none. Losses in workers and reproductives due to the ichneumonid parasitoid Latibulus sp. were determined in a haplometrotic, temperate paper wasp, Polistes riparius , during a 5-year study. Fifty-four to 79% of pre-emergence nests were parasitized on worker brood, resulting in a worker loss of 25-31% on average. Worker brood reared in outer cells were much more often parasitized than those in central ones, possibly because outer cells are more accessible to the parasitoid. Infestation of worker brood was not random but aggregated among nests. Seventy-eight to 100% of nests were parasitized on reproductive brood, and lost 10-34% of reproductives. The number of emerged workers positively correlated with that of reproductives produced and that of cells made during the season.