Department of 

Agriculture Life History and Notes on the 

Forest Service Biology of Sfelkfofa ~~foma~/afa 

Northeastern Forest 

Experiment Station (Coleoptera:NitiduIidae) 

Research Paper NE-644 

Jimmy R. Galford 

Roger N. Williams 

Ann Daugherty 
Abstract 

The life history of Stelidota octomaculata (Say) was studied in Ohio and 

Pennsylvania. This insect damages acorns and affects the establishment of oak 

seedlings. Acorns deployed in wire cages and pitfall traps plus a sampling of 

naturally occurring acorns were used to monitor insect activity. Adults overwinter in 

forest litter and begin feeding on undamaged germinating or damaged acorns in 

spring. Acorns damaged by the beetles may fail to produce seedlings. Beetle 

reproduction occurs in spring and early summer inside acorns both above and 

below ground. Reproduction ceases in late July to early August. Adult activity may 

continue until early December in some years. In the laboratory, a life cycle was 

completed in about 34 days at 220 to 26%. The maximum number of offspring from 

a female was 933 and the maximum lifespan at: room temperature was 238 days. 

Acorns of all oak species tested plus seeds of 28 other species were suitable for 

larval development. 

The Authors 

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

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

ROGER N. WILLIAMS is a professor of entomology with the Ohio Agricultural 

Research and Development Center at Wooster, Ohio. 

ANN DAUGHERTY, formerly a forestry technician with the Northeastern Station's 

Forestry Sciences Laboratory at Delaware, Ohio, is a technician with the Harden 

County (Ohio) Soil and Water Conservation District. 

Manuscript received for publication 2 August 1990 

Northeastern Forest Experiment Station 

5 Radnor Corporate Center 

100 Matsonford Road, Suite 200 

P.O. Box 6775 

Radnor, Pennsylvania 19087 

January 1991 
Introduction 

Stelidota octomaculata (Say) was first reported in 

association with northern red oak, Quercus rubra L., acorns 

collected in August and September in Illinois by Winston 

(1956). He listed this insect with other arthropods found in 

acorns but no other information was presented. Williams 

and Kreuger (1985) reported rearing S. octomaculata in the 

laboratory on chinese chestnuts, Castanea mollissima 

Blume, though it was not one of several sap beetle species 

associated with damaged chestnuts in Ohio groves. Galford 

(1986) reported that a Stelidota sp. was a possible primary 

pest of germinating northern red oak acorns. This species 

was later identified as S. octomaculata and laboratory tests 

confirmed the ablity of this insect to destroy germinating 

acorns (Galford 1987). An unidentified nitidulid was reported 

by Krajicek (1960) in association with red oak acorns that 

germinated in the spring in Iowa but failed to produce 

seedlings. The species involved may have been S. 

octomaculata since this species was found to be a pest of 

germinating red oak acorns in Ohio in spring (Galford et al. 

1988). 

The life history and biology of S. octomaculata were studied 

in the field and laboratory from 1986 to 1989 in Ohio and 

Pennsylvania. This paper reports the results of those 

studies. 

Methods 

Field Studies 

From 1986 to 1988, field studies were conducted in mature 

oak forests in the upland, unglaciated region of southern 

Ohio. In 1989, studies were conducted in the Moshannon 

State Forest in central Pennsylvania, a mountainous, 

unglaciated region. The study areas in southern Ohio were 

in mature oak-hickory forests composed primarily of white 

oak, Quercus alba L., black oak, Q. velutina Lam., chestnut 

oak, Q. prinus L., scarlet oak, Q. coccinea Muenchh., and 

northern red oak, Q. rubra L. In Pennsylvania, the study 

areas were in stands dominated by northern red oak, 

though some white, black andlor chestnut oaks were found. 

Acorns used for field and laboratory studies were collected 

in autumn and stored at 50 to 7% 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. Acorns of 

most species of oak were still usable after 1 to 3 years of 

storage. However, white and chestnut oak acorns 

germinated and filled the bags with roots in 2 to 3 months. 

Acorns of most species of oak found in the Northeast plus 

seeds of 28 other species of trees and shrubs were tested 

as potential hosts for S. octomaculata. The seeds used in 

these studies were collected or purchased as available and 

most were used within a few days after acquisition. 

Unless otherwise noted, only sound, viable acorns without 

signs of damage from other insects were used in these 

studies. Acorns used in the biological studies in the 

laboratory were washed in tap water, soaked for 2 to 3 

minutes in a 2.5 percent sodium hypochlorite (50 percent 

bleach) solution, rinsed in tap water, and then soaked in 

distilled water for 30 minutes. 

