Are primary woody hosts ‘island refuges’ for host‐alternating aphids and important for colonization of local cereals?

Abstract

Only few studies are available dealing with the relation between winter host density and spatial distribution and spring colonization of winter cereals by the host-alternating cereal aphid species Rhopalosiphum padi and Metopolophium dirhodum. Large-scale studies in climatically different agroecosystems in Germany from 2004 to 2006 revealed for R. padi and M. dirhodum larger spring/summer populations in landscapes with higher densities of winter hosts. A small-scale study was performed in winter wheat fields adjacent to a large hedge with several typical winter hosts plants, bird cherry (Prunus padus) and wild rose species (Rosa spp.) to indentify distance effects (0-8, 8-24 and 24-60 m). Weekly measurements of aphid density between May to July showed significantly higher densities of R. padi compared with those of other aphids. Statistical analysis (Tukey-Kramer test and regression analyses) revealed significant gradients from the hedge to the field centre for R. padi and M. dirhodum. In comparative studies, winged R. padi from winter and adjacent summer hosts were genotyped using four microsatellite markers. The results showed that individuals from a certain winter host were not genetically similar with individuals from neighbouring summer hosts; it, therefore, seems that winter host clones did not significantly contribute to population built-up in cereal fields over short distances. It could be concluded that on a regional scale, the density of sources for early migrants of R. padi is important for colonization intensity of surrounding summer hosts, but that the high local movement intensity and the relative small proportion of aphids that could be analysed in such tracking studies are blurring close spatial relations within short time periods.

Genetic Diversity of Sitobion avenae (Homoptera: Aphididae) Populations from Different Geographic Regions in China

“…A study showed that the aphid clones on the winter host plant did not significantly contribute to the spring/summer population build-up in the cereal fields over short distances, but that the density of sources for early migrants, on a regional scale, is important for the establishment of the population [67] . Therefore, the migration of aphids plays an important role in genetic structure.…”

Maintaining genetic diversity and population panmixia through dispersal and not gene flow in a holocyclic heteroecious aphid species

“…Many unique alate clones with high genetic diversity could still potentially colonize a secondary host field but would be difficult to detect because clonal amplification only favors those with the highest reproductive output. In Klueken et al (2011), secondary host colonizers from the primary plant source had a R of 0.96, and the earliest aphid populations on the secondary host had a R of 1.0, suggesting high initial genotypic diversity during secondary host colonization. Selection could be in the form of plant quality (Noma et al, 2010), insecticidal seed treatments (Magalhaes et al, 2009), soybean variety or other characteristics related to common agronomic practices.…”

“…However, in some cases, especially with late populations, genotypic diversities were close or at maximum, that is, every individual was represented by a different clonal genotype. In these instances, we also included common population genetic statistics used in previous aphid genetic studies (Miller et al, 2003;Vialatte et al, 2005;Klueken et al, 2011), as data mirrored randomly admixed populations atypical of clonal reproduction. The probability of two individuals that share a MLG (that is, clones) resulting from a sexual reproduction event was calculated using P sex using GenClone (ArnaudHaond et al, 2007).…”

“…Although mortality from primary to secondary host has not been studied, Ward et al (1998) estimated survival of R. padi during autumn migration to primary hosts at 0.6%. Using four microsatellites, Klueken et al (2011) compared three potential primary plant sources and found that aphids in the nearest secondary host field were genetically similar to just a single primary plant with little or no contribution from the other two potential sources. Perhaps the largest mortality factor, especially when the secondary host is a cultivated crop, is the phenological disjunction between alate aphids on the primary host and secondary host emergence (Ragsdale et al, 2004;Michel et al, 2009a).…”

Probing behavior of bird cherry-oat aphid Rhopalosiphum padi (L.) on native bird cherry Prunus padus L. and alien invasive black cherry Prunus serotina Erhr. in Europe and the role of cyanogenic glycosides

“…At present, the species is regarded as an intensively spreading invasive alien that has the ability to form monospecific stands in nature (Starfinger et al 2003). The recent study by Klueken et al (2012) demonstrated that the colonization of summer hosts by R. padi depends on the density of winter hosts which are a source of early season migrants. It is likely that the increasing abundance of P. serotina may contribute to the bird cherry-oat aphid population build-up in the adjacent cereal crops.…”