Species richness and patch dynamics of fruit-parasitic insects on southeast Alaskan plants

The species richness component of this study revealed that ten plant species were host to 7 fruit-parasite species, and 19 plant species showed no signs of fruit infestation, in the Juneau area of southeast Alaska. Dipterans and Coleopterans were completely absent locally. Many types of plants lacked fruit parasites both locally and among the same host-plant genera in North America north of Mexico. The number of fruit-parasite species per host species locally appears to be influenced by the type of fruit pulp, the number of fruit-parasite species per host genus regionally, and barriers to post-glacial dispersal into the local area such as inadequate time and geographic obstacles. Host geographic range had a weak but negative relationship to the local richness of fruit parasites. The number of plant species in a host genus was unrelated to the local richness of fruit parasites.;The patch dynamics component of this study revealed patch-level variation in the density of two fruit parasites, a moth (Lotisma trigonana Walsingham (Lepidoptera: Copromorphidae)) and a sawfly (Melastola resinicolor Marlatt (Hymenoptera: Tenthredinidae)). The larvae of these fruit parasites consume the seeds of Vaccinium alaskaense (Howell) and Vaccinium ovalifolium (Smith ex Rees) in southeast Alaska. The density of immatures was highest in "medium" patches of forest that have moderate tree cover and was low in both "open" patches with no tree cover and "closed" patches with heavy tree cover. The relationship between fruit-parasite density and fruit density did not show a resource concentration effect at the between-patch level but did show such an effect at the within-patch level. The high density of immature fruit parasites in the medium patches may result from the influence of multiple factors, including fruit density, the weight of seeds per fruit, nitrogen content of seeds, egg survivorship (in L. trigonana), and vertebrate frugivory. Attack by parasitoid wasps appears to have a negligible influence on between-patch variation in the density of immature fruit parasites.