Sprouted acorns of northern red, white, or bur oak were 

wrapped in 114-inch (ca. 6-mm) hardware cloth cages for 

rodent protection and deployed in the Ohio forest in 1986 to 

monitor the activity periods of the nitidulids. A wire flag was 

inserted through each cage into the ground to prevent 

rodents from carrying off the cages and also to mark the 

sites. The cages were thoroughly covered with leaf litter. In 

early March, 10 cages, each containing 5 acorns, were 

deployed at intervals of 3 m on a south slope. At intervals of 

7 to 21 days until November, the cages were removed and 

replaced with others containing fresh acorns. In the 

laboratory, the cages were opened and the acorns 

examined. The acorns were then placed in covered, 1-1 

battery jars to rear out any insects in the acorns. 

On April 9, 1986, in Ohio, 25 whole nuts each of northern 

red oak, chestnut oak, shagbark hickory, Carya ovata (Mill.) 

K. Koch, and 10 nuts of black walnut, Juglans nigra L., were 

deployed individually in wire cages under leaves. An electric 

drill was used to make two 118-inch (ca. 3-mm) holes in the 

sides of each nut. The nuts were alternated 1 m apart in a 

row following the contour of a hill. On April 30 the nuts were 

removed, bagged individually and returned to the laboratory 

where they were examined and placed in rearing jars. 

In October of 1986, 1987, and 1988, 50 northern red oak 

acorns were placed under each of seven wooden-frame 

cages (ca. 91 cm square by 30 cm high) covered on the 

tops and sides with 114-inch hardware cloth but open on the 

bottoms. The cage frames were constructed from pressuretreated 5- by 5-cm lumber. The leaf litter was raked from an 

area ca. 1 m square and the 50 acorns were spaced evenly 

on the area and covered with leaves. A cage was then 

placed over the acorns. Shallow trenches (ca. 5 cm deep) 

were dug under the bottom edges so that the cages sat in 

the ground. Soil and forest litter was raked against the sides 

of the cages to reduce penetration by rodents. In 1986 and 

1987 all of the cages were placed under acorn-bearing 

trees. In 1988, four cages with acorns were placed under 

non-oak species in December when insect activity had 

ceased. 

Acorns that failed to produce seedlings were removed from 

the frame cages in late May, checked for insect damage, 

and placed in rearing jars in the laboratory to rear out any 

insects. Acorns that produced seedlings were cut off the 

seedlings and placed in rearing jars. 

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

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

replaced with 114-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. A 10-02 (296-ml) plastic drinking cup containing a 

crumpled paper towel was placed in each pint jar. Twenty ml 
of water were added to the cup to prevent desiccation of the 

acorn bait. Then 8 to 10 acorn halves were added to each 

jar and lids ptaced on the jars. The jars were buried with the 

lids flush with the ground. Rain shields were provided by 

positioning plastic lids (15 cm in diameter) supported on 

landscaping nails (25 cm long) approximately 7 cm above 

the tops of the jars. 

In 1987, 10 pitfall trap sites were established about 3 m 

apart on a south-facing midslope in southern Ohio. These 

sites were flagged and numbered and used again in 

trapping studies in 1988. The pitfall traps were installed in 

mid-February and removed in late October to early 

December. The traps were checked and the acorn baits 

renewed at intervals of 3 to 21 days as follows: in the 

laboratory the 10-02 plastic cups containing the paper 

towels, water, and the acorn baits were prepared and 

sealed individually in plastic bags numbered according to 

trap site; in the field the new baits were exchanged for the 

old baits, which were bagged and returned to the laboratory 

where the contents of the cups were checked for insects. 

The acorns from the cups were placed in jars.to rear out 

any insects. 

In 1989, 56 pitfall traps were installed on May 1 and 2 in 

Pennsylvania and were checked at intervals of 6 to 9 days 

through June 12. Four traps were installed in each of 

fourteen Qacre plots being used for studies on factors 

limiting oak seedling establishment in Pennsylvania. An 

additional four pitfall traps were installed away from the 

study plots and were checked weekly from June to early 

November to monitor the seasonal activity of S. 

octomaculata in central Pennsylvania. 

A good crop of northern red oak acorns in the autumn of 

1988 in central Pennsylvania allowed periodic sampling of 

acorns throughout the spring and early summer of 1989. 

