United States 

Department of 

Agriculture Notes on the Biology and I 

Forest Service Hosts of Stelidota ferruginea 

Northeastern Forest 

Experiment Station (Coleoptera:Nitidulidae) 

Research Paper NE-654 

Jimmv R. Galford 

~oger N. Williams 

Mary Beacom 
Abstract 

The nitidulid Stelidota ferrugnea Reitter was reared from damaged acorns of 

laurel oak, Quercus laurifolia Michx., and live oak, Q. virginiana Mill., collected in 

Sarasota County, Florida. This sap beetle has been reared in the laboratory solely 

on northern red oak, Q. rubra, acorns for more than 3 years (27 + generations), 

and can breed in viable or nonviable acorns. In the laboratory, S. ferruginea can 

develop in the seeds of several tree species. New information on the biology of 

S. fmginea is presented. 

~ ~ 

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 Agriculture 

Research and Development Center of The Ohio State University at Wooster, Ohio. 

MARY BEACOM formerly was a biological aid with the Northeastern Station's 

Forestry Sciences Laboratory at Delaware, Ohio. - - 

Manuscript received for publication 25 April 1991 

Northeastern Forest Experiment Station 

5 Radnor Corporate Center 

100 Matsonford Road, Suite 200 

P.O. Box 6775 

Radnor, Pennsylvania 19087 

August 1991 
Introduction 

There are three species of nitidulids, also called sap 

beetles, in the genus Stelidota in the United States: S. 

geminata (Say), S. octomaculata (Say), and S. ferruginea 

Reitter. According to Connell (1984), S. ferruginea is 

synonymous with S. strigosa of Horn (1879) and Parsons 

(1943) for specimens collected north of Mexico. S. strigosa 

(Gyllenhal), however, is a valid species found in tropical 

America from Mexico to South America. 

S. gerninata, the strawberry sap beetle, can be an economic 

pest on ripe strawberries. Multimillion dollar losses to this 

sap beetle have been reported (Gertz 1968; Weiss and 

Williarns 1980). The strawberry sap beetle is commonly 

collected from damaged and rotting fruits and vegetables 

(Weiss and Williams 1980). This species also has been 

reared from rotting northern red oak, Quercus rubra L., 

acorns collected in Ohio and Pennsylvania (Galford, 

unpublished). The biology of S. geminata was reported by 

Weber and Gonnell(1975). 

S. octomaculata breeds in acorns (Galford 1987) and can 

affect northern red oak seedling establishment (Galford et 

al. 1988). The life history of this species was reported by 

Galford et al. (1991). S. octomaculata can reproduce in both 

viable and nonviable acorns, above or below ground. 

There is little information on the life history of S. ferruginea. 

Peng and Williams (1990) reported rearing this and other 

sap beetle species on an artificial diet. In the field, adults of 

S. ferruginea has been collected with fruit baits and it has 

been found at sap flows on trees (Weiss and Williams 1980). 

S. ferruginea has been collected in most eastern states from 

Florida to Michigan and as far west as Oklahoma. In this 

paper we report that acorns of laurel oak, Q. laurifolia 

Michx.. and live oak, Q. virginiana Mill., are hosts of S. 

ferruginea in Florida, and present new information on the 

biology of this insect. 

Met hods 

Rearing Beetles from Acorns 

Laurel oak acorns (966) were collected on January 2-4, 1988, 

in a small (ca. 1 ha) woodlot adjoining a drainage canal 

within the city limits of Sarasota, Florida. The woodlot 

contained a mixture of laurel oak, red maple, Acer rubrum 

L., and several species of palm trees. There were few 

herbaceous understory species in the woodlot because of 

the dense shade cast by the closed-canopy overstory. Also, 

the public woodlot may have been occasionally cleared of 

undergrowth by city park maintenance personnel. 

