June 1997 – Southern California, Guadalupe-Nipomo Dunes: Uncovering the Natural History of Coastal Therevids

by Kevin Holston

It is a compelling truth that there is so much about therevids yet to be discovered – or, perhaps more appropriately, uncovered. To date, information of ecological significance that has been published or reported on these flies has been restricted to family level generalizations or to collecting data associated with curated specimens. Understanding therevids began with cataloging the diversity of forms; now it can augmented by detailed ecological studies of similarities and differences between specific groups. From June 16th to June 26th, I “uncovered” a little more about therevids on the coastal dunes of Southern California during preliminary work for a long-term ecological study to be conducted next year.

I began my trip by meeting Mike Irwin, Ev and Marion Schlinger, and Ebbe Neilson in Santa Barbara, California on the 16th of June. After examining sites along the south-facing beaches in the Santa Barbara area, Mike, Ebbe, and I went north on the 17th of June to examine other prospective sites between Santa Barbara and Monterey. We found therevid adults and larvae at several sites, with large populations of adults Acrosathe sp. found within the Guadalupe-Nipomo Dunes Preserve, in the Oso Flaco area. These dunes, rich in habitat diversity, are the most extensive dunes along the southern coast of California, and are, in part, preserved by the Nature Conservancy and the California State Park System. Ebbe left on the evening of the 17th in Monterey; then Mike and I went back south to inland sites near the Salinas River and Arroyo Seco and in Los Padres National Forest, and to coastal sites within the Salinas River State Park and Monterey State Park. After helping me coordinate my efforts with the proper authorities at the prospective study sites, set up malaise traps,and look for therevids at the prospective sites, Mike left to study the pinned therevid specimens in Illinois while I stayed out in California with the live ones (although some of them would soon become museum specimens).

Most of my time following Mike’s departure on the 20th of June was spent “uncovering” information about therevids: sifting larvae and pupae from the Guadalupe-Nipomo Dunes. I looked for and found therevid larvae from various habitats, catching glimpses of coyotes, black-tailed deer, and California quail; and I found the most larvae when I searched under vegetation in sand with minimal exposure to sunlight and wind. Pupae of a genus being described by Webb and Irwin were collected from under lupine (Lupinus arboreus), and many therevid larvae were found on the edge of open dune swales under arroyo willow (Salix lasiolepis) and other plants. These data, recorded at habitats ranging from coastal strand to stabilized backdune areas, will help in establishing associations of therevid species with specific dune habitats. Specimens of tenebrionid larvae (and adults) were also collected from the dunes while sifting for therevids and were fed to therevid larvae or preserved in alcohol.

I was not able to find Thereva nebulosa, a dune-associated species of the genus I am revising, at any of the sites; however, I conducted behavioral observations ofAcrosathe sp. at several locations. Males of this species formed loose agreggations on several stretches of open sand within the stabilized and semi-stabilized back dunes, flying up at passing conspecific males and low-flying hymenoptera. I recorded observations for several females, but observed no mating or oviposition sequences. Additionally, I took notes on the behavior of Tabudamima sp. andPherocera sp. (two species of Pherocera?), collected in stabilized back dune scrub dominated by lupine at several sites. I continued to observe and collect specimens (including Ozodiceromyia sp. from a malaise trap) from these populations of therevids and collect larvae until I left California on the 26th of June.

But the data continues to acrue even though the trip has ended. The larvae collected in California are being reared in the Irwin Lab in Illinois, and I am describing aspects of their morphology and behavior. These descriptions will broaden the scope of taxonomy and ecology associated with these species of therevids once the larvae metamorphose into adults and are identified. Next year, I plan to extend this information futher by examining the distributions of therevids from the shoreline inland over the dunes at several other sites along the western US coast, including the Oso Flaco Area as one of these sites.

This study was made possible with assistance from several principal sources. I was fortunate to receive logistical support and information on prospective study sites from Ev and Marion Schlinger. Rodger W. Kellogg and other staff with the State of California Resources Agency (California Department of Parks And Recreation) were a resource base for all aspects of the fieldwork conducted in the Guadalupe-Nipomo Dunes, Oso Flaco Area. Invaluable botanical data concerning the study sites was generously provided by Karen Wood and The Nature Conservancy. Access to several areas critical to this study was granted through the cooperative efforts of Teixeira Farms and Mills Farms.