Acorn samples were taken from under leaf litter, rodent 

caches, and from newly established seedlings. e 

Laboratory Studies 

Techniques for rearing S. octomaculata on acorns in the 

laboratory have been described (Galford 1987). In these 

studies the nitidulids were reared as follows: Plastic culture 

dishes (150 by 20 mm) were lined with filter paper 

moistened with distilled water; two or three acorns cut into 

halves were placed cut side down on the filter paper and a 

pair of beetles introduced. The filter paper was kept moist 

throughout the studies. The beetles were transferred 

fortnightly to new dishes with fresh acorns until the female 

died. Mature larvae were removed daily from the dishes and 

the number of larvae recorded. 

The beetles are easily sexed as adults or.pupae. The pupae 

are fragile and must be manipulated with a small, 

moistened, camel's-hair brush. The adults are easily 

manipulated with forceps without injury. The common 

character of six abdominal segments in males (the sixth 

being very small) and five in the females was used in sex 

identification. We found thatwith experience the following 

characters also are useful: the sternum just anterior to the 

first abdominal segment is concave in males and flat to 

slightly convex in females; the metatibia are slightly bowed 

in males but not in females; female pupae have two small, 

unnamed, cone-shaped protuberences on the ventral 

surface of the abdomen, just anterior to the anus. These 

structures are lacking on male pupae. 

Twenty culture dishes. each with one pair of beetles, were 

set up for each of the following kinds of acorns: northern 

red, black, white, chestnut, and bur oak, Q. macrocarpa 

Michx.; 10 dishes were set up for chinkapin, Q. 

muehlenbergii Engelm., and five were set up for pin oak, Q. 

palusfris Muenchh. 

Ten dishes, each with one pair of beetles. were set up as 

follows: five dishes were provided with nonviable northern 

red oak acorns which had dead cotyledons that had turned 

brown, and five were provided with viable acorns just 

beginning germination. The nonviable acorns were partially 

cut open to allow the beetles access to the cotyledons. To 

prevent acorns from rolling in the dishes, a small area was 

cut off the side of each acorn with the cut side down on the 

filter paper. 

Sixteen dishes, each with one pair of beetles removed 

between April 9 and May 15, 1988, from pitfall traps in Ohio, 

were set up with northern red oak acorns to observe the 

fecundity and longevity of the spring population of beetles. 

Seeds of other trees and shrubs used to rear the beetles 

were cut open or cracked and placed on moist filter paper. 

The insects were reared as described peviously. Two or 

three dishes, each with three pairs of beetles, were set up 

for each seed species and observed until reproduction 

occurred or the beetles died. 

Mature larvae (wandering larvae without a brownish cast to 

the gut) were removed daily from the culture dishes with 

forceps. Up to 50 larvae were placed in a 1-02 (ca. 30-ml) 

plastic portion cup about three-quarters filled with moist 

masonry sand or moist tissue paper, the latter allowing 

observation of development. 

Eggs were obtained for observation as follows: acorn meats 

were partially sliced with a scalpel and placed in dishes 

containing several mated females; the acorn meats were 

removed daily and checked for eggs which were laid 

between the slices. Acorn slices with eggs attached to them 

were removed from the oviposition dishes and held on moist 

filter paper in petri plates until they hatched. The 

development of these larvae was followed daily to determine 

the number of larval instars and stadia. The widths of the 

head capsules of the larvae were measured daily with a 

binocular micrometer. The number of larval instars was 

further ascertained by measuring the head-capsule width of 

all of the larvae from a 15-day-old culture. The larvae were 

killed in alcohol to facilitate the measurements. 

Sex ratios of the beetles were determined from both 

laboratory-reared and field-collected insects using the 
previously described morphological characters. 

A brief study was conducted on the affects of temperature 

and light on beetle reproduction as follows: forty dishes, 

each with red oak acorns and a pair of beetles, were set up; 

half of the dishes were kept in an environmental chamber at 

26.7% and half in a chamber set at 21.1%. Half of the 

dishes in each chamber were kept in a sealed box double 

covered with black plastic. Both chambers were lighted with 

eight 15-watt florescent bulbs and kept on a 16:8 hour 

lightldark cycle. The beetles were transferred to fresh 

acorns fortnightly. 

Results and Discussion 

Field Study Results 

Because of rodent damage few data were collected in 1986 

from the experiment using acorns deployed in the small 

wire cages. Some cages were ripped apart by large rodents 

while small rodents managed to chew the acorns through 

the wire mesh. Acorn losses to rodents was total in some 

areas, minimal in others. However, enough data were 

collected that year to determine that S. octomaculata 

became active March 21 to 30, started reproducing April 9 

to 30, stopped reproduccion July 10 to 16, and ceased 

activity by October 16. There was little activity from July 16 

to August 26 and peak autumn activity occurred in 

mid-September. 

