Host plant defense produces species-specific alterations to flight muscle protein structure and flight-related fitness traits of two armyworms

Insects manifest phenotypic plasticity in their development and behavior
in response to plant defenses, via molecular mechanisms that produce
tissue-specific changes. Phenotypic changes might vary between species
that differ in their preferred hosts and these effects could extend beyond
larval stages. To test this, we manipulated the diet of southern armyworm
(SAW; Spodoptera eridania) and fall armyworm (FAW; Spodoptera frugiperda)
using a tomatomutant for jasmonic acid plant defense pathway (def1), and
wild-type plants, and then quantified gene expression of Troponin t (Tnt)
and flight muscle metabolism of the adult insects. Differences in Tnt
spliceform ratios in insect flight muscles correlate with changes to
flight muscle metabolism and flight muscle output. We found that SAW
adults reared on induced def1 plants had a higher relative abundance (RA)
of the A isoform of Troponin t (Tnt A) in their flight muscles; in
contrast, FAW adults reared on induced def1 plants had a lower RA of Tnt A
in their flight muscles compared with adults reared on def1 and controls.
Although massadjusted flightmetabolic rate showed no independent host
plant effects in either species, higher flight metabolic rates in SAW
correlated with increased RA of Tnt A. Flight muscle metabolism also
showed an interaction of host plants with Tnt A in both species,
suggesting that host plants might be influencing flight muscle metabolic
output by altering Tnt. This study illustrates how insects respond to
variation in host plant chemical defense by phenotypic modifications to
their flight muscle proteins, with possible implications for dispersal.