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Monterrey pine (Pinus radiata D. Don) suitability for the pine shoot beetle (Tomicus piniperda L.) (Coleoptera: Scolytidae)
Fores~~;ology Management ELSEYIER
Forest Ecology and Management 86 ( 19%) 73-79
Monterrey pine (Pinus rudiata D. Don) suitability for the pine shoot beetle (Tomicus piniperda L.) (Coleoptera: Scolytidae) Ibone Amezaga ’ Department
of’ Pure and Applied
Biology,
Imperial
College
ut Silwood
Park. Ascot, Berkshire
SLS 7PY. UK
Accepted 12 March 1996
Abstract In 1990, the suitability of Pinus radiata D. Don as a host for Tomicus piniperda L. was studied. Special attention was given to the altitude and tree species effect (P. syluestris and P. radiata ) on T. piniperda biology. Despite the mild weather, T. piniperda did not have a second or sister generation at the study sites, and altitude or tree species did not show a significant effect on the life cycle in our study. Beetles developed more slowly and callows weighed less in P. radiata than in P. syloestris, with a consequent effect on survival. However, tree species did not affect brood production. Therefore, we conclude that more severe outbreaks could develop in P. radiata than in P. syfvestris. Keywords:
Bark beetles; Forest pests; Pinus radiata;
Pinus sylvestris;
1. Introduction The pine shoot beetle, Tomicus piniperdu L., is a serious pest of pine in Europe, northern Africa and
Asia (Bouhot et al., 1988; Hui, 1991, Eidmann, 1992) and it was discovered in the United States in 1992 (McCullough and Smitley, 1995). The introduction of an exotic tree species always involves a great deal of hazard. In the Basque Country, northern Spain, Pinus radiatu D. Don was planted on a commercial scale in the last century (Cobos-Suarez and Ruiz-Urrestarazu, 1990). Since then and according to the last inventory (Eusko Jaularitza, 19861, P. rudiatu plantations cover 77% of the total area forested with conifers (61% of the ’ Present address: Department of Plant Biology and Ecology, University of the Basque Country, Apdo. 644, 48080 Bilbao, Spain. 0378-I 127/96/$15.00 PII SO378-
Tomicus piniperda
total forested area). This high density of conifers and specially of P. radiata has led to pest problems (Cobos-Suarez and Ruiz-Urrestarazu, 1990). The main purpose of this paper was to study the suitability of P. rudiuta as a host in comparison with its natural host, P. sylvestris. The possibility of a second or sister generation was specially studied at different altitudes because of the consequences for the forest management in the area.
2. Materials and methods
The study was conducted in the county of Bizkaia, in the Basque region of northern Spain about 30 km away from Bilbao, in 1990. Three study areas were chosen according to altitude, tree species and aspect: (1) Dima located at an altitude of 650 m, surrounded by 30-year-old P. rudiatu and P. sylvestris trees; (2)
Copyright 0 1996 Elsevier Science B.V. All rights reserved.
1 127(96)03791-7
other day and taken to the laboratory to be weighed, and later used for the shoot feeding experiment. In order to assessthe tree specieseffect on the maturation feeding of the pine shoot beetle. emerging parent adults and callows were caged in branches of P. rudiutu and P. sylumris. Unfortunately, mob: of the beetlesdied owing to unknown reasonsbut the attacks seenin the surrounding trees showed that the beetles are capable of shoot-feeding in E’. mdiatti. In an attempt to produce a second generation another set of 30 trees was cut down in Dima (P. sytuesrris) and in Sekutze (P. radium) in July. ‘lhc samplingwas started during the first week o:‘ August and carried out every week. Unfortunately, all the treeswere attacked by Ips sexdentatus, Cdrthoton~icrrs erosus and Pityogenes hidentutus, specie5that have more than one generation per year.
Sekutze south located at an altitude of 250 m facing south, with l&year-old P. radiatu trees; (3) Sekutze north located at an altitude of 250 m facing north, with 18-year-old P. radium trees. In all but Dima. the sampletrees were mainly in the shade. Thirty trees were felled in the three study areas described above. In Dima. where both species of pine could be found, 30 of each specieswere felled at the end of January. In Sekutze, owing to a lack of personnel, trees were felled at the end of February. Trees were laid horizontally parallel to each other on top of two other trunks, which prevented them from touching the ground so all trunk areas could be attacked by the beetles. There was enough spaceto walk between each trunk. The total length of each trunk was measuredalong with the perimeter, bark roughnessand thickness at I m intervals. After T. piniperdu attack, 10% of the trees were sampled at random every other week. T. piniperdu attack started in March but sampling was not begun until May owing to bad weather. The trunks were divided into 1 m lengths and sampled in a 50 cm length in the middle of every other section, starting with number one at the bottom of the tree. The T. piniperdu galleries found were measuredand their location within the log (top, bottom. north face, south face) was recorded. All the insects found were collected and identified. The T. piniperdu Iarve, pupae and callow adults found alive were collected and put into flat-bottomed specimen tubes (75 X 25 mm> and stored in a cool dark box. All the living specimens were weighed and then frozen in the laboratory. Later, the maximum width of the larval head-capsulewas measuredunder a binocular microscope using a micrometer. In order to catch the emerging parent adults and callows, the areas not sampledwere covered with dark plastic with a transparent area where the emerging beetles fell into a glasspot. The emerging beetleswere collected every
Table 1 Maximum Site Sekutze Dima
temperature
(“C)
Jan.
