The spotted lanternfly (SLF), Lycorma delicatula (Hemiptera: Fulgoridae), has the potential to become a global pest and is currently expanding its range in the United States. In this study, we investigated the dispersal patterns of SLF in Ailanthus altissima during its oviposition period in South Korea using fluorescent marking system. Oviposition patterns of SLF were then analyzed by surveying egg masses in A. altissima patches. The recapture rate of fluorescent-marked SLF rapidly decreased < 30% within the first two weeks. During the oviposition period, seven cases of among-patch dispersal of SLF adults were observed with a minimum estimated dispersal distance mainly ranging between 10 - 60 m and a maximum of 1,740 m. Also, the number of A. altissima trees detected with fluorescent-marked SLF increased until late September. Based on the egg mass survey, a total of 159 egg masses were detected from 38 out of 247 A. altissima trees. Furthermore, ca. 80% of egg masses were located < 2.5 m above the ground. Finally, the number of egg masses showed significant positive correlations with the height and diameter at root collar of A. altissima trees; both tree height and DRC were significantly larger from the trees with egg masses.
Research Article
Dispersal and Oviposition Patterns of Lycorma Delicatula (Hemiptera: Fulgoridae) During Oviposition Period in Ailanthus Altissima (Simaroubaceae)
https://doi.org/10.21203/rs.3.rs-1201537/v1
This work is licensed under a CC BY 4.0 License
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Invasive species
spotted lanternfly
tracking
fluorescent marking
overwintering
insect behavior
Lycorma delicatula (White) (Hemiptera: Fulgoridae), spotted lanternfly (SLF), is an invasive agricultural pest native to China.1,2 This pest has invaded South Korea, Japan, and the United States, causing serious problems in agricultural and forest landscapes.1,3−6 In South Korea, SLF was first reported in 2004, and the area of infestation increased over 8,000-fold from 2006 to 2010.7–10 In the US, it was first detected in Berks County, Pennsylvania in 2014. Since then, SLF infestation has expanded to three different states including New Jersey, Virginia, and Delaware by 2019.3,6 Furthermore, recent modeling studies predicted that SLF would become a global threat, in which Asia, Oceania, South America, North America, Africa, and Europe might be susceptible to its invasion based on their temperature profiles.1,6
SLF has a broad range of host plants which facilitate the successful establishment of this pest in new areas. It is known to feed on more than 70 plant species including various ornamental and fruit trees such as apples (Malus spp.) (Rosaceae), grapes (Vitis vinifera) (Vitaceae), and peaches (Prunus persica) (Rosaceae), as well as other woody trees such as black locust (Robinia pseudoacacia) (Fabaceae), willow tree (Salix spp.) (Salicaceae), and Korean evodia tree (Evodia danielli) (Rutaceae).4,10 Moreover, in invaded areas including South Korea and the US, SLF is known to switch hosts during its development, with the range of host plants becoming narrower through its univoltine life cycle.10 After emerging from eggs starting in May, its nymphs feed on a variety of host plants from 81 taxa worldwide.11–14 As they start to develop into adults from late July, SLF adults feed on a narrower range of host plants of 47 taxa. Finally, the adults oviposit egg masses on hosts belonging to 28 taxa between late September and November.4,10−12
Among various host plants of SLF, Ailanthus altissima (Simaroubaceae), the tree-of-heaven, is native to Southeast Asia and known as one of the major host plants in China, South Korea, and the US.4,15 Furthermore, A. altissima has already been introduced and established in multiple continents including East Asia, Europe, and North America, making it readily available for SLF even in areas in which the insects have yet to invade.16 Previous studies indicate the importance of A. altissima as a major host plant of SLF. First, A. altissima is known as the most preferred and suitable feeding host of SLF along with V. vinifera. Lee et al.15 observed a high survivorship of SLF nymphs and adults on A. altissima as well as their preference for this plant compared with different ornamental and fruit trees. Second, A. altissima was reported to be one of the most preferred oviposition sites. 4,10 Liu et al.17 found that A. altissima was one of the four oviposition host plants favored by this insect along with black cherry, black birch, and sweet cherry in Pennsylvania, US. Finally, A. altissima contains high concentrations of cytotoxic alkaloids, which SLF may utilize for their own defence against predators.4,12,18
Therefore, it is essential to understand the abundance and distribution of SLF on A. altissima in order to develop effective management programs. Previous studies demonstrated that SLF adults shift host plants from woody and non-herbaceous plants, on which the insects feed as they emerge in July, towards A. altissima between September and November.11,12,17 In addition, SLF adults are known to mate and reproduce during this period utilizing multiple substrates including A. altissima for oviposition.19 However, the dispersal patterns of SLF adults within and among A. altissima patches after their arrival have not yet been investigated. Especially, given that SLF is a univoltine species in the invaded areas, investigating the dispersal patterns of this pest on A. altissima and characterizing their oviposition pattern can provide valuable information for its management.
