Appl. Entomol. Zool. 42 (3): 403–410 (2007) http://odokon.org/
Boring effect of carpenterworms (Lepidoptera: Cossidae) on sap exudation of the oak, Quercus acutissima
Jiichiro YOSHIMOTO* and Takayoshi NISHIDA Laboratory of Insect Ecology, Graduate School of Agriculture, Kyoto University; Sakyo-ku, Kyoto 606–8502, Japan (Received 10 January 2007; Accepted 12 April 2007)
Abstract Sap often exudes from the trunks of the oak, Quercus acutissima. Carpenterworms (Lepidoptera, Cossidae) are fre- quently observed at these sap sites and believed to be involved in exudation. Field observations from 2002 to 2004 showed that 20–40% of all patches (exuding spots on trees) harbored these insects and that roughly 20% of all patches had only their nests. The peak period of carpenterworm abundance corresponded to the peak number of patches har- boring them in all 3 years (August 2002, September 2003, and July 2004). Patches with carpenterworms or their nests had a wider surface area and exuded more sap than patches without them or their nests. Moreover, their experimental removal resulted in decreased exudate quantity, indicating that these insects promote exudation. These results suggest that carpenterworms contribute greatly to sap exudation through wood boring and that their distribution and abun- dance affect sap resources.
Key words: Borer; carpenter moth; Cossus jezoensis; resource abundance; tree sap
abundance. Thus, studies on these insects should INTRODUCTION unravel the patterns and processes of tree sap com- Sap frequently exudes from wounded areas on munities as well as the proximate mechanisms be- the trunks of broad-leaved trees such as oak, wil- hind sap ooze. However, sap exudation of oak trees low, and elm. Most of these wounds are likely in- has not been studied quantitatively in relation to flicted by wood-boring organisms and it has been carpenterworms. qualitatively documented that their boring is re- Carpenterworms are distributed worldwide; for sponsible for such sap ooze (e.g., Hay, 1974; Ya- example, Cossus cossus is widely distributed mashita, 1999). Quercus acutissima, one of the throughout Asia, Europe, and North Africa (Facci- dominant oak species in temperate secondary oli et al., 1993). Many cossid species are agricul- forests in Japan, exudes a large amount of sap. Var- tural and forestry pests that bore into orchard trees ious insects are attracted to the fermented sap of Q. and various other cultivated trees in many parts of acutissima, including flies, beetles, wasps, butter- the world (e.g., Solomon, 1988; Faccioli et al., flies, and moths (Yoshimoto et al., 2005). At these 1993; Wang and Zhang, 1993). In contrast, such sap sites, carpenterworm larvae (Lepidoptera, Cos- serious damage has not been reported for the three sidae) are frequently observed under bark or in Cossus species in Japan (C. cossus, C. jezoensis, gaps in the bark. This implies a relationship be- and C. insularis), except for eruptive outbreaks on tween carpenterworm boring and sap exudation. apple trees (Odagiri et al., 1985) and Japanese pear Furthermore, a previous study found that resource trees (Nakanishi, 2005). Few ecological surveys abundance (exudate quantity) determines the species have been conducted for these species in an agri- richness and total abundance of insect communities cultural or forestry setting, much less in a natural on tree sap (Yoshimoto et al., 2005). Carpenter- environment such as on oaks. Little information is worms may therefore have an indirect effect on tree available on the fundamental ecology of carpenter- sap communities if they influence resource (sap) worms in Japan, although the sex pheromone of C.
*To whom correspondence should be addressed at: E-mail: [email protected] DOI: 10.1303/aez.2007.403
403 404 J. YOSHIMOTO and T. NISHIDA insularis was recently identified (Chen et al., 2006). This study quantified the distribution and abun- dance of carpenterworms on Q. acutissima trees and elucidated the effects of carpenterworm boring on oak sap exudation. First, we censused carpenter- worms on several sap-exuding trees from 2002 to 2004. Then, patch size (the area of exuding spots) and resource abundance were measured in relation to carpenterworm abundance. Finally, the effects of carpenterworms on exudate quantity were exam- ined by conducting removal experiments.