Feb. 17 I5
reached each month March 24 22
Maximum temperatures in the experimental sites (Table l> do not show substantial differences across altitudes (250 and 650 m>, but Sekutze was always warmer than Dima. 1990 was especially warm and despite the temperaturesbeing well above the threshold for T. piniperdu to emerge from the wintering sites since the beginning of the year (I W-12”C, Bakke, 1968) the first attacks were not observed until the beginning of March. The percentages of larval stages found at each sample date among sites and between tree species showedthat by the beginning of May at sites2 and 3 the biggest proportion of larvae were already in the fourth instar, while at site 1. the biggest proportion was in the third instar (Fig. I). The first pupae were observed on the first sampling date (3 May 1990) at site 2. The first callows were found at all sites by the end of May but in the P. rudiutu samplesat site I.
at the two sites, where the experiments
April 27 26
3. Results
June
May 24 22
27 26
32 32
were carried Aug.
July 38 35
out. through
Sep. 37 -
28 I8
1990 Nov.
Oct. 27 24
__--__-. DCX. 19
20
I. Amezaga/Forest
Ecology
and Munagement
86 (1996)
2nd-7 “’ May 1990
Site 1 r
Site 1s
Site 2
73-79
75
14”‘-1 St” May 1990
Site 3
Site Ir
Site 1s
281h-3 1 Ft May I990
Site 2
Site 3
12”‘-13’h June 1990
100%
100%
80%
60%
60%
60%
40%
40%
20%
20% 0%
0% Sitelr
Sitels
Site2
Site lr
Site3
Fig. I. Percentage of different instar larvae found on each sample at on the survey is Dima and P. syluestris, Site 2 is Sekutze south and Site 3 is Sekutze north).
callows were not found until the middle of June. By then, most of the adults had already left the galleries. The callows continued emerging until 26 June at sites 2 and 3 and P. sylvestris at site 1 while in P. rudiuta trees at site 1 the callows did not stop emerging until 9 July. In general, the life cycle lasted nearly 4 months (beginning of March to the end of June) at Sekutze. In Dima, the breeding lasted l-2 weeks longer (to the middle of July) in P. radiatu trees than in P. syluestris owing to the longer period over which callows emerged from the trunks. Even though a second group of trees were cut at both altitudes no sister and/or secondgeneration was detected. The comparisonbetween the head-capsulewidths of larval instars from P. rudiutu and P. sylvestris did not show any significant difference (Table 2). Also, there was no statistically significant difference in weights between the last two instars emerging
Site 1s
Site 2
Site 3
date at each site (Site Ir is Dima and P. rudiutu,
Site. 1s
from the two tree species, although the last two instars bred on P. syluestris weighed more. However, the weight of the emerging callows was significantly different. Callows bred in P. sylvestris weighed more than thosebred in P. rudiatu (Fig. 2).
Table 2 Mean head-capsule piniperda breeding Instar larvae
width (mm) in P. rudiutu
of the four instar larvae and P. syluestris
x *SE(n) P. radiatu
I II III IV
of T.
0.4065 + 0.86 (20) 0.5601 rtO.31 (127) 0.7673 f 0.22 (524) 0.1001+0.13 (1497)
SE is the standard error. n is the number of measurements.
P. syluestris 0.4200 f 1.77 (5) 0.5644rt: 0.78 (24) 0.7639 f 0.35 (155) 0.1001 +0.24(351)
76
I. Amexzgu
/ Forest
Ecology
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86 (1996)
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Table 3 Mean gallery length (cm) of T. pinipcrdu two tree species present at site (1) (P. Site
Tree species
Site Site Site Site
I 1 2 3
for each site and for the P. q&mtri.~j
rudiutu and
ji *SE(n) 13.45 IO.66 14.8 1 i 0 44 12.80 f 0.53 1 I .8 I i 0.5.3
P. syluestris P. rudiutu P. rudiatu P. rudiatu
Site 1, Dima; site 2, Sekutze SE is the standard error. n is number of replicates.
south; site 3. Sekutzc
north.
Table 4 Mean larval production (no. of larvae found per gallery) in relation to the site and date of sampling Sites
1 2 3
//I
Larval
Callo\vs
instar
Fig.
2. Weight of the last two larval instars and callows of 77 showing the significant effect that tree species had on the callow stage only (bars are standard error bars, the numbers above the bars are the number of galleries sampled or the number of callows caught in the pots). piniperdu,
In order to calculate the production of beetles per gallery, the numbers of larvae per gallery found on the first three sampling dates were used. This is because by the middle of June most of the larvae
Sampling
dates
2-7 May
1990
12+ 1.55 (16) 22.36*5.63(11) 8.33 + 2.12 (6)
on tree/aspect
1990
28-31
22.71 *2.74(14) 28 rt 9.26 (8) 24.75 rt 4.04 (8)
f .? + SE)
May
1990
21.63+2.8(19) 20 + 2.88 (5) 14.25 I 3.75 (4) north.
were already in the pupae or callow stage, which were difficult to find or collect. Tree species had no significant effect on beetle production at site 1, however, the galleries in P. radiatu were longer than the galleriesin P. syluestris
lateral-north
and lateral-south)
at each site and
Site 3
Sum
Shady
SUMY
Site 1s Top Bottom Lateral-north Lateral-south
May
Site 1, Dima; site 2, Sekutze south; site 3, Sekutie The number in brackets is the number of galleries. SE is the standard error.
Table 5 Total number of attacks recorded for each aspect of the whole group of 30 trees (top, bottom, for the two tree species present in site 1 (P. rudiutu and P. syluestris) Position
14-18
(26) (29) (30) (29)
10 (4.4) 52 (23.2) 102 (45.5) 60 (26.7)
Site lr 8 (2.3) 111 (33.1) I47 (43.8) 69 (20.5)
Sum
Site 2 (6.7) (56.3) (89.3) (47.2)
60(15.3) 92 (23.4) 120 (30.6) 120 (30.6)
23 (9.3) 70 (28.3) 86 (34.8) 68 (27.5)
The values in parentheses are for each group of 30 trees at each site and show the percentage of total attacks within which belong to each category in which aspect is divided. Sites are aggregated in two groups according to exposure percentage totals for the aggregated sites are given in the columns headed ‘Sum’. Site Ir, Dima and P. rudiutu; site Is, Dima and P. sylvesnis; site 2, Sekutze south; site 3, Sekutze north.