In our study, we surveyed the abundance and distribution of SLF on A. altissima patches from September to November when SLF adults are known to shift their host plant to A. altissima and lay eggs.12,17 In particular, to investigate the dispersal pattern of SLF within and among different A. altissima patches, we tracked the movement of SLF using a fluorescent marking system (FMS).20,21 Then, in December, we surveyed the location, number, and size of SLF egg masses on A. altissima trees and analyzed the oviposition patterns relative to the traits of A. altissima surveyed.
Effect of fluorescent marking on SLF
Fluorescent marking did not significantly affect the survivorship and flight behavior of SLF adults. First, the survivorship of SLF was not significantly affected by fluorescent marking (χ2 = 0.81, df = 1, P = 0.37; Fig. 1a). Second, no significant effect of fluorescent marking on flight behavior of SLF was observed. Fluorescent-marked and unmarked control groups did not show significant differences in the number of pecking conducted to initiate flight (t = 0.93, df = 1, P = 0.36; Fig. 1b), flight duration (t = 0.71, df = 1, P = 0.48; Fig. 1c), and flight distance (t = 1.23, df = 1, P = 0.22; Fig. 1d). Moreover, the overall propensity of flight direction was not substantially different between fluorescent-marked and unmarked groups; the major flight direction of SLF generally aligned along the north and northeast axes (Fig. 1e).
Dispersal pattern of SLF on A. altissima
Overall, fluorescent-marked SLF adults showed a large decrease in their numbers during the first two weeks of survey yielding average recapture rates of 8.7 ± 6.6% (Mean ± SE) and 10.5 ± 4.3% in Tan stream and Gyeongan stream, respectively (Fig. 2). After the first two weeks, fluorescent-marked SLF adults were occasionally detected from both streams until late October, with no fluorescent-marked individuals observed in November.
With regard to among-patch dispersal of fluorescent-marked SLF, a total of 12 events were recorded in which SLF individuals marked from different patches at the onset of the experiment were observed (Fig. 2; Table 1). Because fluorescent marking in this study did not allow us to identify different individuals, we were able to confirm seven among-patch dispersals among the 12 events recorded (Table 1). For example, it cannot be confirmed whether an SLF individual observed in patch E on October 6th was a new individual that had moved from patch F or the same individual observed on September 25th that remained in patch E. Based on this, among-patch dispersal of SLF was observed from September 25th, where an estimated minimum dispersal distance ranging mainly between 10 and 60 m with a maximum of 1,740 m was observed. Among-patch dispersal was recorded in all study patches except for patch B (Fig. 2; Table 1). In addition, fluorescent-marked SLF was also observed from neighboring patches adjacent to study patches. In Tan stream, fluorescent-marked SLF from patch B was detected two times in the neighboring patch on September 28th and October 1st (Fig. 3). In Gyeongan stream, fluorescent-marked SLF from patch E was observed three times from a neighboring patch located between patch F and G, on September 22nd, 25th, and 29th, and another fluorescent-marked individual from patch G was detected on September 29th (Fig. 3).
