Predator Abundance in Alfalfa Fields in Relation to Aphids, Within-Field Vegetation, and Landscape Matrix

Abstract. The relationships between predatory Heteroptera and their potential prey species were investigated during two crop seasons in an inter-mountain area close to the Pyrenees (Iberian Peninsula). Regression was used to analyze the potential numerical responses shown by heteropterans to aphids and other potential prey during alfalfa intercuts (the plant growth period between cuts) of high aphid occurrence. The most abundant heteropterans were Orius spp., Nabis spp. and mirids, and all were present in alfalfa stands throughout the season. Acyrthosiphon pisum was the prevalent species during the 2 nd intercut, Therioaphis trifolii during the 4 th and Aphis craccivora during the 5 th . We performed simple regression analysis between the Orius sp., Nabis sp. and mirids and the prevalent aphid species, forward multiple regression analysis between heteropterans and all possible soft-bodied prey species; and both analyses for coccinellids, as relative aphid predator specialists. The heteropterans responded numerically to A. pisum but not to T. trifolii or A. craccivora. Heteropterans also showed numerical responses to other potential prey (leafhoppers, thrips, and other soft bodied prey) that remained at low densities throughout the season. All these preys may contribute to the presence of heteropterans in alfalfa stands throughout the season. The results suggest that heteropterans may contribute to reduce A. pisum, particularly at the beginning of the growing season, and on other potential pests when they invade or recolonize alfalfa, and may help to delay or prevent the build-up of these pest populations.

Section: Discussionmentioning

confidence: 78%

Heteropterans as aphid predators in inter-mountain alfalfa

Pons¹,

Lumbierres²,

Albajes³

2009

“…and N. provencalis) and Coccinellidae were more abundant in alfalfa fields when aphid density increased. Previous studies have demonstrated a numerical response by several predatory groups, e.g, coccinellids (Neuenschwander et al, 1975;Frazer et al, 1981;Elliott et al, 2002) or Nabidae (Elliott et al, 2002) to aphids in alfalfa fields. Neuenschwander et al (1975) documented that polyphagous Heteroptera were important in aphid control, when coccinellids were inactive or left the fields.…”

Section: Discussionmentioning

confidence: 99%

“…Additionally, the structure of the landscape matrix may affect predator abundance. Elliott et al (2002) reported that landscape variation was an important factor determining predator abundance, but other factors, including the abundance of alternative prey should be considered, especially for polyphagous predators like Orius spp. and N. provencalis.…”

Section: Discussionmentioning

confidence: 99%

Epigeal aphidophagous predators and the role of alfalfa as a reservoir of aphid predators for arable crops

Pons¹,

Núñez²,

Lumbierres³

et al. 2005

Abstract. The relative occurrence and seasonal abundance of aphidophagous predators (Insecta and Arachnida) were determined in alfalfa fields at two locations in the northeast Iberian Peninsula, using D-Vac and sweep-net sampling techniques. Among the insects, Heteroptera, Dermaptera, Neuroptera, Coleoptera and Diptera were found. The relative abundance of predators was similar at the two locations. Polyphagous predators were much more abundant than aphid specific species. Heteroptera were the most abundant order of insect predators: members of the Nabidae, Anthocoridae and Miridae were very common. Coleoptera were also abundant, represented mainly by the family Staphylinidae. Coccinellidae were less abundant and their occurrence coincided with maximum aphid presence. There was a low occurrence of other aphid-specific predators, i.e. Diptera: Syrphidae and Neuroptera: Chrysopidae. Arachnida varied between localities (from 35% to 65%). Over a five-year period, numerical responses by Orius spp., Nabis provencalis and Coccinellidae to aphids were found using polynomial regression models; however the abundance of predators was weakly explained by aphid abundance. Alfalfa, maize and winter cereals share similar aphid predator groups and these crops partially coincide in time, enabling the movement of predators among crops. The persistence of several predatory groups (Anthocoridae, Nabidae, Staphylinidae, Araneae) during most of the season suggests that alfalfa plays a major role as a reservoir of aphid predators.

“…Even though aphid abundance may be related with the permanence of ladybirds in the landscape, it does not explain the higher abundance of ladybirds in the most fragmented landscapes observed in our study. Several works have noted that the aggregative responses of coccinellids are not well associated with aphid abundance, or that they respond to aphid density only at certain spatial scales (Ives et al, 1993;Elliott et al, 2002;With et al, 2002). At larger scales, other mechanisms like ladybird immigration to the landscape, reproduction and survival may have a stronger influence in determining the abundance of ladybirds (Bowman et al, 2002;Grez et al, 2004).…”

Section: Discussionmentioning

confidence: 99%

Ladybird (Coleoptera: Coccinellidae) dispersal in experimental fragmented alfalfa landscapes

Grez¹,

Zaviezo²,

Ríos³

2005

Abstract. Habitat fragmentation may affect the dispersal behaviour of individuals across the landscape. If there is a high boundary contrast between the remaining fragments and the matrix, individuals should tend to stay inside the fragments, but the configuration of the landscape, i.e. the level of fragmentation and isolation distance between fragments, may modulate this. To test these ideas, we made several mark-recapture experiments with the ladybird Eriopis connexa (Germ.) in manipulated alfalfa model landscapes (30 × 30 m). Specifically we evaluated (i) ladybird movement and permanence in alfalfa and bare ground areas, (ii) how they move across fragment/matrix boundaries, (iii) how their movement between fragments within a landscape is affected by fragmentation level and isolation distance, and (iv) how their permanence in the landscape is affected by fragmentation level and isolation distance. The fragmented alfalfa landscapes had a constant level of habitat loss (84%), but varied in the level of habitat fragmentation (4 or 16 fragments), and isolation distance between fragments (2 or 6 m). We also sampled aphid abundance in the different landscapes through time. We found that ladybirds stay longer and displace less in alfalfa than on bare ground, and that they move less from the alfalfa fragments to the neighbouring bare ground matrix than vice versa. At the landscape level, ladybirds had a higher inter-fragment movement when fragments were closer, they tended to remain in less fragmented landscapes, regardless of their isolation distance. Aphid abundance increased in time, but it was similar in all landscapes. Ladybird movement within fragments, in the matrix and in the boundary between both habitats explains why ladybirds concentrate within alfalfa fragments. However, their dispersal movements at the landscape level do not reflect the higher abundance sometimes found for several species of ladybirds in more fragmented landscapes. At this larger scale, other mechanisms may have a stronger influence in determining the abundance of ladybirds.