Although most of the nuts were lost to rodents, S. 

octomaculata adults were collected from some of the 

deployed red oak and chestnut oak acorns and the hickory 

nuts and black walnuts. There was some reproduction in the 

nuts of all four species. 

Rodent damage associated with the small wire cages that 

occurred in 1986 prompted a change to pitfall traps for 

monitoring beetle activity in 1987 to 1989. Preliminary tests 

in 1986 demonstrated that it was necessary to glue the wire 

discs in the jar lids to prevent rodents from ripping out the 

wire to reach the acorns. Initially the rodents pulled some 

traps out of the ground but they ceased this activity after 

one or two attempts. 

Interestingly, when preliminary tests of the pitfall traps were 

being conducted in late summer of 1986, it was noted that 

rodents rarely disturbed traps baited with oriental, Castanea 

sp., chestnuts. but disturbed all traps baited with acorns, 

hickory nuts, or black walnuts. Also, all primary pests of 

acorns were caught in traps baited with chestnuts: the 

weevils Conotrachelus posticatus Boheman and C. naso 

LeConte; larvae of the acorn moth Valentinia glandulella 

(Riley); and S. octoma'culata. The weevils and the nitidulids 

reproduced in the chestnuts and larvae of the acorn moth 

completed development into adults. American chestnuts, 

Castanea dentata (Marsh.) Borkh., may have been a host of 

the insects before the chestnut blight disease, 

Cryphonectria parasitica (Murr.), eliminated American 

chestnut from eastern forests. 

The results of the pitfall studies in Ohio in 1987 and 1988 

are given in Table 1. Beetle activity began three weeks 

earlier in 1987 than in 1988 due to an early warming trend 

in late February of 1987 compared with the cool, late spring 

that occurred in 1988. Reproduction also commenced 

several weeks earlier in 1987 than in 1988. In both years, 

reproduction ceased in late July or early August when 

daytime temperatures consistently reached 300 to 35%. 

Reproduction was not observed in autumn. Although beetle 

activity slowed during the hottest weeks of summer it never 

entirely stopped. Fewer beetles were caught in 1988 (594) 

than in 1987 (1004). Below normal rainfall and poor acorn 

crops in both years combined with continuous removal of 

trapped beetles may explain the drop in population. 

Table 1 .-Activity periods of S. octomaculata as shown 

by catches in 10 pitfall traps in Ohio, 1987 and 1988 

Trapping Number of Trapping Number of 

dates beetles caught dates beetles caught 

2117 - 314 

314 - 9 

3117 - 24 

3/24 - 417 

417 - 14 

4115 - 22 

4/22 - 28 

4128 - 517 

517 - 21 

5/21 - 612 

612 - 17 

611 7 - 719 

719 - 30 

7130 - 811 9 

8119 - 26 

8126 - 91 1 

911 - 10 

9/10 - 16 

911 6 - 22 

9/22 - 1011 

1011 - 8 

1018 - 15 

10115 - 22 

10122 - 29 

10129- 1114 

Ill4 - 13 

11/13 - 1219 

1219 - 15 

Total 

(Traps removed 1211 5) 

318 - 29 

3129 - 411 

411 - 7 

417 - 15 

4/15 - 26 

4/26 - 515 

515 - 12 

5112- 18 

5118 - 27 

5127 - 611 

611 - 15 

611 5 - 24 

6124 - 718 

718 - 22 

7122 - 815 

815 - 10 

8/10 - 17 

8117 - 24 

8124 - 31 

8131 - 917 

917- 14 

9114 - 21 

9121 - 28 

9/28 - 1014 

1014 - 12 

10112 - 19 

10119 - 26 

Total 

1988 

(Traps removed 10126) 

aReproduction in acorns in traps. 

b~ll traps vandalized. 
In Pennsylvania in 1989, 1,315 beetles were caught in 56 

pitfall traps from May 1 to June 15. This population, while 

not high, combined with the acorn weevil, C. posticatus, and 

the acorn moth, V. glandulella, to destroy all of the aboveground germinating acorns that escaped wildlife predation. 

A drought in central Pennsylvania in 1988 may have 

affected the sap beetle population. Additional studies are 

needed on the population dynamics of the beetles in 

relation to climatic conditions and ecological factors. 

The four pitfall traps maintained from June 14 to November 

9 in Pennsylvania revealed that sap beetles were active 

throughout the summer and early autumn. However, 

reproduction slowed in late July when daytime temperatures 

ranged from 270 to 32% and ceased by August 15. Cold 

weather slowed beetle activity in late October and no 

beetles were caught during the last trap period (November 2 

to 9). 