| Site | Date | Original patcha | Observed patch | No. of L. delicatula observed | Among-patch dispersal | Estimated minimum distance moved |
|---|---|---|---|---|---|---|
| Tan stream | Oct 5th | Patch C | Patch A | 1 | Confirmed | 1,740 m |
| Oct 5th | Patch A / Patch D | Patch C | 1 | Confirmed | 1,740 m / 10 m | |
| Oct 8th | Patch A / Patch D | Patch C | 1 | Unidentified | - | |
| Oct 12th | Patch A / Patch D | Patch C | 1 | Unidentified | - | |
| Oct 5th | Patch C | Patch D | 1 | Confirmed | 10 m | |
| Gyeongan stream | Sep 25th | Patch F | Patch E | 1 | Confirmed | 20 m |
| Oct 6th | Patch F | Patch E | 1 | Unidentified | - | |
| Sep 29th | Patch E | Patch F | 1 | Confirmed | 20 m | |
| Sep 29th | Patch F | Patch G | 1 | Confirmed | 60 m | |
| Oct 2nd | Patch F | Patch G | 2 | Confirmedb | 60 m | |
| Oct 6th | Patch F | Patch G | 1 | Unidentified | - | |
| Oct 13th | Patch F | Patch G | 1 | Unidentified | - | |
| a Original patch indicates the patch in which the observed L. delicatula was fluorescent-marked at the onset of the experiment. | ||||||
| b One individual was confirmed. | ||||||
Fluorescent-marked SLF also displayed within-patch movement in most of the study patches during the observation period (Fig. 4). For within-patch movement, patches A and B were not included in analysis due to low numbers of A. altissima (< 5 trees) in the patches (Table 1). Except for patch C, the cumulative proportions of A. altissima trees on which marked SLF were detected gradually increased in September. In patch D of Tan stream, the number of trees with fluorescent-marked SLF detection showed a gradual increase from the initial 9–36% by September 28th until the end of the survey (Fig. 4c). Similar to patch D, the proportion of A. altissima trees with fluorescent-marked SLF detected at least once showed a gradual increase until October 2nd in Gyeongan stream. The overall number of trees increased gradually from the initial 3%, 11%, and 6–17%, 56%, and 26% in patches E, F, and G, respectively (Fig. 4).
Oviposition pattern of SLF
The height and diameter at root collar (DRC) of A. altissima trees surveyed are presented in Fig. 5. In Tan stream, the tree heights of A. altissima ranged from 0.40 - 5.15 m, and in Gyeongan stream, the heights ranged from 0.20 - 5.90 m (Fig. 5a,b). Among the 116 trees surveyed in Tan stream, those < 2.5 m in their heights comprised 89%, and similarly, in Gyeongan stream, 86% of the 131 trees surveyed were < 2.5 m (Table 2; Fig. 5a,b). The DRC of A. altissima trees ranged from 0.32 - 11.15 cm and from 0.64 - 14.33 cm in Tan and Gyeongan streams, respectively (Fig. 5c,d). Trees with DRC < 5 cm were dominant comprising 85% and 72% of A. altissima trees in Tan stream and Gyeongan stream, respectively. Trees of which trunks were cut off by local administration were present only in Gyeongan stream comprising 45% of A. altissima trees in the stream.