(24.6) (51.7) (65.4) (58.1) each group of trees to suntight and the
I. Amezuga
/Forest
Ecology
(r-test) in site I (Table 3). The production of beetles, according to sampling dates showed maximum hatched larvae on the second and third sampling dates (Table 4) in the coldest sites (one at 600 m and three at 250 and north-facing), while site 2, which might have been the warmest, at 250 m and facing south, had very even production among the three sampling dates. There was a significant correlation between tree height and bark thickness at each site, but no correlation was found between tree height and gallery length at any site. In order to see the effect of aspect (top, bottom, lateral-north and lateral-south) and of sun/shade on the distribution of the attacks of T. piniperdu on the tree, a chi-squared test (x2) was carried out on the number of attacks found on the trees (Table 5). At site 1 the distribution of the attacks between tree species (P. rudiatu and P. sylvestris) did not vary with aspect ( x2 = 6.2; d.o.f., 3). However, when the distribution of the attacks on trees exposed to the sun (site 1) and that of trees in shady sites (sites 2 and 3) were compared, the distribution of the attacks differed significantly ( x2 = 24.21; d.o.f., 3). The main difference was between the attacks on the top and lateral-north of the trees. In the sunny sites, T. piniperdu showed fewer attacks on the top of the laying trees and more on the lateral-north of the trees.
4. Discussion
Temperature is an important agent controlling every part of the life cycle, from swarming time to the length of each of the life stages in the cycle of T. piniperdu (Bakke, 1968; Salonen, 1973). Although the present study included an evaluation of the life cycle of T. piniperda at different elevations in northem Spain, the mild weather of 1990, resulted in little difference in maximum monthly temperatures between the sites. Thus, no effect of altitude between sites was observed. Bakke (Bakke, 1968) observed that in Norway the swarming periods depended on altitude and distance from the coast. The flight period at high altitudes (450 m) inland was nearly a month later than at lowland (20 m) sites near the coast and finished within a single week whereas
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86 (1996)
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lowland flight activity continued over a period of nearly 2 months. In the low-altitude areas (Sekutze north and south, altitude 250 ml, even though the flight might have started early in the year owing to the mild conditions and trees were cut in late February, trees were attacked by the beginning of March, which could be explained by the longer period of flight activity found by Bakke (Bakke, 1968) in Scandinavia at low altitudes. At these two sites, no attacks were observed after those in March. This premise is based on the fact that the trees were observed every week in order to record new attacks, and no new attacks were observed after the beginning of March. However, at Dima (altitude 650 m), even though the trees were felled by the end of January, no attacks were observed until the beginning of March and the few new attacks observed over the next 1 or 2 weeks were by I. sexdentatus and 0. erosus. Another factor that could have obscured any difference in the life cycle between high and low altitudes could have been the fact that the trees at 650 m were exposed to the sun whereas the trees at 250 m were shaded by neighbouring trees. Solar radiation is me main factor influencing the subcortical temperature of trees (see Bakke, 1968, for references). However, bark thickness is also an insulation factor, and thick bark prevents the temperature beneath the bark from reaching high levels, and also retains the heat (Bakke, 1968). At the same time, temperature affects the boring activity of adults and the rate of gallery construction (Salonen, 1973). Thus, even if at low altitude (250 m> the air temperature was nearly always higher than at 650 m, the exposure of the trunks to the sun and the prevalence of thicker bark in the high-altitude trees (trees were at least 30 years old, while at 250 m trees were only 18 years old) could have caused the life cycles to be of similar durations at both altitudes. In the study areas the period from attack until the first callows emerged was approximately 14 weeks. The callow emergence period was 2 weeks longer at 650 m, and continued until the second week of July. Thus, even though the maximum temperatures for the two sites were nearly the same, it could be that the minimum temperatures were different (these data are not available). Salonen (Salonen, 1973) studied the accumulated temperature requirements for vari-
78
I. Amezugu
/Foresr
Ecology
ous stages of the life cycle of T. piniperda and found that the duration of the pre-emergence period varied with temperature. The development of the life cycle was not much affected by the tree species as Laxman (Laxman, 1988) found between Scats pine and Corsican pine. In this study, only the callows in the sampling galleries appeared in P. sylvestris before P. radiata, but the first and last catches in the pots were on the same dates. The weight difference between the callows bred in P. radium and P. syloestris showed that the beetles were able to feed better on their natural host, P. sylvestris than in the exotic tree, P. rudiutu. This could have a later effect on the survival of the beetles when they feed for the rest of the summer in the shoots, because it was found that heavier beetles had survived better than those that were lighter (I. Amezaga, unpublished data, 1992). Laxman (Laxman, 1988) found a significant difference between the fourth instar larval weights reared in Scats pine and Corsican pine, with the former being heavier. However, even though the results indicated an effect of tree species on callow weight, this effect was not evident for the fourth instar larvae. Laxman found a significant difference between fourth instar headcapsule widths, but in the present study there was no tree species effect on them. Brood production was