Crapemyrtle bark scale (CMBS; Acanthococcus lagerstroemiae) has long been reported with a fairly wide host range. Online insect database has accumulated a good amount of host information for CMBS. For example, ScaleNet reported over 20 plant species from 15 families as CMBS hosts, including boxwood (Buxus microphylla), Chinese hackberry (Celtis sinensis), Axlewood (Anogeissus latifolia), Japanese persimmon (Diospyros kaki), food wrapper plant (Mallotus japonicus), Dalbergia eremicola, soybean (Glycine max), Kalm’s St. Johnswort (Hypericum kalmianum), American beautyberry (Callicarpa americana), crapemyrtle (Lagerstroemia indica), giant crapemyrtle (Lagerstroemia speciosa), pomegranate (Punica granatum), common fig (Ficus carica), myrtle (Myrtus spp.), border privet (Ligustrum obtusifolium), Japanese Ternstroemia (Ternstroemia japonica), Needlebush (Glochidion puberum), Paradise apple (Malus pumila), Chinese quince (Pseudocydonia sinensis), Brambles (Rubus spp.) (García Morales M, 2016).
Previous reported CMBS hosts were compiled from many literatures that dates to 1907, therefore some of information need to be verified and confirmed. Recently, as the distribution of CMBS continues to expand beyond its native regions, more specifically in the United States, concerns have been raised regarding the expanded host range for CMBS beyond Lagerstroemia, and the potential threats that CMBS poses to the native and economically important plants in the United States.
To address these issues, our group has conducted several studies on the feeding preference and host range of CMBS. Our trials confirmed new species as CMBS hosts and provided different/additional findings to our previous knowledge regarding CMBS hosts. Here is a summary of our current knowledge on CMBS hosts.
Multiple greenhouse trials were conducted between 2016 and 2020. All tested plants species were inoculated with CMBS-infested crapemyrtle twigs. CMBS infestation was identified as the presence of both male pupae and gravid female ovisacs during our experimental period, indicating the ability of CMBS to complete life cycle and reproduction on test plants.
The infestations of CMBS were confirmed on apple (Malus domestica), common quince (Chaenomeles speciosa), diamond-leaf persimmon (Diospyros rhombifolia), sinicuichi (Heimia salicifolia), ‘Spiced Plum’ crapemyrtle (Lagerstroemia ‘Spiced Plum’), southern crabapple (M. angustifolia), and twelve out of thirty-five pomegranate cultivars. However, the levels of CMBS infestation on these test plant hosts in this study were very low compared to Lagerstroemia and may not cause significant damage. No sign of CMBS infestation was observed on Arapaho blackberry (Rubus ‘Arapaho’), Navaho blackberry (R. ‘Navaho’), R. idaeus ‘Dorman Red’, ‘Prime Ark Freedom’ blackberry (R. fruticosus), ‘Green Gem’ boxwood (Buxus microphylla var. koreana × B. sempervirens), Harland boxwood (B. harlandii), or common persimmon (D. virginiana)in 2019. Although in a follow-up study with increased CMBS inoculation, only one gravid female ovisac was observed on common persimmon in 2020.
Compared to crapemyrtle, all other species had very LOW number of scales, if any. For example, at its peak ‘Spiced Plum’ crapemyrtle had 600 male pupae, sinicuichi had about 25 and all others had less than 10 (or even 5). The manuscript on this study ‘Feeding Preference of Crapemyrtle Bark Scale (Acanthococcus lagerstroemiae) on Different Species’ was published in June 2020 (https://www.mdpi.com/2075-4450/11/7/399).
Table 1 below summarized all our tested plants in four categories: Severe, Moderate, Minor, and None depending on the level of infestation recorded during our CMBS feeding experiments.
Table 1 Summary of crapemyrtle bark scale hosts with different level of infestation.
