Excerpt: White grubs (Coleoptera, Scarabaeidae), the larvae of May and related beetles, are destructive pests in some young pine plantations in the Lake States Region. They live in the soil and feed on roots of trees and other vegetation. Larvae chew off the smaller and girdle the ldrger roots of pine seedlings, and consequently reduce growth, weaken, and kill the seedlings.
Recommendations against planti.ng or for control measures have been made for grub population densities ranging from 4.4/ft2, 2.0/ft.3, 2.0/ft.\u27, down to 0.5 grubs/ft2 of soil surface (Stone and Schwardt, 1943; Rudolf, 1950; Speers and Schmiege, 1961 ; Shenefelt et al., 1954).
A study was carried out to accurately assess or predict grub-caused mortality and damage to seedlings from a given grub population density. This information is necessary for making control recommendations

Fowler, Richard F.

Wilson, Louis F.

English

Valparaiso University

The Great Lakes Entomologist Volume 4 Number 1 -- Spring 1971 Number 1 -- Spring 1971 Article 5 July 2017 White Grub Populations, Phyllophaga Spp., in Relation to Damaged Red Pine Seedlings in Michigan and Wisconsin Plantations (Coleoptera: Scarabaeidae) Richard F. Fowler U.S. Department of Agriculture Louis F. Wilson Michigan State University Follow this and additional works at: https://scholar.valpo.edu/tgle  Part of the Entomology Commons Recommended Citation Fowler, Richard F. and Wilson, Louis F. 2017. "White Grub Populations, Phyllophaga Spp., in Relation to Damaged Red Pine Seedlings in Michigan and Wisconsin Plantations (Coleoptera: Scarabaeidae)," The Great Lakes Entomologist, vol 4 (1) Available at: https://scholar.valpo.edu/tgle/vol4/iss1/5 This Peer-Review Article is brought to you for free and open access by the Department of Biology at ValpoScholar. It has been accepted for inclusion in The Great Lakes Entomologist by an authorized administrator of ValpoScholar. For more information, please contact a ValpoScholar staff member at scholar@valpo.edu. 1971 THE MICHIGAN ENTOMOLOGIST WHITE GRUB POPULATIONS, PHYLLOPHAGA SPP., I N  RELATION TO DAMAGED RED PINE SEEDLINGS I N  MICHIGAN AND WISCONSIN PLANTATIONS (COLEOPTERA: SCARABAEIDAE) Richard F. Fowler and Louis F. ~ i l s o n l  INTRODUCTION White grubs (Coleoptera, Scarabaeidae), the larvae of May and related beetles, are destructive pests in some young pine plantations in the Lake States Region. They live in the soil and feed on roots of trees and other vegetation. Larvae chew off the smaller and girdle the ldrger roots of pine seedlings, and consequently reduce growth, weaken, and kill the sezdlings. Recommendations against planti.ng or for control measures have been made for grub population densities ranging from 4.4/ f t2 ,  2.0/ft.3, 2.0/ft.', down to 0.5 grubs/ft2 of soil surface (Stone and Schwardt, 1943; Rudolf, 1950; Speers and Schmiege, 1961 ; Shenefelt et  al., 1954). A study was carried out to accurately assess or predict grub-caused mortality and damage to seedlings from a given grub population density. This information is necessary for making control recommendations. METHODS AND MATERIALS White grub populations and the degree of root damage on red pine seedlings were studied in 16 recent plantations located on the Hiawatha National Forest, Michigan, and Chequamegon and Nicolet National Forests, Wisconsin. Four of these plantations were established in the spring of 1967 and eight in the spring of 1968. The white grub population estimates were made in the summer, and root damage estimates in the fall of 1968. White grub populations were sampled with a cubic metal frame, 12 inches on a side, driven into the ground to facilitate removal of a 1 ft.3 soil sample. The soil inside the frame was removed and sifted through a 114 inch hardware-cloth screen to  retrieve the grubs. In each of 12 plantations, four samples per line were taken at regular intervals along four parallel lines across the plantation. The four other plantations were sampled more intensively. There thirty soil samples were taken along five parallel lines within a 4-acre block. Root damage was determined by excavating red pine seedlings from the vicinity of the soil sample holes. In 12 plantations, 20 seedlings were dug near each of the 16 soil sample holes (320 seedlings/plantation). In each of the four other plantations, 90 seedlings were dug from five Cacre plots (450 seedlings/plantation). Roots of living as well