| Site | Patch | # of tree | Egg mass detected | # of egg in egg mass | Scattered eggs detected | ||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Surveyed | Detected | Trunk cut off | < 2.5 m | > 2.5 m | Total | Total | Mean ± SE | # | # of eggs | ||
| Tan stream | A | 4 | 0 | 0 | 0 | 0 | 0 | - | - | 0 | 0 |
| B | 4 | 0 | 0 | 0 | 0 | 0 | - | - | 0 | 0 | |
| C | 61 | 8 | 0 | 14 | 2 | 16 | 410 | 29.29 ± 2.51 | 0 | 0 | |
| D | 47 | 12 | 0 | 53a | 0 | 53 | 1,792 | 33.81 ± 2.56 | 6 | 237 | |
| Subtotal | 116 | 20 | 0 | 67 | 2 | 69 | 2,202 | 32.87 ± 2.10 | 6 | 237 | |
| Gyeongan stream | E | 69 | 13 | 23 | 49 | 31 | 80 | 1,804 | 37.58 ± 3.85 | 0 | 0 |
| F | 9 | 2 | 0 | 4 | 0 | 4 | 122 | 30.50 ± 2.90 | 0 | 0 | |
| G | 53 | 3 | 36 | 6 | 0 | 6 | 129 | 21.50 ± 1.71 | 1 | 15 | |
| Subtotal | 131 | 18 | 59 | 59 | 31 | 90 | 2,055 | 35.43 ± 3.26 | 1 | 15 | |
| Total | 247 | 38 | 59 | 126 | 33 | 159 | 4,257 | 34.06 ± 1.88 | 7 | 252 | |
| a In patch D, two egg masses without waxy layer were observed. | |||||||||||
From the two streams, a total of 159 egg masses were found from 38 out of 247 A. altissima trees (Table 2). In Tan stream, 67 out of 69 egg masses were located < 2.5 m above the ground, whereas 59 out of 90 egg masses were detected < 2.5 m above the ground in Gyeongan stream. In both streams, ca. 30% of the egg masses were located < 20 cm above the ground. However, a substantial proportion of egg masses in Gyeongan stream were detected > 2.5 m above the ground, yielding 34% of the total egg masses (Table 2). From the egg masses located < 2.5 m above the ground, a total of 4,257 eggs were detected from 126 egg masses, yielding an average of 34.06 ± 1.88 (Mean ± SE) eggs per egg mass (Table 2). In addition, a total of 252 scattered eggs were recorded from seven A. altissima trees.
When the effects of tree height, DRC, and their interaction, and cut status on the number of egg masses on A. altissima trees in study patches were evaluated using GLM, significant effects of tree height (χ2 = 9.23, df = 4,242, P < 0.01) and DRC (χ2 = 15.14, df = 4,242, P < 0.0001) were detected. Both the tree height and DRC were significantly greater from A. altissima trees with egg masses in Tan stream (height: t = 4.16, P < 0.001; DRC: t = 4.79, P < 0.0001) and Gyeongan stream (height: t = 4.49, P < 0.001; DRC: t = 5.29, P < 0.0001) (Fig. 6).
As a rapidly expanding invasive pest, SLF poses severe threat to agricultural and forest ecosystems. Indeed, there have been continuous research efforts to understand the biology of SLF, especially its seasonal activity and host plant range throughout its developmental stages.12,17,26 In addition, given that SLF is a univoltine insect in the invaded areas including South Korea and US, understanding its dispersal pattern during its oviposition period plays a major role in developing proactive and site-specific management programs targeting the location of egg masses. Therefore, in this study, we addressed within- and among-patch movements of SLF on A. altissima patches, which is known as one of the major host plants for oviposition. We also identified A. altissima tree traits affecting oviposition pattern of SLF.
To reliably track SLF adults, we tested the effect of fluorescent marking on survivorship and flight ability and found no significant adverse effects of fluorescent-marking on SLF adults. Furthermore, the durability of the method was confirmed in the field survey of this study, in which fluorescent-marked individuals were recaptured after a maximum of 47 days. Previously, Nixon et al.27 reported that fluorescent marking did not significantly affect horizontal and vertical dispersal capacity of SLF nymphs and adults. Moreover, Keller et al.22 observed dispersal of SLF nymphs in a deciduous forest, where fluorescent-marked individuals were detected a maximum of 65 m away from the release point. Therefore, the fluorescent marking system can be an effective tool to study the movement of SLF for both nymphs and adults. In addition to the conventional use of fluorescent marking for nighttime tracking20,21,23,28, fluorescent marking was effective in this study for the detection of SLF under the shadow created by tree canopy even during daytime.
