Two important relationships in parasitoid evolutionary ecology are those between adult size and fitness and between host quality and sex ratio. Sexually differential size-fitness relationships underlie predicted sex-ratio relationships. Despite each relationship receiving considerable attention, they have seldom been studied simultaneously or using field data. Here we report the biology of Anoplius viaticus paganus Dahlbom, a little known parasitoid of spiders, using field and laboratory data. We found that larger foraging females were able to select larger host spiders from the field, thus identifying a relatively novel component of the size-fitness relationship. Larger offspring developed from larger hosts and, in agreement with the prediction of the host quality model of sex allocation, were generally female. Data on the size-fitness relationship for males are lacking and, in common with many prior studies, we could not evaluate sexually differential size-fitness relationships as an explanation for the observed sex-ratio patterns. Nonetheless, A. v. paganus exhibited one of the strongest relationships between host size and offspring sex ratio yet reported.

The principal objective of this project was to determine whether Hedera helix was distributed randomly or exhibited host preferences within Drayton Wood, Norwich. 200 random tree samples >10cm diameter were studied. Of these, the CBH (circumference breast height), bark texture, abundance of H. helix and growth form were recorded. The percentage of ground covered by H. helix around the base of the sample trees was also recorded. Finally, the distance of the sample trees from the outer reaches of the wood and canopy cover were measured.Hedera helix was not distributed over potential host trees homogenously, but exhibited host associations. Quercus robur, Crataegus monogyna and Pinus sylvestris tree species were found to have a higher abundance of H. helix than expected by chance, whereas Acer pseudoplatanus and Betula pendula were found to have less H. helix vines than expected. Furthermore juvenile and mature vines were not distributed equally. Acer pseudoplatanus hosted more juveniles and less adults than expected, whereas Quercus robur and Pinus sylvestris hosted less juveniles and more mature vines than expected. Vines were not distributed independently of host size. Those trees <100cm CBH had a lesser stem abundance than expected, whereas those vines >100cm CBH had a greater stem abundance than expected. Host preference was exhibited for those large CBH trees with rough bark as opposed to large CBH trees with smooth bark. There was a higher abundance of H. helix (ground and trunk cover) with distance from the edge. Ground cover was greater under those trees hosting H. helix than those not supporting H. helix.Light did not play a major role in the distribution and abundance of H. helix (ground cover and trunk cover).Key Words: host selectivity, host size, bark texture, ground cover, location, light.