Eugregarine parasitism in dragonfly populations of central Texas with an assessment of fitness costs in Erythemis simplicicollis (Odonata: Libellulidae)

Eugregarine parasites (Apicomplexa: Eugregarinorida) infect a wide variety of invertebrates. Some authors have suggested that eugregarines are rather harmless, but recent studies suggest otherwise. Among odonate-eugregarine investigations, damselflies have been more frequently studied than dragonflies. We surveyed adult dragonfly populations for eugregarines at a constructed, flow-through wetland system and two reservoirs in central Texas for three years. Populations were sampled weekly through the flight seasons and an assessment of fitness costs of infection in a common and widespread dragonfly host species, Erythemis simplicicollis (Libellulidae), was made. Host fitness parameters measured included wing load, egg size, clutch size, and total egg count. Of the 37 dragonfly species surveyed, 14 (38%) hosted eugregarines and 13 of these dragonfly species were previously undocumented as hosts. Among host species, parasite prevalences ranged from 2% – 52%. Intensities ranged from 1 – 201. Parasites were aggregated in host populations. Prevalence and intensity exhibited strong seasonality at one of the reservoirs, but no seasonal trend was detected at the wetland. The fitness parameters measured were not correlated with the presence or intensity of eugregarines. These findings suggest that either eugregarines do not affect wing loading and egg production in E. simplicicollis, or that virulence depends on parasite intensity and/or the specific eugregarine species infecting the hosts.