not significantly affected by tree species. Langstrom and Hellqvist (Langstrom and Hellqvist, 1985) found no significant effect on brood production and adult weight between the T. piniperdu beetles reared on P. contortu and those reared on P. syluestris. However, the total number of eggs laid was smaller and the emergence occurred later on P. contortu. In the present study P. rudiatu gallery length was longer than on P. sylvestris at site 1, possibly owing to a worse quality of food which forced the females to make a longer gallery in order to be able to leave the trunk. Annila and coworkers (Annila et al., 1983) found similar brood production of Tomicus sp. in Scats and Lodgepole pine in Finland. Amman (Amman, 1982) studying Dendroctonus ponderosue Hopkins, bred in lodgepole pine, observed that this beetle was able to reproduce successfully in other pines but with a considerable variation in the brood production. Fuhrer and Muhlenbrock (Fuhrer and Muhlenbrock. 1983) showed
and Manapmrnt
86 (19961
73-79
that different geographical strains of Pityogenes chalcogruphus L. reared on severa conifer hosts had similar brood production on Piceu ubies for all the strains, but variable response to other conifers. T. piniperdu showed a clear tendency to attack the cooler sides of the cut trees (lateral-north of the trees) when trees were in direct sun (Dimal. How. ever, no effect of aspect was found for at the shady sites (Sekutze south and north). Bakke (Bakke, 1968) studying construction of entrance holes in relation to temperature chosen by T. piniperdu, found that 654 of the galleries were constructed between 20” and 24°C (mean temperature being 21.3”C). The maximum temperatures at the time of attack were around 26”-27°C well over the preferred mean temperature (Table 1). The lateral-north side of the trees in direct sun was the cooler side of the tree, the preferred temperatures for brood development, only in the early morning. In the shaded sites, however, the sun did not affect the temperature of the trunks and even though no aspect effect was found, the highest attack was on the lateral-north side. This could be because it was the side of the tree facing north, and the prevailing wind blowing from the north would have kept that side the coolest. In Scandinavia. Saarenman (Saarenmaa. 1983) reported that 7’. piniperdu had a slight tendency to show more attacks on the sunny sides of the bolts, but this could have been because the temperatures were below those that were reached in the present study sites.
5. Conclusions T. piniperda can exploit P. radiata as well as P. sylvestris, even though development is somewhat slower in P. rudiutu. Callows emerging from P. radiuta weighed less, which affects survival later on in the shoots. From the shoot pruning damage seen at the sites where the experimental work was carried out, it is clear that T. piniperdu is capable of maturation feeding in P. rudiatu, nevertheless, more research should be done in order to evaluate its effect on the maturation and survival in shoots. Although, T. piniperdu might start its swarming period as early as January over the entire altitudinal range over which pine plantations can be found in northern Spain, the risk of a second generation seems to be
I. Amezaga/Forest
Ecology
small. Nevertheless, there is no reason to believe that more severe outbreaks could be developed in P. radiata than in P. syluestris.
Acknowledgements
I would like to thank Mick Crawley and Hugh Evans for all their help during the study. I would also like to thank the departments of Forestry of the Basque Government and County Councils of Bizkaia and Araba for the use of their facilities during the field work.
References Amman, G.D., 1982. Characteristics of mountain pine beetle teared in four pine hosts. Environ. Entomol., 11: W-593. Annila, E., Heliovaara, K., Puukko, K. and Rousi, M., 1983. Pest on lodgepole pine (Pinus contorta) in Finland. Commun. Inst. For. Fenn., 115: l-27. Bakke, A., 1968. Ecological studies on bark beetles (Cal., Scolytidae) associated with Scats pine (P inus syluestris) in Norway with particular reference to the influence of temperature. Medd. Nor. Skogsforsoeksves., 21: 443-602. Bouhot, L., Lieutier, F. and Debouzie, D., 1988. Spatial and temporal distribution of attacks by Tomicus piniperda L. and Ips sexdentutus Boem. (Co]., Scolytidae) on Pinus syluestris. J. Appl. Entomol., 106: 356-371.
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Cobos-Suarez, J.M. and Ruiz-Unestarazu, M.M., 1990. Problemas fitosanitarios de la especie Pinus radium D. Don en Espaiia, con especial referencia al Pais Vasco. Bol. San. Veg. Plag., 16: 37-53. Eidmann, H.H., 1992. Impact of bark beetles on forests and forestry in Sweden. J. Appt. Entomol., 114: 193-200. Eusko Jaularitza, 1986. Baso Inbentarioa E.H.K.A.-Inventario Forestal. Servicio Central de Publicaciones de1 Gobiemo Vasco, Vitoria-Gazteiz. Fuhrer, E. and Muhlenbrock, B., 1983. Brutexperimente mit Pityogrnes chulcographus L. as verschiedenen Nadelbaumarten. Z. Angew. Entomol., 96: 228-232. Hui, Y., 1991. On the bionomy of Tomicus piniperda CL.) (Cot., Scolytidae) in the Kunming region of China. J. Appl. Entomol., 112: 366-369. Langstrom, B. and Hellqvist, C., 1985. Pinus contorta as a potential host for Tomicus piniperda L. and 7’. minor (Hart.) (Cal., Scolytidae) in Sweden. Z. Angew. Entomol., 99: 174181. Laxman, J., 1988. Study of the factors affecting breeding success of the pine shoot beetle Tomicus piniperdu (Cal., Scolytidae) with special reference to gale-damage pines. MSc Thesis, Imperial College of Science, Technology and Medicine, London. McCullough, D.G. and Smitley. D.R., 1995. Evaluation of insecticides to reduce maturation feeding by Tomicus piniperdu (Coleoptera: Scolytidae) in Scotch Pine. J. Econ. Entomol., 88: 693-699. Saarenmaa, H., 1983. Modelling the spatial pattern and intraspecific competition in Tomicus piniperda (Cal., Scolytidae). Commun. Inst. For. Fear., 118: l-39. Salonen, K., 1973. On the life cycle, especially on the reproduction biology of Blastophagus piniperdu L. (Cal., Scolytidae). Acta For. Fenn., 127: l-72.
