- Email: [email protected]
Altered feeding preference of beech weevil Rhynchaenus fagi L. for beech foliage under ambient air pollution
Em'ironmental Pollution 75 ~1992) 333-336
Altered feeding preference of beech weevil Rhynchaenus fagi L. for beech foliage under ambient air pollution E. Hiltbrunner & W. Fiiickiger Institute./or Applied Plant Biology. CH-4124 Schiinenhuch. Switzerland {Received 15 February 1991: revised version acceptcd 17 May 1991) The effect of ambient air pollution with increased ozone concentrations on the feeding behaviour of the beech weevil Rhynchaenus lagi 1,. was studied. In a dual choice feeding test the beech weevil preferred leaf disks from beech saplings exposed to ambient air against those from tiltcred air in 65"5% of all cases.
INTRODUCTION
laid mainly in the mid-vein of the leaves. Therc are three larval instars which mine in the leaves and pupal cocoons are formed in the mines. New generation adults emerge approximately 6 weeks after oviposition. There are generally two short periods of feeding in the life span of an adult weevil: directly after emergence and immediately prior to reproduction on beech, which is the only breeding host plant. Beech weevils used in this study were collected from the field. They had been sampled as pupae or as imagines, when still enclosed in the cocoons. After careful removal of the cocoons the pupae terminated rnetamorphosis without any detectable effects upon their behaviour. By choosing these developmental stages, food consumption prior to the feeding test could be excluded. Until the beginning of the test, weevils were individually kept in Petri dishes {Polystyrol (PS), 5"5 cm diameter) with a moistened filter paper at 10 h light/day {3000 lux) and day and night temperatures of 4 5 ' C and 3 - 4 C , respectively.
Insect plant relationships represent a sensitive and dynamic equilibrium produced and maintained by coevolution {Stenseth, 1987). Any changes in this equilibrium by biotic or abiotic factors may affect thc susceptibility of the plants to insects as well as the success of insects on their hosts (Crawley, 1983). In the last few years air pollution has been regarded as an additional abiotic factor affecting insect plant relationships. In particular, various studies on the effects of air pollutants upon aphid plant communities have emphasized the significance of changes in the host plant quality with regard to altered plant colonization and utilization by aphids [McNeill et al., t987: Bolsinger & Fliickiger, 1989: Braun & FI/,ickiger, 1989: Warrington, 1989). Little is known about the impact of air pollutants on the relationships between chewing insects and plants. Therc is even less information about the influence of air pollution upon arboreal insect--tree communities. To examine the effccts of ambient air pollutants on the feeding preference of an arboral chewing insect, the predominating phyllophagous insect species on beech trees, the beech weevil (Rhynchaenuslagi L.) was chosen in the present study.
Plants Three-year-old beech saplings, potted in loess loam soil for 2 years, were exposed in semi-open-top chambers in spring 1988, where they' were conditioned over one year to ambient or filtered air conditions. To minimize positional effects inside the chambers the position of the trees was periodically changed. The chambers were ventilated with either filtered or ambient air. The filtering system consisted of a dust filter (Viledon M F), charcoal, Reox Purafil T M and impregnated charcoal, which reduced NO2, SO2 and Os by 65--85%. At the inlet of the ambient air chamber, a dust filter was
MATERIALS AND METHODS lnsecls Rh.vnchaenusfagi L. (Col: Curculionidae) is a univoltine species which overwinters as an adult and colonizes beech in spring, soon after bud burst. Within this time eggs are 333
334
E. Hiltt~runner. 141: Fliickiger
Table I. Monlhly and maximal houri)' means (#g/m ~) of ozone, and monthly values of nitrogen dioxide and sulphur dioxide at Sch6nenbuch during exposure of the plants Month
03 maximal hourly mean
NO,. monthly
SO,_ monthl',
86 88 72 87 68 26 17 26
212 215 200 213 199 117 107 93
18 19 10 14 lg 32 45 29
3 2 0 3 1 3
14 47 57 63 101 97 87
92 135 172 156 195 213 ._7
45 42 22 19 22 15 17
0 3
monthly
1988 Ma June July August Septem bet October November December 1989 Januvry February March April May June July
I0
16 16 15 5 4 3 3
installed. Measurements inside the chambers revealed a loss of ozone in the ambient air chamber of 20 25% compared with the outside of O a concentrations. The ambient pollution data given in 1"able 1 were obtained from the same site, the permanent monitoring station at Sch6nenbuch {400m above sea level, about 7krn west of Baslek The monitoring equipment is described in detail by Braun and Fltickiger {1989).
and 72 h according to the following scoring system: 0, no feeding tracks of R.fagi; I, a single feeding track; 2, a few feeding tracks, area consumed of leaf disks below 10%; 3, many feeding tracks, area consumed of leaf disks over 1()~¼~. Score classes of disks from the same leaf were added up and the data were analyzed non-parametrically using the Wilcoxon test.