In 1989, the acorn crop failed in central Florida and no 

acorns could be found. On November 23, 1990,452 live oak 

acorns, that had recently fallen were collected in the picnic 

area at Myakka River State Park in Sarasota County, 

Florida. Most of the acorns collected appeared viable and 

only 67 had been damaged by rodents, insects, or other 

animals. Myakka River State Park comprises about 6,000 

ha and has a large component of oak, palm trees, and 

many other native tree and shrub species. Attempts are 

made to maintain the park in a natural state. However, the 

large population of feral hogs in the park readily consume 

the acorn crop and their rooting activities prevent natural 

regeneration of oak and other species of plants. 

In the laboratory the collected acorns were divided into 

three lots and were placed in 1-liter glass jars which were 

covered with glass plates. The jars were kept at 20° to 

25OC. Each day, for 3 months, the acorns from each jar 

were poured into a white plastic box and any insect larvae 

or adults found in the box were removed. 

Nitidulid larvae emerging from the acorns were placed in 

1-02 (30-mi) plastic portion cups filled with moist sterilized 

masonry sand for pupation. The surface of the sand was 

scarified to facilitate larval penetration. The cups were 

capped with plastic lids, kept at 20° to 25OC, and examined 

daily for adults. 

Newly emerged adults were sexed immediately after 

collection. Males and females were placed seperately in 

culture dishes containing red oak acorns cut into halves. 

The beetles were sexed using three characters: females 

have five abdominal segments and males have six 

segments, the sixth being very small: The metasternum 

of the female just anterior of the first abdominal segment 

is flat at the midline while in the male this area is slightly 

concave: The metatibia of the male is distinctly curved or 

bowed and abruply dilated in the distal one-fourth; in the 

female, the metatibia is nearly straight and gradually 

dilated. 

The beetles can be sexed in the pupal stage using a 

binocular microscope and the following character: female 

pupae have two small unnamed cone-shaped 

protuberences on the ventral surface of the abdomen, just 

anterior to the anus. These structures are absent on male 

pupae. The structures are difficult to see on new, white 

pupae and are more easily seen just before adult 

emergence. The pupae are fragile and must be 

manipulated with a small, moistened, artist's brush. 

Only 13 of the 966 acorns collected in 1988 were undamaged. 

The remaining 953 acorns had been damaged by grey 

squirrels, Sciurus carolinensis. In most cases, one-third to 

one-half of the cap ends of the acorns had been eaten by 

the squirrels; they then dropped the uneaten parts. Some of 

the squirrel-damaged acorns sprouted when kept under 

moist conditions in the laboratory. 
Biological Studies 

Thirty pairs of adult S. ferruginea reared from larvae 

emerging from the laurel oak acorns collected in Florida in 

1988 were used for studies on the biology of the beetles. 

The biological studies were conducted in an environmental 

chamber operated at 24O to 25OC. The chamber was lighted 

from below with two 15-watt florescent bulbs and kept on a 

10:14 hour lightldark cycle. 

Acorns used in these studies were collected in autumn or 

early winter and stored at 5O to 7OC in dry sand in sealed 

plastic bags. Acorns of northern red oak, white oak, Q. alba 

L., and bur oak, Q. macrocarpa Michx., were collected in 

Ohio. Laurel oak acorns were collected in Florida. Just 

before use for insect rearing, the acorns were washed in tap 

water, soaked for 2 to 3 minutes in a 50-percent commercial 

bleach solution, rinsed in tap water, and then soaked for 30 

to 40 minutes in distilled water. 

For laboratory rearing of the beetles, 30 plastic culture 

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

moistened with distilled water throughout the study. Each 

culture dish was provided with half an acorn each of red, 

white, laurel, and bur oak, and a pair of unfed beetles. The 

beetles were transferred at 10- to 12-day intervals to new 

dishes containing fresh acorns until the female died. Mature 

larvae (larvae wandering in the dishes) were removed daily 

from the dishes and their numbers recorded. Up to 25 

larvae were placed in a 1-02 plastic portion cup about threequarters filled with moist masonry sand. The contents of 

some cups were inspected periodically to determine the 

progress of development of the life stages. 