In Pennsylvania and Ohio, samples of acorns found under 

leaves, buried acorns, acorns still attached to new 

seedlings, acorns on top of logs, and .acorns removed from 

seedlings sprouting from rodent caches revealed that sap 

beetles reproduce both above and below ground. In Ohio, in 

1987, some acorns planted about 2.5 cm deep in early June 

in forest plots used in other studies were destroyed or 

heavily damaged by S. octomaculata. The most common 

site of reproduction in Pennsylvania was in partially buried 

acorns still attached to new seedlings. In samples taken 

under oak tree canopies in early July, 36 of 67 (54 percent) 

acorns still attached to new seedlings were infested with S. 

octomaculata. Only 7 of 42 (17.percent) acorns still attached 

to new seedlings were infested with larvae in samples taken 

under non-oak species. The latter seedlings originated from 

acorns that had been dispersed by rodents. Four larvae 

were found inside the root of a wilted, first-year oak seedling 

that had several weevil feeding punctures just below the 

crown. The female sap beetle probably laid her eggs inside 

one of the weevil holes. This was the only instance of S. 

octomaculata in oak seedling roots. 

Observations of the acorns placed under the large frame 

cages in Ohio in 1986 to 1988 supported the data from the 

other studies. All of the acorns under the cages were 

destroyed as they germinated in 1986 and 1987 by a 

combination of feeding from the acorn weevil C. posticatus, 

S, octomaculata, and the acorn moth V. glandulella. 

In the spring of 1989, insects destroyed all of the 

germinating acorns under the three cages placed under 

seed-bearing oaks in October; 126 oak seedlings were 

produced from the 200 acorns placed under cages beneath 

non-oak trees in December of 1988 after insect activity had 

stopped. Fifty-seven acorns failed to germinate and only 17 

were destroyed by insects, 12 by S. octomaculata. 

Laboratory Study Results 

Biological data on S. octomaculata from laboratory studies 

conducted at room temperatures (220 to 26oC) are given in 

Table 2.- summa^ of biological data for S. ocfomaculafa 

reared at 220 to 26% on northern red oak acorns 

Life stage Ave. number of days 

Egg to adult 

Preoviposition period 

Egg 

1 st instar 

2nd instar 

3rd instar 

Prepupae 

Pupae 

aptus another 3 or more days to emerge from the pupation 

medium. 

Table 2. A maturation feeding or preoviposition period of 

about 5 days was required. Eggs took 3.5 to 4.5 days to 

hatch, most hatching within 4 days. The beetles had three 

instars as determined by daily observations and 

measurements of head capsules; 87 percent (98 of 11 3) of 

the head-capsule measurements of larvae from a 14-day-old 

culture fell within three classes: 0.28 to 0.32 mm, 0.44 to 

0.48 mm, and 0.64 to 0.68 mm. The stadia averaged 3.5, 

3.0, and 4.5 days for instars 1, 2, and 3 respectively, The 

prepupal period averaged 4.5 days for larvae placed on 

moist sand for pupation. The prepupal period averaged 

almost a day longer for larvae placed on moist tissues for 

pupation. The beetle larvae quickly formed pupation cells in 

sand but not in tissues, which delayed pupation. The pupal 

stage lasted 8 to 10 days with most emerging in 8.5 days. 

However, the beetles did not surface from the sand for 3 or 

more days. 

Measurements of the various life stages of the beetles 

revealed the following; female adults from the laboratory 

cultures ranged in length from 2.5 to 3 mm, averaging 2.8 

mm. Males ranged in length from 2.4 to 3.1 mm and 

averaged 2.8 mm. Adults from the pitfall traps varied more 

in size and were smaller than cultured beetles. Females 

ranged in length from 2.1 to 2.9 mm and averaged 2.6 mm; 

males ranged from 2.3 to 3 mm and averaged 2.7 mm. 

Although not measured, the pronotums of most adult males 

were visibly wider than those of females. Sexual differences 

in pronotum width were noted in S. geminata (Say) by 

Weber and Connell (1975). Eggs of the beetles ranged in 

length from 0.8 to 0.88 mm; live, mature larvae ranged from 

3.2 to 4.8 mm and averaged 4.0 mm. 

In the laboratory, eggs were laid in a variety of situations. 

As stated earlier, the beetles readily laid eggs between 

slices of acorn meats. They also oviposited in holes that had 

been punched in acorn meats with a dissectifig needle. 

Eggs were found on top of soil, sand, or filter paper beneath 

pieces of acorn meats, and between the acorn shell and the 

cotyledons. The beetles also entered acorns via Curculio 

weevil exit holes for oviposition. 
Larvae near maturity quickly emerged from disturbed 

acorns in the laboratory. This behavior would have survival 

value in the forest where wildlife readily consumes acorns. 

