Submitted to: Journal of Invertebrate Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 19, 2004
Publication Date: January 20, 2005
Citation: Oi, D.H., Briano, J.A., Valles, S.M., Williams, D.F. 2005. TRANSMISSION OF VAIRIMORPHA INVICTAE (MICROSPORIDIA: BURENELLIDAE) INFECTIONS BETWEEN RED IMPORTED FIRE ANT (HYMENOPTERA: FORMICIDAE) COLONIES. Journal of Invertebrate Pathology. 88:108-115. Interpretive Summary: Imported fire ants are an invasive insect that infests over 320 million acres in 14 states and causes an estimated $6 billion annually in damage, control, and related expenditures. In the U.S., there is a lack of natural enemies which can suppress populations and mediate the spread of fire ants. In 1986, a pathogen of imported fire ants from South America, called Vairimorpha invictae, was first described by ARS scientists. However, the inability to artificially transmit this pathogen has hindered its evaluation as a biological control agent. Now, for the first time, scientists from the Center for Medical, Agricultural, and Veterinary Entomology in Gainesville, FL (CMAVE) have been able to transmit this pathogen to uninfected fire ant colonies and subsequently perpetuate the infection in other fire ant colonies in the laboratory. In addition, colonies that were infected had 86% fewer adults per colony and 82% less immature ants than uninfected colonies. Data from other studies reported significant declines if fire ant populations in the field when V. invictae infections occur simultaneously with infections of another pathogen that CMAVE scientists are researching, T. solenopsae. With the geographic distribution of natural infections of T. solenopsae increasing in U.S. fire ant populations, the ability to efficiently initiate field infections of V. invictae could result in faster declines in fire ant populations and provide a new, self sustaining tactic to suppress fire ant populations. Such a tactic has the potential to contribute greatly to the long term suppression of fire ants which will benefit everyone who is affected by this stinging, invasive ant.
Technical Abstract: Red imported fire ant, Solenopsis invicta, colonies were successfully infected with the microsporidium Vairimorpha invictae by introducing live larvae, pupae, or dead adults from V. invictae infected field colonies collected in Argentina. Introductions with 4th instar larvae or non-melanized pupae obtained from infected field colonies, resulted in infection of 40% of the inoculated colonies. Introductions of 4th instars or melanized pupae produced from colonies that were initially infected in the laboratory, resulted in infections of 83% of the colonies, thus perpetuating the infection in other colonies. Infection was detected in 2 of 6 colonies after introducing adult worker caste ants that had died with V. invictae. The average number of adults and the volume of immature ants per colony were significantly lower in the infected than in the control colonies. Infected colonies had 86% fewer adults per colony and 82% less immature ants than the controls. A nucleotide amplicon amplified from V. invictae-infected S. invicta was 100% identical to the 16S rRNA gene sequence, thus confirming infection by V. invictae. This is the first report of the artificial transmission of this pathogen to uninfected ant colonies, and its suppression of growth in individual colonies. Key Words: Vairimorpha invictae, microsporidia, Solenopsis invicta, fire ant, pathogen, transmission, biological control