Cb. Montllor et al., REGIONAL DIFFERENCES IN THE DISTRIBUTION OF THE PYRALID MOTH URESIPHITA-REVERSALIS (GUENEE) ON FRENCH BROOM, AN INTRODUCED WEED, The Pan-Pacific entomologist, 71(2), 1995, pp. 92-104
The factors influencing the distribution of the moth Uresiphita revers
alis (Guenee) on French broom, Genista monspessulana (L.), its major h
ost plant in California, were investigated. Within an intensively sear
ched 7000 km(2) area around the San Francisco Bay, larvae were abundan
t on broom in the region east of the Bay, but consistently absent nort
hwest of the Bay. In held experiments there were no differences in egg
mortality, larval development, pupal weight, predation, plant chemist
ry, average ambient temperatures or solar radiation between the two re
gions which might account for the distribution of the insect. Survivor
ship of experimentally placed larvae was dramatically reduced in field
sites northwest of the Bay compared to sites east of the Bay during a
rainy winter season. Winter precipitation was consistently twice as h
igh northwest of the Bay compared to east of the Bay, and large losses
of larvae were associated with rainfall. After three years of drought
in California, larvae were found in a site northwest of the Bay for t
he first time. It is postulated that heavy rain is a major source of m
ortality for these insects, which, along with other unknown factors, m
ay preclude establishment in particular microclimates.