United States 

Department of 

Agriculture 

Forest Service 

I Northeastern Forest 

Experiment Station 

Research Paper NE-656 

Response of Insects to 

Damaged and Undamaged 

Germinating Acorns 

Jimmy R. Galford 

Deloris Weiss-Cottrill 
Abstract 

Damaged germinating northern red oak, Quercus rubra L., acorns in pitfall 

traps were significantly more attractive to two species of acorn insects than 

undamaged germinating acorns. Significantly more adults of the weevil 

Conotrachelus posticatus Boheman and the sap beetle Stelidota octomaculata 

(Say) were caught in traps containing germinating acorns cut into halves versus 

traps containing uncut, germinating acorns. Larvae of the acorn moth Valentinia 

glandulella (Riley) also preferred damaged over undamaged acorns, but few 

larvae were caught and the results were not analyzed. 

The Authors 

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

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

Virginia. 

DELORES WEISS-COTTRILL formerly was a forestry technician with the 

Northeastern Station's Forestry Sciences Laboratory at Delaware, Ohio. 

Manuscript received for publication 11 April 1991 

Northeastern Forest Experiment Station 

5 Radnor Corporate Center 

100 Matsonford Road, Suite 200 

P.O. Box 6775 

Radnor, Pennsylvania 19087-4585 

September 1991 
Introduction 

Studies conducted since 1986 in Ohio and Pennsylvania 

have shown that insects are a primary factor in limiting 

oak seedling establishment (Galford et al. 1988, 1991 a). 

Insects destroy great numbers of germinating acorns, 

especially acorns of northern red oak, Quercus rubra L., 

in the spring. Even when acorn crops are large enough 

to exceed the needs of wildlife, the surplus may be largely 

destroyed by insects as they germinate (Galford et al. 

1991 a). 

There are three major species of insects that damage 

germinating northern red oak acorns in Ohio and 

Pennsylvania: a weevil, Conotrachelus posticatus Boheman; 

a moth, Valentinia glandulella (Riley); and a nitidulid sap 

beetle, Stelidota octomaculata (Say) (Fig. 1). C. posticatus 

overwinters as an adult and, depending on temperatures, 

may begin feeding on radicles df acorns in 

late February to early March in Ohio and mid to late 

March in Pennsylvania. Gibson (1964) provided information 

on the biology of C. posticatus but did not indicate that 

the weevil is a serious pest of germinating acorns. S. 

octomaculata also overwinters as an adult and feeds on 

radicles of germinating acorns (Galford 1987; Galford et 

al. 1991b); it begins activity about 1 to 2 weeks after C. 

posticatus. Both species of insects reproduce in the 

cotyledons of acorns and their developing offspring usually 

c~omplete the destruction of the acorns. V. glandulella 

overwinters as early instar larvae inside acorns damaged 

by rodents or other insects such as Curculio weevils or 

the Cydia moth or filbertworm. V. glandulella can be a 

secondary pest (Riley 1872; Murtfeldt 1894) or a primary 

pest (Galford 1986; Galford et al. 1991 a) of acorns. V. 

glandulella also overwinters as larvae on or near 

undamaged acorns. In the spring as soon as acorns 

germinate, the moth larvae begin feeding on acorn radicles 

and then "bore" into the acorn cotyledons to complete 

development (Galford et al. 1991a). V. glandulella larvae 

are one of the earliest insects to damage germinating red 

oak acorns in the spring, beginning their activity several 

days before C. posticatus. 

Laboratory and field studies demonstrated that C. 

posticatus, S. octomaculata and V, glandulella could feed 

and reproduce in germinating acorns, destroying their 

viability. Except for C. posticatus, the insects also feed 

and reproduce in nonviable acorns in which the cotyledons 

have turned brown. A preliminary laboratory test 

dtemonstrated that S. octomaculata preferred germinating 

a~corns infested with V. glandulella over noninfested 

germinating acorns for reproduction. However, the sap 

beetles also reproduced in some acorns that originally 

were insect free. They readily fed on the radicles of all 

off the insect-free acorns. These observations prompted a 

field study in 1988 to determine the relative attractiveness Figure 1 .-Top to bottom: larva of Valentinia of damaged and undamaged acorns to the insect species 

I glandulella, adult Conotrachelus posticatus, and mentioned. adult Stelidota octomaculata. 
Pitfall trapping studies were conducted rn an upland, 80-t 

year old oak-hickory stand in Vinton County in southern 

Ohio from late winter until late spring of 1988. The trap 

study sites were established on a south-facing midslope 

in a stand dominated by black oak, Q. velutina Lam., 

white oak, Q. alba L., and chestnut oak, Q. prinus L. 