Some larvae pupate inside the acorns but most exit and 

pupate in the soil. 

Beetle Fecundity and Longevity 

Data for fecundity and longevity in Table 3 are for 55 pairs 

of the original 115 pairs started. Because of problems with 

disease in the insects, data were collected only on females 

living at least 4 weeks. Because of the unknown affects and 

possible interaction of the disease and species of acorn 

used for rearing, no analysis was attempted for differences 

in fecundity and longevity of beetles on different species of 

acorns. The most eggs produced by a female was 933 on 

pin oak, a red oak-type acorn; the most produced on white 

oak was 912. Maximum production by a female was 160 

offspring produced in a 14-day period. The maximum 

longevity recorded for females was 238 days on red oak and 

chestnut oak. 

The average number of offspring produced by each of 16 

"wild" females from the pitfall traps in the spring of 1988 

was 193 (range: zero to 552). Female longevity averaged 76 

days and ranged from 10 to 116 days. The spring 

population was tested since spring and early summer are 

the periods of reproduction. Although the averages and 

ranges for fecundity and longevity of the wild beetles were 

lower than those for the laboratory strain, some of the wild 

beetles also died from disease. Pathogenic organisms may 

be common in the beetles and these organisms would 

shorten the lives of beetles, especially under laboratory 

rearing conditions. Thus, averages for fecundity and 

longevity determined under laboratory conditions could vary 

depending on the rearing conditions and health of the 

beetles. 

There were differences in the sex ratios of beetles trapped 

in pitfalls from March to July versus August to November. 

Of 567 beetles trapped in March to July, 349 were females 

and 218 were males. Of 1,071 beetles trapped from August 

to November, 403 were females and 668 were males. Of 

4,796 beetles sexed from the laboratory cultures, 2,578 

were females and 2,218 were males. A chi-square test 

based an assumed sex ratio of 1:l showed that in all cases 

the sex-ratio differences were significant. The pitfall traps 

might be selective for males in late summer and early 

autumn or the traps are less competitive with naturally 

occurring acorns for females. In spring, when natural acorns 

are less abundant because of wildlife predation, females 

may be more easily trapped, or perhaps males do not 

overwinter as well as females and are less abundant in 

spring. 

At least some females caught singly in traps in late 

November and early March were fertile and produced 

offspring without being paired with males. This indicates 

that some females may overwinter in an inseminated state 

or that mating is one of the earliest activities in late winter. 

The beetles can reproduce in both viable and nonviable 

Table 3.-Reproduction and longevity of S. octomaculata reared at 220 to 26% on 

acorns from various species of oak 

Number of pairs 

Type of observed Ave. number Ave. longevity 

acorn (lab strain) of offspring of females 

No. of days 

Red 

Black 

White 

Bur 

Chinkapin 

Chestnut 

Pin 

403 (56 to 71 8) 141 (56 to 238) 

375 (1 91 to 51 6) 110 (51 to 154) 

490 (65 to 9 12) 143 (35 to 225) 

422 (140 to 690) 111 (57 to 149) 

359 (122 to 648) 106 (69 to 166) 

383 (1 85 to 493) 141 (98 to 238) 

644 and 933 84 and 183 

Average of 55 females 

(lab strain) 405 125 

Average of 16 females 

collected in pitfall traps 193 (0 to 552) 76(10 to 116) 
acorns. The average number of offspring produced by each 

of five pairs of beetles kept on viable acorns was 299 while 

the average produced by females reared on inviable acorns 

was 322. This supported observations in Pennsylvania that 

the most common site of beetle reproduction was live 

acorns still attached to newly established seedlings, but that 

reproduction also occurred in nonviable acorns found under 

leaves and on logs and stumps. 

Effects of Light and Temperature on Reproduction 

The brief study on effects of temperature and light on beetle 

reproduction revealed that reproduction stopped at a 

constant 26.70C regardless of day length. Only 12 larvae 

were produced by the 10 pairs of beetles reared on the 16:8 

hour day and only 23 larvae were produced by the adults 

reared in the dark. Most reproduction occurred in the first 

2-week period, and ceased after 4 weeks. By contrast, the 

10 pairs of beetles reared at 21.10C on the long day 

produced 700 larvae in 6 weeks. Adults reared in the dark 

produced more than 1200 larvae in 6 weeks. However, at 

the end of 6 weeks, reproduction had dropped significantly 

in the long-day beetles, indicating that both day length and 

temperature may play a role in beetle reproduction. 

