Submitted to: Journal of Invertebrate Pathology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/22/2002
Publication Date: 12/15/2002
Citation: PEREIRA, R.M., WILLIAMS, D.F., BECNEL, J.J., OI, D.H. YELLOW HEAD DISEASE CAUSED BY A NEWLY DISCOVERED MATTESIA SP. IN POPULATIONS OF THE RED IMPORTED FIRE ANT, SOLENOPSIS INVICTA. JOURNAL OF INVERTEBRATE PATHOLOGY. 2002. v. 81. p. 45-48. Interpretive Summary: A new disease of the imported fire ant has been discovered in Florida by researchers of the USDA-ARS, Center for Medical, Agricultural and Veterinary Entomology. The new disease was named Yellow Head Disease (YHD) due to an atypical yellow-orange color of the heads of infected ants caused by spindle-shaped spores inside the head and others ant body parts. The YHD is widely-distributed in Florida in both multiple-queen and single-queen imported fire ant colonies, being present in 34% of the sites and in 8% of nests surveyed. Field colonies brought into the laboratory have had large mortality of YHD-infected ants. A rapid mortality of infected ants potentially indicates that this disease may have significant impact on fire ant populations, and may serve as a biological control for these pest ants.
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. The abdomen of an infected ant has many spindle-shaped oocysts inside the different body parts, 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. No obvious signs of the disease have been observed in immature stages of the ant, and no stages of the pathogen have yet been observed in imported fire ant larvae or pupae. 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 ants were examined. The YHD is widely-distributed in Florida in both polygyne and monogyne S. invicta colonies. The disease was present in 34% of the sites and in 8% of nests. One colony, and individual ants within this colony, had dual infection with YHD and T. solenopsae. 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.