While conducting research on sunflowers, you discover that an emerging fungal pa
ID: 217729 • Letter: W
Question
While conducting research on sunflowers, you discover that an emerging fungal pathogen kills them by destroying their roots. The fungus uses honeybees, which pollinate your flowers, as a vector to transmit fungal spores among sunflower plants. The next year the farm reseeds, hoping that the fungus has died over the winter. Early in the growing season some plants begin dying again, but then the honeybee population develops colony collapse disorder and all the honeybees die. To compensate for the loss in pollinators, the farmers introduce large numbers of bumblebees. The number of new sunflower plants that become infected during the remainder of the growing season drops to near zero. Using the variables in the susceptible-infected-resistant (S-I-R) model equation: R0 = (S × I × b) ÷ (I × g), explain what has happened to alter the disease dynamics in the second year of your study and how this has occurred.
What do you think happened?
Explanation / Answer
In the susceptible-infected-resistant (S-I-R) model equation:
R0 = (S × I × b) ÷ (I × g)
S indicates the number of susceptible individuals in the population, in this case the sunflower plants, I is the number of infected individuals, b stands for the transmission rate, i.e., the rate at which susceptible plants are infected, g represents the rate of recovery or removal of infected plants from the population and 1/g is the average infectious period.
During the first year the fungal infection spread rapidly using honeybees as the vectors and hence R0= b /g > 1, the number of infected individuals in the sunflower population increased and hence the infection spread rapidly before the infected plants could be removed.
During the second year, as the fungus started to spread, plants started becoming infected but the number of infected plants was still lower than the number of susceptible plants so 'b' was lower. When the honeybees that acted as vectors of the disease, started dying, it further led to drop in value of 'b' and the plant infection entered a latent stage. The chain of transmission eventually broke down as the number of infectants reduced in the population with no vectors of the disease being available. Thus by the time the bumblebees were introduced in the farm, the number of infected plants available for the infection to spread further had gone below threshold and almost removed from the population. Hence, in the second year the spread of infection is seen to be almost nil.
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.