Impact of a milkweed specialist aphid and its honeydew on monarch success

Myzocallis asclepiadis is a North American native aphid species that lives and feeds exclusively on common milkweed (Asclepias syriaca). A. syriaca is a host for other native invertebrates, including monarch butterflies (Danaus plexippus), whose larvae are milkweed specialists (Asclepias spp.). Monarch populations — especially the eastern migratory populations — are in decline, causing alarm for monarch enthusiasts and conservationists and leading to their recent listing as an IUCN endangered species. Current research aims to mitigate abiotic and biotic factors to increase success of summer generations. Due to their frequent spatial overlap, there is potential for M. asclepiadis to impact monarch success. Preliminary analysis from a recent observational field study at Penn State suggests that M. asclepiadis does have a negative impact on the presence of monarch larvae. Previous research has found that M. asclepiadis individuals produce more honeydew than other milkweed aphids, which results in a buildup of sugar on A. syriaca leaves. This layer of honeydew could present a physical barrier to monarch feeding and success, a mechanism which has not been studied to date. Using greenhouse experiments, we investigated the impact of M. asclepiadis and its honeydew on monarch larval survival, development, and behavior. In the future, we will examine the impact on adult oviposition preferences and strive to incorporate our results into management recommendations to increase monarch survival in the presence of M. asclepiadis.