Between December 2001 and December 2003, collections of flower visitors of Eryngium horridum (Apiaceae) were carried out in areas of Rio Pardo Valley, RS, Brazil. This plant is perennial, commonly found in dry fields, presenting a wide distribution. Its flowering period ranges from November to January in Rio Grande do Sul. A total of 1,066 insects were captured, 569 of them belonging to Syrphidae. Sixty species of Syrphidae were identified, distributed in 16 genera. The genus Palpada Macquart, 1834 was considered dominant, and Ornidia Lepeletier & Serville, 1828 and Toxomerus Macquart, 1855 considered abundant. Palpada furcata (Wiedemann, 1819) was the most abundant species. The syrphids showed a preference for temperatures between 28 and 32ºC, and were more frequently collected between 10 and 14 hours, with peaks between 10 and 11 hours. The females were more frequent. The predominance of robust and agile syrphids over those with lower proportions, such as Toxomerus and Allograpta Osten Sacken, 1875, may have been a result of interespecific competition. Eristalinus taeniops (Wiedemann, 1818) is newly recorded from Rio Grande do Sul state. The high diversity and abundance of the species collected from flowers of E. horridum are indicators of the importance of this plant on the diet of the syrphids, since it possesses an elevated number of inflorescences that bloom in months of low resource availability in the study area.
Flower flies; diversity; abundance; fenology
