Predators of monarch butterfly eggs and neonate larvae are more diverse than previously recognised

Sara L Hermann,Douglas A Landis,Nathan L Haan,Carissa Blackledge,Andrew T Myers

doi:10.1038/s41598-019-50737-5

Sara L Hermann, Douglas A Landis + Show 3 more

Open Access

https://doi.org/10.1038/s41598-019-50737-5

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Abstract

Conserving threatened organisms requires knowledge of the factors impacting their populations. The Eastern monarch butterfly (Danaus plexippus L.) has declined by as much as 80% in the past two decades and conservation biologists are actively seeking to understand and reverse this decline. While it is well known that most monarchs die as eggs and young larvae, few studies have focused on identifying what arthropod taxa contribute to these losses. The aim of our study was to identify previously undocumented predators of immature monarchs in their summer breeding range in the United States. Using no-choice feeding assays augmented with field observations, we evaluated 75 arthropod taxa commonly found on the primary host plant for their propensity to consume immature monarchs. Here we report 36 previously unreported monarch predators, including representatives from 4 new orders (Orthoptera, Dermaptera, Lepidoptera and Opiliones) and 11 taxa (Acrididae, Gryllidae, Tettigoniidae, Forficulidae, Anthocoridae, Geocoridae, Lygaeidae, Miridae, Nabidae, Erebidae and Opilliones). Surprisingly, several putative herbivores were found to readily consume immature monarchs, both in a targeted fashion or incidentally as a result of herbivory. This work expands our understanding of the monarch predator community and highlights the importance of unrecognized predation on insects of conservation concern.

Highlights

Reports of declining insect populations globally have spurred widespread concern and prompted dramatic headlines[1,2,3]
These include 4 orders of arthropods not previously reported to consume immature monarchs (Orthoptera, Dermaptera, Lepidoptera, and Opiliones), including 11 new families and 25 species
Monarch neonates were consistently consumed by 11 taxa including: several Oecanthus and Allonemobius species, N. americoferus, adult P. maculiventris, Chysopidae larvae, F. auricularia, various Coccinellidae and Formicidae (Table 1)

Summary

Introduction

Reports of declining insect populations globally have spurred widespread concern and prompted dramatic headlines[1,2,3]. The Eastern migratory monarch population undertakes an annual long-distance migration from breeding grounds in the eastern United States (US) and Canada to overwintering grounds in central Mexico This population has declined at an alarming rate since the mid-1990s13, suggesting the migratory phenomenon is in peril[14]. Multiple hypotheses have been advanced to explain this decline, including loss of overwintering habitat[13,15], threats along the migration routes[16], and loss of milkweed host plants from the summer breeding range[17,18]. A study conducted in Minnesota, US considered cumulative proportion survival of monarchs in a restored prairie and found only 20% of eggs survived to hatching, with

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