Forest Ecology and Management 86 ( 19%) 73-79
Monterrey pine (Pinus rudiata D. Don) suitability for the pine shoot beetle (Tomicus piniperda L.) (Coleoptera: Scolytidae) Ibone Amezaga ’ Department
of’ Pure and Applied
Biology,
Imperial
College
ut Silwood
Park. Ascot, Berkshire
SLS 7PY. UK
Accepted 12 March 1996
Abstract In 1990, the suitability of Pinus radiata D. Don as a host for Tomicus piniperda L. was studied. Special attention was given to the altitude and tree species effect (P. syluestris and P. radiata ) on T. piniperda biology. Despite the mild weather, T. piniperda did not have a second or sister generation at the study sites, and altitude or tree species did not show a significant effect on the life cycle in our study. Beetles developed more slowly and callows weighed less in P. radiata than in P. syloestris, with a consequent effect on survival. However, tree species did not affect brood production. Therefore, we conclude that more severe outbreaks could develop in P. radiata than in P. syfvestris. Keywords:
Bark beetles; Forest pests; Pinus radiata;
Pinus sylvestris;
1. Introduction The pine shoot beetle, Tomicus piniperdu L., is a serious pest of pine in Europe, northern Africa and
Asia (Bouhot et al., 1988; Hui, 1991, Eidmann, 1992) and it was discovered in the United States in 1992 (McCullough and Smitley, 1995). The introduction of an exotic tree species always involves a great deal of hazard. In the Basque Country, northern Spain, Pinus radiatu D. Don was planted on a commercial scale in the last century (Cobos-Suarez and Ruiz-Urrestarazu, 1990). Since then and according to the last inventory (Eusko Jaularitza, 19861, P. rudiatu plantations cover 77% of the total area forested with conifers (61% of the ’ Present address: Department of Plant Biology and Ecology, University of the Basque Country, Apdo. 644, 48080 Bilbao, Spain. 0378-I 127/96/$15.00 PII SO378-
Tomicus piniperda
total forested area). This high density of conifers and specially of P. radiata has led to pest problems (Cobos-Suarez and Ruiz-Urrestarazu, 1990). The main purpose of this paper was to study the suitability of P. rudiuta as a host in comparison with its natural host, P. sylvestris. The possibility of a second or sister generation was specially studied at different altitudes because of the consequences for the forest management in the area.
2. Materials and methods
The study was conducted in the county of Bizkaia, in the Basque region of northern Spain about 30 km away from Bilbao, in 1990. Three study areas were chosen according to altitude, tree species and aspect: (1) Dima located at an altitude of 650 m, surrounded by 30-year-old P. rudiatu and P. sylvestris trees; (2)
Copyright 0 1996 Elsevier Science B.V. All rights reserved.
1 127(96)03791-7
other day and taken to the laboratory to be weighed, and later used for the shoot feeding experiment. In order to assessthe tree specieseffect on the maturation feeding of the pine shoot beetle. emerging parent adults and callows were caged in branches of P. rudiutu and P. sylumris. Unfortunately, mob: of the beetlesdied owing to unknown reasonsbut the attacks seenin the surrounding trees showed that the beetles are capable of shoot-feeding in E’. mdiatti. In an attempt to produce a second generation another set of 30 trees was cut down in Dima (P. sytuesrris) and in Sekutze (P. radium) in July. ‘lhc samplingwas started during the first week o:‘ August and carried out every week. Unfortunately, all the treeswere attacked by Ips sexdentatus, Cdrthoton~icrrs erosus and Pityogenes hidentutus, specie5that have more than one generation per year.
Sekutze south located at an altitude of 250 m facing south, with l&year-old P. radiatu trees; (3) Sekutze north located at an altitude of 250 m facing north, with 18-year-old P. radium trees. In all but Dima. the sampletrees were mainly in the shade. Thirty trees were felled in the three study areas described above. In Dima. where both species of pine could be found, 30 of each specieswere felled at the end of January. In Sekutze, owing to a lack of personnel, trees were felled at the end of February. Trees were laid horizontally parallel to each other on top of two other trunks, which prevented them from touching the ground so all trunk areas could be attacked by the beetles. There was enough spaceto walk between each trunk. The total length of each trunk was measuredalong with the perimeter, bark roughnessand thickness at I m intervals. After T. piniperdu attack, 10% of the trees were sampled at random every other week. T. piniperdu attack started in March but sampling was not begun until May owing to bad weather. The trunks were divided into 1 m lengths and sampled in a 50 cm length in the middle of every other section, starting with number one at the bottom of the tree. The T. piniperdu galleries found were measuredand their location within the log (top, bottom. north face, south face) was recorded. All the insects found were collected and identified. The T. piniperdu Iarve, pupae and callow adults found alive were collected and put into flat-bottomed specimen tubes (75 X 25 mm> and stored in a cool dark box. All the living specimens were weighed and then frozen in the laboratory. Later, the maximum width of the larval head-capsulewas measuredunder a binocular microscope using a micrometer. In order to catch the emerging parent adults and callows, the areas not sampledwere covered with dark plastic with a transparent area where the emerging beetles fell into a glasspot. The emerging beetleswere collected every
Table 1 Maximum Site Sekutze Dima
temperature
(“C)
Jan.
