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Title: Bionomics of Orasema simplex (Hymenoptera: Eucharitidae) a parasitoid of Solenopsis fire ants (Hymenoptera: Formicidae) in Argentina


Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/9/2008
Publication Date: 1/7/2009
Citation: Varone, L., Briano, J. 2009. Bionomics of Orasema simplex (Hymenoptera: Eucharitidae) a parasitoid of Solenopsis fire ants (Hymenoptera: Formicidae) in Argentina. Biological Control.

Interpretive Summary: The fire ants were introduced into the United States free of their natural enemies and became important economic and urban pests. Since the 1970s, surveys have been conducted in South America and over 35 natural enemies were found, including pathogens, parasites, parasitoids, and predators. Among the parasitoids, Orasema simplex, a small wasp that attacks ant brood, was studied as a candidate for biological control. Experiments were carried out in the laboratory to estimate the survival of the female wasps, the number of eggs, and the oviposition substrates. Biological parameters such as offspring sex ratio, development success and time from egg to adult were recorded. Also the life cycle of the wasps was reproduced under laboratory conditions. Field experiments were conducted to determine the activity of the wasps and the plants used for oviposition. Finally, the potential of Orasema simplex as a biological control agent is discussed.

Technical Abstract: Biological characteristics of the parasitoid Orasema simplex Heraty (Hymenoptera: Eucharitidae), a potential candidate for the biological control of fire ants in the United States were investigated. Female survivorship, fertility and oviposition preferences were studied in the laboratory. Naturally parasitized colonies were examined to determine offspring sex ratio, development success and time, and to artificially parasitize healthy ant colonies. In addition, field studies were carried out to establish natural oviposition substrates and adult activity patterns. Orasema simplex female survivorship was 3.6 ± 1.5 days. Newly emerged females contained 613.5 ± 114.0 mature eggs. The adult development success in natural parasitized colonies was 22.2% with a female-biased sex ratio (4:1). The time required from planidia to adult was 29.5 ± 5.4 days. In the field, adults were mostly found around the ant nests at midday. A broad range of plant species used as oviposition substrates was observed. The transfer of planidia to healthy ant colonies was achieved but the development success was very low. Orasema simplex appears to have a limited potential as a fire ant biological control agent because of cosmetic damage to a wide variety of plants used for oviposition. However, further studies are necessary to evaluate the real damage exerted by oviposition punctures.