The effects of global warming on disease transmission in the fall armyworm Spodoptera frugiperda

Background/Question/Methods

Climate change research has mostly focused on the effects of global warming on abiotic interactions. How climate change alters biotic interactions between species has not been as well studied.  Biotic interactions that are tightly linked, such as those between a predator and its prey or a host and its pathogen, will most likely be affected by climate change and provide insight into these processes.  To examine the effects of increased temperatures on host-pathogen interactions, we conducted field and laboratory experiments on the fall armyworm Spodoptera frugiperda and its species-specific nucleopolyhedrovirus (SfNPV), a baculovirus.  Baculovirus systems for forest and crop-defoliating Lepidopterean larvae, such as the fall armyworm, offer a tractable and easily-manipulated system to study the effects of climate change.  In order for bacoluvirus transmission to occur, healthy larvae must eat foliage contaminated with infectious virus particles.  Thus, we manipulated both the temperature and number of virus particles on leaf tissue to determine how increased temperatures affected disease transmission.

Results/Conclusions

In the field, we established control and experimental plots in which we manipulated temperature by using open-top chambers (OTC).  In each plot, we planted a single soybean plant, a common food source for the fall armyworm, on which we placed a known number of infected first-instar larvae and enclosed each plant in a mesh bag.  After the infected larvae died, we placed healthy fourth-instar larvae on the plant.  We allowed them to feed for four days, collected them, and, then, reared them until death or pupation.  To further elucidate the potential mechanisms for observed changes in the field, we carried out a series of laboratory experiments to determine how changes in temperature affect development, feeding, and infection rates. The field transmission experiment indicates that transmission rates will likely change due to an increase in temperature.  In particular, increased temperatures increase disease transmission at intermediate levels of virus.  These changes are most likely due to a combination of factors related to development, feeding, and infection rates.