as dying and recently dead seedlings were scored for feeding injury according to a Damage Index modified from Johnston and Eaton (1939) as follows: Score 1 - no grub injury 2 - up to  33% of fibrous roots destroyed by grubs 3 - 3466% of fibrous roots destroyed by grubs 4 - 67-99% of fibrous roots destroyed by grubs; also included seedlings completely stripped of fibrous roots but which had grown some new root tips. 5 - 100% of fibrous roots destroyed or tap root severed above all fibrous roots. l ~ e m b e r s  of the U.S. Department of Agriculture, Forest Service: Entomologist, Northeastern Area, State and Private Forestry, St. Paul, Minnesota 55101; and Principal Insect Ecologist, North Central Forest Experiment Station, headquartered at the East Lansing Research Unit, in cooperation with Michigan State University, East Lansing, Michigan 48823. 1Fowler and Wilson: White Grub PopulationsPublished by ValpoScholar, 201724 THE MICHIGAN ENTOMOLOGIST Vol. 4, No. 1 An average Damage Index was con~puted for each plantation. A DI of 1.00 means there was no injury and a DI of 5.00 means all seedlings were destroyed. Six genera, Phyllophaga, Serica, Diplotaxis, Dichelonyx, Aphodius, and Geotrupes, were identified from larvae in the plantations on 12 ranger districts. Adults are needed for species identifications (Boving 1937). Phyllophaga accounted for 56% of all grubs, Serica 3 1%, and other genera 13%. Phyllophaga spp. includes some of the largest and most destructive white grubs, but not all species are equally damaging. Graham (1958) reports 78%, 4876, and 3% red pine seedlings killed by three separate species of Phyllophaga. The members of this genus have a 3-5 year life cycle in the Lake States. Serica spp. are smaller than Phyllophaga and less important in pine plantations (Craighead 1950, Graham 1958, Ives and Warren, 1965). Graham (1958) reported 13% and 18% of his seedlings killed by these grubs which have a 2-3 year life cycle. Diplotaxis spp., and Dichelonyx spp., both with small larvae and 2-3 year life cycles, are uncommon in Lake States plantations. but have caused some injury (Craighead 1950, Graham 1958). Aphodius spp. and Geotrupes spp are dung feeders, although some Aphodius spp. may feed on living roots. Regression analyses were run to  see if Damage Index and percentage of trees damaged were related to  white grub population levels. The relationship between Damage Index and percentage of trees damaged was also examined. RESULTS The Damage Index was found to be related to 1) mean n~~mbers  of Phyllophaga per ft.3 ; 2) mean numbers of Phyllophaga and Serica per f t 3  ; and 3)  mean numbers of white grubs of all genera per f t 3 .  The addition of numbers of grubs in genera other than Phyllophaga to the grub count did not improve the precision of making damage estimates. Thus, in the plantations used in this study, data of Phyllophaga alone were sufficient to make damage predictions (Fig. 1). This was true even though the count of Serica grubs far exceeded Phyllophaga in one instance. MEAN PHYLLOPHAGA PER CUBIC FOOT OF SOIL - 4 - X w n Z w3- (3 Fig. 1. Relationship between mean number of Phyllophaga larvae per cubic foot of soil and degree of damage to red pine seedlines. White discs are 1967 plantings, black discs 1968. Y = 0.96 + 2.07 ( I  - e'P.s2X )r' = .66 S.E. = 0.55 n = 16 0 0 In order to improve the relationship between Damage Index and the Phyllophaga population, larval size should be considered because large larvae eat more than small ones. Head capsule widths were therefore measured and plotted in a frequency histogram to u I ' u n 0 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2The Great Lakes Entomologist, Vol. 4, No. 1 [2017], Art. 5https://scholar.valpo.edu/tgle/vol4/iss1/51971 THE MICHIGAN ENTOMOLOGIST 25 separate grubs by instars. The following Feeding Index was formulated to adjust for larval size: FI=[Nl + 2N2 + 4N3 + 8N41 /n where N1, N2, etc., are the numbers of larvae in instars 1, 2, etc., and n is the mean number of larvae collected per plantation. We assumed that the amount of feeding damage doubled for each instar. Hence the factors 1, 2,  4, 8, based on observations of sawflies by Wilson (1966). A closer relationship between the Damage Index and the PI7yllophaga population resulted (Fig. 2). PHYLLOPHAGA FEEDlNG INDEX Fig. 2. Relationship between mean number of Phyllophaga larvae per cubic foot of soil adjusted for larval size (feeding index) and degree of damage to  red pine seedlings. White discs are 1967 plantings, black discs 1968. A similar relationship exists between percentage of trees damaged by grubs and mean number of Phyllophaga (Fig. 3). This relationship likewise improves when larval size (as a feeding index) is included (Fig. 4). o ! ~ l ~ , ~ l ~ l r , . l r l L  I 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 MEAN PHYLLOPHAGA PER CUBIC FOOT OF SOIL Fig. 3.  