MATERIALS AND METHODS Study sites. This study was conducted in tem- Fig. 1. A photograph of a carpenterworm larva (indicated perate secondary forests in Iwakura (35°05 N, by a circle) inhabiting in its nest made of frass (indicated by a 135°47 E) and on Mount Uryu (35°02 N, 135°48 E) broken line) and of sap-attracted insects (a noctuid moth and a cockroach). in Kyoto, Japan. Both sites are dominated by oak trees, with conifers and various broad-leaved trees also present. Iwakura is dominated by Q. acutis- carpenterworms were examined at Iwakura from sima, whereas Mt. Uryu is dominated by both Q. May to September from 2002 to 2004. Observa- acutissima and Q. serrata. tions were conducted on 3 days per month, except Ecology of carpenterworms. An adult carpen- for May 2002 (4 days), May 2003 (2 days), and ter moth that emerged out of a Q. acutissima tree August 2004 (2 days). A patch (an exuding spot) in Iwakura was identified as C. jezoensis (Ma- was defined as a discrete area on a tree covered tsumura). This species (oriental carpenter moth) with sap exudate. A newly formed patch was indi- bores mainly into Quercus trees, whereas C. insu- vidually sampled when the patch was connected laris utilizes willows much more often than oaks with neighboring patches by sap flow or when it (Nakamuta et al., 2007), and C. cossus is rarely was divided into several sub-patches by sap drying found on oaks in western Japan (K. Ueda, pers. after a decrease in exudation. The number of indi- comm.). Accordingly, we hereafter regarded all viduals in patches on two Q. acutissima trees (trees carpenterworm individuals on Q. acutissima in the A and B) was recorded for 3 years and another Q. study sites as individuals of C. jezoensis. acutissima tree (tree C) was also sampled in 2004. Adult C. jezoensis emerge from June to August, We sampled visible individuals and as many indi- laying their eggs in bark crevices. Larvae hatch ap- viduals hiding inside their nests as possible by proximately 2 weeks after oviposition, and the slightly stripping the nests if necessary. The pres- larval period can be 2 years long (Enda, 1994; Ya- ence or absence of nests (or parts of nests) was also jima, 2005). Larvae bore into phloem and xylem, determined when no carpenterworm was observed. creating galleries, although young, small larvae The census was omitted for tree B on 2 days in rarely tunnel into wood (T. Ichikawa, unpublished June 2002, 1 day in July 2002, and 1 day in July data). They construct nests with frass under bark or 2003. in bark gaps and inhabit them (Fig. 1). Larvae can Resource quantification. The surface area of a become quite large in the final instar ( 50 mm in patch was quantified to represent patch size. On 8 body length or 5 mm in head width). They feed days from July to October 2003, photographs were on wood and tree sap, also preying on other insects taken with a digital camera for randomly chosen attracted to sap (T. Ichikawa, unpublished data), al- patches on the trees after each carpenterworm cen- though their feeding habits have yet to be clarified sus. The patches in the photos were blacked out in detail. using Adobe Photoshop 5.0 (Adobe Systems, San Sampling. The distribution and abundance of Jose, CA). Then, each blackened area was meas- Carpenterworms and Sap Exudation 405 ured using Lia32 (free software developed by K. carpenterworms was recorded for each patch. All Yamamoto) for Windows 95. carpenterworms in the treatment patches were re- The weight of sap that had accumulated on a moved with a pair of tweezers, except for two indi- patch and the weight of sap exuded per hour were viduals which were removed with a syringe needle both measured to represent resource abundance. that had the point stopped with bond. Control On 6 days from July to October 2003, sap present patches were disturbed equivalently to treatment on a patch was wiped off with paper towels within patches by partly stripping the nests. The manipu- 2h after taking photos or censusing. Then, exuded lations described so far (sampling and removal) sap was absorbed on paper towels for 1 h following were performed between 20:00 and 22:00 h. Then, the methods of Yoshimoto et al. (2005). The sap- the weight of exuded sap was measured for 1 h soaked towels were stored in a plastic bag and after 22:00 for all the patches, using the methods of weighed in the laboratory. Any incidental material Yoshimoto et al. (2005). Finally, the whole area of (e.g., dust, litter, small insects) on the paper was re- each patch was caged with a wire mesh (3 mm moved before weighing. Sap quantity was deter- mesh; Yoshida Taka & Co. Ltd., Osaka, Japan) to mined by subtracting the mean weight of the paper prevent inter-patch movement of carpenterworms. towels (mean SE 2.231 0.027 g, n 10) and the The periphery of the wire mesh was joined to sev- plastic bag (3.622 0.016 g, n 10) from the total eral sheets of fine polypropylene mesh (Dio Global weight of each sample. For three samples that were Net; Dio Chemicals, Ltd., Tokyo, Japan), which put in other types of plastic bags, each of the bags were pinned on the trunk. All of these procedures was weighed for the calculations. For a sample