators may be more abundant in the rough. When pesticides are used in the fairway, the differences between predator activity in the fairway and the rough may be even greater.

The abundance of predators may vary threefold from one golf course to another.

Summary and future research
So far we have shown that ataenius adults and larvae are consistently more abundant in fairways compared with rough, whereas predatory insects are more abundant in the rough. At this point we believe that the standard use of pesticides in the fairway but not the rough only partially explains why this happens. The impact of fairway and rough mowing practices on predatory insects needs to be explored further. We also need to know whether fungicides have any impact on insect predators or on the milky spore disease that may infect as much as 70 percent of the ataenius larvae.

References

1. Cartwright, O.L. 1974. Ataenius, Aphotaenius and Psuedataenius of the United States and Canada (Coleoptera: Scarabaeidae: Aphidiinae). Smithsonian Contributions in Zoology 154:1-106.
2. Hoffman, C.H. 1935. Biological notes on Ataenius cognatus (Lec.), a new pest of golf greens in Minnesota (Scarabaeidae-Coleoptera). Journal of Economic Entomology 28:666-667.
3. Jerath, ML. 1960. Notes on larvae of nine genera of Aphodiinae in the United States (Coleoptera: Scarabaeidae). Proceedings of the U.S. National Museum 111:43-94.
4. Kawanishi, C.Y., C.M. Splittstoesser, H. Tashiro and K.H. Steinkraus. 1974. Ataenius spretulus, a potentially important turf pest, and its associated milky disease bacterium. Environmental Entomology 3:177-181.
5. Niemczyk, H.D., and D.M. Dunbar. 1976. Field observations, chemical control, and contact toxicity experiments on Ataenius spretulus, a grub pest of turf grass. Journal of Economic Entomology 69:345-348.
6. Sears, M.K. 1979. Damage to golf course fairways by Aphodius granarius (L.) (Coleoptera: Scarabaeidae). Proceedings of the Entomological Society of Ontario 109:48.
7. Smitley, D.R. 1994. Entomology research, p. 27-34. In: 64th Annual Michigan Turfgrass Conference Proceedings, January 18-20, 1994, Lansing, Mich.
8. Smitley, D.R., T.W. Davis and N.L. Rothwell. 1998. Spatial distribution of Ataenius spretulus, Aphodius granarius (Coleoptera: Scarabaeidae), and predaceous insects across golf course fairways and roughs. Environmental Entomology 27:1336-1349
9. Tashiro, H. 1987. Turfgrass insects of the United States and Canada. Cornell University Press, Ithaca, N.Y.
10. Vittum, P.J. 1995. Black turfgrass ataenius, p. 35-37. In: R.L. Brandenburg and M.G. Villani (eds.), Handbook of turfgrass insect pests. Entomological Society of America, Lanham, Md.
11. Weaver, J.E., and J.D. Hacker. 1978. Bionomical observations and control of Ataenius spretulus in West Virginia. W.Va. Univ. Agric. For. Exp. Stn. Curr. Rep. 72.
12. Wegner, G.S., and H.D. Niemczyk. 1979. The Ataenius of Ohio. Ohio Journal of Science 79:249-255.
13. Wegner, G.S., and H.D. Niemczyk. 1981. Bionomics and phenology of Ataenius spretulus. Annals of the Entomological Society of America 74:374-384.

David Smitley, Ph.D., is an assistant professor in entomology at Michigan State University, and Terrance Davis is a research technician in the department.