As previously reported from many mark-recapture studies, the recapture rate of fluorescent-marked SLF also showed a consistent decrease during the study period with a rapid decrease during the early survey period22,32,33. Indeed, the recapture rates dropped on average by 10% during the first two weeks. Nevertheless, our results provide empirical evidence for the first time demonstrating active dispersal of natural SLF population among A. altissima patches. During the survey, we recorded 12 cases between September and October in which SLF individuals that had been marked from different patches at the onset of the experiment, were found in study patches. Based on these observations, we confirmed that at least seven SLF individuals displayed among-patch dispersal. Marked SLF were recaptured up to 27 days after the onset of the survey. In general, the marked individuals were found in A. altissima patches located close to the original patches from which SLF were marked at the onset of the survey. The estimated minimum dispersal distance of marked SLF ranged between 10 and 60 m in most cases. Indeed, SLF has been reported to show descending flight behavior and short-range dispersals with each flight-bout ranging from 20 to 40 m in field conditions.26,29 Interestingly, one marked SLF in this study was found to have dispersed at least 1.7 km within 22 days suggesting strong dispersal capacity during its oviposition period. Although it has not been evaluated in field conditions, Wolfin et al.29 suggested that the potential flight distance of SLF could be > 3 km based on laboratory observation.
Based on the survey of egg masses, we found that the tree height and DRC of A. altissima had significant effects on the number of egg masses on A. altissima trees. In addition, our data suggest that SLF preferred larger A. altissima trees for oviposition in the areas of this study. These findings can serve as important information to prioritize sampling and management efforts based on tree characteristics especially when targeting the removal of egg masses from A. altissima. Indeed, a large-scale management practice was conducted in South Korea to identify and remove SLF egg masses during the early stages and outbreak of this invasive species34. With regard to vertical locations of egg masses on A. altissima, ca. 80% of the masses were found within 2.5 m above the ground. In the surveyed areas, A. altissima trees were < 6 m in their height due to their age and local management practices such as tree trunk cutting. This would make it easier for investigators to locate and remove SLF egg masses for management practice. However, caution is needed when surveying substantially larger A. altissima as reported in previous studies in the US. Keller et al.30 found that 75% of egg masses were located above 6 m on A. altissima trees when the tree heights ranged from 5.5 - 23.8 m, and the lowest number of egg masses was located zero to 3 m above the ground.
In this study, we found that SLF actively disperses in A. altissima patches during oviposition period and SLF selectively oviposits on A. altissima trees in relation to tree characteristics. That is, although SLF adults were frequently observed on A. altissima trees while feeding or resting during the study, only a small portion of those trees were used for oviposition sites by SLF. This selective oviposition of SLF may be attributed to the differential importance of A. altissima as feeding host versus oviposition substrate. SLF adults display higher preference towards A. altissima compared with other host plants from late August in South Korea and the US.12,17 Nevertheless, SLF are known to deposit eggs on surfaces of various substrates including 28 taxa of host plants and inorganic materials such as stones and metal fences.11,19 Indeed, a large number of SLF egg masses were detected on E. danielli and cement walls in the vicinity of A. altissima patches inspected in our survey (personal observation). Therefore, further studies are warranted to examine how SLF adults utilize different oviposition substrates following feeding on preferred host plants such as A. altissima and how this alternation would affect the likelihood of successful overwintering of egg masses or their survival against natural predators.
As one of the major host plants of SLF, A. altissima is already present in many countries expanding its geographical range, and the invasion of SLF is expected to be facilitated by the distribution of A. altissima. Especially in South Korea and the US, this invasive species displays preference toward A. altissima in September through November when adults mate and oviposit, highlighting the importance of A. altissima in the life history of SLF.4,12,17 In this study, we report for the first time dispersal patterns of natural SLF populations on A. altissima with a maximum of 1.7 km dispersal distance between A. altissima patches. We identified significant traits of A. altissima affecting the number of SLF egg masses on the trees. Our findings provide baseline information for developing proactive and efficient management strategies against SLF based on their dispersal and oviposition patterns on a major host plant.
