The Ruellia erinose Mite (Eriophyidae: Acalitus simplex): A pest of the Mexican petunia (Acanthaceae: Ruellia simplex)

Acalitus simplex is an eriophyoid mite that infests solely plants of the genus Ruellia, inducing the development of erinea. The erinea progress through four stages, each characterized by a different color: hyaline, white, purple, and silver. Little is known about the taxonomical status of A. simplex and no data are available about its interactions with Ruellia species. The study aims to: i) clarify the uncertain taxonomy ii) investigate population density inside each erineum stage and iii) assess the erinea development time.

Morphological and molecular analyses were conducted on specimens from Brazil, Florida and Hawaii, by sequencing the CO1 gene and using different microscope techniques. Population density in each erineum stage was investigated by recording the emergence of A. simplex every 24 hours. Erinea developmental time was assessed after infesting R. simplex with 30 adult A. simplex females. The progression of the erinea was recorded every 72 hours until all reached the silver stage.

All the specimens were identified as A. simplex, showing similar morphology and 99% sequence similarity. The population density varied significantly across the erineum stages, with white and purple containing the largest number of A. simplex while the hyaline and silver had the lowest. The white stage persists longer on the plant than the hyaline and silver.

The research outcomes will offer tools to accurately identify A. simplex, provide information on erinea progression over time and assess population density at each erineum stage. Addressing these topics could enhance the development of mitigation strategies for A. simplex infestations.