Aphid colony turn‐over influences the spatial distribution of the grain aphid Sitobion avenae over the wheat growing season

Abstract

1 Temporary habitats are characterized by the appearance and disappearance of patches in which resources are available for a limited period only. Organisms living in those environments usually exhibit adaptive traits, such as a high ability to find and exploit new patches. Among them are phytophagous insects, such as crop pests living in agroecosystems. Understanding how phytophagous insects invade a new patch is of great agricultural importance. 2 Here, we investigated how aphids colonize a wheat field by studying the spatial and temporal dynamics of their populations at large (field) and fine (group of host plants) scales. 3 The sampling design consisted of counting and locating aphid colonies within 30 0.25 m 2 squares randomly spaced in a 1.5-ha winter wheat field over 2 months. All colonies were precisely located within the squares and their composition in terms of morphs was determined. 4 We show that: (i) immigration of winged aphids was a major factor driving the aphid population dynamics during a large part of the season and (ii) within the field, populations established late in the growing season. Aggregated, populations of aphids became progressively homogeneously distributed at the field scale. At the scale of a 0.25 m 2 square, infested plants were clustered in randomly distributed small patches, and aphid colonies experienced high extinction rates, suggesting failure in population establishment. 5 Because immigration may considerably influence both population dynamics and spatial distribution, our study suggests that future predictive models should give a greater weight to spring immigrants.

Weeds, aphids, and specialist parasitoids and predators benefit differently from organic and conventional cropping of winter cereals

“…However, it was perhaps not surprising given that in previous studies it was pointed out that there was no significant periodicity in the dynamics of the aphid or predators, suggesting that there was no clear predator-prey cycle (Leslie et al 2009). It is also likely that other factors were involved such as the ability of aphids to move of their colonies and to develop rapidly (Winder et al 1999) or the difficulty to estimate the impact of predators because of the ephemeral interactions with the aphid prey (Fievet et al 2007). There were also indications that weather directly affected peak density of M. dirhodum and its impact on the spatial distribution of Coccinella septempunctata populations (Leslie et al 2009).…”

Grain aphid population structure: no effect of fungal infections in a 2‐year field study in Denmark

“…This also indicates a limited clonal selection in the parthenogenetic phase of S. avenae in single field samples. Winged aphids are important for S. avenae population dynamics during a large part of the season ( Fievet et al , 2007 ) due to their high migration capacity over large distance, but also due to local movements. In addition, apterous S. avenae showed a high disposition to move between plants within fields ( Dean, 1973;Holmes, 1988;DeBarro et al , 1994 ); thus, migration may explain the time-dependent differentiation.…”

Seasonal variations of host resources influence foraging strategy in parasitoids

“…Observations over the last decades indicate that during winter, population densities are very low, and R. padi is the dominant species in the aphid community, followed by S. avenae, then M. dirhodum, both being rare during winter (Krespi, 1990;Andrade et al, 2013). During spring, total aphid population densities increase, with S. avenae and M. dirhodum becoming the dominant species, whereas R. padi nearly disappears from the community in cereal fields (Krespi, 1990;Fievet et al, 2007). Aphid and parasitoid densities are low in winter, but parasitism rate can reach 38% (Andrade et al, 2013).…”