Sub-lethal viral exposure and growth on drought stressed host plants changes resource allocation patterns and life history costs in the speckled wood butterfly, Pararge aegeria

This study in­ves­ti­gated the in­ter­ac­tive ef­fects of growth on drought stressed host plants and pathogen chal­lenge with the bac­ulovirus Au­to­grapha cal­i­for­nica nu­cle­opoly­he­drovirus (AcM­NPV) on sur­vival and fit­ness-re­lated traits us­ing the Speck­led Wood but­ter­fly, Pararge aege­ria (L.). Ex­po­sure to AcM­NPV sig­nif­i­cantly re­duced sur­vival to pu­pa­tion. For sur­viv­ing lar­vae, sub-lethal in­fec­tion sig­nif­i­cantly de­creased daily mass ac­qui­si­tion rates and pu­pal mass. Growth on drought stressed plants in­creased daily mass ac­qui­si­tion rates re­sult­ing in heav­ier pu­pae, and in­creased re­source al­lo­ca­tion to adult re­pro­duc­tion. The in­ter­ac­tion be­tween host plant drought and vi­ral ex­po­sure re­sulted in dif­fer­ent re­source al­lo­ca­tion strate­gies, and thus dif­fer­ent growth tra­jec­to­ries, be­tween lar­vae. This in turn re­sulted in sig­nif­i­cantly dif­fer­ent al­lo­met­ric re­la­tion­ships be­tween lar­val mass (at in­oc­u­la­tion) and both de­vel­op­ment time and in­vest­ment in flight mus­cles. For lar­vae with rel­a­tively lighter masses there was a cost of re­sist­ing in­fec­tion when growth oc­curred on drought stressed host plants, both within the lar­val stage (i.e. longer lar­val de­vel­op­ment times) and in the adult stage (i.e. lower in­vest­ment in flight mus­cle mass). This multi-fac­tor study high­lights sev­eral po­ten­tial mech­a­nisms by which the com­plex in­ter­play be­tween low host plant nu­tri­tional qual­ity due to drought, and pathogen ex­po­sure, may dif­fer­en­tially in­flu­ence the per­for­mance of P. aege­ria in­di­vid­u­als across mul­ti­ple life stages.