Nectary use for gaining access to an ant host by the parasitoid Orasema simulatrix (Hymenoptera, Eucharitidae)
Journal of Hymenoptera Research
Eucharitidae is the only family of insects known to specialize as parasitoids of ant brood. Eggs are laid away from the host onto or in plant tissue, and the minute first-instars (planidia) are responsible for gaining access to the host through some form of phoretic attachment to the host ant or possibly through an intermediate host such as thrips. Orasema simulatrix (Eucharitidae: Oraseminae) are shown to deposit their eggs into incisions made on leaves of Chilopsis linearis (Bignoniaceae) in
... (Bignoniaceae) in association with extrafloral nectaries (EFN). Nectary condition varies from fluid-filled on the newest leaves, to wet or dry nectaries on older leaves. Filled nectaries were about one third as common as dry nectaries, but were three times as likely to have recent oviposition. Larger numbers of undeveloped eggs, or eggs with mature planidia inside, were associated with filled and wet EFN. For emerged planidia, the distribution was shifted from a concentration at filled nectaries to an even greater concentration at wet nectaries. More planidia were found in EFN (9.50 ±2.85) than outside EFN (1.00 ± 0.60). Planidia were tested for their attachment to adult and larval ants and to adult and immature thrips (potential intermediate host), but the results do not support simple attachment as a viable means for transfer and successful parasitism. Pheidole desertorum was identified as the host ant, and at night is the dominant ant in the tree canopy of C. linearis. Feeding at the EFN by the host ant, and the direct association with planidia near to or in the EFN, is interpreted as a novel means of accessing the host brood. Geographic Area of Investigation. Data collections, observations, and ant baiting experiments were conducted at four sites near the Southwestern Research Station (SWRS) near Portal, AZ. Ambient temperatures over the year range from night time lows near 5°C in early spring or late autumn to daytime highs of 40°C during summer. Additional sampling and casual observations of O. simulatrix on Chilopsis were made at several other localities in California, Texas and New Mexico, at sites ranging from sea level to nearly 2500 meters. Study Sites. Site 1 (31°52'36"N, 109°03'32"W) was in a stand of six trees (maximum height about 4 m) of C. linearis in Arizona in the foothills of the Chiricahua Mountains, approximately 8 km east of Foothills Road on Portal Road (leading to San Simon). The habitat was high desert, dominated by sparse trees of Larrea tridentata Coville (Zygophyllaceae), Acacia constricta Benth. (Fabaceae) and Prosopis sp. (Fabaceae), a variety of shrubs including Yucca (Agavaceae), Fouqueria splendens Engelmann (Fouqueriaceae), Opuntia spp. (Cactaceae), and annual herbs in the genera Parthenium, Baileya, Senecio, Gutierrezia (all Asteraceae) and Sphaeralcea (Malvaceae). Site 2 (31°56'14"N, 108°57'59"W) consisted of seven trees in New Mexico in the Peloncillo Mountains, 7 km east of US Highway 80 on New Mexico Highway 9. Site 2 was less vegetated than Site 1, with L. tridentata and C. linearis being the dominant tree species. Shrubs and annuals were also less abundant and diverse. Site 3 (31°55'14"N, 109°42"W) consisted of five trees approximately 0.8 km north of the intersection of Foothills Road and Portal Road. Site 3 was rocky, and the dominant vegetation a mix of L. tridentata, A. constricta and Prosopis sp. Site 4 (31°54'50"N, 109°07'42"W) consisted of 5 trees and began at the intersection of the above-mentioned roads, and extended south and east along Portal Road. The trees were spread over a distance of 0.25 km alongside the road, within 50m of the road edge. The dominant tree species were the same as for Site 3. In 1999, Sites 1 and 2 were abandoned for study because of low activity of O. simulatrix. At Site 2, the area was in extreme drought, and no wasps were recovered. Site 1 was abandoned because the Arizona Department of Highways chose to improve the shoulders of Portal Road and leveled the entire stand of C. linearis. Therefore, in 1999, studies were shifted to Sites 3 and 4, which were approximately 1 km apart. Sites 3 and 4 were revisited in September 2011 for additional collections of leaves, immature stages of eucharitids, and foraging ants. Insect and Plant Identifications. Museum collections examined were University of California, Riverside, CA (UCRC), Texas A&M University, College Station, TX (TAMU), University of Arizona, Tucson, AZ (UAZC), and the Southwestern Research Station, Portal, AZ (SWRS). Voucher specimens of wasps, ants and thrips were deposited in the UCR Entomology Research Museum (UCRC) (voucher code BC1). Ants were determined or verified by S. Cover (Museum of Comparative Zoology) or R. Snelling (Los Angeles County Museum). Slide mounted thrips were identified by L.