Salinity and shade preferences result in ovipositional differences between sympatric tiger beetle species

1. Adult tiger beetles of the genus Cicindela often co‐occur within a habitat but larvae do not. Larvae are sedentary and form usually permanent burrows at the site of oviposition where they require 1–3 years for development. 2. To test niche partitioning based on ovipositional preference, the behaviour 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 thousand (ppt) and the latter preferring 12 ppt. In the field, C. circumpicta larvae were associated with lower salinities (1–3 ppt) and vegetation along the edges of salt flats while C. togata larvae were found on open salt flats often near halophytes (average salinity = 7.8 ppt). 4. In the field, females chose sites for oviposition in response to shade but not vertical landmarks. In a direct test, 53 of 56 new larval burrows occurred 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. circumpicta eggs, 78% placed in shaded treatments hatched, while significantly fewer (22%) hatched in exposed treatments. For C. togata, 43% of eggs placed in the shade hatched, while no eggs placed in exposed treatments hatched. 6. These results support the hypothesis of niche partitioning between C. circumpicta and C. togata based on ovipositional choice and resulting larval habitat.