A Neonicotinoid Insecticide at a Rate Found in Nectar Reduces Longevity but Not Oogenesis in Monarch Butterflies, Danaus plexippus (L.). (Lepidoptera: Nymphalidae)
James DG. Insects, September 2019.
Read the paper Free to read · doi:10.3390/insects10090276
What this paper is about
Research on neonicotinoids and monarchs had concentrated on caterpillars. This study fed adult monarchs imidacloprid at 23.5 parts per billion, a concentration reported from wild nectar and pollen.
The butterflies died sooner but continued to produce eggs normally, so the damage shows in lifespan rather than fertility.
Summarised here from the abstract below. Not the authors’ words.
Abstract
The monarch butterfly in North America has suffered a serious population decline since the mid-1990s. The introduction and widespread use of neonicotinoid insecticides during the same time period has been suggested as a potential driver of this decline but no studies have looked at the impact of these insecticides on adult monarchs. A brief laboratory study assessed the impact of Imidacloprid, the most commonly used neonicotinoid, on western monarch butterfly longevity and oogenesis. Imidacloprid at 23.5 ppb, a field-realistic rate reported from wild nectar and pollen, was fed ad libitum to newly-eclosed monarchs in a sugar-based diet for 22 days. Treated monarchs showed reduced longevity, suffering 78.8% mortality by day 22, compared to 20% in untreated monarchs. Prior to death, butterflies exhibited signs of poisoning including uncoordinated flapping of wings and uncontrolled vibrating of wings and body. Imidacloprid did not reduce egg production. Shortened adult longevity has serious consequences for monarch population development, migration and overwintering. The potential widespread impact of imidacloprid-contaminated crop and wild flower nectar, may be a significant driver of monarch population decline. More research on the impact of neonicotinoid insecticides on the monarch and other butterflies should be viewed as a serious priority.
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Milkweed USA. (2026). A Neonicotinoid Insecticide at a Rate Found in Nectar Reduces Longevity but Not Oogenesis in Monarch Butterflies, Danaus plexippus (L.). (Lepidoptera: Nymphalidae) (listing). Retrieved DATE, from https://milkweedusa.com/research/a-neonicotinoid-insecticide-at-a-rate-found-in-nectar-2019/
"A Neonicotinoid Insecticide at a Rate Found in Nectar Reduces Longevity but Not Oogenesis in Monarch Butterflies, Danaus plexippus (L.). (Lepidoptera: Nymphalidae) (listing)." Milkweed USA, 2026, https://milkweedusa.com/research/a-neonicotinoid-insecticide-at-a-rate-found-in-nectar-2019/. Accessed DATE.
Milkweed USA. "A Neonicotinoid Insecticide at a Rate Found in Nectar Reduces Longevity but Not Oogenesis in Monarch Butterflies, Danaus plexippus (L.). (Lepidoptera: Nymphalidae) (listing)." Last modified 2026-08-01. Accessed DATE. https://milkweedusa.com/research/a-neonicotinoid-insecticide-at-a-rate-found-in-nectar-2019/.
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title = {A Neonicotinoid Insecticide at a Rate Found in Nectar Reduces Longevity but Not Oogenesis in Monarch Butterflies, Danaus plexippus (L.). (Lepidoptera: Nymphalidae) (listing)},
author = {{Milkweed USA}},
year = {2026},
url = {https://milkweedusa.com/research/a-neonicotinoid-insecticide-at-a-rate-found-in-nectar-2019/},
note = {Accessed DATE}
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