Black sooty mold is one of the major issues with heavy crapemyrtle bark scale (CMBS; Acanthococcus lagerstroemiae) infestation, which greatly reduces the aesthetic value of host plants. Black sooty mold can be seen not only on crapemyrtles (Lagerstroemia spp.) but also on alternative hosts infested with CMBS such as American beautyberry (Callicarpa americana) and pomegranates (Punica granatum) (Figure 1). Sooty mold is a collective term that comprises of several genera of fungi including Aureobasidium, Antennariella, Cladosporium, Capnodium, Limacinula, and Scorias [1]. These fungi grow on the honeydew secreted by sucking insects (such as CMBS nymphs) when they are actively feeding on the plant [2,3].
Honeydew secretion is commonly found in all hemipteran insects such as aphids (Aphidoidea) and mealybugs (Pseudococcidae). The damages to plant health related to CMBS honeydew secretion is indirect since this sugar-rich sticky substance is not pathogenic to plants. However, sooty mold blocks sunlight on leaves and reduces photosynthesis. The heavy load of honeydew deposit might explain the presence of ants that are commonly seen around active CMBS infestation. Research showed that the ants (Formicidae) could be actively ‘farming’ aphids by harvesting the honeydew [4,5], which suggests that similar mutualistic relationship might exist between ants and CMBS. Honeydew collected from hemipterans have been studied extensively for understanding insect physiology, however, limited research was done to study CMBS honeydew.
The following videos of CMBS honeydew secretion was obtained during daily observation of CMBS samples. Crapemyrtle bark scale secreted out liquid after being gently stimulated by the hair of a fine brush. This could be potentially a new method of obtaining CMBS honeydew for further chemical analysis.
Related publications:
- Nelson, S. Sooty mold. 2008.
- Wang, Z.; Chen, Y.; Diaz, R.; Laine, R.A.J.J.o.i.p. Physiology of crapemyrtle bark scale, Acanthococcus lagerstroemiae (Kuwana), associated with seasonally altered cold tolerance. 2019, 112, 1-8.
- Gu, M.; Merchant, M.; Robbins, J.; Hopkins, J.J.T.A.; EHT, M.A.E.S. Crape Myrtle Bark Scale: A New Exotic Pest. 2014, 49.
- Offenberg, J.J.B.E.; Sociobiology. Balancing between mutualism and exploitation: the symbiotic interaction between Lasius ants and aphids. 2001, 49, 304-310.
- Stadler, B.; Dixon, A.F.J.A.R.E.E.S. Ecology and evolution of aphid-ant interactions. 2005, 36, 345-372.