Fluorescent marking
Dispersal of SLF adults was tracked using a fluorescent marking system (FMS), which has been demonstrated to be applicable for multiple insect species including SLF nymphs.20–22 To mark the SLF, either red, yellow, or blue fluorescent paint (BioQuip Products, USA) was diluted with distilled water (1:4). The mixture was then gently sprayed three times (ca. 20 mg each time) on each SLF individual using a mist sprayer from a distance of 30 to 50 cm (Supplementary information SI 1). Throughout the field survey, a handheld ultraviolet (UV) laser (PX 600 mW, class IIIB purple laser, 405 nm, Big Lasers, USA) was used to detect fluorescent-marked SLF individuals.23
Effect of fluorescent marking on SLF
Prior to field survey, the potential effects of fluorescent marking on the survivorship and flight behavior of SLF adults (sex ratio 1:1) were evaluated. SLF adults were collected using sweeping nets (BioQuip Products, USA) from Gyeonggi-do, South Korea (37o 47’ 85.95” N, 127o 11’ 64.58” E) in September 2020. Two hours after fluorescent marking of SLF, both fluorescent-marked and unmarked SLF were subjected to survivorship and flight behavior assessment.
Survivorship of insects was measured on two A. altissima trees (ca. 2 m in height) located in Gachon University, South Korea (37o 45’ 38.50” N, 127o 13’ 37.75” E). Two fluorescent-marked and two unmarked insects were placed in a cylindrical mesh cage (25 × 30 cm (radius × height)) enclosing a tree branch; a total of 20 groups were tested (n = 40). Then, survivorship of SLF was determined once every two days until no individuals were alive. Survivorship was compared between fluorescent-marked and unmarked SLF using Kaplan-Meir survivorship analysis (JMP 12, SAS Institute Inc., USA).
Effect of fluorescent marking on flight behavior of SLF was evaluated in an open space (986 m2) in Gachon University, South Korea (37o 45’ 08.37” N, 127o 12’ 79.69” E) at 26 ± 1°C and a relative humidity of 30 ± 5%. To induce flight of SLF adults, a wooden square rod (3 × 3 × 100 cm (width × length × height)) was established upright at the center of the arena. The SLF adult was placed individually 10 cm away from the top on the wooden square rod. Once the insect climbed up the rod and settled, it was gently pecked on the forewings using tweezers to initiate its flight.24,25 Once the insect took off, an operator followed the individual until it landed on the ground (n = 30). The number of pecks to initiate the flight, flight duration, and flight distance of SLF were compared using t-test (JMP 12, SAS Institute Inc., USA).
Field study sites
Dispersal patterns of SLF adults in A. altissima patches and their oviposition patterns were investigated in multiple A. altissima patches located along two streams in Gyeonggi-do, South Korea: Tan stream in Seongnam-si (37o 48’ 01.80” N, 127o 11’ 56.03” E) and Gyeongan stream in Gwangju-si (37o 41’ 54.21” N, 127o 27’ 12.37” E). Both Tan and Gyeongan streams run along suburban residential areas in respective cities, with pedestrian lanes built along the streams. We selected seven A. altissima patches as study patches when more than 10 SLF adults were found per patch (Fig. 3). In the study patch, all SLF individuals or ca. up to 30 adults were florescent-marked. In addition, when the number of SLF adults was less than 10 from an A. altissima patch, those patches were designated as neighboring patches (Fig. 3). Dispersal and oviposition of SLF adults were monitored from both study and neighboring patches during the study.
