United States 1 Department of @ I Agriculture Millipede Damage to 

Forest Service 

Northeastern Forest 

Germinating Acorns of 

Experiment Station 

@ Research Paper NE-667 

Northern Red Oak 

Jimmy R. Galford 

L. R. Auchmoody 

Russell S. Walters 

H. Clay Smith 
Abstract 

Millipedes have not been reported as pests of germinating acorns. Studies in 

Pennsylvania on the impact of insects on northern red oak (Quercus rubra L.) 

seedling establishment revealed that the millipede Ptyoiulus impressus (Say) 

damaged the radicles of germinating acorns. Up to 17 percent of the acorn radicles 

in areas with heavy acorn crops were damaged in 1991. Millipede feeding began in 

late March to early April, several days prior to feeding activity of insects that damage 

or destroy germinating acorns. 

The Authors 

JIMMY R. GALFORD is a research entomologist with the Northeastern Forest 

Experiment Station's Timber and Watershed Laboratory at Parsons, West Virginia. 

L. R. AUCHMOODY and RUSSELL S. WALTERS are research foresters with the 

Northeastern Forest Experiment Station's Forestry Sciences Laboratory at Warren, 

Pennsylvania. 

H. CLAY SMITH is a research foresterProject Leader with the Northeastern Forest 

Experiment Station's Timber and Watershed Laboratory at Parsons, West Virginia. 

Manuscript received for publication 1 1 May 1992. 

Northeastern Forest Experiment Station 

5 Radnor Corporate Center 

100 Matsonford Road, Suite 200 

P.O. Box 6775 

Radnor, Pennsylvania 19087-4585 

i July 1992 
Introduction 

Since 1989, studies have been conducted in central 

Pennsylvania on the impact of insects in limiting northern 

red oak (Quercus rubra L.) seedling establishment. Three 

species of insects have been identified as the major 

destroyers of germinating red oak acorns: a weevil, 

Conotrachelus posticatus Boheman, a sap beetle, 

Stelidota octomaculata (Say), and a moth, Valentinia 

glandulella (Riley) (Galford et al. 1991). However, a new 

type of damage to the radicles of germinating red oak 

acorns was noted in Pennsylvania in late March and early 

April of 1990. The chewing damage on some of the 

radicles was unlike that caused by the insects mentioned, 

and only 50 percent of the acorns with radicle damage 

contained insect larvae. Preliminary investigations indicated 

that millipedes might be responsible for the damage. 

Although some species of millipedes have been reported 

as pests of plants, none has been reported feeding on 

germinating acorns (Richard Hoffman, Va. Mus. Nat. Hist., 

1992, pers. commun.). Winston (1 956) and Galford (1 988) 

did not report the millipede as an arthropod affecting red 

oak acorns in Illinois and Ohio. However, an undetermined 

species of millipede occasionally was observed feeding on 

germinating white oak (Q. alba L.) and red oak acorns in 

central and southern Ohio (Galford, unpublished). It is not 

known whether millipede feeding on acorns in the Ohio 

studies occurred before or after damage to the acorns from 

other agents. 

The species of millipede suspected of damaging 

germinating acorns in Pennsylvania was identified as 

Ptyoiulus impressus (Say) (Family: Parajulidae). A 

preliminary study demonstrated that it feeds on the 

radicles of germinating red oak acorns. Field and 

laboratory studies were conducted in 1991 to learn more 

about P. impressus as a pest of germinating acorns. 

This paper reports the results of those studies. 

Methods 

Field Studies 

Observations of acorn samples collected in late March 

and April of 1990 indicated that arthropod damage to 

germinating acorns began soon after the radicles began to 

elongate and were still very small. Many of the 1990 

acorns already had been damaged by more than one 

species of arthropod. To determine when arthropod feeding 

damage began and which species initiated damage, we 

began collecting acorns in 1991 in late winter soon after 

the acorns began to swell and open but before actual 

germination (radicle growth). 

In 1991, samples of northern red oak acorns were collected in the Moshannon State Forest in Clearfield County 

in central Pennsylvania and in Warren County at the 

northwestern edge of the Allegheny National Forest. 

Acorns were collected from February 27 until April 22 on 

four sites in the two counties. As many as 100 acorns 

were collected at each site at 6- to 14-day intervals 

depending on snow cover, radicle development, and 

arthropod activity. Germinating acorns or acorns that had 

opened for germination were collected randomly at each 

site; about equal numbers of acorns with or without leaf 

cover were collected. In the laboratory, the acorn samples 

were examined individually for damage under a binocular 

microscope. When possible, a determination of the 

arthropod species causing the damage was made. After 

examination, the acorns from a sample site were placed in 

a loosely covered jar to rear out any insects in them. 

