Conclusions
A better understanding of the effects of multiple stressors,
particularly the complex interactions between pesticide exposure and
resistance for host-pathogen outcomes, is critical for effective pest
and vector control strategies and the protection of important insect
pollinators . Here, we identified antagonistic interactions between Bt
and OP that mitigated the effects of pesticides on fitness-related host
traits. Our results suggest that both pesticides and Bt individually
influence important demographic parameters like development time and
mortality rate, but that co-exposed hosts may actually perform better
than those exposed to pesticides alone. We also observed dampened
expression of important candidate genes upon dual exposure to OP andBtt and in Pyr-resistant individuals exposed to Bttcompared to the main effect of Btt exposure. Are these
within-host interaction effects sufficient to alter the dynamics of
disease in insect populations? Mathematical models would be useful to
address this question, as the answer will likely depend on feedbacks
from ecological variables like intraspecific competition, relative
transmission among single- and co-exposed hosts, and the relative costs
of pesticides and infection to host reproductive rates . Moreover, our
data suggest that the rise of pesticide resistance within populations
could reduce the magnitude of the interaction effects, likely altering
population outcomes. Overall, our results shine light on the
physiological and evolutionary processes that shape interactions among
two important ecological stressors and should prompt further study of
their interactions at multiple levels of biological organization on
ecological and evolutionary time scales.
Acknowledgements: We would like to thank three anonymous
reviewers for comments that helped improve previous versions of the
manuscript. We would like to thank William Galardi for assistance in
preliminary dose response experiments and Siqin Liu for assistance with
population maintenance. We are also grateful to Justin Critchlow and
Justin Buchannan for guidance with in vitro bacterial growth
curves. Last, we would like to thank Juan Luis Jurat-Fuentes for
comments on the manuscript. This work is funded by USDA NIFA
2019-67012-29659 provided to S.S.L.B. N.K.E.S. and A.T.T. were supported
in part by Alfred P. Sloan Foundation Fellowship FG-2020-12949 to A.T.T.