Data from: Viral prevalence is higher, while relative infection loads are lower, in later developmental stages of a univoltine insect herbivore

Pathogens represent critical agents of mortality for insects, yet their
ecological impacts remain poorly understood in many natural
systems.  Developmental resistance (i.e., a reduction in disease
susceptibility as hosts mature), along with age-related changes in ecology
and behavior, are expected to give rise to variation in pathogen pressure
across the host life cycle. However, the dynamics of pathogen infection
across long larval periods such as those in diapausing insects are
relatively unexplored. We used field-collected Euphydryas phaeton
caterpillars (Lepidoptera: Nymphalidae) to evaluate how interactions with
a naturally occurring entomopathogen, Junonia coenia densovirus, varied
across host development and diapause. We compared the frequency and
severity of viral infection during three stages of the life cycle:
post-diapause, pre-diapause, and diapause. Field-collected post-diapause
caterpillars were reared until death before viral screening, while
field-collected pre-diapause caterpillars were subsampled for viral
screening, allowing a portion to enter diapause to determine viral
prevalence and load following overwintering. Viral prevalence was higher
in post-diapause caterpillars, pupae, and adults, compared to relatively
immature pre-diapause caterpillars. However, early-instar (pre-diapause)
caterpillars that were infected with the virus harbored higher relative
viral loads, compared to late-instar (post-diapause) caterpillars, pupae,
and butterflies. In addition, viral prevalence was generally similar
across sampling regions, while viral loads exhibited inconsistent regional
differences across developmental stages. These results demonstrate that
viral prevalence and load can vary considerably across the life cycle of
an insect host and suggest that regional variation in infection severity
may be more evident during certain stages of development than others.
Moving forward, field and lab studies investigating the consequences of
pathogen infection should consider host developmental stage, as infection
parameters can change across development.