RESUUI'S Comparing the concentrations of N O 2, SO 2 and 03 during the predisposition time of the plants, air pollution was dominated by ozone (Table 1). During 146 days ( 1149 h of exposure time) ozone concentrations amounting to over 1201tg O3,m 3 were measured (this value should be exceeded only once a year in Switzerland, according to the Swiss clean air act). l,Jnder these ozone concentrations effects upon the beech saplings were expected. Any significant differences, however, between the two treatments were not detectable with regard to visible injury, shoot growth and mineral nutrient status in the foliage (data not shown). In the choice feeding test the beech weevil showed a significant feeding preference for leaf disks from trees fumigated with ambient air alter 24 h (Fig. I ). This initial preference was not maintained over time, so after 48 and 72 h the difference in the feeding behaviour of the weevil betxvccn these two groups of leaf disks was not significant.
DISCUSSION Dual choice feeding test A previously conducted experiment, where cages with weevils were fixed directly to the experimental plants, revealed a predominant influence of increased temperatures (due to the cages) on the feeding behaviour of the weevil. Therefore a choice feeding test was considered to be appropriate to examine the impact of ambient air pollution on this insect-plant relationship. Leaves of the second leaf flush and of the same age {determined by bud and leaf marking) were used for the choice feeding test. A m o n g these leaf samples there were no visually discernible differences. Two leaf disks, each 1 cm in diameter, were cut from the same leaf of a tree which was fumigated either by filtered air or by ambient air. The tour disks were arranged in a Petri dish (PS, 5.5cm diameter) with a moistened filter paper and one single beech weevil was released in the centre of the dish. For each pair of trees (from a total of seven pairs) live replications were conducted. The Petri dishes were kept at 18_+2C and a 12:12 (L:D) photoperiod (25001ux). To avoid disturbing the feeding weevil by touching the leaf disks (in case of direct measurements) the feeding preference was examined by ocular estimation after 24, 48
There arc only a few studies concerning the impact of air pollution on chewing insect plant relationships (review in Hughes, 1988; Riemer & Whittaker, 1989). Most of the investigated insects on herbaceous plants have shown a feeding preference for ozone-treated flfliagc. The Mexican bean beetle, Epilachna rarirestis
Preference
for leaf disks from
f i l t e r e d air
ambient
a',r
34.5% of cases
65.5% of cases
Fig. I. Choice feeding test with Rhynchaenus [agi L. on leaf disks of beech trces in liltered and ambient air. Figures are differences of score classes {summarized per leaf}. Feeding preference significant after 24h I ' p < 0 0 5 . Wilcoxon test, n = 35).
Air pollution effects on beech weevil.feeding Mulsant, the best studied insect in this context, preferred leaves from soybean Glvxine m a x (L.) Merr. exposed to increasing ozone concentrations (Endress & Post, 1985; Chappclka et al., 1988). In addition, Endress and Post 11985) reported that the beetles still preferrcd ozonated foliage to the controls 23 days after the last fumigation. The tomato pinworm Ke(feria lycopersicella Wals. also responded positively to tomato plants which had been prefumigated by ozone (550/lg,."m 3) two or four times at 3day intervals t\~r 3h. But survival and developmental rates of the larvac dccreased by fumigation during feeding (Trumble et al., 1987). Similar observations were made by Whittaker et al. 11989) with the chrysomelid beetle Gastrophysa viriduh~ Degeer on R u m e x ohtus(lolius L. The survival and productivity of the larval stages were higher on fumigated weeds (approximately 140 ltg O3."m31. Nevertheless, leaf consumption was lower on these plants compared with untreatcd plants. This meant that the larvae had to consume less leaf area of fumigated leaf per milligram of biomass production. Whittaker et a/. (19891 assumed that the ozonated foliage was more nutritious or less well defended than control