Relationship between mean number of Phyllophaga larvae per cubic foot of soil and percentage red pine seedlings damaged. White discs are 1967 plantings, black discs 1968. 3Fowler and Wilson: White Grub PopulationsPublished by ValpoScholar, 201726 THE MICHIGAN ENTOMOLOGIST Vol. 4, No. 1 100 D W $ 80- I a - PERCENTAGE T R E E S  DAMAGED 0 0 a 4- X W oFig. 5. Relationship between degree of larval Phyllophaga damage and percentage of red pine seedlings damaged. White discs are 1967 plantings, black discs 1968. D Y = 5.34 + 65.41 ( I -  e'O.OeX ) r2 = .70 n = 15 b o j . , , , ~ , = , ~ , ~ , . , - , . , n , 8 ,  0 20 40 60  80 100 120 140 160 180 200 220 PHYLLOPHAGA FEEDING INDEX Fig. 4. Relationship between mean number of Phyl lopl~aga larvae per cubic foot of soil adjusted for larvae size (feeding index) and percentage red pine seedlings damaged. White discs are 1967 plantings, black discs 1968. The regression line of Damage Index over percentages of trees examined appears to give a good estimate of the Damage Index when more than 10% and less than 90% of the seedlings are damaged (Fig. 5). This relationship is useful in certain types of surveys where seedlings can be dug but time does not permit root scoring. Y = 1.08 t 0.03X r2 = .89 S.E. = 0.22 n = 16 DISCUSSION AND CONCLUSIONS Z - w 3- 0 4 I - 4 0 2 - 0 10 20 30 40 50 60 70 80 90 100 The results indicate that a reasonable seedling damage estimate from Phyllophaga grubs can be made before planting or in a freshly planted stand. After estimating the larval population from a survey, the damage can be estimated from Figures 1-4. Percentage of trees damaged can also be used to  arrive at a Damage Index from Figure 5 when Phyllophaga injury is suspected. 4The Great Lakes Entomologist, Vol. 4, No. 1 [2017], Art. 5https://scholar.valpo.edu/tgle/vol4/iss1/5197 1 THE MICHIGAN ENTOMOLOGIST 27 The most serious result of grub feeding is seedling mortality which may extend beyond the fourth growing season. From the data collected, a reasonable estimate of seedling mortality into the second growing season can be made. If we assume nonsurvival of seedlings scored 4 and 5 (67-10070 root-killed) by the second growing season that appeared alive during the first season in addition to the actual first year mortality from all agents, a graph can be constructed showing minimum (score 5) and maximum (score 4 and 5) predicted mortality for various grub populations (Fig. 6). A plantation with 0.5 g r u b ~ / f t . ~  would lose between 16 and 34% of its seedlings by the second growing season after planting, including non-grub mortality estimated to be about 4% by that time. o! . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  I 0 .25 .50 75 1.00 1.25 1.50 MEAN PHYLLOPHAGA P E R  CUBIC FOOT OF SOIL Fig. 6. Estimated mortality (within triangle) of red pine seedlings from P11yllopl1aga feeding one year after planting including initial 4% mortality from other agents. Several authors have suggested that a population of 0.5 grubs (per ft.' or ft.3) or more is a "damaging" population. Second season mortality predictions suggest that control should be considered at levels lower than 0.5 grubs, especially since mortality in third and fourth years could substantially increase that presently predicted. A reasonable grub population level for which control would always be necessary cannot be given until actual third and fourth year mortality has been determined, but it would most likely be less than 0.25 gmbs/ft.' if the maximum acceptable seedling mortality were 20%. ACKNOWLEDGEMENT We express our gratitude to Mr. David J. Hall, graduate student, Department of Forestry, Michigan State University, who helped with the field collections and identified the white grubs. LITERATURE CITED Boving, A. G. 1937. Keys to the larvae of 4 groups and 43 species of the genus Phyllophaga. USDA Bur. Entomol., Plant Quar. E-417. 9 p. Craighead, F. C. 1950. Insect enemies of eastern forests. U.S. Dep. Agr. Misc. Publ. 657. 