What is pathogen-mediated insect superabundance?

Abstract

When increasing abundance of insect vectors is manifest across multiple fields of a crop at the landscape scale, the phenomenon is sometimes referred to as insect superabundance. The phenomenon may reflect environmental factors (i.e. environmentally mediated insect superabundance , EMiS), including climatic change. A number of pathogens, however, are also known to modify the quality of infected plants as a resource for their insect vectors. In this paper, we term increasing vector abundance when associated with pathogen modification of plants as pathogen-mediated insect superabundance (henceforth PMiS). We investigate PMiS using a new epidemiological framework. We formalize a definition of PMiS and indicate the epidemiological mechanism by which it is most likely to arise. This study is motivated by the occurrence of a particularly destructive cassava virus epidemic that has been associated with superabundant whitefly populations in sub-Saharan Africa. Our results have implications for how PMiS can be distinguished from EMiS in field data. Above all, they represent a timely foundation for further investigations into the association between insect superabundance and plant pathogens.

Epidemiological and ecological consequences of virus manipulation of host and vector in plant virus transmission

“…In Eq (22) α is the underlying rate at which vectors die, and δ controls any increase in the death rate as more plants are visited per feed. Since the number of plants visited per feed is constrained via θ ± �1, the form we have taken corresponds to an additional death rate for all values δ>0.…”

“…From Eq (4), the probability a viruliferous vector lands on a susceptible plant is S/(S+ν + I) and the probability a viruliferous vector lands on an infected plant is ν + I/(S+ν + I). As the population density of infected plants (I) is small at the time of introduction, then from Eq (22), the per capita death rate of viruliferous vectors, h + (S,I) is approximately α(1+δ(1/ω + −1)). These vectors additionally lose infectivity at rate τ.…”

“…Where a virus modifies plant quality sufficiently to improve it as a feeding resource, this can lead to an accompanying increase in vector abundance termed as pathogen-mediated insect superabundance [ 22 ]. However, vector preferences are not always consistent across different hosts, even when virus-infected plants are generally higher quality hosts [ 23 , 24 ].…”

The role of pathogen‐mediated insect superabundance in the East African emergence of a plant virus

“…

preceding paper (Donnelly & Gilligan, 2020), we refer to this phenomenon as insect superabundance to signify high incidence at both the individual plant scale as well as the landscape scale (note that some authors prefer to refer to this phenomenon using the terminology of 'insect outbreak', or, simply 'high insect abundance').Superabundance may simply reflect high environmental suitability for the vector (henceforth we call this scenario environmentmediated insect superabundance, EMiS). An alternative cause of superabundance is the invasion of a novel insect vector strain capable of reaching higher abundance than the previously dominant strain (henceforth we call this scenario invasive vector insect superabundance, INViS).

…”

“…preceding paper (Donnelly & Gilligan, 2020), we refer to this phenomenon as insect superabundance to signify high incidence at both the individual plant scale as well as the landscape scale (note that some authors prefer to refer to this phenomenon using the terminology of 'insect outbreak', or, simply 'high insect abundance').…”