United States 

Department of 

Agriculture Elm Leaf Beetle Performance 

Forest Service on Ozone-Fumigated Elm 

Northeastern Forest 

I Experiment Station 

Research Paper NE-661 Jack H . Barg er 

Richard W. Hall 

i Alden M. Townsend 
Abstract 

Leaves harvested in 1986 from clonally propagated elm hybrids ('Pioneer', 'Homestead', 

'970') previously fumigated in open-top chambers with ozone at 15 parts per hundred 

million (pphm) or with charcoal-filtered air (CFA) were evaluated for water and nitrogen 

content or were fed to adult elm leaf beetles (ELB), Xanthogaleruca = (Pyrrhalta) 

luteola (Muller), to determine host suitability for beetle fecundity and survivorship. 

For all three hybrids, EL9 females fed ozone-fumigated leaves laid significantly fewer 

eggs than females fed CFA-fumigated leaves. Fecundity of females fed '970' leaves 

was higher than for females fed 'Pioneer' or 'Homestead' foliage. Fumigation treatment 

had no significant effect on leaf nitrogen or water content. There was a significant 

positive linear relationship between leaf nitrogen content and beetle fecundity for all 

hybrids combined. In 1988, hybrid '970' was fumigated with CFA, 15, 30, or 45 

pphm ozone to determine concentration effects on EL9 fecundity, leaf consumption, 

and survivorship. Significantly fewer eggs were laid only at the higher concentration 

of ozone. Mean leaf area consumed by beetles did not vary among fumigation 

treatments. For both years, beetle survivorship was unaffected by hybrid or ozone 

concentration. 

The Authors 

JACK H. BARGER is a research entomologist with the USDA Forest Service, 

Northeastern Forest Experiment Station, Delaware, Ohio. 

RICHARD W. HALL is a associate professor of entomology and associate 

dean of the College of Biological Sciences at The Ohio State University, 

Columbus. 

ALDEN M. TOWNSEND is a research leader with the US. National Arboretum 

in Washington, D.C. 

Manuscript received for publication 30 October 1991 

Northeastern Forest Experiment Station 

5 Radnor Corporate Center 

100 Matsonford Road, Suite 200 

P.O. Box 6775 

Radnor, Pennsylvania 19087-4585 

March 1992 
Introduction 

Host-plant quality for a variety of insects has been shown 

to be affected by atmospheric deposition. In earlier studies, 

we demonstrated that fecundity of elm leaf beetle (ELB), 

Xanthogaleruca = (Pyrrhalta) luteola (Muller), on certain 

elms, Ulmus spp., was negatively affected by acidic 

precipitation (Hall et al. 1988). Other studies have shown 

that ozone fumigation influences insect feeding preference 

.and suitability of host plants for insect nutrition (Elden et 

al. 1978; Endress and Post 1985; Trumble et al. 1987; 

Coleman and Jones 1988; Jones and Coleman 1988). 

Because higher levels of ozone are found in urban areas 

and because municipalities often replace American elms, 

Ulmus americana L., with Dutch elm disease-resistant elm 

hybrids that are susceptible to EL6 defoliation, it is important 

to explore the relationships between ozone sensitivity of 

elm and susceptibility to EL6 herbivory before 

recommending replacement use of these elms to municipal 

arborists. This study was conducted to determine whether 

ozone pollution influences host quality of elm for EL6 

and how EL6 fecundity, leaf consumption rate, and 

survivorship are affected. 

Materials and Methods 

bioassays. Leaves not immediately used in bioassays 

'were sealed in plastic bags and were refrigerated at 

10°C for up to 4 days. At the end of 13th week of 

fumigation, all remaining leaves were harvested for 

completing the bioassays. EL6 were field-collectecl in 

August as mature third instars from local Siberian elm 

(Ulmus pumila L.) and held in a growth chamber at 25°C 

on a photoperiod of 15:9 (L:D) until adult emergence. 

Pairs (male plus female) of newly eclosed, unfed, adult 

ELB were assigned to 15 by 100-mm plastic petri dishes 

containing foliage from each tree (replicated five times) 

which had been subjected to each fumigation treatment. 

Every 3 or 4 days, leaves were replaced and beetle 

mortality and fecundity were recorded. Number of eggs 

per female was calculated for each tree. Bioassays were 

run in a laboratory at 25r2"C under constant light for 2 

weeks. 