679 P. Graham, S. A. 1958. Problems caused by insects in the Lake States. 10th Int. Congr. Entomol. 1956 Proc. 4: 261-274. 5Fowler and Wilson: White Grub PopulationsPublished by ValpoScholar, 201728 THE MICHIGAN ENTOMOLOGIST Vol. 4, No. 1 Ives, W. G. H. and G. L. Warren. 1965. Sequential sampling for white grubs. Can. Entomol. 97: 596-604. Johnston, H. R. and C. B. Eaton. 1939. White grubs in forest nurseries of the Carolinas. U.S. Dep. Agr. Bur. Entomol., Plant Quar. E-486. 9 p. Rudolf, P. 0 .  1950. Forest plantations in the Lake States. U.S. Dep. Agr. Tech. Bull. 1010. 171 p. Shenefelt, R. D., H. R. Liebig and R. C. Dosen. 1954. Protecting machine transplanted trees from white grubs. Univ. Wisc. Forest Res. Notes 17. 3 p. Speers, C. F. and D. C. Schmiege. 1961. White grubs in forest tree nurseries and plantations. U.S. Dep. Agr. Forest Pest Leafl. 63. 4 p. Stone E. L., Jr. and H. H. Schwardt. 1943. White grub injury to young plantations in New York. J. Forest. 41 : 842-844. Wilson, L. F. 1966. Effects of different population levels of the European pine sawfly on young Scotch pine trees. J. Econ. Entomol. 59: 1043-1049. ANNUAL VARIATION IN STARTING DATE OF SPRING FEEDING BY THE EUROPEAN PINE SHOOT MOTH IN A MICHIGAN PLANTING William E. Miller North Central Forest Experiment Station, IJSDA Forest Service, St. Paul, Minnesota. ABSTRACT New tents spun in five successive springs by the European pine shoot moth (Rhyacionia buoliana [Schiff.] ) in a Michigan planting of red pine (Pinus resinosa Ait.) occurred about 2 days later each year. This trend is believed due to  habitat cooling as trees grow larger. In another planting feeding was more advanced on small trees than on large trees. INTRODUCTION Feeding in buds and elongating shoots, the European pine shoot moth (Rhyacionia buoliana (Schiff.)) disrupts the growth of young pines. It can be suppressed with contact poisons in the spring or summer at earliest signs of feeding. After wintering in or  near injured buds, partly grown larvae turn to  fresh buds in April. Before boring in, each larva spins a silken, tentlike anteroom. Tents are soon coated with resin and other debris. This makes them conspicuous and useful for accurately timing suppression treatments (Miller 1967). Pointing (1963) has described early spring larval activity in detail. A study was done to learn more about how starting date of spring feeding varies from year t o  year. Few starting dates have been reported. In northeastern Ohio, three observations ranged from April 13 to  20  (Miller and Neiswander 1955). These were based on casual checks in a different pine planting each year. In southern Michigan, more rigorous studies yielded two starting dates: April 14 (Graham and Williams 1958) and April 17 (Haynes and Butcher 1962). Apparently, starting dates have not been reported for more than one year in the same planting. A 5-year record of incipient tent spinning was made in a red pine (Pinus resinosa Ait.) planting near East Lansing, Michigan. Later, an observation in a different red pine planting tested whether starting date varied with tree size. In brief, results show that incipient spring feeding occurred later each year. It also appeared earlier on small trees than on larger ones. 6The Great Lakes Entomologist, Vol. 4, No. 1 [2017], Art. 5https://scholar.valpo.edu/tgle/vol4/iss1/5

White Grub Populations, Phyllophaga Spp., in Relation to Damaged Red Pine Seedlings in Michigan and Wisconsin Plantations (Coleoptera: Scarabaeidae)

ValpoScholar

The Great Lakes Entomologist 
Volume 4 
Number 1 -- Spring 1971 Number 1 -- Spring 
1971 
Article 5 
July 2017 
White Grub Populations, Phyllophaga Spp., in Relation to 
Damaged Red Pine Seedlings in Michigan and Wisconsin 
Plantations (Coleoptera: Scarabaeidae) 
Richard F. Fowler 
U.S. Department of Agriculture 
Louis F. Wilson 
Michigan State University 
Follow this and additional works at: https://scholar.valpo.edu/tgle 
 Part of the Entomology Commons 
Recommended Citation 
Fowler, Richard F. and Wilson, Louis F. 2017. "White Grub Populations, Phyllophaga Spp., in Relation to 
Damaged Red Pine Seedlings in Michigan and Wisconsin Plantations (Coleoptera: Scarabaeidae)," The 
Great Lakes Entomologist, vol 4 (1) 
Available at: https://scholar.valpo.edu/tgle/vol4/iss1/5 
This Peer-Review Article is brought to you for free and open access by the Department of Biology at ValpoScholar. 