Feb. 17 I5
reached each month March 24 22
Maximum temperatures in the experimental sites (Table l> do not show substantial differences across altitudes (250 and 650 m>, but Sekutze was always warmer than Dima. 1990 was especially warm and despite the temperaturesbeing well above the threshold for T. piniperdu to emerge from the wintering sites since the beginning of the year (I W-12”C, Bakke, 1968) the first attacks were not observed until the beginning of March. The percentages of larval stages found at each sample date among sites and between tree species showedthat by the beginning of May at sites2 and 3 the biggest proportion of larvae were already in the fourth instar, while at site 1. the biggest proportion was in the third instar (Fig. I). The first pupae were observed on the first sampling date (3 May 1990) at site 2. The first callows were found at all sites by the end of May but in the P. rudiutu samplesat site I.
at the two sites, where the experiments
April 27 26
3. Results
June
May 24 22
27 26
32 32
were carried Aug.
July 38 35
out. through
Sep. 37 -
28 I8
1990 Nov.
Oct. 27 24
__--__-. DCX. 19
20
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86 (1996)
2nd-7 “’ May 1990
Site 1 r
Site 1s
Site 2
73-79
75
14”‘-1 St” May 1990
Site 3
Site Ir
Site 1s
281h-3 1 Ft May I990
Site 2
Site 3
12”‘-13’h June 1990
100%
100%
80%
60%
60%
60%
40%
40%
20%
20% 0%
0% Sitelr
Sitels
Site2
Site lr
Site3
Fig. I. Percentage of different instar larvae found on each sample at on the survey is Dima and P. syluestris, Site 2 is Sekutze south and Site 3 is Sekutze north).
callows were not found until the middle of June. By then, most of the adults had already left the galleries. The callows continued emerging until 26 June at sites 2 and 3 and P. sylvestris at site 1 while in P. rudiuta trees at site 1 the callows did not stop emerging until 9 July. In general, the life cycle lasted nearly 4 months (beginning of March to the end of June) at Sekutze. In Dima, the breeding lasted l-2 weeks longer (to the middle of July) in P. radiatu trees than in P. syluestris owing to the longer period over which callows emerged from the trunks. Even though a second group of trees were cut at both altitudes no sister and/or secondgeneration was detected. The comparisonbetween the head-capsulewidths of larval instars from P. rudiutu and P. sylvestris did not show any significant difference (Table 2). Also, there was no statistically significant difference in weights between the last two instars emerging
Site 1s
Site 2
Site 3
date at each site (Site Ir is Dima and P. rudiutu,
Site. 1s
from the two tree species, although the last two instars bred on P. syluestris weighed more. However, the weight of the emerging callows was significantly different. Callows bred in P. sylvestris weighed more than thosebred in P. rudiatu (Fig. 2).
Table 2 Mean head-capsule piniperda breeding Instar larvae
width (mm) in P. rudiutu
of the four instar larvae and P. syluestris
x *SE(n) P. radiatu
I II III IV
of T.
0.4065 + 0.86 (20) 0.5601 rtO.31 (127) 0.7673 f 0.22 (524) 0.1001+0.13 (1497)
SE is the standard error. n is the number of measurements.
P. syluestris 0.4200 f 1.77 (5) 0.5644rt: 0.78 (24) 0.7639 f 0.35 (155) 0.1001 +0.24(351)
76
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r
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86 (1996)
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Table 3 Mean gallery length (cm) of T. pinipcrdu two tree species present at site (1) (P. Site
Tree species
Site Site Site Site
I 1 2 3
for each site and for the P. q&mtri.~j
rudiutu and
ji *SE(n) 13.45 IO.66 14.8 1 i 0 44 12.80 f 0.53 1 I .8 I i 0.5.3
P. syluestris P. rudiutu P. rudiatu P. rudiatu
Site 1, Dima; site 2, Sekutze SE is the standard error. n is number of replicates.
south; site 3. Sekutzc
north.
Table 4 Mean larval production (no. of larvae found per gallery) in relation to the site and date of sampling Sites
1 2 3
//I
Larval
Callo\vs
instar
Fig.
2. Weight of the last two larval instars and callows of 77 showing the significant effect that tree species had on the callow stage only (bars are standard error bars, the numbers above the bars are the number of galleries sampled or the number of callows caught in the pots). piniperdu,
In order to calculate the production of beetles per gallery, the numbers of larvae per gallery found on the first three sampling dates were used. This is because by the middle of June most of the larvae
Sampling
dates
2-7 May
1990
12+ 1.55 (16) 22.36*5.63(11) 8.33 + 2.12 (6)
on tree/aspect
1990
28-31
22.71 *2.74(14) 28 rt 9.26 (8) 24.75 rt 4.04 (8)
f .? + SE)
May
1990
21.63+2.8(19) 20 + 2.88 (5) 14.25 I 3.75 (4) north.
were already in the pupae or callow stage, which were difficult to find or collect. Tree species had no significant effect on beetle production at site 1, however, the galleries in P. radiatu were longer than the galleriesin P. syluestris
lateral-north
and lateral-south)
at each site and
Site 3
Sum
Shady
SUMY
Site 1s Top Bottom Lateral-north Lateral-south
May
Site 1, Dima; site 2, Sekutze south; site 3, Sekutie The number in brackets is the number of galleries. SE is the standard error.
Table 5 Total number of attacks recorded for each aspect of the whole group of 30 trees (top, bottom, for the two tree species present in site 1 (P. rudiutu and P. syluestris) Position
14-18
(26) (29) (30) (29)
10 (4.4) 52 (23.2) 102 (45.5) 60 (26.7)
Site lr 8 (2.3) 111 (33.1) I47 (43.8) 69 (20.5)
Sum
Site 2 (6.7) (56.3) (89.3) (47.2)
60(15.3) 92 (23.4) 120 (30.6) 120 (30.6)
23 (9.3) 70 (28.3) 86 (34.8) 68 (27.5)
The values in parentheses are for each group of 30 trees at each site and show the percentage of total attacks within which belong to each category in which aspect is divided. Sites are aggregated in two groups according to exposure percentage totals for the aggregated sites are given in the columns headed ‘Sum’. Site Ir, Dima and P. rudiutu; site Is, Dima and P. sylvesnis; site 2, Sekutze south; site 3, Sekutze north.