Leaf samples from each tree were weighed, dried, and 

reweighed to determine water content. Leaf nitrogen content 

was determined by micro-Kjeldahl analysis (McKenzie and 

Wallace 1954). Data were subjected to an analysis of 

variance (alpha = 0.05) and a Student-Newman-Keuls 

multiple comparison test at the 5-percent level (Sokal and 

Rohlf 1981). The relationship between leaf water and 

nitrogen content and beetle fecundity was examined by 

linear regression analysis. 

1986 Experiment 

I988 Experiment 

One- and two-year-old potted elm trees [cuttings of the 

clonally propagated hybrids 'Pioneer', 'Homestead', and 

'970' (Townsend and Masters 1984a,b)] growing in MetroMix 500 (W. R. Grace and Co., Cambridge, MA) were 

fumigated for 12 weeks in open-top chambers (Heagle et 

al. 1973) located at the USDA Forest Service's Forestry 

Sciences Laboratory at Delaware, Ohio. Fumigation 

treatments' began on 20 May when trees were in full leaf. 

Fumigation treatments were 15 parts per hundred million 

(pphm) ozone and charcoal-filtered air (CFA at < 2 pphm 

ozone). Ozone was generated by passing oxygen over an 

ultraviolet light source (Model 03V10-0, Ozone Research 

and Equipment Corp., Phoenix, AZ) and was added to the 

CFA stream entering between each chamber's lower flowdistribution' films. Chamber ozone concentration was 

monitored within the flow-distribution area with a Ultraviolet , 

Photometric Analyzer (Model 49, ThermoElectron, 

Hopkinton, 'MA) calibrated with an ozone source having a 

rate of proquction traceable to a standard obtained from 

the National Bureau of Standards. There were 7 to 11 trees 

of each hybrid per chamber, and two chambers for each 

treatment (total of four chambers). 

At the end of 12th week of fumigation (1 1 August), about 

50 percent of the leaves were randomly harvested from 

each tree. Some leaves were used for determining nitrogen 

and water content and others for conducting beetle 

Two-year-old potted trees of hybrid '970' were subjected 

to four f~~migation treatments of 15-, 30-, and 45-pphm 

ozone and CFA (1986 conditions). We choose '970' 

because of the 1986 experiment results and because 

'970' was more readily available than other elm hybrids. 

There were 10 elm trees per chamber, and two chambers 

per fumigation treatment (total of eight chambers). 

Fumigation treatments began 23 May and continued for 

13 weeks. 

EL6 was field-collected in August from local English elm 

(U. procera Salisbury) as mature third instars and held 

as in 1986. Bioassays using harvested leaves were 

conducted as in 1986 except that the temperature was 

increased by 5°C to 30 -c 2°C. Bioassay temperature was 

increased to increase fecundity (King and Price 1986) 

and perhaps accentuate treatment differences. No nitrogen 

and water content analyses were conducted in 1988. 

Leaf area was determined with a Delta-T Area Meter 

System (Model PM-SIOA, Delta-T Devices LTD, Cambridge, 

UK) before and after each bioassay. The difference between 

the two measurements represented the leaf area consumed 

by ELB. Leaf consumption per EL6 pair and number of 

eggs per females were calculated for each tree and 

analyzed as in 1986. Leaf consumption and fecundity 

data were also subjected to linear regression analyses. 
Results in either 'Pioneer' or 'Homestead'. When the data were 

pooled for all hybrids, there was a weak but significant 

relationship between leaf water content and ELB fecundity 

(r2 = 0.04; n = 106; P<0.05) (Fig. 4). 

I986 Experiment 

Ozone fumigation had no significant effect (F=2.0; 

DF= 1,100; P=0.16) on leaf nitrogen content (Fig. 1). 

Nitrogen content was highest in '970' foliage while 

'Homestead' had significantly more nitrogen than 'Pioneer' 

(Fig. 1). Within each hybrid there were no significant 

relationships between leaf nitrogen content and ELB 

fecundity. But when data for all hybrids were pooled, there 

was a significant relationship (r2 = 0.31 ; n = 106; P<0.01) 

between percent nitrogen content and fecundity (Fig. 2). 

For each hybrid, female beetles fed ozone-fumigated leaves 

laid significantly fewer (F= 4.1 ; DF = 1,100; P= 0.04) eggs 

than females fed CFA-fumigated leaves (Table 1). A higher 

percentage of females fed '970' oviposited than did the 

other two hybrids. Moreover, females laid significantly more 

(F=40.6; DF=2,100; P<0.01) eggs on '970' than on the 

other two hybrids (Fig. 5). 