It has been accepted for inclusion in The Great Lakes Entomologist by an authorized administrator of ValpoScholar. 
For more information, please contact a ValpoScholar staff member at scholar@valpo.edu. 
1971 THE MICHIGAN ENTOMOLOGIST 
WHITE GRUB POPULATIONS, PHYLLOPHAGA SPP., I N  RELATION 
TO DAMAGED RED PINE SEEDLINGS I N  MICHIGAN 
AND WISCONSIN PLANTATIONS 
(COLEOPTERA: SCARABAEIDAE) 
Richard F. Fowler and Louis F. ~ i l s o n l  
INTRODUCTION 
White grubs (Coleoptera, Scarabaeidae), the larvae of May and related beetles, are 
destructive pests in some young pine plantations in the Lake States Region. They live in the 
soil and feed on roots of trees and other vegetation. Larvae chew off the smaller and girdle 
the ldrger roots of pine seedlings, and consequently reduce growth, weaken, and kill the 
sezdlings. 
Recommendations against planti.ng or for control measures have been made for grub 
population densities ranging from 4.4/ f t2 ,  2.0/ft.3, 2.0/ft.', down to 0.5 grubs/ft2 of soil 
surface (Stone and Schwardt, 1943; Rudolf, 1950; Speers and Schmiege, 1961 ; Shenefelt et  
al., 1954). 
A study was carried out to accurately assess or predict grub-caused mortality and damage 
to seedlings from a given grub population density. This information is necessary for making 
control recommendations. 
METHODS AND MATERIALS 
White grub populations and the degree of root damage on red pine seedlings were studied 
in 16 recent plantations located on the Hiawatha National Forest, Michigan, and 
Chequamegon and Nicolet National Forests, Wisconsin. Four of these plantations were 
established in the spring of 1967 and eight in the spring of 1968. The white grub population 
estimates were made in the summer, and root damage estimates in the fall of 1968. 
White grub populations were sampled with a cubic metal frame, 12 inches on a side, 
driven into the ground to facilitate removal of a 1 ft.3 soil sample. The soil inside the frame 
was removed and sifted through a 114 inch hardware-cloth screen to  retrieve the grubs. In 
each of 12 plantations, four samples per line were taken at regular intervals along four 
parallel lines across the plantation. The four other plantations were sampled more 
intensively. There thirty soil samples were taken along five parallel lines within a 4-acre 
block. 
Root damage was determined by excavating red pine seedlings from the vicinity of the 
soil sample holes. In 12 plantations, 20 seedlings were dug near each of the 16 soil sample 
holes (320 seedlings/plantation). In each of the four other plantations, 90 seedlings were 
dug from five Cacre plots (450 seedlings/plantation). Roots of living as well as dying and 
recently dead seedlings were scored for feeding injury according to a Damage Index 
modified from Johnston and Eaton (1939) as follows: 
Score 1 - no grub injury 
2 - up to  33% of fibrous roots destroyed by grubs 
3 - 3466% of fibrous roots destroyed by grubs 
4 - 67-99% of fibrous roots destroyed by grubs; also included seedlings completely 
stripped of fibrous roots but which had grown some new root tips. 