Adult beetles and mature larvae were easily manipulated 

with forceps without injury. The fragile pupae were 

manipulated with a moistened, camel's-hair brush. 

Fecundity for each pair of beetles was determined. 

Fourteen to sixteen days after a pair of adult beetles had 

been removed from a culture dish, the acorns in each plate 

were dissected. Numbers of larvae, pupae, and new adults 

were counted and added to a tally of offspring produced by 

that particular pair of beetles. 

Number of larval instars was determined by measuring the 

head-capsule width of all larvae from a 14-day-old culture. 

Larvae were kept on ice while the head capsules of the 

larvae were measured with a binocular micrometer. Larval 

lengths were measured concurrently. The size of beetle 

eggs found in the culture dishes was determined with a 

binocular micrometer; 630 adults were sexed as described 

previously to determine the sex ratio. 

To determine the preovipositional period, four culture 

plates, each containing two pairs of beetles and four red 

oak acorn halves were used. Beetles introduced into the 

culture dishes were unfed and had been allowed to emerge 

naturally from the sand in the pupation cups. At 24-hour 

intervals, the beetles were transferred five times to new 

culture dishes containing fresh acorns. The culture dishes 

from each ovipositional period were examined daily to 

determine the maturation period. 

Nuts of the following tree species were tested as suitable 

hosts for the development of one or more generations of S. 

ferruginea: white, red, and bur oak; black oak, Q. velutina 

Lam.; pin oak, Q. palustris Muenchh.; chinquapin oak, Q. 

muehlenbergii Engelm.; and chestnut oak, Q. prinus L.; 

oriental chestnut, Castanea sp.; black walnut, Juglans nigra 

L.; Persian (English) walnut, J. regia L.; shagbark hickory, 

Carya ovata (Mill.) K. Koch; pecan, C. illinoensis (Wang) K. 

Koch;-American beech, Fagus grandifolia Ehrh.; filbert, 

Corylus sp.; and Brazil nut, Bertholletia excelsa H.B.K. Field 

corn, Zea mays L., also was tested as a laboratory host. 

Nuts or seeds of these species were cut open or cracked to 

allow insect feeding and ovipostion. Nuts were placed on 

moist filter paper in culture dishes and insects were reared 

as described previously. 

Results and Discussion 

Insects Reared from Field-Collected Acorns 

Two hundred and forty-five S. ferruginea adults were reared 

from 327 larvae that emerged from the 953 laurel oak 

acorns collected in 1988 in Sarasota, Florida. In addition, 37 

adults of S. geminata were reared from the same acorns. 

These adults were abnormally small and easily confused 

with adults of S. ferruginea. Also emerging from the laural 

oak acorns were 403 larvae of the weevil Conotrachelus 

posticatus Boheman, 1 larva of a Curculio sp., 135 adult 

moths of Valentinia glandulella (Riley), and 30 adults of the 

moth Moodna ostrinella (Glemens). Several undetermined 

species of insects also emerged from the acorns, including 

parasites of the acorn insects. 

Forty-six larvae of S. ferruginea were reared from 452 live 

oak acorns collected in 1990 in Myakka River State Park in 

Sarasota County, Florida, confirming live oak acorns as a 

host for the species. The small number of damaged acorns 

(67) in the collection plus the dilution effect of the large 

acorn crop in the park may have been factors in the small 

number of sap beetles reared from the acorns. Also, an 

unknown number of acorn insects escaped from the 

container of live oak acorns during transit from the field to 

the laboratory. 

Numbers and species of acorn insects emerging from the 

live oak acorns collected in 1990, other than nitidulids, were 

not closely monitored. However, in addition to the acorn 

insect species reared from the laurel oak acorns in 1988, 

several larvae of the weevil C. naso LeConte emerged from 

the live oak acorns. Gibson (1964) provided information on 

the biology and life history of C. naso and other 

Conotrachelus weevils that feed on acorns. 
Biological Data Summary 

Biological data on 23 pairs of F, beetles reared at 24O to 

25OC and a 10:14 hour lighffdark cycle are given in Table 1. 