leaves. Jeffords and Endress (1984) revealed an ozone concentration-dependent feeding preference of an arboreal insect, thc gypsy moth Lvmantria dispar L., for fumigated white oak tMiage. The larvae chose leaves with exposure to the highest concentration (300,ug O3m-~; 11 fumigations for 7 h) over the other trcatmcnts, but preferred foliage fumigated with 601~g O3.m 3 to that exposed to 180 l~g O3. m ~. Although the ozone treatment in this study can be partly compared with the ozone concentrations occurring under natural conditions, the possibility of nonlinear behaviour patterns of insects should be taken into account. Coleman and Jones 11988a) looked at thc feeding response of Plagio~h'ra cersicoh)ra L. on leaves from cottonwoods Populus dehoides aftcr a single, acute dose of ozone 1393,ug.m3; fumigation for 5 hi. The larvae as well as the adults of the beetle consumed more leafarea of ozone-treated foliage. Considering ozone as the dominating air pollutant at the experimental site of the present study, the observed feeding prcference of the beech weevil corresponds to that of the investigated insects. The decreasing preference aftcr 48 and 72 h may be explained by physiological and biochemical changes in the leaf disks over time. It is well known that excision may initiate wound responses [e.g. production of wound ethylene, induction and degradation of enzyme systems such as peroxidase) (Macheix et al., 1986) and could interact with the insect's perception of the nutritional quality of the leaf disks tLewis & van Emden, 1986). However, Raina et al. (19801 found in feeding assays with Epilachna carivestis Mulsant that thc leaf palatability was not severely changed if the disks were kept turgid. Therefore it can be assumed that the biochemical changes in the leaf disks did not differ between the treatment groups and the feeding
335
preference after 24h reflects the differing host plant qualities of the beech saplings. Although a pollutant-induced change of the plants can be supposed, nothing is known about the specific mechanisms involved. Moreover, it should be noted that the nutritional quality of the leaves used in this study was not directly examined. Determinations of foliar content of free amino acids, nitrogen, phosphorus and potassium in leaves of the first leaf flush from the same trees revealed that nitrogenous compounds in the leaf tissue did not have a determining or promoting effect on the success of the beech weevil on its host plant (Hiltbrunner, 1990), as has been shown for different insect plant systems (McNeill & Southwood, 1978: Brodbeck & Strong, 1987: Mattson & Scriber, 1987J. On the other hand, Braun and Fliickiger 11989) observed a significant effect of ambient ozone on the amino acid.sugar ratio in the phloem exudate of oneyear-old beech saplings under the same fumigation system. Following ambient air treatment the content of asparagine, glutamine and 7-amino-butyric acid as well as the sum of all amino acids were significantly increased. The determinations of the phloem exudate were conducted with leaves sampled in August, thus the leaves were exposed to higher ozone concentrations for a longer time compared with the leaf samples in the present study. It is known that the feeding preference of insects may not correlate positively with insect development and reproductive fitness on the preferred plants {Chew, 1980). Coleman and Jones (1988h1 reported a decreasing rcproductive fitness of Plagiodera cersicolora on ozonefumigated cottonwoods, though the beetles preferred to feed on ozone-treated foliage. Therefore it is not clear how the altered feeding behaviour of the beech weevil affects the whole life history pattern of the insect and hence the insect performance on beeches. To examine the influence of air pollution on this insect-plant community further investigations are needed, above all comprehensive investigations about pollutant-induced changes of the host plant quality' and their impact on different developmental stages of the weevil.
ACKNOWLEDGEMENTS We wish to thank the cantonal forestry administrations of northwestern Switzerland for financial support.
