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United States Department of Agriculture

Agricultural Research Service

Title: No detection of Vairimorpha invictae in fire ant decapitating flies reared from V. invictae- infected ants

Authors
item Oi, David
item Porter, Sanford
item Valles, Steven
item Briano, Juan - USDA/ARS-ARGENTINA

Submitted to: Imported Fire Ants Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: June 1, 2008
Publication Date: March 1, 2009
Citation: Oi, D.H., Porter, S.D., Valles, S.M., Briano, J.A. 2009. No detection of Vairimorpha invictae in fire ant decapitating flies reared from V. invictae- infected ants. Imported Fire Ants Conference Proceedings. 24:121-122.

Interpretive Summary: Vairimorpha invictae is a microsporidian entomopathogen that is under evaluation as a biological control agent for red imported fire ants, Solenopsis invicta. Infections of V. invictae alone and in combination with another pathogen of fire ants, Thelohania solenopsae, have resulted in declines of 53-100% in S. invicta populations in Argentina (Briano 2005). Parasitic flies in the genus Pseudacteon have been released for the biological control of fire ants in the USA. Three species have been established (P. tricuspis, P. curvatus, P. litoralis), and a fourth (P. obtusus) has been approved for release (S.D.P. per. com.) These flies are endoparasitoids, where an egg oviposited into an adult fire ant hatches into a maggot that migrates to the head of the ant where it develops and pupates. The parasitized ant’s head detaches from its body prior to adult fly eclosion (Porter 1988). Microsporidian infections have occurred in parasitoid wasps that developed in infected lepidopteran hosts. Deleterious effects on infected wasps may impact integrated pest management programs where parasitoids are an important component (Schuld et al. 1999). The objective of this study was to determine if V. invictae could be detected in the parasitioid P. obtusus that were reared from V. invictae-infected S. invicta host. Adult worker caste S. invicta from two V. invictae infected colonies were exposed for 3 days to P. obtusus in the laboratory. Infection rates of the workers were 85% for each colony based on individual wet mounts of the workers (n=20 per colony) examined by microscopy. After exposure to the flies, adult ants were held until decapitation. Ant heads and bodies were collected individually and categorized as: 1) heads that could be matched definitively with bodies (head partially attached to body); 2) heads that probably belonged to particular bodies (head near body); and 3) heads that could not be assigned to specific bodies. Individual headless bodies were examined for V. invictae spores by microscopy. Within categories 1 & 2, heads that were associated with V. invictae-infected bodies were grouped together. Adult P. obtusus that emerged were separated by sex and grouped into samples of 7-13 individuals and tested for the presence of V. invictae by PCR. P. obtusus adults that emerged from category 3 heads were sexed and grouped into sets of 16-21 flies for V. invictae PCR detection. There was no evidence of V. invictae infection in P. obtusus adults that definitively developed (n=25) or mostly likely developed (N=34) in infected ants. This indicated that the adult flies were not acquiring infection despite development in infected ant hosts. S. invicta bodies that could not be matched with their head capsules had an estimated infection rate of 87% (82/94) based on ants from all 3 categories. V. invictae was not detected in any of the P. obtusus that emerged from the unmatched heads (N=318). These results further defined the host specificity of V. invictae and indicated that V. invictae will not directly interfere with P. obtusus parasitism.

Technical Abstract: Vairimorpha invictae is a microsporidian entomopathogen that is under evaluation as a biological control agent for red imported fire ants, Solenopsis invicta. Infections of V. invictae alone and in combination with another pathogen of fire ants, Thelohania solenopsae, have resulted in declines of 53-100% in S. invicta populations in Argentina. Parasitic flies in the genus Pseudacteon have been released for the biological control of fire ants in the USA. Three species have been established (P. tricuspis, P. curvatus, P. litoralis), and a fourth (P. obtusus) has been approved for release. These flies are endoparasitoids, where an egg oviposited into an adult fire ant hatches into a maggot that migrates to the head of the ant where it develops and pupates. Prior to adult emergence the head of the parasitized ant detaches from the body. Adult worker caste S. invicta from two V. invictae infected colonies were exposed to P. obtusus in the laboratory, and then allowed to develop in the infected ants. There was no evidence of V. invictae infection in P. obtusus adults that developed in heads that were matched to infected bodies (n=39). S. invicta bodies that could not be matched with their head capsules had an estimated infection rate of 87%. V. invictae was not detected in any of the P. obtusus that emerged from the unmatched heads (N=318). These results further defined the host specificity of V. invictae and indicated that V. invictae will not directly interfere with P. obtusus parasitism.

Last Modified: 10/22/2014
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