Seven of the original 30 pairs from the study escaped. Each 

pair of beetles produced an average of 497 offspring 

(range: 174 to 823). Average longevity of females was 123 

days (range:74 to 188 days). The longevity of male beetles 

was not recorded though many of the males outlived their 

mates. Development from eggs to newly eclosed adults 

averaged 22 days and ranged from 20 to 26 days. Although 

some beetles surfaced from the sand pupation medium 2 

days after eclosion, most did not surface for 3 or 4 days. 

Eggs took 3 to 4 days to hatch. Development from newly 

eclosed larvae to mature larvae averaged 9 days. The 

duration of the individual instars was not determined. The 

prepupal period averaged 3.5 days and the pupal period 

averaged 6 days. 

Measurement of the head capsule width of 107 larvae from 

a 14-day-old culture revealed three distinct peaks of 0.24 

mm, 0.40 mm, and 0.56 mm. Thus, S. ferruginea has the 

same number of larval instars as S. geminata (Weber and 

Connell 1975) and S. octomaculata (Galford et al. 1991). 

First-instar larvae ranged in length from 0.96 to 1 .I2 mm, 

second instars were 1.6 to 2.16 mm, and third-instar mature 

larvae were 3.5 to 4.08 mm. 

Females began to lay viable eggs between 24 to 48 hours 

after they were paired with males and placed on acorns. 

Egg production increased greatly after the second day. The 

sausage-shaped beetle eggs ranged in length from 0.56 mm 

to 0.68 mm and averaged 0.64 mm. Newly laid eggs were 

shiny with a pearl-like appearance and slowly developed a 

dull, opaque appearance just before hatch. 

Of 690 beetles sexed from the laboratory culture, 328 were 

females and 302 were males. Adult beetles ranged in length 

from 1.7 to 2.6 mm and averaged 2.3 mm. There was no 

significant difference in length between males and females. 

Beetles with the widest thoraxes generally were males but 

thorax width was not a reliable character for routine sexing 

of the insects. 

Nuts of all tree species tested allowed development of S. 

ferruginea from eggs to adults. Multiple generations have 

been reared on several kinds of nuts but northern red oak 

oak acorns are used for routine rearing because their high 

tannin content inhibits the development of many 

troublesome microorganisms. 

S. ferruginea has been found breeding naturally in laurel 

and live oak acorns in Florida. In the laboratory, beetles will 

reproduce in nuts of several tree species. We have reared 

S. ferruginea solely on northern red oak acorns for more 

than 27 generations with no apparent decline in the insects. 

We have used both viable and nonviable acorns. 

Preliminary tests have shown that S. ferruginea can destroy 

small, germinating northern red oak and laurel oak acorns 

under laboratory conditions. Adults readily consume the 

tender radicles of acorns as they germinate. Adults then 

oviposit in the acorns and the combination of adult and 

larval feeding can destroy acorn viability. However, the 

larger radicles of medium to large germinating acorns are 

less damaged by the small beetles. Seedlings can be 

produced even from heavily infested acorns. Germinating 

acorns of several small-seeded oak species in the South 

could be readily damaged by S. ferruginea. However, field 

studies are needed to determine if the insects have any 

impact on oak seedling establishment. 

S. ferruginea resembles S. octomaculata in that both feed 

on acorn radicles and both are capable of reproducing in 

both viable and nonviable acorns. As a result these two 

Stelidota species can be either primary or secondary pests 

of acorns whereas S. geminata breeds only in nonviable 

acorns. We have found it difficult to maintain a laboratory 

culture of S. geminata solely on acorns. Thus, acorns are 

likely opportunistic hosts of S. geminata but are major hosts 

of S. ferruginea and S. octornaculata. 

