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2. Effects of habitat loss and fragmentation on the abundance and species richness of aphidophagous beetles and aphids in experimental alfalfa landscapes
- Creator:
- Grez, Audrey A., Zaviezo, Tania, Díaz, Sandra, Camousseigt, Bernardo, and Cortés, Galaxia
- Type:
- article, model:article, and TEXT
- Subject:
- Habitat fragmentation, habitat loss, experimental landscapes, coccinellids, carabids, aphids, and alfalfa
- Language:
- English
- Description:
- In agro-ecosystems, habitat loss and fragmentation may alter the assemblage of aphidophagous insects, such as foliar-foraging (coccinellids) and ground-foraging predators (carabids), potentially affecting intraguild interactions. We evaluated how habitat loss (0, 55 and 84%), fragmentation (1, 4 and 16 fragments) and their combination affected the abundance and species richness of coccinellids and carabids, and aphid abundance, both in the short-term (summer: December to February) and over a longer time span (autumn: March to May), when different demographic mechanisms may participate. We created four types of 30 × 30 m patches (landscapes) in which alfalfa was grown: Control (1F - 0%, 30 × 30 m patch of alfalfa with no fragmentation or habitat loss), 4F - 55% (4 alfalfa fragments, with 55% total habitat loss), 4F - 84% (4 alfalfa fragments, with 84% total habitat loss), and 16F - 84% (16 alfalfa fragments, with 84% total habitat loss). Each landscape type was replicated five times. Insects were sampled by sweep-netting and pitfall traps, from December (summer) to May (autumn). Total abundance and species richness of carabids, in the short-term, was highest in the 16F - 84% landscapes. Total abundance of adult coccinellids was similar among landscapes, but at the species level Hyperaspis sphaeridioides, in the short-term, and Adalia bipunctata, in the long-term, had their highest densities in fragments within landscapes with high habitat loss (84%), independently of habitat fragmentation. Species richness in the long-term was higher in the landscapes with 84% habitat loss. Among aphids, in the long term Aphis craccivora was less abundant in landscapes with high habitat loss and fragmentation (16-84%), while Therioaphis trifolii showed the opposite trend. These results suggest that habitat loss and fragmentation may increase the density and diversity of aphidophagous insects, while their effects on aphids are more variable.
- Rights:
- http://creativecommons.org/publicdomain/mark/1.0/ and policy:public
3. Measuring and modelling the dispersal of Coccinella septempunctata (Coleoptera: Coccinellidae) in alfalfa fields
- Creator:
- van der Werf, Wopke , Evans, Edward W., and Powell, James
- Type:
- article, model:article, and TEXT
- Subject:
- biological control, Coccinella septempunctata, sevenspotted lady beetle, Coccinellidae, dispersal, immigration, landscape, mark-recapture, modelling, space, Utah, alfalfa, sugar-spraying, and volatiles
- Language:
- English
- Description:
- Dispersal of the sevenspotted lady beetle, Coccinella septempunctata, was measured in a series of mark-release-recapture experiments in Utah alfalfa. In three experiments, samples were taken in a radial pattern around the release point. Released beetles for the most part left the 0.36 ha (68 m diameter) sample area within 24 hours, and their average residence time in the sample area was calculated as 12, 6 and 1.6 h in the three experiments, respectively. The spatial distribution of beetles around the point of release could be described with normal distributions whose variance increased linearly in time with 3.8, 1.1 and 0.34 m2 per hour. In three additional field experiments the departure of marked beetles was compared between sugar-sprayed plots and control plots. Residence time was 20-30% longer in sugar-sprayed plots than in control plots, with mean residences of 5.3, 3.6, and 2.9 h in the sugar-sprayed plots in the three experiments, respectively, and means of 4.4, 2.7, and 2.4 h in the control plots. The density of unmarked beetles rose by a factor of 10-20 in the sugar sprayed plots during the first 4 to 6 hours following early morning spraying of sugar. This rapid and substantial increase in density cannot be explained by the slightly longer residence time in sugar-sprayed plots. We hypothesize that the aggregation in sugar-sprayed plots is mostly due to greatly increased immigration into those plots, in response to volatiles produced by the plant-pest-predator assembly.
- Rights:
- http://creativecommons.org/publicdomain/mark/1.0/ and policy:public
4. Non-host volatiles do not affect host acceptance by alate virginoparae of Rhopalosiphum padi (Hemiptera: Aphididae) settled on the host plant surface
- Creator:
- Olivares-Donoso, Ruby and Niemeyer, Hermann M.
- Type:
- article, model:article, and TEXT
- Subject:
- Wheat, alfalfa, EPG, host acceptance, feeding behaviour, and aphid moods
- Language:
- English
- Description:
- Using electrical penetration graphs to monitor aphid feeding, it was shown that volatiles of a non-host plant (alfalfa, Medicago sativa L.) did not disrupt the process of host acceptance by alate virginoparae of the birdcherry-oat aphid, Rhopalosiphum padi L., once it was settled on a host plant (wheat, Triticum aestivum L.).
- Rights:
- http://creativecommons.org/publicdomain/mark/1.0/ and policy:public