5 - 100% of fibrous roots destroyed or tap root severed above all fibrous roots. 
l ~ e m b e r s  of the U.S. Department of Agriculture, Forest Service: Entomologist, Northeastern Area, 
State and Private Forestry, St. Paul, Minnesota 55101; and Principal Insect Ecologist, North Central Forest 
Experiment Station, headquartered at the East Lansing Research Unit, in cooperation with Michigan State 
University, East Lansing, Michigan 48823. 
1
Fowler and Wilson: White Grub Populations
Published by ValpoScholar, 2017
24 THE MICHIGAN ENTOMOLOGIST Vol. 4, No. 1 
An average Damage Index was con~puted for each plantation. A DI of 1.00 means there 
was no injury and a DI of 5.00 means all seedlings were destroyed. 
Six genera, Phyllophaga, Serica, Diplotaxis, Dichelonyx, Aphodius, and Geotrupes, were 
identified from larvae in the plantations on 12 ranger districts. Adults are needed for species 
identifications (Boving 1937). Phyllophaga accounted for 56% of all grubs, Serica 3 1%, and 
other genera 13%. 
Phyllophaga spp. includes some of the largest and most destructive white grubs, but not 
all species are equally damaging. Graham (1958) reports 78%, 4876, and 3% red pine 
seedlings killed by three separate species of Phyllophaga. The members of this genus have a 
3-5 year life cycle in the Lake States. 
Serica spp. are smaller than Phyllophaga and less important in pine plantations (Craighead 
1950, Graham 1958, Ives and Warren, 1965). Graham (1958) reported 13% and 18% of his 
seedlings killed by these grubs which have a 2-3 year life cycle. 
Diplotaxis spp., and Dichelonyx spp., both with small larvae and 2-3 year life cycles, are 
uncommon in Lake States plantations. but have caused some injury (Craighead 1950, 
Graham 1958). Aphodius spp. and Geotrupes spp are dung feeders, although some 
Aphodius spp. may feed on living roots. 
Regression analyses were run to  see if Damage Index and percentage of trees damaged 
were related to  white grub population levels. The relationship between Damage Index and 
percentage of trees damaged was also examined. 
RESULTS 
The Damage Index was found to be related to 1) mean n~~mbers  of Phyllophaga per ft.3 ; 
2) mean numbers of Phyllophaga and Serica per f t 3  ; and 3)  mean numbers of white grubs 
of all genera per f t 3 .  The addition of numbers of grubs in genera other than Phyllophaga to 
the grub count did not improve the precision of making damage estimates. Thus, in the 
plantations used in this study, data of Phyllophaga alone were sufficient to make damage 
predictions (Fig. 1). This was true even though the count of Serica grubs far exceeded 
Phyllophaga in one instance. 
MEAN PHYLLOPHAGA PER CUBIC FOOT OF SOIL 
- 
4 - 
X 
w 
n 
Z 
w3- 
(3 
Fig. 1. Relationship between mean number of Phyllophaga larvae per cubic foot of soil and degree of 
damage to red pine seedlines. White discs are 1967 plantings, black discs 1968. 
Y = 0.96 + 2.07 ( I  - e'P.s2X )
r' = .66 
S.E. = 0.55 
n = 16 
0 0 
In order to improve the relationship between Damage Index and the Phyllophaga 
population, larval size should be considered because large larvae eat more than small ones. 
Head capsule widths were therefore measured and plotted in a frequency histogram to 
u 
I ' 
u 
n 0 
0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 
2
The Great Lakes Entomologist, Vol. 4, No. 1 [2017], Art. 5
https://scholar.valpo.edu/tgle/vol4/iss1/5
1971 THE MICHIGAN ENTOMOLOGIST 25 
separate grubs by instars. The following Feeding Index was formulated to adjust for larval 
size: FI=[Nl + 2N2 + 4N3 + 8N41 /n where N1, N2, etc., are the numbers of larvae in instars 
1, 2, etc., and n is the mean number of larvae collected per plantation. We assumed that the 
amount of feeding damage doubled for each instar. Hence the factors 1, 2,  4, 8, based on 
observations of sawflies by Wilson (1966). A closer relationship between the Damage Index 
and the PI7yllophaga population resulted (Fig. 2). 
PHYLLOPHAGA FEEDlNG INDEX 
Fig. 2. Relationship between mean number of Phyllophaga larvae per cubic foot of soil adjusted for larval 
size (feeding index) and degree of damage to  red pine seedlings. White discs are 1967 plantings, 
black discs 1968. 
