Ecological and life-history traits predict temporal trends in biomass of boreal moths

Dramatic insect declines, and their consequences for ecosystems
globally, have received considerable attention recently. Yet, it is still
poorly known if ecological and life-history traits can explain declines
and whether insect decline occurs also at high latitudes. Insects’
diversity and abundance are dramatically lower at high latitudes compared
to the tropics, and insects might benefit from climate warming in
high-latitude environments.  We adopted a trait- and
biomass-based approach to estimate temporal change between 1993 and 2019
in Finnish macro-moth communities by using data from 85 long-running light
traps. We analysed spatio-temporal variation in biomass of moth functional
groups with Joint Dynamic Species Distribution Models while accounting for
environmental variables.  We did not detect any declining trends
in total moth biomass of moth functional groups, and most groups were
stable over time. Moreover, biomass increased for species using coniferous
trees, lichens, or mushrooms as hosts, multivoltine species, as well as
monophagous and oligophagous species feeding on trees. We found that
length and temperature of the growing season, winter climatic conditions,
and habitat structure all partially explained variation in moth biomass.
Although boreal moth communities are rapidly changing due to species
turnover, in terms of total biomass they seem to contradict the trend of
dramatic insect declines observed globally. This may lessen the immediate
possibility of negative bottom-up trophic cascades in boreal food webs.