Some northern red oak trees were located low on the 

slope and in the cove at the bottom of the slope. 

Northern red oak acorns used in these studies were 

collected from a single isolated lawn tree so that the 

acorns would be homogeneous. They were stored at 5" 

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

As they were needed for study, acorns were removed 

from storage and placed on moist paper toweling in loosely 

sealed jars to initiate germination. 

Pitfall traps were constructed using 1-pint (473-ml) glass 

canning jars with two-piece metal lids. The sealing lid 

was replaced with %inch mesh hardware cloth of equal 

diameter. The hardware cloth was glued inside the band 

with epoxy ribbon adhesive to prevent rodents from pulling 

it out. About 7 cm2 of cotton wadding was placed in 

each jar along with 20 ml of distilled water. The moist 

cotton wadding kept the acorns from desiccating and 

providing a rooting medium. Five acorns that were just 

beginning to germinate were placed in each of the five 

jar traps. In each of five other traps were placed five 

germinating acorns cut longitudinally in half with a hand 

pruner. Lids were placed on the jars and the jars were 

buried with the lids flush with the ground. Rain shields 

for the traps were provided by positioning plastic lids (15 

cm in diameter) about 7 cm above the tops of the traps. 

On March 8, 1988, 10 pitfall trap sites were installed 

about 3 m apart in the previously described stand. The 

traps were removed and replaced with clean jars containing 

fresh acorn baits at intervals of 3 to 14 days until July 8, 

1988, for a total of 18 trapping periods. A trap site was 

alternately baited with damaged or undamaged acorns to 

offset any difference due to trap site location. The old 

traps were placed in sealed plastic bags and returned to 

the laboratory where the contents were checked for insects. 

The acorns from the traps were placed in jars to rear V. 

glandulella larvae into adult moths. Most adult moths 

emerged within 8 to 10 weeks. After 10 weeks the acorns 

were dissected and any larvae or pupae found were 

counted. 

Results and Discussion 

Significantly more weevils and sap beetles were caught 

in traps baited with germinating acorns cut into halves 

than with whole germinating acorns (Table 1). The 

difference might have been even greater had it been 

possible to change the baits more frequently. Insects 

entering a trap and feeding on uncut germinating acorns 

the first night after trap deployment could have enhanced 

the attraction of that trap. Also, since nothing is known 

about the pheromones of C. posticatus and S. octomaculata, 

the insects initially trapped could have subsequently 

influenced the catch. Attraction of both sexes to the maleproduced phermone of the nitidulid Carpophilus hemipterus 

(L.), the driedfruit beetle, is enhanced by volatiles from a 

food source (Bartelt et al. 1990). Thus, if S. octomaculata 

has a similar pheromonelhost interaction, the insects 

initially trapped could have enhanced subsequent insect 

response to the traps. 

Data on V. glandulella moth larvae were not analyzed 

because too few were trapped. However, more moth 

larvae were caught using cut acorns versus whole acorns. 

This moth overwinters as early instar larvae on or near 

acorns in forest litter. Thus, the area of attraction and 

response of the small moth larvae would be limited 

compared to the more mobile adults of C. posticatus and 

S. octomaculata. 

The numbers of insects caught were lower than expected 

based on studies conducted in previous years in the 

area. However, 1987 and 1988 were below normal in 

rainfall and there were few acorns in autumn of 1987 for 

Table 1.-1988 catch of acorn insects in 10 pitfall 

traps baited with undamaged germinating acorns or 

damaged acorns (germinating acorns cut into halves) 

Damaged acorns Undamaged acorns 

Trap- Wee- Sap Wee- Sap 

Ping vils beetles Moths vils beetles Moths 

dates caught caught caught caught caught caught 

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

Total 96a 108~ 16 16 34 12 

aSignificantly different at 1% level from whole acorns (t test, 

t = 0.0317). 

bSignificantly different at 1% level from whole acorns (t test, 

t = 0.0116). 
insect feeding. lnsect activity also was slowed by cool 

temperatures until late April. The sudden drop in the 

catch of weevils in late May (Table 1) resulted from high 

temperatures which sent the weevils into reproductive 

diapause or aestivation until late summer. 