A similar relationship exists between percentage of trees damaged by grubs and mean 
number of Phyllophaga (Fig. 3). This relationship likewise improves when larval size (as a 
feeding index) is included (Fig. 4). 
o ! ~ l ~ , ~ l ~ l r , . l r l L  I 
0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 
MEAN PHYLLOPHAGA PER CUBIC FOOT OF SOIL 
Fig. 3.  Relationship between mean number of Phyllophaga larvae per cubic foot of soil and percentage red 
pine seedlings damaged. White discs are 1967 plantings, black discs 1968. 
3
Fowler and Wilson: White Grub Populations
Published by ValpoScholar, 2017
26 THE MICHIGAN ENTOMOLOGIST Vol. 4, No. 1 
100 
D 
W $ 80- 
I 
a - 
PERCENTAGE T R E E S  DAMAGED 
0 
0 a 
4- 
X 
W o
Fig. 5. Relationship between degree of larval Phyllophaga damage and percentage of red pine seedlings 
damaged. White discs are 1967 plantings, black discs 1968. 
D 
Y = 5.34 + 65.41 ( I -  e'O.OeX ) 
r2 = .70 
n = 15 
b 
o j . , , , ~ , = , ~ , ~ , . , - , . , n , 8 ,  
0 20 40 60  80 100 120 140 160 180 200 220 
PHYLLOPHAGA FEEDING INDEX 
Fig. 4. Relationship between mean number of Phyl lopl~aga larvae per cubic foot of soil adjusted for larvae 
size (feeding index) and percentage red pine seedlings damaged. White discs are 1967 plantings, 
black discs 1968. 
The regression line of Damage Index over percentages of trees examined appears to give a 
good estimate of the Damage Index when more than 10% and less than 90% of the seedlings 
are damaged (Fig. 5). This relationship is useful in certain types of surveys where seedlings 
can be dug but time does not permit root scoring. 
Y = 1.08 t 0.03X 
r2 = .89 
S.E. = 0.22 
n = 16 
DISCUSSION AND CONCLUSIONS 
Z - 
w 3- 
0 
4 
I - 
4 
0 
2 - 
0 10 20 30 40 50 60 70 80 90 100 
The results indicate that a reasonable seedling damage estimate from Phyllophaga grubs 
can be made before planting or in a freshly planted stand. After estimating the larval 
population from a survey, the damage can be estimated from Figures 1-4. Percentage of 
trees damaged can also be used to  arrive at a Damage Index from Figure 5 when Phyllophaga 
injury is suspected. 
4
The Great Lakes Entomologist, Vol. 4, No. 1 [2017], Art. 5
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197 1 THE MICHIGAN ENTOMOLOGIST 27 
The most serious result of grub feeding is seedling mortality which may extend beyond 
the fourth growing season. From the data collected, a reasonable estimate of seedling 
mortality into the second growing season can be made. If we assume nonsurvival of seedlings 
scored 4 and 5 (67-10070 root-killed) by the second growing season that appeared alive 
during the first season in addition to the actual first year mortality from all agents, a graph 
can be constructed showing minimum (score 5) and maximum (score 4 and 5) predicted 
mortality for various grub populations (Fig. 6). A plantation with 0.5 g r u b ~ / f t . ~  would lose 
between 16 and 34% of its seedlings by the second growing season after planting, including 
non-grub mortality estimated to be about 4% by that time. 
o! . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  I 
0 .25 .50 75 1.00 1.25 1.50 
MEAN PHYLLOPHAGA P E R  CUBIC FOOT OF SOIL 
Fig. 6. Estimated mortality (within triangle) of red pine seedlings from P11yllopl1aga feeding one year after 
planting including initial 4% mortality from other agents. 
Several authors have suggested that a population of 0.5 grubs (per ft.' or ft.3) or more is 
a "damaging" population. Second season mortality predictions suggest that control should 
be considered at levels lower than 0.5 grubs, especially since mortality in third and fourth 
years could substantially increase that presently predicted. A reasonable grub population 
level for which control would always be necessary cannot be given until actual third and 
fourth year mortality has been determined, but it would most likely be less than 0.25 
gmbs/ft.' if the maximum acceptable seedling mortality were 20%. 