REFERENCES Bolsinger, M. & Fliickiger, W. (1989). Ambient air pollution induced changes in amino acid pattern of phloem sap in host phmts • .relevance to aphid infestation. Fro'iron. Pollut., $6, 2O9 16. Braun, S. & Eliickiger, W. (19891. Effect of ambieht ozone and acid mist on aphid development. Enciron. Pollut., 56, 177 82. Brodbeck, B. & Strong, D. [1987). Amino acids nitrition of herbi,,orous insects and sm:ss to the host plant. In Insect
336
E. Hilthrunner, W. Fliickiger
Outbreaks: Ecological and Evoh~tionary Proccs.~es. cd. E Barbosa & J.R. Schuhz. Academic Press. Nov, York, pp. 347-63. Chappelka, A. H., Kraemer, M. E., Mebrahtu, T.. Rangappa, M. & Benepal, P. S. (19881. Effects of ozone on soybean resistance to the Mexican bean beetle (Epilachna varil"e.~ti.~ Mulsant.). Environ. Exp. Bot., 28, 147-52. Chew, E. 11980). Food plant preferences of Pieric butterflies and crucifcrous food plants. Oecologia, 46, 347 53. ('olcman, S. J. & Jones, C. G. 11988a). Plant stress and insect behavior: Cottonwood, ozone and the feeding and oviposition preference of a beetle. Oecologh,, 76, 51-6. Coleman, S. J. & Jones, C. G. 11988h}. Plant stress and insect performance: Cottonwood, ozone and a leaf beetle. Occologia, 76, 57 61. Crawlcy, M. J. (1983). Herhivory: The D.vnamics ol Animal Phmt Interactions. Blackwell Scientilic Publications, Oxford, 437 pp. Endrcss, A. G. & Post, S. K. (1985). Altered feeding preference of Mexican bean beetle. Epilactma t'arivestis Mulsanl.. Ior ozonated soybean foliage. Environ. Pollut., 39, 9 16. Hiltbrunner, E. (199(h. Fehlhioh~gi,whe Unter.suchun,e tiber den Bel~dl der Buche [Fagus silvatica L.) dutch den Buchen~pringriissler {R hy nchaen us fagi L.I an ausge wiihlt('n I! 'aldhc.~tiimh,n in ~k,r Nordwestschweiz. Master thesis, Univcrsit,,, of Basle, 103 pp. Hughes, P. R. (1988). Insect populations on host plants subjected to air pollution. In Pl~ml Stress--hzsect Interaction.s, ed. E.A. Heinrichs. Wiley, New York, pp. 249 319. Jcffords, M. R. & Endress, A. G. (19841. A possible role of o/one m trcc dcloliation by the gypsy moth (l,cpidoptcra: Lymantriidac). ~2m'iron. Entomo[., 13, 1249 52. Lcv,is, A. C. & van Emdcn, H. F. (1986). Assz,,',s for insect feeding. In In.sect Phmt Interactions, cd. J. R. Miller & 1". A. Miller. Springer-Verlag. New, York, pp. 95 119. Macheix, J. J., Fleuriet, A. & Qucssada, M. P. 119861. Involvement of phenols and pcroxidascs in wound healing
and grafting, in Molecular attd Physiological Aspects o / Plant Peroxidases, ed. H. Greppin, C. Penel & Th. Gaspar. University of Geneva, Switzerland, pp. 267-86. Mattson, W. J. & Scriber, J. M. 11987). Nutritional ecology of insect folivores of woody trees: Nitrogen, water, fiber and mineral considerations. In Nutritional Ecology ol bisects, Mitc.~ and Spiders and Related Invertebrates, ed. F. Slansky Jr & J. R. Rodriguez. Wiley, New York, pp. 105-46. McNcill, S. & Southwood, T. R. E. (1978). The role of nitrogen in the de,,elopment of insect.:plant relationships. In Biochemical .,l.Vwcts e~/ Phmt and Aninlal Coevolution, ed. J. B. Harborne. Academic Press, London, pp. 77 98. McNcill, S., Aminu-Kano, M., Houlcn, G., Bullock, J.M., Citronc. S. & Bell, J. N. B. (19871. The interaction between air pollution and sucking insects, in Acid Rain: Scient([ic and Technical A&'wwes, cd. R. Perry & R. M. Harrison. Selper, London. pp. 602 7. Raina. A. K., Bcncpal, P. S. & Sheikh. A. Q. (1980). Effects of excised and intact leaf methods, leaf size and plant age on the Mexican bean beetle feeding. Entomol. E W. Appl., 27, 303-6. Riemer, J. & Whittaker. J. B. (19891. Air pollution and insect herbivores: Observed interactions and possible mechanisms. In In,sect Phmt htteractions, Vol. 1, cd. E.A. Bernays. CRC Press, Boston, MA, pp. 73-105. Stcnscth, N. C. (1987). Evolutionary processes and insect outbreaks. In Insect Outbreaks: Ecological and Evolutionary Pr,,esse.~. cd. P. Barbosa & J. R. Schultz. Academic Press, Nc~x York, pp. 533 63. 1 rumble. J. T., Hare. J. D., Musselmann. R. C. & McCool, P. M. (19,~71. Ozone-induced changes in host plant suitability: Interactions of Kci/eria lycopersicella and Lycopersicon c wu/entum. J. Chem. Ecol., 13, 203 18. Warrington. S. (1989). Ozone enhances the grov,th rate of cereal aphids..4grit. Ecosystems Environ., 26, 65 8. Whittaker. J. B., Kristiansen, I,. W.. Mikkclscn, T. N. & Moore, R. 11989). Responses to ozone of insect feeding on a crop and wccd species. Environ. Pollut., 62, 89 101.
