Aphid population response to agricultural landscape change: A spatially explicit,individual-based model

A spatially explicit individual-based simulation model has been developed to represent aphid population dynamics in agricultural landscapes. The application of the model to Rhopalosiphum padi (L.) population dynamics is detailed, including an outline of the construction of the model, its parameterisation and validation. Over time, the aphids interact with the landscape and with one another. The landscape is modified by varying a simple pesticide regime, and the multi-scale spatial and temporal implications for a population of aphids is analysed. The results show that a spatial modelling approach that considers the effects on the individual of landscape properties and factors such as wind speed and wind direction provides novel insight into aphid population dynamics both spatially and temporally. This forms the basis for the development of further simulation models that can be used to analyse how changes in landscape structure impact upon important species distributions and population dynamics.     

Defensive behavior of ants in a mutualistic relationship with aphids

Mutualistic relationships between ants and aphids are well studied but it is unknown if aphid-attending ants place a greater relative importance on defending aphids from aphid-predators or from competing ant colonies. We tested the hypothesis that aphid-attending ants defend their aphids against aphid-predators more aggressively than against ants from neighboring colonies. We conducted introduction trials by placing an individual non-predatory insect, an aphid-predator, or a foreign conspecific ant on the leaf of a resident ant. We found that ants did not attack non-predatory insects, but did attack competing ants and aphid-predators. When we presented resident ants with both the threats (i.e., predator and competitor) at the same time, residents always attacked potential competitors as opposed to aphid-predators. We suggest this behavior may reduce the likelihood of raids by neighboring colonies. Ants appear to balance both the energetic costs of making an attack and the costs associated with losing aphids to a predator, against the benefits of signaling their defensive ability to rivals and/or preventing rivals from gaining knowledge of a potential food resource.     

Response of the bird cherry-oat aphid (Rhopalosiphum padi) to climate change in relation to its pest status, vectoring potential and function in a crop-vector-virus pathosystem

Global climate change threatens world food production via direct effects on plant growth and alterations to pest and pathogen prevalence and distribution. Complex relationships between host plant, pest, pathogen and environment create uncertainty particularly involving vector-borne diseases. We attempt to improve the understanding of the effects of climate change via a detailed review of one crop-vector-pathogen system.The bird cherry-oat aphid, Rhopalosiphum padi, is a global pest of cereals and vector of yellow dwarf viruses that cause significant crop losses in cereals. R. padi exhibits both sexual and parthenogenetic reproduction, alternating between crops and other host plants. In Australia, only parthenogenesis occurs due to the absence of the primary host, thus the aphid continuously cycles from grasses to cereals, allowing for continuous virus acquisition and transmission.We have reviewed the potential impact of future climate projections on R. padi population dynamics, persistence, abundance, dispersal and migration events as well as the interactions between vector, virus, crop and environment, all of which are critical to the behaviour and development of the vector and its ability to transmit the virus. We identify a number of knowledge gaps that currently limit efforts to determine how this pathosystem will function in a future climate.     

Predator–prey fuzzy model

In this work we have used fuzzy rule-based systems to elaborate a predator–prey type of model to study the interaction between aphids (preys) and ladybugs (predators) in citriculture, where the aphids are considered as transmitter agents of the Citrus Sudden Death (CSD). Simulations were performed and a graph was drawn to show the prey population, the potentiality of the predators, and a phase-plane. From this phase-plane, a classic model of the Holling–Tanner type is fitted and its parameters were found. Finally, we have studied the stability of the critical points of the Holling–Tanner model.     

Aphid and episodic O3 injury in arugula plants (Eruca sativa Mill) grown in open-top field chambers

Aphid attacks and tropospheric ozone (O₃) cause stress and considerable damage in both wild and cultivated plants. Induced defense responses to aphid attacks and O₃ exposure share signaling pathways with common points. We investigated the plant–aphid interaction under O₃ exposure using open-top O₃ chambers. Ozone leaf injury was lower in aphid-infested plants than in aphid-free plants, although herbivore damage was not evident. Aphid population growth was strongly affected by previous exposure to O₃ but no direct effect of O₃ was observed. The possibility that during O₃ episodes, herbivores may reduce O₃ damage on host plants and that the offspring of the exposed aphids have lower population growth rates opens new and intriguing questions about potential effects of future increased tropospheric O₃ levels on plant–insect interactions.