Records were kept for 4 to 5 weeks of any insects that 

emerged from these acorns. The acorns were then 

removed from the jar and cut open with pruning shears. 

Any insect larvae inside the acorns were counted and the 

condition of acorn cotyledons recorded. 

In late October 1991, 100 germinating chestnut oak 

(Q. prinus L.) acorns were collected randomly from 

under a tree with a heavy crop of acorns in a forest in 

Warren County. In the laboratory, each acorn radicle was 

examined for insect and/or millipede feeding damage. The 

acorns were placed in a jar for 3 weeks to rear out any 

insects. Then each acorn was cut open to determine the 

extent of internal damage. 

Laboratory Studies 

Northern red oak acorns used in the laboratory studies 

were collected in the autumn of 1990 and stored at 5" to 

7°C in dry sand or peat moss in sealed plastic bags. 

Several small holes 2 to 3 mm in diameter were punched 

in the bags for aeration. Several days before use, the 

acorns were removed from the bags and soaked for 20 

minutes in distilled water. Floating acorns were discarded. 

The acorns were then placed on moist paper towels in a 

lightly sealed container at room temperature to promote 

germination. Germination usually occurred within 3 weeks. 

Acorns of white oak and chestnut oak were collected in 

late October 1991 and stored in dry sand in sealed plastic 

bags. Because it is difficult to store white and chestnut 

oak acorns for more than 1 or 2 months without the 

acorns either germinating or desiccating, tests of acorns of 

these species were conducted soon after they were 

collected. Viable acorns of white and chestnut oak 

germinated within 7 days when placed on moist paper 

towels at room temperature. 

Adults of P. impressus were collected in Clearfield and 

Warren Counties in late September and October of 1991 

using pitfall traps baited with red oak acorns cut into 

halves (Galford 1991). Some millipedes also were 

collected by searching under leaf litter. 

In the laboratory, the millipedes were kept in glass culture 

dishes (100 by 80 mm) about one-third filled with a 

mixture of equal parts of moist peat moss, sand, and 

perlite. Two or three dead oak leaves were laid on top of 

the medium for the millipedes to hide under but no other 

potential food source was provided during acorn feeding 

tests. The contents of the jars were misted periodically 

with distilled water. No more than one pair (male plus 

1 
female) of millipedes was kept in each dish to prevent 

possible cannibalism and/or asphyxiation caused by 

secretions from the repugnatorial glands. P. impressus are 

easily sexed; the legs of the male on the seventh body ring 

are modified into sex organs (gonopods) and the first pair 

of legs are greatly enlarged. By contrast, females have legs 

on the seventh body ring and the first pair of legs are not 

enlarged. 

Acorn feeding tests were conducted as follows: one 

germinating red oak acorn (radicle 2 to 10 mm long) was 

introduced into each of seven culture dishes containing a 

pair of millipedes. After 72 hours, the acorns were removed 

and inspected for feeding damage. Three replicates using 

only red oak acorns were conducted. In another feeding 

test involving choice, three germinating acorns (one each of 

red, white, and chestnut oak) were placed in each of seven 

culture dishes and exposed to the millipedes for 24, 48, 72, 

or 120 hours. The 120-hour test was conducted first. At the 

end of each test period, the acorns were removed and 

inspected for damage and new, undamaged acorns were 

placed in culture. dishes for the next test period. The 

millipedes were not starved between test periods. All tests 

were conducted at 18" to 25°C under a 10114 hour light/ 

dark cycle under normal fluorescent laboratory lighting. 

Results and Discussion 

Field Study Results 

Table 1 gives the results of the study of millipede damage 

to germinating acorns in 1991 in Warren and Clearfield 

Counties. In both counties, millipede damage to acorn , 

radicles began March 20 to 27. Damage increased weekly 

until April 22 when the last sample was collected (Fig. 1). 

Sampling was discontinued in late April when most of the 

acorn radicles had been damaged by more than one 

species of arthropod and it became impossible to 

determine which species initiated the primary damage. 

Once damaged, acorns become more attractive to some 

species of insects (Galford and Weiss-Cottrill 1991). It is 

common for two or more species to attack the same acorn 

simultaneously, and millipede-damaged acorns may be 

attacked by insects within a few days or even hours. 