|Level of infestationZ||Severe||Moderate||Minor||None|
|Plant species/ common names||Callicarpa americana ‘Bok Tower’/Beautyberry||Callicarpa acuminata/ Mexican beautyberry Bodinier beautyberry||Callicarpa bodinieri ‘Profusion’/Bodinier beautyberry||Buxus harlandii/Harland boxwood|
|Callicarpa dichotoma ‘Issai’/Beautyberry||Callicarpa japonica var. luxurians/Beautyberry||Chaenomeles speciosa/ Common quince||Buxus microphylla var. koreana × Buxus sempervirens/boxwood|
|Callicarpa longissima ‘Alba’/Beautyberry||Callicarpa pilosissima/Beautyberry||Disopyros rhombifolia/Diamond-leaf Persimmon||Ficus pumila/Harland boxwood Climbing fig|
|Lagerstroemia ‘Spiced Plum’/Crapemyrtle||Callicarpa randaiensis/Beautyberry||Diospyros virginiana/Common Persimmon||Ficus roxburghii/Broad-leaf fig|
|Lagerstroemia caudata/Crapemyrtle||Callicarpa salicifolia/Willowleaf beautyberry||Ficus tikoua/Sandi leaf fig ivy||Rubus ‘Arapaho’/Blackberry|
|Lagerstroemia fauriei ‘Kiowa’/ Japanese Crapemyrtle||Heimia salicifolia/Sinicuichi||Glycine max/Soybean||Rubus ‘Navaho’/Blackberry|
|Lagerstroemia limii/Crapemyrtle||Hypericum kalmianum/Kalm’s st. johnswort||Malus angustifolia/ Southern crabapple||Rubus fruticosus/Blackberry|
|Lagerstroemia subcostata/Taiwan Crapemyrtle||Lagerstroemia speciosa/Giant crapemyrtle||Punica granatumY/ Pomegranate||Rubus idaeus ‘Dorman Red’/Raspberry|
|Lythrum californicum/ California loosestrife|
|Spiraea japonicaX/ Japanese meadowsweet|
Z Levels of CMBS infestation were defined as: Severe (>100 female ovisacs per plant), Moderate (10-100 female ovisacs per plant), Minor (<10 female ovisacs per plant), and None (no CMBS pupae or ovisacs).
Y Twelve out of thirty-five pomegranate cultivars were confirmed with minor CMBS infestation. CMBS infestations were found on ‘Double Pink’, ‘Gissarskii Rozovyi’, ‘Kandahar’, ‘Kara Bala Miursal’, ‘Kazake’, ‘Mollar’, ‘Pecos’, ‘Angel Red’, ‘San Antonio’, ‘Sogidavna’, ‘Sumbar’, and ‘Surh-Anor’. No sign of CMBS infestation were observed on ‘Al-Sirin-Nar’, ‘Apseronski Krasnyi’, ‘Austin’, ‘Azadi’, ‘Bala Miursal’, ‘Christina’, ‘Desertnyi’, ‘Elf’, ‘Entek Habi Saveh’, ‘Girkanets’, ‘JD’, ‘Kara Kalinski’, ‘Larkin’, ‘Molla Nepes’, ‘Mollar’, ‘Mridula’, ‘Russian 18’, ‘Salavatsk’, ‘Sirenevyi’, ‘Spanish Sweet’, ‘Sweet’, ‘Vkusanyi’, and ‘Wonderful’ in 2016 and 2019 trials.
X need to be confirmed through DNA identification.
Host suitability among Lagerstroemia
The primary hosts of CMBS, as where CMBS got the common name from, are considered to be crapemyrtle or Lagerstroemia spp.. However, other than the previously reported L. indica and L. fauriei, which are the most popular parentage of commercially available Lagerstroemia cultivars, the host suitability for CMBS among many other species in this genus remained unknown.
In an independent study (manuscript published at https://www.mdpi.com/2075-4450/12/1/6), six Lagerstroemia species (L. caudata, L. fauriei ‘Kiowa’, L. indica ‘Dynamite’, L. limii, L. speciosa, and L. subcostata) and California loosestrife (Lythrum californicum) were evaluated for CMBS suitability. Greenhouse experiment was conducted over a 25-week period and CMBS infestation were found on all tested plant species, although L. speciosa and Lythrum californicum had relatively low levels of infestation. For example, among the species with most severe infestations, L. limii had around 1,000 male pupae and 600 female ovisacs, respectively, per plant at the peak of CMBS population. In contrast, L. speciosa had the highest around 45 male pupae and 57 female ovisacs, respectively.
The result suggests that the susceptibility towards CMBS differs among different Lagerstroemia species, and the species with low CMBS infestation, such as L. caudata and L. speciose may be utilized in the future breeding programs to develop CMBS resistant Lagerstroemia cultivars.
Host suitability among Callicarpa and Ficus Species
American Beautyberry, or Callicarpa americana, was one of the earlier alternative host reported for CMBS in the United States (Wang et al., 2016). The fact that Callicarpa americana is a native species in the US was worrisome, therefore, there was a need to evaluate the potential threat of CMBS to the genus of Callicarpa.
A greenhouse trials confirmed CMBS infestation on nine Callicarpa species (C. acuminata, C. americana ‘Bok Tower’, C. bodinieri ‘Profusion’, C. dichotoma ‘Issai’, C. japonica var. luxurians, C. longissima ‘Alba’, C. pilosissima, C. randaiensis, and C. salicifolia) in 2019. Similar to all other species evaluated, the tested Callicarpa species can be categorized into three groups (severe, moderate, and minor) according to the level of CMBS infestation during the experiment. The most severe infestation recorded was on C. dichotoma ‘Issai’ (around 332 male pupae and 246 female ovisacs, respectively), while C. bodinieri ‘Profusion’ suffered the least (around 12 male pupae and 6 female ovisacs, respectively) from CMBS infestation. Unfortunately, none of all the Callicarpa evaluated was completely immune from CMBS attack.