In Tan stream, four study patches (patches A-D) and one neighboring patch, which were distributed over ca. 1,760 m, were selected (Fig. 3a). Areas around the patches were generally covered with grass and shrubs, and the areas were occasionally managed by local administration. Deciduous trees were regularly planted along the pedestrian lanes. There were a total of four, four, 61, and 47 A. altissima trees in patches A to D, respectively (Table 2). Compared with Tan stream, A. altissima patches were located closely to each other in Gyeongan stream: three study patches (patches E-G) and three neighboring patches were spread over only ca. 90 m (Fig. 3b). Vegetation surrounding A. altissima patches consisted of grasses and small shrubs as well as deciduous trees planted along the border of residential area nearby. There were a total of 69, nine, and 53 A. altissima trees in patches E to G, respectively (Table 2). Unlike Tan stream, 45% of A. altissima trees had trunks having cut off by local administration in Gyeongan stream (Table 2; Fig. 5).
Dispersal pattern of SLF on A. altissima
Three fluorescent paint colors were used to mark SLF individuals in the study patches (Fig. 3; SI 1). Insects that took off during marking were captured and excluded from the experiment. Among the selected study patches, SLF adults were generally distributed throughout each patch, while SLF adults were observed only from one out of 61 A. altissima trees in patch C. As a result, in Tan stream, 15 (color of paint used to fluorescent-marking; red), 31 (yellow), 11 (blue), and 32 (red) adults were marked from patches A to D, respectively, whereas in Gyeongan stream, 30 (red), 30 (blue), and 33 (yellow) adults were marked from patches E to G, respectively. Starting from September 14th, 2020 in Tan stream and September 18th in Gyeongan stream, fluorescent-marked SLF adults on A. altissima trees in both study and neighboring patches were counted with a UV laser twice a week (Fig. 3). Survey continued until no individuals were observed from the study patches.
Oviposition pattern of SLF on A. altissima
Oviposition pattern of SLF was surveyed on all A. altissima trees in the study patches in December in both streams (Table 2). For the survey, SLF egg masses were categorized into three types as follows: egg mass with waxy layer, egg mass without waxy layer, and scattered eggs (SI 2). Eggs that were not covered with waxy layer and did not form aggregates were categorized as scattered (SI 2). In the field, A. altissima trees were visually inspected to identify SLF egg mass, and the number of egg masses and their distances from the ground were recorded. In addition, the number of eggs per egg mass was recorded for egg masses located < 2.5 m above the ground. When egg masses were covered with waxy layer, brushes were used to gently remove the powder-like waxy layer.
To characterize the A. altissima trees surveyed for SLF egg mass, we recorded the following morphological characteristics: tree height, DRC, and cutting status. Heights of A. altissima trees < 2 m were measured using an iron steel measuring tape, and those > 2 m were estimated with reference to the investigator’s height. DRC of A. altissima was determined by measuring the circumference of the stem at the root collar using a tape measure. In case of multi-stemmed A. altissima trees, the diameter of each stem was first determined individually, and the DRC of the tree was calculated using the following equation:
where n is the number of stems and di denotes the stem diameter of the A. altissima tree.
The effects of A. altissima height, DRC, their interactions, and cutting status of the trees on the number of egg masses were analyzed using a generalized linear model (GLM) assuming a Poisson distribution with a log link function for each stream (JMP 12, SAS Institute Inc., USA). The significant factors in A. altissima trees detected with egg masses were compared with those without egg masses using a t-test (JMP 12, SAS Institute Inc., USA).
POLICY STATEMENT
Experiments involving Ailanthus altissima were conducted in compliance with relevant institutional, national, and international guidelines and legislation.
ACKNOWLEDGEMENT
This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT). (No. 2021R1A2C1010679)
AUTHOR CONTRIBUTIONS
D-H. L., M. J., Y.S. L and D-H. G. conceptualized and designed the study; D-H. G, M. J. and J-W. K. performed the field experiments; M. J. and J-W. K. performed statistical analysis; M. J. and J-W. K. wrote the manuscript; D-H. L. and Y.S. L. critically reviewed and amended the manuscript.
COMPETING INTERESTS
The authors declare no competing interests.
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No competing interests reported.