were repeated 3, 5, 7, and 11 days after carpenter- with part of the paper towel partly missing due to worm removal. Despite thorough caging, a few car- an incidental tear, its weight was estimated from penterworms (mostly small) were found at the the percentage of the remaining area to the whole treatment patches after the initial removal. This area of the towel, which was measured using may have been due to invasion through the narrow Lia32. For a patch measured for more than 1 h, its gaps between the mesh and trunk and to unde- weight was calculated on a per-hour basis. tectable individuals hiding under bark or inside The accumulated amount of sap was also weighed wood. These individuals were removed immedi- on 6 days from July to September 2004, as in 2003. ately after being found at the treatment patches. The weights of paper towels and the plastic Both meshes that had a caged control patch and a bag used for the calculations in 2004 were treatment patch on tree E were removed by some 2.257 0.012 g (n 10) and 3.649 0.007 g (n 10), unknown factor after 3 days. These patches were respectively. For some extremely resource-poor still used for the experiment after being re-caged patches, it was impossible to estimate accumulated because the number of carpenterworm individuals amount properly because the paper towels did not in those patches was almost equal to that in other absorb much sap; negative values were obtained in patches on that day. We could not remove a large several cases, probably because the total sap weight individual in a treatment patch on tree D and we was within the error of towel weight. These nega- accidentally removed an individual in a control tive values were analyzed together with other posi- patch on tree F on day 5. These two patches were tive values. excluded from the analyses. Removal experiment. Carpenterworms were ex- After quantifying the wet weight of sap in the perimentally removed to examine their role in sap laboratory, the sap-soaked towels and the plastic exudation in late September 2005. Ten patches on bags were dried in an outdoor cage for 2 to 3 days three Q. acutissima trees (tree D, n 7; tree E, to measure dry weight. Both wet and dry weights n 2; tree F, n 1) at Mt. Uryu were used as the ex- were derived through the same calculations de- perimental patches. Patch area was arbitrarily de- scribed previously. The weights of paper towels termined in the experiments; some large, con- and the plastic bag used for the calculations nected patches with several exuding spots were di- were 2.287 0.020 g (n 10) and 3.739 0.005 g vided into smaller patches to increase sample size. (n 10), respectively. Negative values were ob- Half of the patches were assigned to control (n 5) tained in several cases of dry weight, probably be- or treatment (n 5) categories after the number of cause the total dry weight was within the error of 406 J. YOSHIMOTO and T. NISHIDA towel weight. These negative values were analyzed together with other positive values. Data analyses. An analysis using the index of mean crowding (the m-m* regression method; Iwao, 1968) was used to quantify the distribution of carpenterworms at the patch level in each year. The index (m*) and mean number of individuals per patch (m) were obtained for each census day, and m* was regressed against m. The slope (b) is 1 when individuals are aggregated, b 1 when individuals are randomly distributed and b 1 Fig. 2. The percentage of patches (exuding spots on trees) categorized by the presence or absence of carpenterworms and when individuals are evenly distributed. their nests over the 3 years. The ‘Larvae’ category (patches Patch area did not differ significantly between harboring carpenterworms) was subdivided according to the the patches with carpenterworms and those with number of individuals per patch. ‘None’: patches without car- only nests. These two categories were therefore penterworms or their nests, ‘Nest unidentified’: the cases when combined and called ‘carpenterworm-related we did not check for the nests or could not distinguish them at patches, n: the total number of patches sampled each year. patches’. Welch’s test was used to test for differ- ences in patch area between carpenterworm-related patches and patches without carpenterworms or their nests. One sample (a carpenterworm-related patches had neither carpenterworms nor their nests patch) that was observed in October 2003 was in- in 2003 (36.1%) and in 2004 (30.9%), but the per- cluded in the analysis to increase sample size. The centage was much lower in 2002 (3.0%). same analysis examined differences in accumu- In the m-m* regression analysis, the slope was lated sap amount in 2004. The analysis was used 1 and significantly different from zero in both for neither the accumulated amount nor exudate 2002 (b 1.775, n 12, p 0.01) and 2004 (b produced per hour in 2003 because of insufficient 1.532, n 12, p 0.01), whereas it was nearly equal sample size. to 1 and was not significantly different from zero in The difference in wet weight of exudate per hour 2003 (b 1.184, n 11, p 0.504). The intercept between the control (n 4) and treatment (n 4) did not significantly differ from zero in any of the 3 patches in the removal experiment was tested using years (2002, a 0.453, p 0.597; 2003, a 0.366, repeated measures ANOVA after the data were p 0.663; 2004, a 0.263, p 0.581). These results log-transformed. Differences in sap concentration indicate aggregated distributions in patches in both index, defined as the ratio of dry weight to wet 2002 and 2004, and a random distribution in weight, were analyzed similarly. Carpenterworms patches in 2003. were considered to significantly affect exudation if The total number of patches gradually increased the interaction between treatment (removal) and from May, reaching a peak in September, after a time (date) was significant. These analyses were slight decline in July (2002 and 2003) or August conducted using STATISTICA (StatSoft, Inc., (2004; Fig. 3). The number of patches harboring Tulsa, OK). carpenterworms reached a peak during different periods in each year (August 2002, September 2003, and July 2004). Patches with only nests were RESULTS frequently observed in September during all 3 Distribution and abundance of carpenterworms years, although another peak occurred in June in More than one-third of all patches harbored both 2003 and 2004. carpenterworms in 2002 (39.4%) and in 2004 Carpenterworm abundance was much lower in (36.5%), but fewer were observed in 2003 (22.4%; 2003 than in the other 2 years (Fig. 4). On both Fig. 2). Among these patches, most had only one trees in 2002, abundance began to increase in late individual in all years. Roughly one-fifth of all July and reached a peak in late August (Fig. 4a). patches had only nests (2002, 22.7%; 2003, 21.8%; Tree A had another small peak in late June 2002. 2004, 18.5%). Approximately one-third of all In 2003, carpenterworm abundance had two peaks Carpenterworms and Sap Exudation 407
cantly correlated with the accumulated amount of sap (Kendall t 0.653, n 25, p 0.001) and with exudate produced per hour (Kendall t 0.753, n 25, p 0.001). The accumulated exudate was significantly related to exudate produced per hour (b 1.824, R2 0.925, n 27, p 0.001), demon- strating that the accumulated amount can be an in- dicator of resource abundance.
Removal experiment Exudate quantity decreased more in the treat- ment patches than in the control patches after 20 September (Fig. 5a), which was detected as a sig- nificant interaction between removal and date (Table 2). The removal effect was not significant, and exudate quantity significantly varied with date regardless of removal. For the sap concentration index, the effect of date was significant, indicating that concentration also varied periodically (Fig. 5b, Table 2). Neither removal nor the interaction was significant.
DISCUSSION Distribution and abundance of carpenterworms Of all patches, 20–40% harbored carpenter- worms and roughly 20% had only nests in all years (Fig. 2). The presence of carpenterworm nests can Fig. 3. Seasonal fluctuation in the number of patches, cat- indicate either that the insects had previously been egorized by the presence or absence of carpenterworms and at the patches or that they were still hiding unde- their nests (the same categories as used in Fig. 2) in (a) 2002, tected. These results suggest that carpenterworms (b) 2003, and (c) 2004. occurred in 40–60% of all patches. The removal experiment showed a positive effect of carpenter- on tree B, in late June and early September, while worms on exudation, indicating that 40–60% of the pattern differed on tree A (Fig. 4b). In 2004, a patches were likely to have been created by carpen- unimodal fluctuation was seen for all three trees; terworms, although the experiments did not carpenterworm abundance reached a peak in late demonstrate that sap exudation is triggered by car- July and decreased after August (Fig. 4c). Tree B penterworm boring. The proportion of patches had the highest abundance peak, although it had a without carpenterworms or their nests was ex- lower abundance than tree A after mid-August. tremely low in 2002, which is possibly due to in- Tree C had the lowest abundance throughout the sufficient sampling; the percentage may be under- observation period. estimated because of several cases in which nests were not checked or not distinguished. Carpenterworm–sap relationship The results of the m-m* analysis showed that Carpenterworm-related patches had a signifi- carpenterworms were aggregated in patches during cantly larger surface area and more accumulated 2002 and 2004. They frequently moved out of sap than patches without carpenterworms or their patches, as observed in the experiment, presumably nests (Table 1). Correlation analyses of the data in- to seek better nesting sites. Such active inter-patch cluding tree C in Iwakura and the two trees on Mt. movement may contribute to their aggregation in Uryu in 2003 showed that surface area was signifi- favorable habitats. Individuals often make sounds 408 J. YOSHIMOTO and T. NISHIDA
Fig. 4. Seasonal fluctuation of carpenterworm abundance on trees A and B in (a) 2002 and (b) 2003, and (c) on trees A–C in 2004. The census was omitted for tree B on two days in June 2002, one day in July 2002 and one day in July 2003.
