Submitted to: Imported Fire Ants Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: June 15, 2002
Publication Date: August 20, 2002
Citation: Pereira, R.M., Williams, D.F., Becnel, J.J., Oi, D.H. 2002. Yellow Head Disease (YHD) caused by a Newly Discovered Mattesia sp. in Populations of the Red Imported Fire Ant, Solenopsis invicta. Imported Fire Ants Conference Proceedings. p. 23-24. Technical Abstract: Surveys in Florida revealed a new protozoan in S. invicta populations. The new disease was named Yellow Head Disease (YHD) due to an atypical yellow-orange color of large the heads of workers and female alates. Many spindle-shaped oocysts occur inside the different body parts of infected ants, but especially in the head and the appendages. Oocysts occur in pairs and develop from bilobed structures also observed in fresh mounts and Giemsa-stained preparations of body contents. These structures have led to the tentative classification of this pathogen in the genus Mattesia. Oocysts are 18.7 ± 0.80 µm (mean ± sem; n=50) long and 10.3 ± 0.80 µm in width, with the length-to-width ratio at 1.83 ± 0.15. The disease has not been observed in immature stages of the ant. Oocyst dimensions and shape, presence of oocysts in adult ants, and the yellow-head sign are evidence that YHD and its causative agent are new discoveries without established taxonomic identification. A total of 64 sites and 1017 nests were surveyed in Florida and the disease was present in 34% of the sites and in 8% of nests. The YHD occurs in both polygyne and monogyne S. invicta colonies, and has been observed in association with T. solenopsae in a single colony, and individual ants within this colony. Field colonies brought into our laboratory have had large mortality of YHD-infected ants within days after arrival. A rapid mortality of infected ants potentially indicates that this disease may have significant impact on fire ant populations.