The greater response by the insects to the cut acorns 

probably was due to increased volatiles emitted by the 

damaged acorns. In late summer and early autumn, the 

insects coming out of aestivation or newly emerged adults 

must quickly locate hosts suitable for feeding and 

reproduction. Fresh acorns damaged by rodents, birds, or 

other insects are readily detected by the insects and they 

migrate to the seed-bearing trge. Once beneath the tree, 

damaged acorns are the primary sources for feeding and 

reproduction of the insects. If white oak-type acorns, 

which geminate soon after falling, are present, feeding 

and oviposition will occur in undamaged acorns as soon 

as they germinate. In the case of red oak-type acorns, 

which do not germinate until the following spring, the 

acorn insects overwinter near or on the acorns and begin 

feeding soon after the acorns germinate in late winter or 

early spring. 

In summary, damaged acorns are more attractive to the 

major insects that feed on germinating acorns. However, 

insect feeding and reproduction also occurs readily in 

undamaged germinating acorns once the insects are 

attracted to an area. In most years when only a few oak 

trees in the forest bear acorns, the crop is largely destroyed 

by a combination of concentrated rodent and insect feeding. 

As a result, few if any oak seedlings became established. 

In years of large to bumper acorn crops, the needs of 

both wildlife and insects are met and significant oak seedling 

establishment may occur. However, bumper acorn crops 

may not always result in good oak seedling establishment. 

The largest acorn crop in several years in central 

Pennsylvania in 1989 did not lead to good seedling 

establishment in the spring of 1990 even when acorns 

were protected from predation from most mammals (Galford 

et al. 1991a). Less than adequate moisture in late winter 

and early spring resulted in poor acorn germination and 

insects destroyed the majority of the acorns that 

germinated. 

Acknowledgments 

We thank H. Clay Smith, Ken Mongeau, and 

Drs. Roger N. Williams, Jack Barger, and William 

N. Cannon, Jr. for their helpful suggestions and 

reviews. 

Literature Cited 

Galford, J.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. 1987. Effect of Stelidota octomaculata 

(Coleoptera:Nitidulidae) on germinating acorns under 

laboratory conditions. In: Hay, Ronald L.; Woods, 

Frank W.; DeSelm, Hal, eds. Proceedings, 6th central 

hardwood forest conference; 1987 February 24-26; 

Knoxville, TN. Knoxville TN: University of Tennessee: 

41 9-422. 

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

1988. Insects and other pests affecting oak 

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. 

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

Walters, Russell S. 1991 a. 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: US. 

Department of Agriculture, Forest Service, Northeastern 

Forest Experiment Station: 271 -280. 

Galford, Jimmy R.; Williams, Roger N.; Daugherty, Ann. 

1991b. Life history and notes on the biology of 

Stelidota octomaculata (Coleoptera:Nitidul idae). Res. 

Pap. NE-644. Radnor, PA: U.S. Department of 

Agriculture, Forest Service, Northeastern Forest 

Experiment Station. 7 p. 

Gibson, Lester P. 1964. Biology and life history of 

acorn-infesting weevils of the genus cConotrachelus 

(Co1eoptera:Curculionidae). Annals of the 

Entomological Society of America. 57: 521 -526. 

Murtfeldt, M.E. 1894. Acorn insects, primary and 

secondary. lnsect Life. 6: 31 8-324. 

Riley, C.V. 1872. The acorn moth. Canadian Entomologist. 

4: 18-19. 

Bartelt, Robert J.; Dowd, Patrick F.; Plattner, Ronald D.; 

Weisleder, David. 1990. Aggregation pheromone of 

driedf ruit beetle, Carpophilus hemipterus. Windtunnel bioassay and identification of two novel 

tetraene hydrocarbons. Journal of Chemical Ecology. 

16: 1015-1039. 
Galford, Jimmy R.; Weiss-Cottrill, Deloris. 1991. Response of insects to 

damaged and undamaged germinating acorns. Res. Pap. NE-656. 

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

Forest Experiment Station. 3 p. 

Damaged germinating northern red oak, Quercus rubra L., acorns in pitfall 

traps were significantly more attractive to two species of acorn insects than 

undamaged germinating acorns. Significantly more adults of the weevil 

Conotrachelus posticatus ohe em an and the sap beetle Stelidota octomaculata 

(Say) were caught in traps containing germinating acorns cut into havles 

than in traps containing uncut germinating acorns. Larvae of the acorn moth 

Valentinia glandulella (Riley) also preferred damaged over undamaged acorns, 

but few larvae were caught and the results were not analyzed. 

I ODC 145.7 x 416.2 Quercus-181.525 

Keywords: Acorn pests; oak regeneration; Valentinia glandulella; 

Conotrachelus posticatus; Stelidota octomaculata 

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