The complete life history of S. ferruginea has not yet been 

studied. Beetles are known to be active in Sarasota County, 

Florida, from November into February when live and laurel 

oak acorn hosts are available. Adults of this species have 

been collected in spring, summer, and autumn in other 

states. Because S. ferruginea readily reproduces in many 

kinds of seeds in the laboratory, the beetles may use hosts 

other than acorns for field reproduction. However, acorns 

are one of the largest seeds and most abundant seed 

sources available in eastern forests and may be the most 

common hosts of the beetles throughout their known range. 

S. ferruginea has been collected as far north as Michigan 

and Wisconsin but we did not collect this insect in 5 years 

of extensive studies of insects feeding on acorns in 

southern Ohio. Thus, it is probably a southern species that 

occasionally migrates north. Research is needed to 

determine the abundance of this insect throughout its range 

and it's effect, if any, on oak seedling establishment. 
Table 1 .-Summary of biological data for S. ferruginea reared on northern 

red oak acorns at 24O to 25OC on a 10:14 hour lightdark cycle 

Life stage Ave. number 

of days (range) 

Egg to newly eclosed adult 

Preoviposition period 

Egg 

1st instar to mature larvae 

Prepupae 

Pupae 

Female longevity 

Fecundity (Ave. no. of eggs1 

23 females) 

Acknowledgment 

We thank Drs. Jack H. Barger, William N. Cannon, and 

John W. Peacock for their helpful suggestions and reviews. 

We especially thank Dr. Walter A. Connell for his taxonomic 

help and review. 

Literature Cited 

Connell, W. A. 1984. Nearctic Nitidulidae-synonymy and 

additions since Parsons revision (Coleoptera). The 

Coleopterists Bulletin. 38(2): 160-1 64. 

Galford, Jimmy R. 1987. Effect of Stelidota octomaculata 

(Co1eoptera: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.; 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. 

Gertz, R. F. 1968. The biology and control of Sdelidofa 

geminata (Say). Proceedings North Central Branch 

Entomological Society of America. 23(1) 52. Abtract. 

Gibson, Lester P. 1964. Biology and life histoy of acorninfesting weevils of the genus Conotrachelus 

(Coleoptera: Curculionidae). Annals of the 

Entomological Society of America. 57: 526-526. 

Horn, G. H. 1879. Revision of the Nitidulidae of the 

United States. Transactions of the American 

Entomological Society. 7: 267-336. 

Parsons, C. T. 1943. A revision of Nearctic Nitidulidae 

(Coleoptera). Bulletin of the Museum of Comparative 

ZOO~O~Y. 92(3): 1 19-278. 

Peng, 6.; Williams, R.N. 1990. Multiple-species rearing 

diet for sap beetles (Coleoptera: Nitidulidae). Annals 

of the Entomological Society of America. 83: 11 55-11 159. 

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

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

Annals of the Entomological Society of America. 68: 

649-653. 

Weiss, M. J.; Williams, R. N. 1980. An annotated 

bibliography of the genus Stelidota Erichson 

(Coleoptera: Nitidulidae, Nitidulinae). Circ. 255. 

Wooster, OH: Ohio Agricultural Research and 

Development Center. 37 p. 
Galford, Jimmy R.; Williams, Roger N.; Beacom, Mary. 1991. Notes on the 

biology and hosts of Stelidota ferruginea (Coleoptera:Nitidulidae). 

Res. Pap. NE-654. Radnor, PA: U.S. Department of Agriculture, Forest 

Service, Northeastern Forest Experiment Station. 4 p. 

The nitidulid Stelidota ferruginea Reitter was reared from damaged acorns 

of laurel oak, Quercus laurifolia Michx., and live oak, Q. virginiana Mill., 

collected in Sarasota County, Florida. This sap beetle has been reared in 

the laboratory solely on northern red oak, Q. rubra, acorns for over 3 years 

(27 + generations) and can breed in viable or nonviable acorns. In the 

laboratory, S. ferruginea can develop in the seeds of several species of 

trees. New information on the biology of S. ferruginea is presented. 

I ODC 145.7 x 19.29 Steiidota ferruginea-151:453 

Keywords: Nitidulidae; Stelidota; acorn insects. 

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