The ectoparasitization ofColeophora alticolella(Lepidoptera) in relation to its aititudinal distribution

Abstract

Abstract.1. The parasitization of the larvae ofColeophora alticolella. feeding onJuncus squarrosus, was investigated at a series of altitudes from 15 to 520m above sea‐level in northern England during 1977 and 1978.2. Six species of primary parasitoid and one hyperparasitoid were reared from this host. Five of the primary parasitoids were ectophagous; only two specimens of the endoparasitoid,Gonotypus melanostoma, were reared.3. All of the parasitoid species were recorded at 15 m but fewer at sites of higher altitude. Only one species,Scambus brevicomis, was recorded above 305 m, and none above 395 m. The hyperparasitoid,Tetrastichus endemus, waspresent only at 15 m.4. Percentage parasitization was highest at 15 m; it was reduced from 51% to only 2% between 215 and 305 m in 1978. There was an increase in host density over this altitudinal range.5. Three species,Scambus brevicomis. Elachertus olivaceusandEuderus viridis, accounted for most of the parasitization, but their relative proportions vaned at different altitudes.6. The sex‐ratios of the parasitoids reared fromColeophora alticolellaranged from 3.2% females forScambus brevicomis, which is considered to also use larger hosts, to 99.4% females forElachertus olivaceus, which develops by thelytokous parthenogenesis.7.Euderus viridisandScambus brevicomisstarted to attack theColeophora alticolellalarvae at a later date at 245 m than at 15 m, but attack byElachertus olivacatswas not delayed at the higher site.