The single sampling of germinating chestnut oak acorns 

collected in October 1991 revealed that millipedes also 

damage acorn radicles in autumn (Table 1). Most of the 

radicles damaged by an undetermined species or species 

may have been damaged by millipedes because no 

Conotrachelus weevils were reared from the acorns. Also, 

several millipedes were found under the leaf litter when the 

acorn sample was collected. Most insect damage in the 

sample was light and caused by the 1st and 2nd instars of 

the moth V. glandulella (Galford 1986). 

Laboratory Study Results 

In the study in which only red oak acorns were offered to 

millipedes for feeding, the radicles of 18 of 21 acorns were 

fed upon to some extent. These studies revealed that 

feeding damage by P. impressus on the radicles of 

Table 1.-Arthropod damage to germinating acorns in Warren and Clearfield 

Counties, Pennsylvania, in 1991 

Sampling Acorns in Sample Acorn radicles in sample 

date damaged by: 

Warren Clearfield Millipedes Insectsa Undeterminedb 

......................................... Number .................................... 

2/27 25 0 0 0 

2/27 25 0 0 0 

313 25 0 0 0 

313 25 0 0 0 

3/20 25 0 1 0 

3/20 25 0 0 0 

3/26 25 2 0 0 

3/27 25 3 0 0 

418 50 7 8 0 

419 50 8 18 0 

411 5 100 17 29 11 

4/22 100 16 26 4 1 

1 0130 1 00" 15 22 60 

"Primarily damage from adults of the weevil Conotrachelus posticatus and larvae of 

the moth Valentinia glandulella. 

bArthropod species initiating primary damage not known (multiple species involved). 

Chestnut oak acorns (earlier samples were acorns of northern red oak). 
Figure 1 .-Acorn radicle damaged by millipede feeding 

germinating acorns varied with the length of the radicles at 

the time when acorns were first exposed to millipedes. 

When the radicle was only 2 to 5 mm long and just 

emerging from the acorn, only the radicle tip was 

consumed. The millipedes rarely fed for a short distance 

into the acorn. If the acorn radicle was large in diameter, 

the millipede might eat the tip and then feed for a short 

distance inside the radicle, hollowing it out. Damage to 

radicles longer than 5 mm occurred anywhere on the 

radicle but usually on the side. This damage ranged from a 

shallow-round hole chewed into the radicle to a deep hole 

extending nearly through it. Longitudinal feeding along the 

length of a radicle resulted in a short, shallow groove or a 

deep groove several millimeters long. The most common 

damage observed in the forest was radicle tips eaten just 

as they emerged from the acorn. Another type of radicle 

damage observed in the forest was small round holes 

chewed by immature millipedes; however, only adult 

millipedes were used in the laboratory studies. The weevil 

C. posticatus also eats holes in acorn radicles but these 

usually are smaller in diameter, more cylindrical, and 

deeper than those caused by immature millipedes. But 

damage from both arthropods is variable and can be 

confused. 

In the laboratory, millipedes sometimes burrowed into the 

potting medium and fed on the tender, white roots of 

acorns that had rooted. However, the feeding damage was 

not extensive. Root damage in the field also has been 

observed, especially where acorns root in deep leaf litter, 

but it has not been established that millipedes caused the 

damage. Larvae of two species of noctuid moths, Polia 

detracta (Wlk.) and Anorfhodes tarda (Gn.), can cause 

similar damage to roots (Galford et al., unpublished). 

P. impressus preferred red oak acorns but fed on white 

and chestnut acorns (Table 2). The first choice test, 

conducted for 120 hours, did not reveal a clear preference 

for red oak. However, 24-, 48-, and 72-hour tests with the 

same millipedes used in the 120-hour test revealed a 

preference for red oak acorns. Thus, after the millipedes 

had a 5-day period to become conditioned to the three 

kinds of acorns, red oak acorns were preferred in 

subsequent choice tests. 

In a given year in a particular location or site, the actual 

impact of P. impressus on red oak seedling establishment 

would be difficult to ascertain unless the same acorns were 

inspected daily in the forest beginning with the first sign of 

millipede feeding on acorns. In one sample collected in 

1991, 17 percent of the acorn damage was attributed to 

Table 2.-Number of radicles of germinating acorns damaged by millipedes, by 

test sequencdduration and acorn typea 

Acorn radicles damaaed 

Acorn type 120-hr 24-hr 48-hr 72-hr Total 

White 5 1 0 1 7 of 28 

Red 7 4 4 5 20 of 28 

Chestnut 5 2 1 2 10 of 28 

"One germinating acorn each of white, red, and chestnut oak placed in each of 

seven culture dishes containing a pair of millipedes. 
millipedes. Yet, the actual percentage probably was higher. 