Altered feeding preference of beech weevil Rhynchaenus fagi L. for beech foliage under ambient air pollution E. Hiltbrunner & W. Fiiickiger Institute./or Applied Plant Biology. CH-4124 Schiinenhuch. Switzerland {Received 15 February 1991: revised version acceptcd 17 May 1991) The effect of ambient air pollution with increased ozone concentrations on the feeding behaviour of the beech weevil Rhynchaenus lagi 1,. was studied. In a dual choice feeding test the beech weevil preferred leaf disks from beech saplings exposed to ambient air against those from tiltcred air in 65"5% of all cases.
INTRODUCTION
laid mainly in the mid-vein of the leaves. Therc are three larval instars which mine in the leaves and pupal cocoons are formed in the mines. New generation adults emerge approximately 6 weeks after oviposition. There are generally two short periods of feeding in the life span of an adult weevil: directly after emergence and immediately prior to reproduction on beech, which is the only breeding host plant. Beech weevils used in this study were collected from the field. They had been sampled as pupae or as imagines, when still enclosed in the cocoons. After careful removal of the cocoons the pupae terminated rnetamorphosis without any detectable effects upon their behaviour. By choosing these developmental stages, food consumption prior to the feeding test could be excluded. Until the beginning of the test, weevils were individually kept in Petri dishes {Polystyrol (PS), 5"5 cm diameter) with a moistened filter paper at 10 h light/day {3000 lux) and day and night temperatures of 4 5 ' C and 3 - 4 C , respectively.
Insect plant relationships represent a sensitive and dynamic equilibrium produced and maintained by coevolution {Stenseth, 1987). Any changes in this equilibrium by biotic or abiotic factors may affect thc susceptibility of the plants to insects as well as the success of insects on their hosts (Crawley, 1983). In the last few years air pollution has been regarded as an additional abiotic factor affecting insect plant relationships. In particular, various studies on the effects of air pollutants upon aphid plant communities have emphasized the significance of changes in the host plant quality with regard to altered plant colonization and utilization by aphids [McNeill et al., t987: Bolsinger & Fliickiger, 1989: Braun & FI/,ickiger, 1989: Warrington, 1989). Little is known about the impact of air pollutants on the relationships between chewing insects and plants. Therc is even less information about the influence of air pollution upon arboreal insect--tree communities. To examine the effccts of ambient air pollutants on the feeding preference of an arboral chewing insect, the predominating phyllophagous insect species on beech trees, the beech weevil (Rhynchaenuslagi L.) was chosen in the present study.
Plants Three-year-old beech saplings, potted in loess loam soil for 2 years, were exposed in semi-open-top chambers in spring 1988, where they' were conditioned over one year to ambient or filtered air conditions. To minimize positional effects inside the chambers the position of the trees was periodically changed. The chambers were ventilated with either filtered or ambient air. The filtering system consisted of a dust filter (Viledon M F), charcoal, Reox Purafil T M and impregnated charcoal, which reduced NO2, SO2 and Os by 65--85%. At the inlet of the ambient air chamber, a dust filter was
MATERIALS AND METHODS lnsecls Rh.vnchaenusfagi L. (Col: Curculionidae) is a univoltine species which overwinters as an adult and colonizes beech in spring, soon after bud burst. Within this time eggs are 333
334
E. Hiltt~runner. 141: Fliickiger
Table I. Monlhly and maximal houri)' means (#g/m ~) of ozone, and monthly values of nitrogen dioxide and sulphur dioxide at Sch6nenbuch during exposure of the plants Month
03 maximal hourly mean
NO,. monthly
SO,_ monthl',
86 88 72 87 68 26 17 26
212 215 200 213 199 117 107 93
18 19 10 14 lg 32 45 29
3 2 0 3 1 3
14 47 57 63 101 97 87
92 135 172 156 195 213 ._7
45 42 22 19 22 15 17
0 3
monthly
1988 Ma June July August Septem bet October November December 1989 Januvry February March April May June July
I0
16 16 15 5 4 3 3
installed. Measurements inside the chambers revealed a loss of ozone in the ambient air chamber of 20 25% compared with the outside of O a concentrations. The ambient pollution data given in 1"able 1 were obtained from the same site, the permanent monitoring station at Sch6nenbuch {400m above sea level, about 7krn west of Baslek The monitoring equipment is described in detail by Braun and Fltickiger {1989).
and 72 h according to the following scoring system: 0, no feeding tracks of R.fagi; I, a single feeding track; 2, a few feeding tracks, area consumed of leaf disks below 10%; 3, many feeding tracks, area consumed of leaf disks over 1()~¼~. Score classes of disks from the same leaf were added up and the data were analyzed non-parametrically using the Wilcoxon test.
