DOI: 10.5061/dryad.37972
title: Data from: Hoverfly preference for high honeydew amounts creates enemy-free space for aphids colonizing novel host plants

description: The existence of an enemy-free space can play an important role in aphid
 host race formation processes, but little is known about the mechanisms
 that create an area of low predation pressure on particular host plants.
 In this paper we identify a mechanism generating lower predation pressure
 that promotes the maintenance of the different host races of the pea aphid
 (Acyrthosiphon pisum) complex, a well-studied model for ecological
 speciation. The pea aphid consists of at least 15 genetically distinct
 host races which are native to specific host plants of the legume family,
 but can all develop on the universal host plant Vicia faba. Previous work
 showed that hoverfly (Episyrphus balteatus) oviposition preferences
 contribute to the enemy-free space that helps to maintain the different
 pea aphid host races, and that higher amounts of honeydew are more
 attractive to ovipositing hoverflies. Here we demonstrated that aphid
 honeydew is produced in large amounts when aphid reproduction rate was
 highest, and so is an important oviposition cue for hoverflies under field
 conditions. However, on less suitable host plants, where honeydew
 production is reduced, pea aphids enjoy lower predation rates. A reduction
 in enemy pressure can mitigate the performance disadvantages of aphids
 colonizing a novel host, and probably plays an important role in pea aphid
 host race formation.
description: data_Vosteen et al.
 2016_Journal of Animal EcologyVosteen et al. 2016_R
 Skript_Fig. 2 quantitative honeydew collectionFig. 2 – honeydew
 collection: Dry weight of honeydew collected from different pea aphid
 clone – host plant combinations during 24 h. Plants were infested with 50
 adult pea aphids. Honeydew amount was analyzed with a one-way-ANOVA. In
 cases of non-homogenous variances, data were log-transformed. The Tukey
 Honest Significant Difference method was used for post-hoc
 comparison.Vosteen et al. 2016_R
 Skript_Fig. 3 honeydew attractivityFig. 3 – hoverfly
 oviposition experiment: To test which cues elicit hoverfly oviposition
 under field conditions, eggs were counted on plants that were previously
 aphid infested, non-infested plants treated with aphid honeydew and
 non-treated control plants in the presence and absence of pea aphids.
 Plants were left for 30 h in the field and hoverfly eggs were counted
 afterwards. A randomized block design was used in this experiments. Each
 block consisted of all six treatments. Number of hoverfly eggs was
 analyzed with a generalized linear mixed effects model with a poisson
 error distribution, using blocks as random effects (random intercept) and
 treatments as fixed effects. P-values for explanatory variables were
 obtained by sequentially deleting explanatory variables and comparison of
 the more complex model with the simpler model with a likelihood ratio test
 (Zuur et al. 2009). Factor level reductions were used to reveal
 differences between levels of a treatment (Crawley
 2013).Vosteen et al. 2016_R
 Skript_Fig. 4a relative attractivityFig. 4a – honeydew
 quality: Honeydew collected from 6 different pea aphid clone – host plant
 combinations was applied to Vicia faba. Plants were left for 30 h in the
 field and hoverfly eggs were counted afterwards. A randomized block design
 was used in this experiments. Each block consisted of all six treatments.
 Number of hoverfly eggs was analyzed with genaralized linear mixed effect
 model with poisson distribution.Vosteen et al. 2016_R
 Skript_Fig. 4a honeydew
 quality.rVosteen et al. 2016_R
 Skript_Fig. 4b honeydew quantityFig. 4b – honeydew
 quantity: Six, 12 or 18 droplets of this honeydew collected from Pisum
 race aphids feeding on Vicia faba were applied to uninfested Vicia faba.
 Plants were left for 30 h in the field and hoverfly eggs were counted
 afterwards. A randomized block design was used in this experiments. Each
 block consisted of all three treatments. Number of hoverfly eggs was
 analyzed with a generalized linear mixed effect model.Vosteen et al. 2016_R
 Skript_Fig. 5 less suitable plant 2014Fig. 5 – less suitable
 plants I: Trifolium and Pisum race aphids were placed both on Trifolium
 pratense and Pisum sativum, so that each race was reared on its native
 host and a less suitable plant. Plants were left for 14 days in the field
 and number of hoverfly eggs, hoverfly larvae and surviving aphids was
 recorded several times. A randomized block design was used in this
 experiments. Each block consisted of all four treatments. Data was
 analyzed with mixed effects models using blocks as random effects (random
 intercept) and treatments as fixed effects. P-values for explanatory
 variables were obtained by sequentially deleting explanatory variables and
 comparison of the more complex model with the simpler model with a
 likelihood ratio test (Zuur et al. 2009). Factor level reductions were
 used to reveal differences between levels of a treatment (Crawley 2013).
 Number of hoverfly eggs and larvae were analyzed with generalized linear
 mixed models with either a Poisson error distribution, or a negative
 binomial error distribution (glmm with the lmer function of the lme4
 package (Bates et al. 2014) whichever fitted best the data of a certain
 experiment. In cases were only a few hoverfly eggs or larvae were present
 and several plants without hoverfly eggs or larvae occurred, presence /
 absence data were used and analyzed with Bernoulli
 glmms.Vosteen et al. 2016_R
 Skript_Fig. 6 less suitable plant 2014_AugFig. 2 – less suitable
 plants II: Trifolium and Pisum race aphids were placed both on Trifolium
 pratense and Pisum sativum, so that each race was reared on its native
 host and a less suitable plant. Plants were left for 6 days in the field
 and number of hoverfly eggs, hoverfly larvae and surviving aphids was
 recorded two times. A randomized block design was used in this
 experiments. Each block consisted of all four treatments. Survival of
 aphid colonies was analyzed with a generalized linear mixed effect model
 with a binomial distribution. Presence of hoverflz eggs and hoverflz
 larvae was analyzed with a generalized linear mixed effect model with
 poisson error distribution.Vosteen et al. 2016_R
 Data_Fig. 2e quantitative honeydew collectionfile used for
 statistical analysis in RVosteen et al. 2016_R
 Data_Fig. 2f quantitative honeydew collectionfile used for
 statistical analysis in RVosteen et al. 2016_R
 Data_Fig. 3 honeydew attractivityfile used for
 statistical analysis in RVosteen et al. 2016_R
 Data_Fig. 4a honeydew qualityfile used for
 statistical analysis in RVosteen et al. 2016_R
 Data_Fig. 4b honeydew quantityfile used for
 statistical analysis in RVosteen et al. 2016_R
 Data_Fig. 5 less suitable plant 2014file used for
 statistical analysis in RVosteen et al. 2016_R
 Data_Fig. 6 less suitable plant 2014_Augfile used for
 statistical analysis in R