The effect of egg load and host deprivation on oviposition behaviour in aphidophagous hoverflies

1. Two species of aphidophagous hoverfly, Episyrphus balteatus and Syrphus ribesii, were tested for the effects of egg load and host deprivation on oviposition choices. 2. Egg load affected the total number of eggs laid in E. balteatus but not in S. ribesii, however it did not affect the proportion laid on any one aphid in E. balteatus but did affect the proportion laid on any one aphid in S. ribesii. The rank order of preferences remained unchanged by age or host deprivation. 3. The dominant effects on host choices were aphid species (in both syrphids) and presentation order (in E. balteatus). 4. Being deprived of hosts increased egg load substantially in E. balteatus, and increasing time of deprivation also had an effect on discrimination; there was no effect of host deprivation in S. ribesii. 5. Reasons for these patterns are discussed.