RESUUI'S Comparing the concentrations of N O 2, SO 2 and 03 during the predisposition time of the plants, air pollution was dominated by ozone (Table 1). During 146 days ( 1149 h of exposure time) ozone concentrations amounting to over 1201tg O3,m 3 were measured (this value should be exceeded only once a year in Switzerland, according to the Swiss clean air act). l,Jnder these ozone concentrations effects upon the beech saplings were expected. Any significant differences, however, between the two treatments were not detectable with regard to visible injury, shoot growth and mineral nutrient status in the foliage (data not shown). In the choice feeding test the beech weevil showed a significant feeding preference for leaf disks from trees fumigated with ambient air alter 24 h (Fig. I ). This initial preference was not maintained over time, so after 48 and 72 h the difference in the feeding behaviour of the weevil betxvccn these two groups of leaf disks was not significant.
DISCUSSION Dual choice feeding test A previously conducted experiment, where cages with weevils were fixed directly to the experimental plants, revealed a predominant influence of increased temperatures (due to the cages) on the feeding behaviour of the weevil. Therefore a choice feeding test was considered to be appropriate to examine the impact of ambient air pollution on this insect-plant relationship. Leaves of the second leaf flush and of the same age {determined by bud and leaf marking) were used for the choice feeding test. A m o n g these leaf samples there were no visually discernible differences. Two leaf disks, each 1 cm in diameter, were cut from the same leaf of a tree which was fumigated either by filtered air or by ambient air. The tour disks were arranged in a Petri dish (PS, 5.5cm diameter) with a moistened filter paper and one single beech weevil was released in the centre of the dish. For each pair of trees (from a total of seven pairs) live replications were conducted. The Petri dishes were kept at 18_+2C and a 12:12 (L:D) photoperiod (25001ux). To avoid disturbing the feeding weevil by touching the leaf disks (in case of direct measurements) the feeding preference was examined by ocular estimation after 24, 48
There arc only a few studies concerning the impact of air pollution on chewing insect plant relationships (review in Hughes, 1988; Riemer & Whittaker, 1989). Most of the investigated insects on herbaceous plants have shown a feeding preference for ozone-treated flfliagc. The Mexican bean beetle, Epilachna rarirestis
Preference
for leaf disks from
f i l t e r e d air
ambient
a',r
34.5% of cases
65.5% of cases
Fig. I. Choice feeding test with Rhynchaenus [agi L. on leaf disks of beech trces in liltered and ambient air. Figures are differences of score classes {summarized per leaf}. Feeding preference significant after 24h I ' p < 0 0 5 . Wilcoxon test, n = 35).
Air pollution effects on beech weevil.feeding Mulsant, the best studied insect in this context, preferred leaves from soybean Glvxine m a x (L.) Merr. exposed to increasing ozone concentrations (Endress & Post, 1985; Chappclka et al., 1988). In addition, Endress and Post 11985) reported that the beetles still preferrcd ozonated foliage to the controls 23 days after the last fumigation. The tomato pinworm Ke(feria lycopersicella Wals. also responded positively to tomato plants which had been prefumigated by ozone (550/lg,."m 3) two or four times at 3day intervals t\~r 3h. But survival and developmental rates of the larvac dccreased by fumigation during feeding (Trumble et al., 1987). Similar observations were made by Whittaker et al. 11989) with the chrysomelid beetle Gastrophysa viriduh~ Degeer on R u m e x ohtus(lolius L. The survival and productivity of the larval stages were higher on fumigated weeds (approximately 140 ltg O3."m31. Nevertheless, leaf consumption was lower on these plants compared with untreatcd plants. This meant that the larvae had to consume less leaf area of fumigated leaf per milligram of biomass production. Whittaker et a/. (19891 assumed that the ozonated foliage was more nutritious or less well defended than control