LOCDIS

Safety in numbers or beware thy neighbour: collective motion and disease transmission in a migratory pest

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 Obiettivo del progetto (Objective)

'A key principle in the evolutionary ecology of disease is the degree to which hosts invest in defence against parasites and pathogens. Established concepts in this area include (1) that disease risk is a function of host density and (2) that risk of disease leads to selection on the host to minimize the potential costs of disease. A clear prediction that arises from these concepts is that hosts living at high densities should invest more in defence than those living at low densities: a hypothesis known as “positive density-dependent prophylaxis” (DDP). For the past three years I have studied the African armyworm system (Spodoptera exempta), a devastating crop pest which expresses an extreme form of density-dependent phenotypic plasticity positive-DDP in response to host crowding. An equally destructive agricultural pest, the Australian Plague Locust (APL), Chortoicetes terminifera, has been suggested to exhibit “negative-DDP”, with certain key immune functions shown to be lower in gregarious than in the solitary insects. This project will attempt to determine why species with similar migratory activity appear to have evolved contrary behavioural and immunological strategies to combat disease transmission. The APL is an ideal model system to study the effects of crowding and migration, occurring in a socio-politically stable continent, allowing state-of-the-art field and laboratory experimentation. I will use my knowledge of migratory host-pathogen dynamics and expertise in experimental biology to investigate three main objectives, a) to determine the spatial and temporal pattern of natural disease epizootics in APL populations, b) to compare immune function and disease resistance in gregarious and solitary locusts, and c) to quantify the impact of protein availability on immune function, host behaviour and disease resistance. This research will contribute to the knowledge-base in global food security and nutrition biology.'

Introduzione (Teaser)

Combating pest outbreaks using biological approaches is gaining ground on chemical pesticides. European researchers investigated how pest infections are influenced by nutrition and environmental conditions.

Descrizione progetto (Article)

According to evolutionary ecology theory, disease risk is a function of host density. From this, one can deduce that hosts living at high densities are faced with a higher risk of contracting disease and should invest more in defence against parasites and pathogens. This hypothesis is known as positive density-dependent prophylaxis and is evident in various crop pests, including the African armyworm, Spodoptera exempta.

However, the destructive agricultural pest Australian plague locust (APL), Chortoicetes terminifera, constitutes an exception to the above evolutionary principle. In this insect, certain key immune functions tend to be lower in groups than in solitary insects.

The scope of the EU-funded LOCDIS project was to determine why certain species are present with such contrary behavioural and immunological strategies to combat disease transmission. In this context, the consortium investigated the spatial and temporal pattern of natural disease epizootics in APL populations. Using next-generation DNA sequencing they identified which microbial strains were associated with different locust field populations.

Next, they compared the immune function and disease resistance in locusts raised in groups or in solitary conditions. To this end, they tested the survival of different insects against the fungus Metarhizium acridum. They also quantified the impact of locust diet on immune function, host behaviour and disease resistance.

Scientists discovered that dietary protein influenced immune responses to a greater extent than carbohydrates, but this was not sufficient to protect locusts from fungal disease. One theory proposed was that the fungus was feeding on the protein in the insect's haemolymph, thereby overcoming host immune effectors. In field locust populations, immune function was tightly associated with haemolymph protein content and body lipid content, clearly underscoring the importance of nutritional physiology to locust survival.

These findings have obvious implications for pest outbreaks and the use of biological pesticides in the control of locust populations.