Although reproduction has not been detected in autumn in 

the forest most of the beetles removed from pitfall traps in 

late summer and autumn would readily commence 

reproduction in the laboratory. However, periods of reduced 

reproduction have been noted in the laboratory cultures and 

additional studies are needed an the interrelationships of 

temperature and day length on beetle reproduction. 

Seeds Suitable for Reproduction 

Table 4 lists the species whose seeds were suitable hosts 

for S. octomaculata in the laboratory. Black cherry, Prunus 

serotina Ehrh., seeds were tested but the beetles did not 

feed on black cherry seed, either cracked or germinated. 

Although S. octomaculata bred in black walnuts and hickory 

nuts deployed in the forest in 1986, we have never found 

the beetles naturally in seeds other than acorns. 

Field Observations of Sap Beetle Damage 

During these studies field observations of adult S. 

octomaculata feeding damage revealed that the tender 

radicle (root) shoots of acorns are preferred feeding sites in 

early spring. Dry winters such as occurred in Ohio in 1986 

to 1988, delay germination of red oak acorns. When an 

early warming trend occurs in late February or early March, 

damage to radicles by insects is heavy. When a dry spring 

occurs and seedbeds are not ideal, damaged acorns 

desiccate without resprouting. In ideal situations, acorns 

may resprout after being damaged by insects so long as 

rainfall is adequate and there is no further damage to the 

acorns. However, the resulting seedlings do not develop the 

carrot-like taproot that enables them to survive dry periods 

Table 4.-Species whose seeds supported development 

of S. octomaculata 

Scientific name Common name 

Acer saccharum Marsh 

A. saccharinum L. 

A. rubrum L. 

Aesculus glabra Willd. 

Asimina triloba (L.) Dunal 

Carpinus caroliniana Walt. 

Carya cordiformis (Wang.) K. Koch 

C. illinoensis (Wang.) K. Koch 

C. ovata (Mill.) K. Koch 

Castanea sp. 

Cornus florida L. 

Corylus americana Walt. 

Corylus sp. 

Fagus grandifolia Ehrh. 

Fraxinus americana L. 

F. pennsylvanica Marsh. 

Gleditsia triacanthos L. 

Gymnocladus dioicus (L.) K. Koch 

Hamamelis virginiana L. 

Juglans cinerea L. 

J. nigra L. 

J. regia L. 

Lindera benzoin (L.) Blume 

Nyssa sylvatica Marsh. 

Pyrus sp. 

Quercus alba L. 

Q, bicolor Willd. 

Q. coccinea Muenchh. 

Q. ilicifolia Wang. 

Q. imbricaria M ic hx. 

Q. laurifolia Michx. 

Q. macrocarpa Michx. 

Q. muehlenbergii Engelm. 

Q.,palustris Muenchh. 

Q. prinus L. 

Q. rubra L. 

Q. velutina Lam. 

Vitis sp. 

Sassafras albidum (Nutt.) Nees 

Viburnum acerifolium L. 

Sugar maple 

Silver maple 

Red maple 

Ohio buckeye 

Common pawpaw 

Ironwood or bluebeech 

Bitternut hickory 

Pecan 

Shagbark hickory 

Oriental chestnuts 

Dogwood 

American hazelnut 

Filbert 

American beech 

White ash 

Green ash 

Honeylocust 

Kentucky coffeetree 

Witch-hazel 

Butternut 

Black walnut 

English or Persian walnut 

Spicebush 

Black tupelo 

Crabapple 

White oak 

Swamp white oak 

Scarlet oak 

Bear or scrub oak 

Shingle oak 

Laurel oak 

Bur oak 

Chinkapin oak 

Pin oak 

Chestnut oak 

Red oak 

Black oak 

Wild grape 

Sassafras 

Maple-leaf viburnum or 

arrow-wood 

in late summer. During the summer drought of 1987 in 

Ohio, examination of the roots of dying white oak seedlings 

that were established in the fall of 1986 revealed that all of 

the dying seedlings lacked the long taproot characteristic of 

oak seedlings. The radicles of these seedlings had been 

damaged in the fall of 1986 by the weevil C. posticatus. 

Although some of the acorns had resprouted and were able 

to root before winter, many were frost-heaved in the spring 

because they lacked the long taproot to anchor them in the 

ground. Seedlings not completely heaved from the ground 

subsequently died in the drought. 
Summary Literature Cited 

S. octomaculata is both a primary and secondary pest of 

acorns in Ohio and Pennsylvania. The beetle overwinters as 

an adult, feeds on germinating or damaged acorns in late 

winter, and begins reproduction in late March to May. The 

most common sites of reproduction are partially buried 

acorns still attached to newly established oak seedlings and 

inviable acorns that escape predation by rodents. 

