Numbers
7 species in North America (
nearctica.com)
Identification
Adults resemble solitary wasps in general shape and color. They have a petiolate abdomen with segment 2 long and narrow, and the others broader and shorter.
Superficially, species of Physocephala resemble those of the genus Physoconops, but may be readily separated from that genus by examining the position of the anterior cross vein (rm) in relation to the discal cell (1st M2) (fig. 2B & 2C in PDF doc listed under Internet References below).
An additional character of value is the irregularly-thickened base of the hind femur present in species of Physocephala. In Physoconops, the hind femur is uniformly-thickened.
Range
most of United States and southern Canada
also occurs in Eurasia, Australia, South Africa, and Central America (based on Internet search)
Habitat
adults visit flowers of herbaceous plants during the day
Season
adults fly from late spring to late summer
Food
adults feed on flower nectar
larvae are internal parasites of bees and wasps (the hosts are not killed as a result)
Life Cycle
P. tibialis has been reported to parasitize workers of the bumble bee Bombus bimaculatus. Adults apparently alight and inject an egg into the abdomen of their host while in flight.
A study in Alberta showed that bumble bees parasitized by P. texana had the same lifespan as unparasitized individuals.
Internet References
http://essig.berkeley.edu/CIS/cis06_2.pdf - 4 megabyte PDF doc with illustration of wing venation in
P. texana, and literature citation of
P. tibialis parasitizing worker bumble bees (Sidney Camras and Paul D. Hurd,Jr. The Conopid Flies of California, U. of California at Berkeley)
pinned adult image showing head and thorax of unidentified
Physocephala species (Insects of Cedar Creek, Minnesota)
general information on Physocephala [the included key applies to European species only] (M. Van Veen, Netherlands)
parasitism of bumble bees by
P. texana in Alberta (M.C. Otterstatter, U. of Calgary)
