Rainforest conversion to monoculture plantations restructures functional communities of braconid parasitoid wasps

The conversion of rainforests into rubber and oil palm plantations drives biodiversity loss in Southeast Asia. Parasitoid wasps are highly diverse and play an essential role in ecosystems by regulating herbivore populations. Declines in density and diversity of parasitoid wasps, after land‐use change is well‐documented, but potential functional losses remain elusive. We studied taxonomic and functional dimensions of braconid wasps (Hymenoptera: Braconidae), sampled by canopy fogging from 32 research plots in Jambi Province, Sumatra, Indonesia. Four land‐use systems were compared: 1) lowland rainforest, 2) jungle rubber (low impact rubber agroforestry), and smallholder monocultures of 3) rubber and 4) oil palm. The abundance, biomass, richness, and rarity of braconids was about 50% lower in rubber and oil palm than in rainforest. In jungle rubber, braconid wasps were generally as abundant and diverse as in rainforest. Taxonomic community composition differed substantially between rainforest and jungle rubber on the one hand, and monocultures on the other, mediated by aboveground temperature, vegetation cover, tree biomass, stand structural complexity and herbivore host abundance. Functional community composition was similar in rainforest and jungle rubber, but differed from and between monocultures, mediated by aboveground temperature, vegetation cover, tree height, and the density of trees and understory plants. Functional trait analysis suggests that rubber plantations, like rainforest and jungle rubber, are dominated by large idiobiont braconids targeting concealed beetle larvae hidden in wood, whereas oil palm plantations are dominated by small koinobiont braconids attacking caterpillars and eggs on the foliage. The findings demonstrate that taxonomic composition of braconid wasps severally degrades from structurally diverse, natural ecosystems to smallholder monocultures, and that functional composition differs between plantation types. Overall, our results point toward land‐use specific taxonomic and functional parasitoid wasp communities in tropical landscapes, providing biological control against different groups of herbivores in smallholder agriculture in Southeast Asia.