Millipede activity begins just days before insect activity and, 

as mentioned earlier, once both kinds of arthropods are 

actively feeding on the same acorn, it is difficult to 

differentiate damage and determine which species was the 

primary attacker. However, it is clear that P. impressus by 

itself and in conjunction with insects adversely affects oak 

seedling establishment in Pennsylvania in some areas in 

some years. The impact of millipedes no doubt varies 

considerably due to site, climatic conditions, acorn crops, I and other variables such as insect and rodent populations. 

I Under ideal conditions, many, if not most, of the acorns I 

1 damaged by P. impressus can resprout and root. But, 

under natural forest conditions, most of the damaged 1 acorns succumb to desiccation, rodents, or insects. 

Research on oak regeneration in Pennsylvania has 

revealed that red oak seedling establishment is adversely 

affected on some sites in some locations largely due to 

Literature Cited 

Galford, Jimmy R. 1986. Primary infestation of 

sprouting chestnut, red, and white oak acorns by 

Valentinia glandulella (Lepidoptera: Blastobasidae). 

Entomological News. 97: 109-1 12. 

Galford, Jimmy R.; Peacock, John W.; Wright, Susan L. 

1988. Insects and other pests affecting oak I regeneration. In: Smith, H. Clay; Perkey, Arlyn W.; 

Kidd, William E., Jr., eds. Guidelines for regenerating 

Appalachian hardwood stands: workshop proceedings, 

1988 May 24-26; Morgantown, WV. SAF Publ. 88-03, 

Morgantown, WV: West Virginia University Books: 

21 9-225. 

destruction of the germinating acorns by a complex of 

arthropods including P. impressus. The 1991 acorn 

samples were collected in areas that had heavy crops of 

acorns in 1990. Thousands of acorns per hectare survived 

predation from rodents, bear, deer, and other animals to 

germinate in the spring. Thus, the impact of arthropod 

damage observed in spring of 1991, though significant, 

was diluted by the heavy acorn crop. 

Acknowledgments 

We thank Dr. Richard Hoffman, Virginia Museum of Natural 

History, and Dr. Rollin Shelly, North Carolina State 

Museum of Natural Science, for their taxonomic help. We 

also thank Drs. Jack Barger, William Cannon, Jr., Northeastern Forest Experiment Station, Delaware, Ohio, and 

Subbash Domir, National Arboretum, Delaware, Ohio, for 

their helpful reviews and Perry Fox, technician, Northeastern Forest Experiment Station at Warren, Pennsylvania. 

Galford, Jimmy R.; Auchmoody, L. R.; Smith, H. Clay; 

Walters, Russell S. 1991. Insects affecting 

establishment of northern red oak seedlings in 

central Pennsylvania. In: McCormick, Larry H.; 

Gottschalk, Kurt W., eds. Proceedings, 8th central 

hardwood forest conference; 1991 March 4-6; 

University Park, PA. Gen. Tech, Rep. NE-148. Radnor, 

PA: U.S. Department of Agriculture, Forest Service, 

Northeastern Forest Experiment Station: 271 -280. 

Winston, P. W. 1956. The acorn microsere, with special 

reference to arthropods. Ecology. 37: 120-1 32. 
Galford, Jimmy R.; Auchmoody, L. R.; Walters, Russell S.; Smith, H. Clay. 

1992. Millipede damage to germinating acorns of northern red oak. 

Res. Pap. NE-667. Radnor, PA: U.S. Department of Agriculture, Forest 

Service, Northeastern Forest Experiment Station. 4 p. 

Millipedes have not been reported as pests of germinating acorns. Studies in 

Pennsylvania on the impact of insects on northern red (Quercus rubra L.) 

seedling establishment revealed that the millipede Ptyoiulus impressus (Say) 

damaged the radicles of germinating acorns. Up to 17 percent of the acorn 

radicles in areas with heavy acorn crops were damaged in 1'991. Millipede 

feeding began in late March to early April, several days prior to feeding activity 

of insects that damage or destroy germinating acorns. 

Keywords: Diplopoda; Parajulidae; Ptyoilus impressus; acorn pest; oak 

regeneration 
Headquarters of the Northeastern Forest Experiment Station is in Radnor, Pennsylvania. Field laboratories are maintained at: 

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