There were no significant differences in mortality of males 

or females among the three hybrids andtor the fumigation 

treatments. 

Ozone fumigation had no significant effect (F =O.8; 

DE= 1,100; P=0.37) on leaf water content (Fig. 3). 

Water content was significantly higher in hybrid '970' than 

I 

CFA 

OZONE 

'Pioneer' 'Homestead' '970' 

Figure 1.-Mean percent leaf nitrogen content (dry weight) from three 

elm hybrids fumigated with 15 pphm ozone or charcoal-filtered air 

(CFA) for 12 weeks in 1986. 
- 'Pioneer' 

0 - 'Homestead' 

0 - '970' 

8 

r =0.31 

Percent Leaf Nitrogen (dry wt.) 

Figure 2.-Relationship between percent nitrogen content per unit dry 

weight of leaves and mean number of eggs laid in two weeks by 

EL6 on leaves of three elm hybrids fumigated with 15 pphm ozone or 

charcoal-filtered air (CFA) for 12 and 13 weeks, respectively, in 1986. 

CFA 

OZONE 

'Pioneer' 'Homestead' '970' 

Figure 3.-Mean percent leaf water content from three elm hybrids 

fumigated with 15 pphm ozone or charcoal-filtered air (CFA) for 12 

weeks in 1986. 
A - 'Pioneer' 

0 - 'Homestead' 

0 - '970' 

Percent Leaf Water 

Figure 4.-Relationship between percent water content of leaves and 

number of eggs laid in two weeks by ELB on leaves of three elm 

hybrids fumigated with 15 pphm ozone or charcoal-filtered air (CFA) 

for 12 and 13 weeks, respectively, in 1986. 

CFA 

OZONE 

'Pioneer' 'Homestead' '970' 

Figure 5.-Mean number of eggs laid per female by EL6 on leaves 

from three elm hybrids fumigated with 15 pphm ozone or charcoal-filtered 

air (CFA) for 13 weeks in 1986. 
1988 Experiment 

In general, fecundity of EL6 was negatively influenced 

(F= 7.66; DF = 3,76; P<0.01) by ozone fumigation of the 

I host plant '970' (Fig. 6). A Student-Newman-Keuls multiple 

comparison test showed a significant ozone effect on 

fecundity but only at 45 pphm, the highest concentration 

tested (Table 2). 

I 

Mean leaf consumption by ELB fed ozone-fumigated leaves 

was greater than leaf area consumed by EL6 fed CFAfumigated leaves, but there was no significant relationship 

between ozone concentration and leaf area cons~lmed 

(6 = 0.0001 ; n = 80; P = 0.9) (Table 2). 

The relationship between fecundity and leaf consumption 

is shown in Figure 7 for all treatments combined. There 

is a statistically significant positive linear relationship 

between EL6 fecundity and leaf area consumed (6'=0.16; 

n=80; P<0.01). 

There were no significant differences in mortality of males 

or females among any of the fumigation treatments. 

Table 1.-1986 mean fecundity of EL6 fed leaves, leaf nitrogen content per 

unit dry weight, and leaf water content of elm trees fumigated in open-top 

chambers with charcoal-filtered air (CFA) or 15 pphm ozone 

'Pioneer' 'Homestead' '970' 

Variable CFA Ozone CFA Ozone CFA Ozone 

No. treesihybrid 17 18 19 16 18 18 

No. eggs/femalea 52.8(~8.7)' 36.6( t 4.7) 52.8(?6.9) 43.7( t 5.0) 115.5(?9.1) 101.1(~ 11.0) 

Nitrogenb 1.5(i0.0) 1.5(0.1) 1 .7(0.1) 8(0) 2.3(i0.1) 2.5(r0.1) 

Percent water 62.5(i 0.6) 63.2(i 0.3) 63.3(+0.7) 63.8(?0.7) 6-5.O(rO.4) 65.1(&0.5) 

aFive females were fed on each tree. 

bPercent dry weight. 

'Values are the mean kSEM. 

Table 2.~1988 mean fecundity and mean leaf area consumed by ELB fed excised 

foliage of the elm hybrid '970' fumigated in open-top chambers with charcoalfiltered air (CFA) or one of three concentrations of ozone 

15 pphm 30 pphm 45 pphm 

Variable CFA ozone ozone ozone 

No. of trees 20 20 20 20 

Fecunditya 221.5(r15.1)aC 226.4(?14.l)a 186.l(t 13.6)a 142.2(*12.2)b 

Leaf area consumedb 244.2(6.2)a 264.5(i 11.4)a 257.6(? 15.3)a 244.4(r 14.6)a 

aFive pairs of ELB were fed on each tree. 

mm2 per beetle pair. 

