Discovery and confirmation of New Crapemyrtle Bark Scale Hosts (Spiraea and Callicarpa) through DNA Barcoding

Discovery and confirmation of New Crapemyrtle Bark Scale Hosts (Spiraea and Callicarpa) through DNA Barcoding

Crapemyrtle bark scale (CMBS; Acanthococcus lagerstroemiae Kuwana), a new emerging sap-sucking pest from East Asia, poses a unique risk to the green industry. The polyphagous feeding habit of Crapemyrtle bark scale has allowed it to attack a wide range of plant species, including soybean, apple, and pomegranate. The news of this insect spreading beyond its primary host, crapemyrtle, is worrisome to the industry and the scientific community, as the implication of a fast-spreading invasive insect to the ecosystem is enormous.

Recently, reports of naturally occurring CMBS infestations on alternative hosts. For instance, American beautyberry (Callicarpa americana, Fig. 1A) and Hypericum kalmianum L. (St. Johnswort), both native species in the United States, were found to be infested with CMBS in the field (Schultz & Szalanski, 2019; Wang et al., 2016). In 2019, a scale infestation (suspected to be a CMBS infestation) observed on Spiraea japonica (Fig. 1B) at University of Arkansas (Little Rock, AR 72204). Again, later in 2020, another incident of unknown scale infestation, later identified as CMBS, was reported in Concord, North Coralina, USA. The infested plant was identified as Spiraea thunbergia (Fig. 1C), which was planted sometimes between 1953 and 2016, and for long time without scale infestation. The scale infestation was believed to be initiated after two CMBS infested crapemyrtle that were accidentally planted nearby.

Fig 1. Severe infestation of Acanthococcus lagerstroemiae on alternative hosts. (A) Callicarpa americana (red arrows: female ovisacs; blue arrows: male sacs). (B) Nymphs (red arrows) on Spiraea japonica. (C) Live nymphs (red arrows) collected from infested S. thunbergia for DNA extraction (yellow arrows: broken ovisacs).

All the scale insect samples were collected and sent to our laboratory for further analysis and species identification, using morphology and DNA barcoding techniques. Naturally occurring CMBS infestations were confirmed on American beautyberry (Callicarpa americana L.), a native plant species in the United States, and spirea (Spiraea L.) (Fig 2). We also studied the genetic relationships between CMBS specimens and their hosts from different geographic locations using molecular approaches. The new infestation of CMBS found on Spiraea raises the alarm that other economically important crops in the Amygdaloideae subfamily (subfamily under Rosaceae) might be susceptible to CMBS attacks.

Fig 2. New CMBS alternative hosts (Spiraea and Callicarpa) discovered in the United States.

According to the latest phylogeny study of Rosaceae, Chaenomeles, Malus, and Spiraea (confirmed CMBS host genera) were grouped under subfamily of Amygdaloideae (Xiang et al., 2017), in which at least 54 other genera were reported (Potter et al., 2007). Furthermore, Amygdaloideae includes many economically important crops such as apricot, almond, cherry, plum, and peach (Xiang et al., 2017)(Fig 3). Therefore, further investigations are needed to evaluate the potential threat of CMBS to other valuable crops in the Rosaceae family, especially in the subfamily of Amygdaloideae.

Fig 3. Confirmed CMBS alternative hosts in Rosaceae (upper images) and other economic important crops (bottom images) in Rosaceae.

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