ACKNOWLEDGEMENT 
We express our gratitude to Mr. David J. Hall, graduate student, Department of Forestry, 
Michigan State University, who helped with the field collections and identified the white 
grubs. 
LITERATURE CITED 
Boving, A. G. 1937. Keys to the larvae of 4 groups and 43 species of the genus Phyllophaga. 
USDA Bur. Entomol., Plant Quar. E-417. 9 p. 
Craighead, F. C. 1950. Insect enemies of eastern forests. U.S. Dep. Agr. Misc. Publ. 657. 679 
P. 
Graham, S. A. 1958. Problems caused by insects in the Lake States. 10th Int. Congr. 
Entomol. 1956 Proc. 4: 261-274. 
5
Fowler and Wilson: White Grub Populations
Published by ValpoScholar, 2017
28 THE MICHIGAN ENTOMOLOGIST Vol. 4, No. 1 
Ives, W. G. H. and G. L. Warren. 1965. Sequential sampling for white grubs. Can. Entomol. 
97: 596-604. 
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Dep. Agr. Bur. Entomol., Plant Quar. E-486. 9 p. 
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171 p. 
Shenefelt, R. D., H. R. Liebig and R. C. Dosen. 1954. Protecting machine transplanted trees 
from white grubs. Univ. Wisc. Forest Res. Notes 17. 3 p. 
Speers, C. F. and D. C. Schmiege. 1961. White grubs in forest tree nurseries and plantations. 
U.S. Dep. Agr. Forest Pest Leafl. 63. 4 p. 
Stone E. L., Jr. and H. H. Schwardt. 1943. White grub injury to young plantations in New 
York. J. Forest. 41 : 842-844. 
Wilson, L. F. 1966. Effects of different population levels of the European pine sawfly on 
young Scotch pine trees. J. Econ. Entomol. 59: 1043-1049. 
ANNUAL VARIATION IN STARTING DATE OF SPRING FEEDING 
BY THE EUROPEAN PINE SHOOT MOTH IN A MICHIGAN PLANTING 
William E. Miller 
North Central Forest Experiment Station, IJSDA Forest Service, St. Paul, Minnesota. 
ABSTRACT 
New tents spun in five successive springs by the European pine shoot moth (Rhyacionia 
buoliana [Schiff.] ) in a Michigan planting of red pine (Pinus resinosa Ait.) occurred about 2 
days later each year. This trend is believed due to  habitat cooling as trees grow larger. In 
another planting feeding was more advanced on small trees than on large trees. 
INTRODUCTION 
Feeding in buds and elongating shoots, the European pine shoot moth (Rhyacionia 
buoliana (Schiff.)) disrupts the growth of young pines. It can be suppressed with contact 
poisons in the spring or summer at earliest signs of feeding. After wintering in or  near 
injured buds, partly grown larvae turn to  fresh buds in April. Before boring in, each larva 
spins a silken, tentlike anteroom. Tents are soon coated with resin and other debris. This 
makes them conspicuous and useful for accurately timing suppression treatments (Miller 
1967). Pointing (1963) has described early spring larval activity in detail. 
A study was done to learn more about how starting date of spring feeding varies from 
year t o  year. Few starting dates have been reported. In northeastern Ohio, three 
observations ranged from April 13 to  20  (Miller and Neiswander 1955). These were based on 
casual checks in a different pine planting each year. In southern Michigan, more rigorous 
studies yielded two starting dates: April 14 (Graham and Williams 1958) and April 17 
(Haynes and Butcher 1962). Apparently, starting dates have not been reported for more 
than one year in the same planting. 
A 5-year record of incipient tent spinning was made in a red pine (Pinus resinosa Ait.) 
planting near East Lansing, Michigan. Later, an observation in a different red pine planting 
tested whether starting date varied with tree size. In brief, results show that incipient spring 
feeding occurred later each year. It also appeared earlier on small trees than on larger ones. 
6
The Great Lakes Entomologist, Vol. 4, No. 1 [2017], Art. 5
https://scholar.valpo.edu/tgle/vol4/iss1/5


https://scholar.valpo.edu/cgi/viewcontent.cgi?article=1135&amp;context=tgle

White Grub Populations, Phyllophaga Spp., in Relation to Damaged Red Pine Seedlings in Michigan and Wisconsin Plantations (Coleoptera: Scarabaeidae)

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