(24.6) (51.7) (65.4) (58.1) each group of trees to suntight and the
I. Amezuga
/Forest
Ecology
(r-test) in site I (Table 3). The production of beetles, according to sampling dates showed maximum hatched larvae on the second and third sampling dates (Table 4) in the coldest sites (one at 600 m and three at 250 and north-facing), while site 2, which might have been the warmest, at 250 m and facing south, had very even production among the three sampling dates. There was a significant correlation between tree height and bark thickness at each site, but no correlation was found between tree height and gallery length at any site. In order to see the effect of aspect (top, bottom, lateral-north and lateral-south) and of sun/shade on the distribution of the attacks of T. piniperdu on the tree, a chi-squared test (x2) was carried out on the number of attacks found on the trees (Table 5). At site 1 the distribution of the attacks between tree species (P. rudiatu and P. sylvestris) did not vary with aspect ( x2 = 6.2; d.o.f., 3). However, when the distribution of the attacks on trees exposed to the sun (site 1) and that of trees in shady sites (sites 2 and 3) were compared, the distribution of the attacks differed significantly ( x2 = 24.21; d.o.f., 3). The main difference was between the attacks on the top and lateral-north of the trees. In the sunny sites, T. piniperdu showed fewer attacks on the top of the laying trees and more on the lateral-north of the trees.
4. Discussion
Temperature is an important agent controlling every part of the life cycle, from swarming time to the length of each of the life stages in the cycle of T. piniperdu (Bakke, 1968; Salonen, 1973). Although the present study included an evaluation of the life cycle of T. piniperda at different elevations in northem Spain, the mild weather of 1990, resulted in little difference in maximum monthly temperatures between the sites. Thus, no effect of altitude between sites was observed. Bakke (Bakke, 1968) observed that in Norway the swarming periods depended on altitude and distance from the coast. The flight period at high altitudes (450 m) inland was nearly a month later than at lowland (20 m) sites near the coast and finished within a single week whereas
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86 (1996)
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lowland flight activity continued over a period of nearly 2 months. In the low-altitude areas (Sekutze north and south, altitude 250 ml, even though the flight might have started early in the year owing to the mild conditions and trees were cut in late February, trees were attacked by the beginning of March, which could be explained by the longer period of flight activity found by Bakke (Bakke, 1968) in Scandinavia at low altitudes. At these two sites, no attacks were observed after those in March. This premise is based on the fact that the trees were observed every week in order to record new attacks, and no new attacks were observed after the beginning of March. However, at Dima (altitude 650 m), even though the trees were felled by the end of January, no attacks were observed until the beginning of March and the few new attacks observed over the next 1 or 2 weeks were by I. sexdentatus and 0. erosus. Another factor that could have obscured any difference in the life cycle between high and low altitudes could have been the fact that the trees at 650 m were exposed to the sun whereas the trees at 250 m were shaded by neighbouring trees. Solar radiation is me main factor influencing the subcortical temperature of trees (see Bakke, 1968, for references). However, bark thickness is also an insulation factor, and thick bark prevents the temperature beneath the bark from reaching high levels, and also retains the heat (Bakke, 1968). At the same time, temperature affects the boring activity of adults and the rate of gallery construction (Salonen, 1973). Thus, even if at low altitude (250 m> the air temperature was nearly always higher than at 650 m, the exposure of the trunks to the sun and the prevalence of thicker bark in the high-altitude trees (trees were at least 30 years old, while at 250 m trees were only 18 years old) could have caused the life cycles to be of similar durations at both altitudes. In the study areas the period from attack until the first callows emerged was approximately 14 weeks. The callow emergence period was 2 weeks longer at 650 m, and continued until the second week of July. Thus, even though the maximum temperatures for the two sites were nearly the same, it could be that the minimum temperatures were different (these data are not available). Salonen (Salonen, 1973) studied the accumulated temperature requirements for vari-
78
I. Amezugu
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Ecology
ous stages of the life cycle of T. piniperda and found that the duration of the pre-emergence period varied with temperature. The development of the life cycle was not much affected by the tree species as Laxman (Laxman, 1988) found between Scats pine and Corsican pine. In this study, only the callows in the sampling galleries appeared in P. sylvestris before P. radiata, but the first and last catches in the pots were on the same dates. The weight difference between the callows bred in P. radium and P. syloestris showed that the beetles were able to feed better on their natural host, P. sylvestris than in the exotic tree, P. rudiutu. This could have a later effect on the survival of the beetles when they feed for the rest of the summer in the shoots, because it was found that heavier beetles had survived better than those that were lighter (I. Amezaga, unpublished data, 1992). Laxman (Laxman, 1988) found a significant difference between the fourth instar larval weights reared in Scats pine and Corsican pine, with the former being heavier. However, even though the results indicated an effect of tree species on callow weight, this effect was not evident for the fourth instar larvae. Laxman found a significant difference between fourth instar headcapsule widths, but in the present study there was no tree species effect on them. Brood production was not significantly