Scrutinizing Acalitus simplex Flechtmann et Etienne (Eriophydiae): an Important Pest of Ruellia (Acanthaceae)

Authors: DE GIOSA, MARCELLO - University Of Florida; ATAIDE, LIVIA - University Of Florida; DALE, ADAM - University Of Florida; HAHN, DANIEL - University Of Florida; WU, XINGBO - University Of Florida; Ochoa, Ronald; BOLTON, SAMUEL - Florida Department Of Agriculture And Consumer Services; Cloonan, Kevin; REVYNTHI, ALEXANDRA - University Of Florida

Submitted to: Experimental and applied acarology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/11/2025
Publication Date: 7/9/2025
Citation: De Giosa, M., Ataide, L.M., Dale, A.G., Hahn, D.A., Wu, X., Ochoa, R., Bolton, S., Cloonan, K.R., Revynthi, A.M. 2025. Scrutinizing Acalitus simplex Flechtmann et Etienne (Eriophydiae): an Important Pest of Ruellia (Acanthaceae). Experimental and applied acarology. https://doi.org/10.1007/s10493-025-01040-8.
DOI: https://doi.org/10.1007/s10493-025-01040-8

Interpretive Summary: Acalitus simplex is a small herbivorous mite species that feeds on plants in the genus Ruellia, commonly called wild petunias. Ruellia are important ornamental plants and are widely used as landscape plants because they exhibit stunning flower colors, require minimal maintenance, and can adapt to different environmental conditions. When the A. simplex mite feeds on Ruellia plants they cause lesions called erinea to form. Erinea are caused by the abnormal development of plant hairs called trichomes, that create an ideal environment for the mites to conceal themselves. This makes controlling and managing the A. simplex mite very difficult, and due to the mites’ small size little is known about the ecology and systematics of this pest. Thus, scientists at the University of Florida, the Florida Department of Agriculture and Consumer Services, and the USDA-ARS conducted surveys in Anguilla, Brazil, Florida, and Hawaii to compare different morphological and molecular characteristics of A. simplex mites. Additionally, the development of erinea on a popular Ruellia plant, Ruellia simplex, was also described. Results from these studies described three additional Ruellia hosts for A. simplex and estimated the developmental time and population densities of mites in four different stages of erinea on R. simplex. This information may lead to enhanced monitoring strategies for this pest, and aid in the timing of pesticide applications to develop a more precise management strategy against this mite pest.

Technical Abstract: Acalitus simplex Flechtmann and Etienne is an erinose eriophyoid mite that feeds exclusively on plants in the genus Ruellia. Plants in the genus Ruellia are commonly referred to as wild petunias and are frequently sold as ornamentals and are widely present in landscapes. This study presents a comprehensive identification of A. simplex collected from Anguilla, Brazil, Florida, and Hawaii through the sequencing of the mitochondrial cytochrome oxidase I gene and different microscopy techniques. The collected A. simplex were similar with consistent morphological characteristics and high molecular homogeneity. In addition to their association with Ruellia simplex, new host plant associations for A. simplex in Florida are reported including Ruellia blechum, Ruellia squarrosa, and Ruellia caroliniensis. Experiments were conducted to define the different erinea stages, determine the number of days required for their development, and estimate population densities in each stage. Four erinea stages were observed on R. simplex, hyaline (stage 01), white (stage 02), purple (stage 03) and beige (stage 04). At 25 ± 2 oC, 12:12/L:D and 50 ± 10% RH the duration of the hyaline, white and beige erinea was 12.4±0.7 (mean ± SE), 44.4±1.3, 20.5±0.9 days respectively. Additionally, these experiments showed that white erinea progress into the purple stage only under fluctuating environmental conditions. Population densities varied significantly across the erineum stages, with white and purple containing the highest number of A. simplex while the hyaline and beige stages had the lowest. This study enhances our understanding of A. simplex and R. simplex interactions, the most widely cultivated Ruellia species. These findings provide insights for developing integrated pest management strategies to mitigate this pest.