Aims Vegetation sampling employing observers is prone to both inter-observer and intra-observer error. Three types of errors are common: (i) overlooking error (i.e. not observing species actually present), (ii) misidentification error (i.e. not correctly identifying species) and (iii) estimation error (i.e. not accurately estimating abundance). I conducted a literature review of 59 articles that provided quantitative estimates or statistical inferences regarding observer error in vegetation studies. Important Findings Almost all studies (92%) that tested for a statistically significant effect of observer error found at least one significant comparison. In surveys of species composition, mean pseudoturnover (the percentage of species overlooked by one observer but not another) was 10–30%. Species misidentification rates were on the order of 5–10%. The mean coefficient of variation (CV) among observers in surveys of vegetation cover was often several hundred % for species with low cover, although CVs of 25–50% were more representative of species with mean covers of >50%. A variety of metrics and indices (including commonly used diversity indices) and multivariate data analysis techniques (including ordinations and classifications) were found to be sensitive to observer error. Sources of error commonly include both characteristics of the vegetation (e.g. small size of populations, rarity, morphology, phenology) and attributes of the observers (e.g. mental fatigue, personal biases, differences in experience, physical stress). The use of multiple observers, additional training including active feedback approaches, and continual evaluation and calibration among observers are recommended as strategies to reduce observer error in vegetation surveys.

We studied the oviposition behavior and larval development of Pseudacteon phorid flies, which are parasitoids of Solenopsis fire ants. Four South American Pseudacteon spp., P. litoralis Borgmeier, P. tricuspis Borgmeier, P. wasmanni (Schmitz) and P. curvatus Borgmeier (which attack S. invicta Buren), and 2 North American Pseudacteon spp., P. browni Disney and P. crawfordi Coquillett (which attack S. geminata [F.]), were evaluated. In laboratory tests, larger Pseudacteon spp. attacked larger Solenopsis workers. The mean worker size preferred was significantly larger than the colony mean worker size for all but the smallest phorid species, P. curvatus, which preferred workers significantly smaller than the colony mean. Within Pseudacteon spp., larger females preferred larger workers, but this relationship was significant only for the 2 North American species. Natural parasitism rates of Solenopsis workers by the 2 North American Pseudacteon spp. in the field were low (0–2.42% per colony), but >90% of the overall size range of worker ants showed evidence of parasitism. Between 11.8 and 31.0% of apparent oviposition attempts resulted in successful parasitism. Mean larval development times ranged from 13.0 to 18.4 d at 30°C and were shorter for North American species. Larval stages required 24.8–36.5% longer to develop at 25°C than at 30°C. Mean pupal development times ranged from 15.6 to 18.7 d at 30°C. In general, larger Pseudacteon spp. had longer larval and pupal development times. Overall, North and South American Pseudacteon spp. were similar in terms of oviposition behavior and development.