Table1. Resource variables by patch category (‘carpenterworm-related’: patches with carpenterworms or their nest; ‘none’: patches without carpenterworms or nests)
2003 2004 Resource variables Patch category Mean SE nt p Mean SE nt p
Surface area (cm2) Carpenterworm-related 628.531 254.442 13 —— 2.393 0.034 —— None 18.794 13.585 4 — — Accumulated Carpenterworm-related 0.454 0.268 7 2.171 0.677 40 —— 2.781 0.008 amount (g) None 0.112 0.026 2 0.275 0.081 9 Exudate amount (g/h) Carpenterworm-related 0.948 0.395 7 —— —— —— None 0.167 0.030 2 — —
The difference in each variable was examined using Welch’s test. to threaten others by banging their heads violently they aggregate at favorable patches. In 2003, we onto wood (T. Ichikawa, unpublished data). This observed a random distribution of carpenterworms. aggressive behavior would not greatly affect their This distribution pattern may have been related to distribution on trees, although it may contribute to the much lower abundance of carpenterworms in the avoidance of severe fights with other individu- 2003, when overcrowding at favorable patches als and possibly to their spaced distribution when should have occurred less frequently. Carpenterworms and Sap Exudation 409
nests were most abundant in September, which dif- fered from the peak period of carpenterworm abun- dance in 2002 and 2004. Individuals often moved out of patches, as mentioned above, whereas old nests usually remained for a while after being abandoned. Accordingly, the time lag in the peak period in 2002 could have been attributable to fre- quent nest creation associated with carpenterworm increase. In 2004, however, patches with nests were most abundant in June when carpenterworm abun- dance had yet to peak. This may imply that carpen- terworm abundance was underestimated in June 2004. Since the phenology of the carpenter moth is poorly understood, as described in the Introduction, further study on the larval period and adult occur- rence are necessary to fully determine the relation- ship between patch occurrence and carpenterworm abundance.
Fig. 5. Temporal variation of (a) exudate quantity Boring effects of carpenterworms (mean SE) and (b) sap concentration index (mean SE) at the Carpenterworm-related patches had more sur- control (closed circles) and treatment (open circles) patches in face area and more accumulated sap than patches the removal experiment. without them or their nests, and their experimental removal resulted in a decreased amount of exudate. Table2. The results of repeated measures ANOVA testing These results suggest that carpenterworms promote the effect of carpenterworm removal on wet weight and sap exudation through boring into wood. The re- concentration of sap exudate in the field experiments moval effect itself was not significant, which is due to the smaller difference between control and treat- Source df MS Fp ment patches in the first half of the study period. Exudate quantity The sap amount began to decrease a few days after Removal 1 1.009 2.495 0.165 carpenterworm removal, indicating that exudation Date 4 0.066 5.883 0.002 continues for a while after boring has stopped. Al- Removal Date 4 0.050 4.457 0.008 though we could not completely exclude carpenter- Error 24 0.011 Sap concentration index worms in the treatment patches, it is certain that Removal 1 31.535 0.869 0.387 the density of large individuals, which are likely to Date 4 87.861 5.912 0.002 have stronger effects on exudation, was lowered Removal Date 4 15.857 1.067 0.394 considerably through caging and repeated removal. Error 24 14.862 Accordingly, our results demonstrate the role of carpenterworms in sap exudation, and the effect of incomplete removal on the results seems to have The peak period of abundance roughly corre- been minor. sponded to peak abundance of patches having car- The experimental removal of carpenterworms penterworms in each year, although the seasonal did not significantly change sap concentration fluctuation pattern varied yearly and among trees index, which might suggest that their effects are (Figs. 3 and 4). Fewer patches with carpenter- minor on sap quality. Since our methods of esti- worms were observed in 2003 than in the other mating sap concentration were rather rough, it is years and carpenterworm abundance was also still unclear if carpenterworms alter sap quality lower throughout the study period in 2003. These through boring. The influence of carpenterworms results imply that the fluctuation of carpenterworm is likely relatively greater on sap quantity than on abundance affects patch occurrence. Patches with sap quality. Both the amount and concentration of 410 J. YOSHIMOTO and T. NISHIDA sap exudate varied greatly among dates, regardless M. Sakai and K. Ueda for identifying the carpenter moth. This of carpenterworm presence, which may have been work was supported in part by the 21st century COE program attributable to abiotic factors such as temperature, for Innovative Food and Environmental Studies pioneered by Entomomimetic Sciences, from the Ministry of Education, humidity, and water content of soil, or to changes Culture, Sports, Science and Technology of Japan. in tree metabolism. It is fairly unusual for a mass flux of tree sap to REFERENCES occur so frequently and for so long a period as is Akaishi, D., N. Kamata and K. Nakamura (2006) Initial observed on oak trees in Japan. 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