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.
Highlights
The monarch butterfly, Danaus plexippus L., has suffered serious population decline in the eastern and western United States since the mid-1990s [1,2,3,4,5,6]
While this study suggests that monarchs feeding on neonicotinoid-contaminated nectar have reduced longevity, this may not be the only impact
Newly-eclosed monarch butterflies fed ad libitum a sugar solution containing 23.5 ppb of the neonicotinoid insecticide, imidacloprid, which is within the range of neonicotinoid concentrations found in nectar, had reduced longevity, suffering 78.8% mortality 22 days post-eclosion, compared to
Summary
The monarch butterfly, Danaus plexippus L., has suffered serious population decline in the eastern and western United States since the mid-1990s [1,2,3,4,5,6]. Migrating monarchs need abundant nectar resources to fuel the migration and fall nectar resources may have declined during the past 25 years due to agricultural and urban development along migration routes and climate changes [16,17,18,19]. Another substantial change to the landscape since the mid-1990s has been the introduction, widespread use and environmental contamination by neonicotinoid insecticides [20]
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