Salinity and shade preferences result in ovipositional differences betweensympatric tiger beetle species

1. Adult tiger beetles of the genus Cicindela often co-occur within a habit at but larvae do not. Larvae are sedentary and form usually permanent burro ws at the site of oviposition where they require 1-3 years for development. 2. To test niche partitioning based on ovipositional preference, the behavi our of two sympatric salt marsh tiger beetles, Cicindela circumpicta and C. togata (Coleoptera: Cicindelidae), were examined. 3. In laboratory studies, female C. circumpicta and C. togata distinguished between experimental salinities, with the former preferring 4 parts per th ousand (ppt) and the latter preferring 12 ppt. In the field, C. circumpicta larvae were associated with lower salinities (1-3 ppt) and vegetation alon g the edges of salt flats while C. togata larvae were found on open salt fl ats often near halophytes (average salinity = 7.8 ppt). 4. In the field, females chose sites for oviposition in response to shade b ut not vertical landmarks. In a direct test, 53 of 56 new larval burrows oc curred in shaded treatments, three in nonshaded controls. 5. Compared with nonshaded controls, shade increased survival of eggs that were collected in the laboratory and placed in the field. For C. circumpict a eggs, 78% placed in shaded treatments hatched, while significantly fewer (22%) hatched in exposed treatments. For C. togata, 43% of eggs placed in t he shade hatched, while no eggs placed in exposed treatments hatched. 6. These results support the hypothesis of niche partitioning between C. ci rcumpicta and C. togata based on ovipositional choice and resulting larval habitat.