Reproduction ceases in mid-July to early August when 

daytime air temperatures are consistently above 300C and' 

does not resume until the following spring. Laboratory tests 

demonstrated that beetle reproduction ceases within 4 

weeks at a constant 26.70C. 

The impact of S. octomaculata on the establishment of oak 

seedlings is not completely known. Although a primary pest, 

this beetle also is highly attracted to acorns damaged by 

other insects (Galford 1987), including C. posticatus and V. 

glandulella. The latter two insects begin feeding on 

germinating acorns in the spring about 2 to 4 weeks before 

S. octomaculata becomes active. Thus, in many cases S. 

octomaculata merely acts in concert with the other pests in 

destroying germinating acorns. Current studies in 

Pennsylvania indicate that many acorns planted about 2.5 

to 5 cm deep in autumn may be destroyed in early spring 

when they germinate by a combination of feeding from C. 

posticatus and S. octomaculata. These insects can enter 

friable soil to reach subsurface acorns. The frequency of 

this behavior is unknown and it may be determined by the 

availibility of surface acorns for insect feeding and 

reproduction. Thus, some damage to germinating acorns by 

S. octomaculata is occurring underground. Additional 

studies are needed to determine the extent of damage. 

Acknowledgments 

We thank H. Clay Smith, Dan Fickle, Drs. Jack H. Barger 

and William N. Cannon. Jr., and Jerry Crews for their 

helpful suggestions and reviews. 

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. 

Krajicek, J. E. 1960. Some factors affecting oak and black 

walnut reproduction. Iowa Journal of Science. 34: 

631-634. 

Weber, R. G.; Connell, W. A. 1975. Stelidota geminata 

(Say): studies of its biology (Coleoptera:Nitidulidae). 

Annals of the Entomological Society of America. 68: 

649-653. 

Williams, R. N.; Kreuger, H. R. 1985. Nitidulids 

(Coleoptera:Nitidulidae) associated with chinese 

chestnuts. Entomological News. 96: 214-218. 

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

reference to arthropods. Ecology. 37: 120-132. 
Galford, Jimmy R.; Williams, Roger N.; Daugherty, Ann. 1991. Life history 

and notes on the biology of Stelidota octomaculata 

(Coleoptera:Nitidulidae). Res. Pap. NE-644. Radnor, PA: U.S. 

Department of Agriculture, Forest Service, Northeastern Forest 

Experiment Station. 7 p. 

The life history of Stelidota octomaculata (Say) was studied in Ohio and 

Pennsylvania. This insect damages acorns and affects the establishment of 

oak seedlings. Acorns deployed in wire cages and pitfall traps plus a 

sampling of naturally occurring acorns were used to monitor insect activity. 

AdLllts overwinter in forest litter and begin feeding on undamaged 

germinating or damaged acorns in March. Acorns damaged by the beetles 

may fail to produce seedlings. Beetle reproduction occurs in spring and 

early summer inside acorns both above and below ground. Reproduction 

ceases in late July to early August. Adult activity may continue until early 

December in some years. In the laboratory, a life cycle was completed in 

about 34 days at 220 to 26%. The maximum number of offspring from a 

female was 933 and the maximum lifespan at room temperature was 238 

days. Acorns of all species tested plus seeds of 28 other species were 

suitable for larval development. 

ODC 145.7 x 19.29 Stelidota octomaculata-l51:453 

Keywords: Nitidulidae; oak regeneration; acorn pests 

*U. S. GOVERNMENT PRINTING OFFICE: 1991 1548-088120007 
Headquarters of the Northeastern Forest Experiment Station is in Radnor, Pennsylvania. Field laboratories are maintained at: 

Amherst, Massachusetts, In cooperation with the University of Massachusetts 

Berea, Kentucky, in cooperation with Berea College 

Burlington, Vermont, in cooperation with the University of Vermont 

Delaware, Ohio 

Durham, New Hampshire, irr cooperation with the University of New Hampshire 

Hamden, Connecticut, in cooperation with Yale University 

Morgantown, West Virginia, in cooperation with West Virginia University 

Orono, Maine, in cooperation with the University of Maine 

Parsons, West Virginia 

Princeton, West Virginia 

Syracuse, New York, in cooperation with the State University of New York, College of Environmental Sciences and Forestry at Syracuse University 

University Park, Pennsylvania, in cooperation with The Pennsylvania State University 

Warren, Pennsylvania 

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