leaves. Jeffords and Endress (1984) revealed an ozone concentration-dependent feeding preference of an arboreal insect, thc gypsy moth Lvmantria dispar L., for fumigated white oak tMiage. The larvae chose leaves with exposure to the highest concentration (300,ug O3m-~; 11 fumigations for 7 h) over the other trcatmcnts, but preferred foliage fumigated with 601~g O3.m 3 to that exposed to 180 l~g O3. m ~. Although the ozone treatment in this study can be partly compared with the ozone concentrations occurring under natural conditions, the possibility of nonlinear behaviour patterns of insects should be taken into account. Coleman and Jones 11988a) looked at thc feeding response of Plagio~h'ra cersicoh)ra L. on leaves from cottonwoods Populus dehoides aftcr a single, acute dose of ozone 1393,ug.m3; fumigation for 5 hi. The larvae as well as the adults of the beetle consumed more leafarea of ozone-treated foliage. Considering ozone as the dominating air pollutant at the experimental site of the present study, the observed feeding prcference of the beech weevil corresponds to that of the investigated insects. The decreasing preference aftcr 48 and 72 h may be explained by physiological and biochemical changes in the leaf disks over time. It is well known that excision may initiate wound responses [e.g. production of wound ethylene, induction and degradation of enzyme systems such as peroxidase) (Macheix et al., 1986) and could interact with the insect's perception of the nutritional quality of the leaf disks tLewis & van Emden, 1986). However, Raina et al. (19801 found in feeding assays with Epilachna carivestis Mulsant that thc leaf palatability was not severely changed if the disks were kept turgid. Therefore it can be assumed that the biochemical changes in the leaf disks did not differ between the treatment groups and the feeding
335
preference after 24h reflects the differing host plant qualities of the beech saplings. Although a pollutant-induced change of the plants can be supposed, nothing is known about the specific mechanisms involved. Moreover, it should be noted that the nutritional quality of the leaves used in this study was not directly examined. Determinations of foliar content of free amino acids, nitrogen, phosphorus and potassium in leaves of the first leaf flush from the same trees revealed that nitrogenous compounds in the leaf tissue did not have a determining or promoting effect on the success of the beech weevil on its host plant (Hiltbrunner, 1990), as has been shown for different insect plant systems (McNeill & Southwood, 1978: Brodbeck & Strong, 1987: Mattson & Scriber, 1987J. On the other hand, Braun and Fliickiger 11989) observed a significant effect of ambient ozone on the amino acid.sugar ratio in the phloem exudate of oneyear-old beech saplings under the same fumigation system. Following ambient air treatment the content of asparagine, glutamine and 7-amino-butyric acid as well as the sum of all amino acids were significantly increased. The determinations of the phloem exudate were conducted with leaves sampled in August, thus the leaves were exposed to higher ozone concentrations for a longer time compared with the leaf samples in the present study. It is known that the feeding preference of insects may not correlate positively with insect development and reproductive fitness on the preferred plants {Chew, 1980). Coleman and Jones (1988h1 reported a decreasing rcproductive fitness of Plagiodera cersicolora on ozonefumigated cottonwoods, though the beetles preferred to feed on ozone-treated foliage. Therefore it is not clear how the altered feeding behaviour of the beech weevil affects the whole life history pattern of the insect and hence the insect performance on beeches. To examine the influence of air pollution on this insect-plant community further investigations are needed, above all comprehensive investigations about pollutant-induced changes of the host plant quality' and their impact on different developmental stages of the weevil.
ACKNOWLEDGEMENTS We wish to thank the cantonal forestry administrations of northwestern Switzerland for financial support.