affected by tree species. Langstrom and Hellqvist (Langstrom and Hellqvist, 1985) found no significant effect on brood production and adult weight between the T. piniperdu beetles reared on P. contortu and those reared on P. syluestris. However, the total number of eggs laid was smaller and the emergence occurred later on P. contortu. In the present study P. rudiatu gallery length was longer than on P. sylvestris at site 1, possibly owing to a worse quality of food which forced the females to make a longer gallery in order to be able to leave the trunk. Annila and coworkers (Annila et al., 1983) found similar brood production of Tomicus sp. in Scats and Lodgepole pine in Finland. Amman (Amman, 1982) studying Dendroctonus ponderosue Hopkins, bred in lodgepole pine, observed that this beetle was able to reproduce successfully in other pines but with a considerable variation in the brood production. Fuhrer and Muhlenbrock (Fuhrer and Muhlenbrock. 1983) showed
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86 (19961
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that different geographical strains of Pityogenes chalcogruphus L. reared on severa conifer hosts had similar brood production on Piceu ubies for all the strains, but variable response to other conifers. T. piniperdu showed a clear tendency to attack the cooler sides of the cut trees (lateral-north of the trees) when trees were in direct sun (Dimal. How. ever, no effect of aspect was found for at the shady sites (Sekutze south and north). Bakke (Bakke, 1968) studying construction of entrance holes in relation to temperature chosen by T. piniperdu, found that 654 of the galleries were constructed between 20” and 24°C (mean temperature being 21.3”C). The maximum temperatures at the time of attack were around 26”-27°C well over the preferred mean temperature (Table 1). The lateral-north side of the trees in direct sun was the cooler side of the tree, the preferred temperatures for brood development, only in the early morning. In the shaded sites, however, the sun did not affect the temperature of the trunks and even though no aspect effect was found, the highest attack was on the lateral-north side. This could be because it was the side of the tree facing north, and the prevailing wind blowing from the north would have kept that side the coolest. In Scandinavia. Saarenman (Saarenmaa. 1983) reported that 7’. piniperdu had a slight tendency to show more attacks on the sunny sides of the bolts, but this could have been because the temperatures were below those that were reached in the present study sites.
5. Conclusions T. piniperda can exploit P. radiata as well as P. sylvestris, even though development is somewhat slower in P. rudiutu. Callows emerging from P. radiuta weighed less, which affects survival later on in the shoots. From the shoot pruning damage seen at the sites where the experimental work was carried out, it is clear that T. piniperdu is capable of maturation feeding in P. rudiatu, nevertheless, more research should be done in order to evaluate its effect on the maturation and survival in shoots. Although, T. piniperdu might start its swarming period as early as January over the entire altitudinal range over which pine plantations can be found in northern Spain, the risk of a second generation seems to be
I. Amezaga/Forest
Ecology
small. Nevertheless, there is no reason to believe that more severe outbreaks could be developed in P. radiata than in P. syluestris.
Acknowledgements
I would like to thank Mick Crawley and Hugh Evans for all their help during the study. I would also like to thank the departments of Forestry of the Basque Government and County Councils of Bizkaia and Araba for the use of their facilities during the field work.
References Amman, G.D., 1982. Characteristics of mountain pine beetle teared in four pine hosts. Environ. Entomol., 11: W-593. Annila, E., Heliovaara, K., Puukko, K. and Rousi, M., 1983. Pest on lodgepole pine (Pinus contorta) in Finland. Commun. Inst. For. Fenn., 115: l-27. Bakke, A., 1968. Ecological studies on bark beetles (Cal., Scolytidae) associated with Scats pine (P inus syluestris) in Norway with particular reference to the influence of temperature. Medd. Nor. Skogsforsoeksves., 21: 443-602. Bouhot, L., Lieutier, F. and Debouzie, D., 1988. Spatial and temporal distribution of attacks by Tomicus piniperda L. and Ips sexdentutus Boem. (Co]., Scolytidae) on Pinus syluestris. J. Appl. Entomol., 106: 356-371.
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Cobos-Suarez, J.M. and Ruiz-Unestarazu, M.M., 1990. Problemas fitosanitarios de la especie Pinus radium D. Don en Espaiia, con especial referencia al Pais Vasco. Bol. San. Veg. Plag., 16: 37-53. Eidmann, H.H., 1992. Impact of bark beetles on forests and forestry in Sweden. J. Appt. Entomol., 114: 193-200. Eusko Jaularitza, 1986. Baso Inbentarioa E.H.K.A.-Inventario Forestal. Servicio Central de Publicaciones de1 Gobiemo Vasco, Vitoria-Gazteiz. Fuhrer, E. and Muhlenbrock, B., 1983. Brutexperimente mit Pityogrnes chulcographus L. as verschiedenen Nadelbaumarten. Z. Angew. Entomol., 96: 228-232. Hui, Y., 1991. On the bionomy of Tomicus piniperda CL.) (Cot., Scolytidae) in the Kunming region of China. J. Appl. Entomol., 112: 366-369. Langstrom, B. and Hellqvist, C., 1985. Pinus contorta as a potential host for Tomicus piniperda L. and 7’. minor (Hart.) (Cal., Scolytidae) in Sweden. Z. Angew. Entomol., 99: 174181. Laxman, J., 1988. Study of the factors affecting breeding success of the pine shoot beetle Tomicus piniperdu (Cal., Scolytidae) with special reference to gale-damage pines. MSc Thesis, Imperial College of Science, Technology and Medicine, London. McCullough, D.G. and Smitley. D.R., 1995. Evaluation of insecticides to reduce maturation feeding by Tomicus piniperdu (Coleoptera: Scolytidae) in Scotch Pine. J. Econ. Entomol., 88: 693-699. Saarenmaa, H., 1983. Modelling the spatial pattern and intraspecific competition in Tomicus piniperda (Cal., Scolytidae). Commun. Inst. For. Fear., 118: l-39. Salonen, K., 1973. On the life cycle, especially on the reproduction biology of Blastophagus piniperdu L. (Cal., Scolytidae). Acta For. Fenn., 127: l-72.