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Title: Activity patterns and parasitism rates of fire ant decapitating flies (Diptera:Phoridae:Pseudacteon spp.) in their native Argentina

Author
item CALCATERRA, LUIS - USDA-ARS-OIRP-SABCL
item DELGADO, ALICIA - THE CONSERVATION LAND TRU
item TSUTSUI, NEIL - UNIVERSITY OF CALIFORNIA

Submitted to: Annals of the Entomological Society of America
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/14/2007
Publication Date: 5/1/2008
Citation: Calcaterra, L., Delgado, A., Tsutsui, N.D. 2008. Activity patterns and parasitism rates of fire ant decapitating flies (Diptera:Phoridae:Pseudacteon spp.) in their native Argentina. Annuals of the Entomological Society of America 101(3):pp 539-550

Interpretive Summary: Daily and seasonal rhythms are intrinsic to virtually all life forms. In insects, as in many other organisms, the most evident rhythms are related with behaviors such as locomotion, flight, foraging, and oviposition. These behaviors are usually restricted to certain times of the day, because they are often synchronized with periodic events in the environment such as light and temperature cycles), or more episodic events related to food availability, predation, and competition. Little is known about phenological patterns in many insect groups, such as scuttle flies. Scuttle flies are one of the most biologically diverse groups of insects. Many of them are parasitoids or specific predators of other insects. The few studies of temporal rhythms in these flies were conducted almost exclusively on the fire ant decapitating flies because of the flies’ potential as biological control agents of the red and black imported fire ants in the United States. This work examines the annual and daily activity patterns of two parasitoid fly communities of the red imported fire ant in northeastern Argentina. Activity patterns observed in the field were placed in the context of climatic variables and genetic relationships among fly species. Relationships among fly species were established based on their activity patterns and phylogenetic reconstruction. Additionally, parasitism rates of fire ant colonies naturally attacked in the field by decapitating flies are reported for the first time from South America. Most species were active throughout the year, though abundances were variable over time and between sites. The highest occurrence peaks of flies were recorded in spring, while the lowest were in summer. Fly abundance was higher close dusk, whereas species diversity was highest at midday. The parasitism rate by the nine species recorded was low (0.23%). The highest percentage of parasitized workers was found in spring (0.5%) and occurred in the gallery forest habitat.

Technical Abstract: Technical Abstract: This work describes the annual and daily activity patterns of two parasitoid fly communities of the fire ant S. invicta (Hymenoptera: Formicidae) in their native Argentina. Pseudacteon (Diptera: Phoridae) flies were censused monthly for one year at two sites in northwestern Corrientes province. Climatic variables and phylogenetic relationships among flies were used to explain the patterns observed. Additionally, parasitism rates of S. invicta colonies naturally attacked in the field by Pseudacteon flies are reported for the first time from its native habitat. A total of 4,528 flies (86.3% females) of eight Pseudacteon species were collected attacking ants in the field. Pseudacteon litoralis Borgmeier and P. nocens Borgmeier represented 71-79% of female flies censused in both sites. Most species were active throughout the year, though abundances were variable over time and between sites. The highest occurrence peaks of flies were recorded in spring, while the lowest were in summer. Fly abundance was higher close to dusk, whereas species diversity was highest at midday. The presence and abundance of four species were explained by climatic variables. However, the variation exhibited in the activity patterns could not be explained by their genetically programmed circadian rhythms. Relationships among species were established based on their activity patterns and phylogenetic reconstruction. Overall, the parasitism rate by the nine species recorded was low (0.23%). The highest percentage of parasitized workers was found in spring (0.5%) and occurred within the most complex habitat (gallery forest). The highest parasitism rate per site and colony was also for this habitat in spring (1.16 and 2.81%, respectively). The highest rates of emergence were recorded for Pseudacteon nudicornis Borgmeier.