REFERENCES Bolsinger, M. & Fliickiger, W. (1989). Ambient air pollution induced changes in amino acid pattern of phloem sap in host phmts • .relevance to aphid infestation. Fro'iron. Pollut., $6, 2O9 16. Braun, S. & Eliickiger, W. (19891. Effect of ambieht ozone and acid mist on aphid development. Enciron. Pollut., 56, 177 82. Brodbeck, B. & Strong, D. [1987). Amino acids nitrition of herbi,,orous insects and sm:ss to the host plant. In Insect
336
E. Hilthrunner, W. Fliickiger
Outbreaks: Ecological and Evoh~tionary Proccs.~es. cd. E Barbosa & J.R. Schuhz. Academic Press. Nov, York, pp. 347-63. Chappelka, A. H., Kraemer, M. E., Mebrahtu, T.. Rangappa, M. & Benepal, P. S. (19881. Effects of ozone on soybean resistance to the Mexican bean beetle (Epilachna varil"e.~ti.~ Mulsant.). Environ. Exp. Bot., 28, 147-52. Chew, E. 11980). Food plant preferences of Pieric butterflies and crucifcrous food plants. Oecologia, 46, 347 53. ('olcman, S. J. & Jones, C. G. 11988a). Plant stress and insect behavior: Cottonwood, ozone and the feeding and oviposition preference of a beetle. Oecologh,, 76, 51-6. Coleman, S. J. & Jones, C. G. 11988h}. Plant stress and insect performance: Cottonwood, ozone and a leaf beetle. Occologia, 76, 57 61. Crawlcy, M. J. (1983). Herhivory: The D.vnamics ol Animal Phmt Interactions. Blackwell Scientilic Publications, Oxford, 437 pp. Endrcss, A. G. & Post, S. K. (1985). Altered feeding preference of Mexican bean beetle. Epilactma t'arivestis Mulsanl.. Ior ozonated soybean foliage. Environ. Pollut., 39, 9 16. Hiltbrunner, E. (199(h. Fehlhioh~gi,whe Unter.suchun,e tiber den Bel~dl der Buche [Fagus silvatica L.) dutch den Buchen~pringriissler {R hy nchaen us fagi L.I an ausge wiihlt('n I! 'aldhc.~tiimh,n in ~k,r Nordwestschweiz. Master thesis, Univcrsit,,, of Basle, 103 pp. Hughes, P. R. (1988). Insect populations on host plants subjected to air pollution. In Pl~ml Stress--hzsect Interaction.s, ed. E.A. Heinrichs. Wiley, New York, pp. 249 319. Jcffords, M. R. & Endress, A. G. (19841. A possible role of o/one m trcc dcloliation by the gypsy moth (l,cpidoptcra: Lymantriidac). ~2m'iron. Entomo[., 13, 1249 52. Lcv,is, A. C. & van Emdcn, H. F. (1986). Assz,,',s for insect feeding. In In.sect Phmt Interactions, cd. J. R. Miller & 1". A. Miller. Springer-Verlag. New, York, pp. 95 119. Macheix, J. J., Fleuriet, A. & Qucssada, M. P. 119861. Involvement of phenols and pcroxidascs in wound healing
and grafting, in Molecular attd Physiological Aspects o / Plant Peroxidases, ed. H. Greppin, C. Penel & Th. Gaspar. University of Geneva, Switzerland, pp. 267-86. Mattson, W. J. & Scriber, J. M. 11987). Nutritional ecology of insect folivores of woody trees: Nitrogen, water, fiber and mineral considerations. In Nutritional Ecology ol bisects, Mitc.~ and Spiders and Related Invertebrates, ed. F. Slansky Jr & J. R. Rodriguez. Wiley, New York, pp. 105-46. McNcill, S. & Southwood, T. R. E. (1978). The role of nitrogen in the de,,elopment of insect.:plant relationships. In Biochemical .,l.Vwcts e~/ Phmt and Aninlal Coevolution, ed. J. B. Harborne. Academic Press, London, pp. 77 98. McNcill, S., Aminu-Kano, M., Houlcn, G., Bullock, J.M., Citronc. S. & Bell, J. N. B. (19871. The interaction between air pollution and sucking insects, in Acid Rain: Scient([ic and Technical A&'wwes, cd. R. Perry & R. M. Harrison. Selper, London. pp. 602 7. Raina. A. K., Bcncpal, P. S. & Sheikh. A. Q. (1980). Effects of excised and intact leaf methods, leaf size and plant age on the Mexican bean beetle feeding. Entomol. E W. Appl., 27, 303-6. Riemer, J. & Whittaker. J. B. (19891. Air pollution and insect herbivores: Observed interactions and possible mechanisms. In In,sect Phmt htteractions, Vol. 1, cd. E.A. Bernays. CRC Press, Boston, MA, pp. 73-105. Stcnscth, N. C. (1987). Evolutionary processes and insect outbreaks. In Insect Outbreaks: Ecological and Evolutionary Pr,,esse.~. cd. P. Barbosa & J. R. Schultz. Academic Press, Nc~x York, pp. 533 63. 1 rumble. J. T., Hare. J. D., Musselmann. R. C. & McCool, P. M. (19,~71. Ozone-induced changes in host plant suitability: Interactions of Kci/eria lycopersicella and Lycopersicon c wu/entum. J. Chem. Ecol., 13, 203 18. Warrington. S. (1989). Ozone enhances the grov,th rate of cereal aphids..4grit. Ecosystems Environ., 26, 65 8. Whittaker. J. B., Kristiansen, I,. W.. Mikkclscn, T. N. & Moore, R. 11989). Responses to ozone of insect feeding on a crop and wccd species. Environ. Pollut., 62, 89 101.