'Values are the mean 2SEM. Means in rows followed by the same letter are not significantly 

different according to Student-Newman-Keuls multiple comparison test at the 0.05 level. 
CFA 15 30 45 

Ozone Concentration (pphm) 

Figure 6.-Mean number of eggs laid per female by elm leaf beetles 

on leaves from elm hybrid '970' fumigated with three concentrations of 

ozone or charcoal filtered air (CFA) for 13 weeks in 1988. 

O - CFA '970' 

A -15pphm a 

- 30 pphm 

o - 45 pphm AA 

2 

r =0.16 (3: 

00 

A IJ /// 

ZOO 

150 

100 

5 0 

0 

2 

Mean Leaf Area Consumed (mm ) 

Figure 7.-Relationship between mean number of eggs per female 

laid in two weeks and leaf area consumed by ELB fed leaves of the 

elm hybrid '970' fumigated with three concentrations of ozone or charcoalfiltered air (CFA) for 13 weeks in 1988. 
Discussion 

We used excised leaves rather than attached leaves to 

test for differences in herbivory and fecundity because we 

were able to maintain greater accuracy and proficiency in 

the bioassays and because the ELB is a known specialist. 

It is generally recognized and accepted that the feeding 

preference of an insect specialist is strongly directional. 

Thus we believed it unlikely that subtle changes in leaf 

chemistry due to harvesting (artificial defoliation) would 

override a strong directional feeding and ovipositional 

preference (Risch 1985; Hall 1986). We also believed that 

any harvesting effects on leaf chemistry would be similar 

for all treatment bioassays. Further, some studies have 

shown that the remaining leaves on certain insect-defoliated 

plants contain increased levels of various feeding deterrents 

(Schultz and Baldwin 1982; Karban and Carey 1984), or, 

conversely, contain increased levels of feeding stimulants 

(Chambliss and Jones 1966; Carroll and Hoffman 1980). 

Still other studies have demonstrated that the remaining 

leaves on artificially defoliated plants are less likely to be 

chemically affected than the remaining leaves on plants 

defoliated by herbivores (Capinera and Roltsch 1980; 

Ka.rban and Carey 1984). 

In 1987 we attempted to conduct ELB bioassays on 

attached leaves rather than excised leaves, using modified 

petri dishes, to minimize possible confounding effects of 

harvesting on leaf chemistry (Risch 1985). The caging 

procedures necessary to maintain EL6 on the tree foliage 

were exceptionally labor intensive and it was difficult to 

maintain the proper microenvironment of caged leaves and 

test insects. Also, bioassayed leaves in the cages had to 

be harvested immediately to accurately determine both leaf 

area consumed and fecundity. Thus, even with this 

procedure we could not have prevented possible changes 

in leaf chemistry of the remaining attached leaves. These 

obscuring factors resulted in the loss of our 1987 

experiment. Obviously, much research needs to be 

conducted on induced chemical changes in leaves as a 

direct result of insect herbivore defoliation compared to 

induced changes by indirect artificial defoliation before 

choosing a particular bioassay technique. 

Studies by Jeffords and Endress (1984) to determine 

feeding preference of gypsy moth larvae (Lymantria dispar 

L.) for leaves from white oak (Quercus alba L.) seedlings 

fumigated for 77 hours with various levels of ozone showed 

that larvae preferred leaves from seedlings exposed to the 

highest ozone level tested (15 pphrn). While no ozone 

exposures in their study were made on oak above 15 pphm, 

their results correspond to ours, that is, mean ELB leaf 

consumption also was greatest in absolute terms on trees 

fumigated at 15 pphm ozone. However, in our studies, mean 

leaf consumption decreased gradually as ozone 

concentration increased above 15 pphm, but consumption 

remained generally higher on leaves fumigated with ozone 

than on leaves fumigated with CFA (Table 2). Jones and 

Coleman (1988), found that adults and larvae of the beetle, 

Plagiodera versicolora Laich., preferred to feed on and 

consumed more of cottonwood leaf discs, Populus deltoides 

Bartr., that had been previously exposed to a single acute 

dose of ozone (20 pphm) for 5 hours compared to controls 

in choice experiments. In our studies, the lowest level of 

ozone fumigation used, 15 pphm, was considered acute 

and occurs infrequently under ambient conditions in the 

Ohio River Valley where this experiment was conducted 

(Pinkerton and Lefohn 1987; Lefohn and Pinkerton 1988). 