Three Ficus species (F. pumila, F. roxburghii, and F. tikoua) were also evaluated in this study. No signs of CMBS infestation found on either F. pumila or F. roxburghii. F. tikoua had very minor CMBS infestation, which only 3 male pupae and 2 gravid female ovisacs per plant observed during the 25-week period in 2019.
Soybean, or Glycine max, was documented as one of the alternative hosts of CMBS in Asia. As an economically important agricultural crop in the United States, soybean generates over 40 billion in raw production value annually, and the United States continues to be one of the largest producers and exporters of soybean in the world (Hart, 2017). Therefore, it is reasonable to raise concern for the potential threat of CMBS to damage the soybean production in the United States.
We have conducted several greenhouse trials to evaluate the potential threat of CMBS to soybean. Although we’ve observed CMBS on soybean plants under controlled environment, the infestation level is very LOW. Figure 3 shows the presence of active nymphs and opened female ovisac with visible pink eggs in it, as well as signs of black sooty mold accumulation, indicating CMBS feeding and reproducing on soybean.
Minor CMBS infestations were observed on several Callicarpa species including C. dichotoma ‘Duet’, C. rubella, C. formosana and C. americana in a 2017 greenhouse observation (Figure 4).
In 2018, very minor infestation (as low as one gravid female observation) were identified both on ‘Bear’s Black fig and ‘Fuji’ apple seedling in a 2018 greenhouse observation. These greenhouse observation leads to our further investigation of the expanded CMBS host range and comprehensive greenhouse trials since then.
Observation in landscape and DNA identification
In 2018, an unknown scale infestation was first observed on Hypericum kalmianum (St. Johnswort) in a demonstration garden plot of Virginia Tech and the Virginia Agricultural Experiment Station in Virginia Beach, VA, USA. It was later confirmed by Schultz et al., through both morphological and molecular examinations, that this infestation on Hypericum was indeed caused byCMBS (Schultz, Szalanski, & Entomology, 2019).
More recently in 2020, a scale infestation (suspected to be a CMBS infestation) observed on Spiraea japonica ‘Shirobana’ at University of Arkansas, has been confirmed morphologically. My PhD student, Runshi Xie, conducted molecular identification tests on the scale specimen collected from scale-infested Spiraea plants from Arkansas and North Carolina. Certain portion of the genomic DNA of unknown specimens has been sequenced and compared to CMBS sample, and they were confirmed to be CMBS. Further CMBS feeding preference studies among Hypericum and Spiraea species is currently undergoing.
Non-suitable hosts of CMBS
We also identified certain species or genus as not the suitable hosts for CMBS, despite some of which has previously been documented as CMBS hosts. For example, we have NOT seen CMBS infestation on Myrtus communis or Ligustrum curvifolium in our greenhouse trials. Although Buxus and Rubus were genus listed as CMBS hosts, we did not find any infestation on them. It is possible that the previously reported CMBS hosts from these genera were varieties or cultivars naturally found or developed in the native region, where CMBS was originally found.
Above information sums up our current knowledge on CMBS hosts. Do we need to panic? NO! In our experience, we have only seen visible/severe sooty mold on the plants with ‘Severe’ infestation (Table 1; Figure 2) and mostly people don’t even notice the existence of CMBS without the presence of sooty mold. Damage to plant health in categories other than ‘Severe’ is probably neglectable.
Our CMBS feeding experiments were conducted in greenhouse, where verified CMBS-infested crapemyrtle stems with viable infestation were used to inoculate all test plants. Our method was proven successful in confirming the suitability of a potential new host for CMBS, however, this type of experiment can be time consuming and not suitable for wide application. Therefore, our group is current developing alternative methods, including Electric Penetration Graph system for detecting CMBS feeding behavior as well as DNA identification, in order to more effectively confirm and evaluate CMBS hosts.
García Morales M, D. B., Miller DR, Miller GL, Ben-Dov Y, Hardy NB. (2016). ScaleNet: A literature-based model of scale insect biology and systematics. (Publication no. 10.1093/database/bav118.). Retrieved January 30th, 2021 http://scalenet.info.
Hart, C. (2017). The economic evolution of the soybean industry. In The soybean genome (pp. 1-9): Springer.
Schultz, P. B., Szalanski, A. L. J. J. o. A., & Entomology, U. (2019). Hypericum kalmianum (St. Johnswort) Confirmed as a New Host of the Crapemyrtle Bark Scale in Virginia, USA. 35(1), 12-15.
Wang, Z., Chen, Y., Gu, M., Vafaie, E., Merchant, M., & Diaz, R. (2016). Crapemyrtle Bark Scale: A New Threat for Crapemyrtles, a Popular Landscape Plant in the U.S. Insects, 7(4), 78. doi:10.3390/insects7040078