|Abstract or Summary
- The genus Tiaja Oman consists of eight known species of flightless
leafhoppers of the subfamily Megophthalminae found along the
western coast of North America between British Columbia and
northern Mexico. Species occurring from the San Francisco Bay
area northward are restricted to a narrow coastal zone within 1 km of
the ocean; some of those species that occur farther south may be
found inland as well as on the coast. Members of the genus occupy
an unusual habitat in that most individuals are found on the undersides
of their host plants or in the litter layer beneath them. Flightlessness
and the position the insects occupy on their host plants are seen as
adaptations to enhance survival in a windswept environment.
Life history studies of T. friscana (Ball) and T. arenaria Oman
show that nymphs normally pass through five nymphal ins tars
although some individuals may have four or six nymphal ins tars. The
final nymphal ins tar is of longer duration than any of the preceding
ins tars but the length of the developmental period appears to depend
on temperature conditions in the rearing chamber. The northernmost
species, T. arenaria, is univoltine with obligatory diapause
while T. friscana and T. montara Oman, two species of the central
California coast, are multivoltine with no diapause under favorable
conditions. Other species are presumed to be multivoltine.
Host association studies show that members of the genus Tiaja
are usually found associated with woody shrubs and that these shrubs
may serve as feeding but not necessarily oviposition hosts. The oviposition
host of T. arenaria is Fragaria chiloensis (L.) Duch.
Infraspecific variation in disjunct populations of T. friscana is
examined. These populations lie 550 km apart and the range of
another species, T. montara, intervenes. Crossbreeding experiments
show that while there is some genetic differentiation as a
result of isolation, the populations are similar enough and hybridize
to a sufficient extent to be considered members of the same species.
Crossbreeding experiments between T. friscana and T. montara
show that these allopatric species from the San Francisco Bay
area hybridize to some extent when artificially placed together.
However, fertility is considerably reduced compared to parental
crosses and this is taken as evidence of the reliability of morphological
features used for species differentiation in this genus. Factors
influencing the success rates of these crosses are discussed. The presence of members of the genus on islands and in
populations isolated from the remainder of a species despite the
limited mobility of the group is discussed. It is speculated that
dispersal of T. arenaria to Vancouver Island subsequent to Pleistocene
glaciation, dispersal of T. insula Sawbridge to Santa Barbara
Island following its submersion in the late Pleistocene, and the
colonization of San Simeon by T. iris cana can be attributed to dispersal
by drift of egg-containing host plant material aided by ocean
currents and prevailing winds.
Taxonomic information includes a discussion of the place of
the Megophthalminae within the Cicadellidae, recharacterization of
the genus Tiaja, a revised key to the eight known species, and
species recharacterizations including morphological data, distributions,
seasonal occurrence, and host and habitat information. Criteria
for differentiation of nymphal ins tars through setal patterns
and wing pad development are discussed and illustrated.
It is concluded that further study of the habitats, life history,
behavior, and cytogenetics of the Ulopinae and other members of the
Megophthalminae will be necessary before current data on Tiaja can
be used to help redefine relationships within and between these subfamilies.