We used whole leaves in our bioassays and our plants 

were fumigated for much longer periods (12 to 13 weeks), 

seven hours per day, and five days per week before being 

tested for ELI3 suitability. While our study was intentionally 

designed to promote ozone effects, there may be an ozone 

concentration threshold for herbivory near 15 pphm, the 

lowest level used. Leaf consumption was higher at 15 pphm 

than with CFA but consumption did not continue to increase 

proportionally with increases in ozone fumigation (Table 

2). Because our ozone exposure regime did not follow 

ambient conditions but was delivered at constant high rates, 

plant acclimation processes may have occurred over our 

longer exposure time, allowing compensatory physiological 

characteristics to ameliorate the ozone effects (Sasek and 

Richardson 1989). 

Factors other than the amount of leaf material consumed 

may have influenced fecundity. Results from our studies 

showed a significant decrease in EL6 fecundity on all three 

ozone-fumigated elm hybrids at the' 15-pphm level in 1986 

(Table 1) and at the 45-pphm level for hybrid '970' in 1988 

when compared with CFA (Table 2). While there was 

evidence that EL6 may have compensated for lower quality 

foliage by increased herbivory (1988 study), the nutritional 

benefits of additional herbivory were not reflected by 

increased fecundity. Components of leaf chemistry and/or 

texture may have changed in response to the ozone 

fumigation (Fluckiger et al. 1988), both of which are 

important to insect fecundity. Qualitative or quantitative 

changes in nitrogenous compounds, carbohydrates, lipids, 

and particularly secondary compounds such as phenotics 

(Meyer and Montgomery 1987), or changes in respiration 

or transpiration have been suggested as the cause of such 

differences (Hughes and Laurence 1984; Hall and Young 

1986). Such changes are complex and we may never be 

able to determine the reasons for differences observed in 

this study. Further, in the 1986 study, type of elm hybrid 

affected EL6 fecundity in absolute terms more than 

ozone fumigation. It is apparent, however, that ozonefumigated leaves do not meet the optimal nutritional needs 

of ELB. 

The impact of ozone on ELB fecundity and herbivory varied 

depending on concentration. It is ironic that although ozone 

has been shown to decrease vigor and growth of trees 

(McLaughlin et al. 1982; Heck et al. 1986), it may actually 

increase insect herbivory. Such a response might be 

expected since many insects show compensatory 

consumption, i.e., eating more as host quality declines. 

Further studies should focus on the changes in the 

biochemical componepts of elm leaves in response to an 

ozone-fumigation scenario that follows constant percentages 

of the ambient temporal fluctuations in ozone concentration, 
and how these changes may affect ELB fecundity and 

herbivory. Additional research also is needed to determine 

the degree of egg viability and larval development on the 

ozonated foliage. While EL6 was generally less fecund on 

fumigated foliage, egg viability and larval survival and 

development may increase. 

Acknowledgments 

M. G. Mayer, USDA Forest Service, W. 0. Masters, USDA 

Agricultural Research Service, R. Beale, B. A. Giles, M. 

R. Hamerski, J. L. Murphy, T. N. Saunders and C. E. 

Young, Department of Entomology, The Ohio State 

University, assisted with this project. We thank R. A. Haack, 

W. N. Cannon, Jr., J. R. Galford, L. R. Schreiber, and 

L. S. Dochinger, for critical reviews of an earlier draft of 

this manuscript. 

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beetle performance on ozone-fumigated elm. Res. Pap. NE-661. 

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

Forest Experiment Station. 9 p. 

Leaves (1986) from elm hybrids ('Pioneer', 'Homestead', '970') previously 

fumigated in open-top chambers with ozone or with charcoal-filtered air 

(CFA) were evaluated for water and nitrogen content or were fed to adult 

elm leaf beetles (ELB), Xanthogaleruca = (Pyrrhallta) luteola (Muller), to 

determine host suitability for beetle fecundity and survivorship. ELB females 

fed ozone-fumigated leaves laid significantly fewer eggs than females fed 

CFA-fumigated leaves. Leaf nitrogen or water content was unaffected. 

Hybrid '970' (1988) was fumigated with CFA or with ozone concentrations 

to determine effects on ELB fecundity, leaf consumption, and survivorship. 

Significantly fewer eggs were laid at the higher concentration of ozone. 

Keywords: Fecundity; herbivory; survivorship; suitability; open-top 

chamber 

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