Effects of early-life exposure to sublethal levels of a common neonicotinoid insecticide on the orientation and migration of monarch butterflies (Danaus plexippus)

Abstract

Migratory insects use a variety of innate mechanisms to determine their orientation and maintain correct bearing. For long-distance migrants, such as the monarch butterfly (Danaus plexippus), these journeys could be affected by exposure to environmental contaminants. Neonicotinoids are synthetic insecticides that work by affecting the nervous system of insects, resulting in impairment of their mobility, cognitive performance, and other physiological and behavioural functions. To examine how neonicotinoids might affect the ability of monarch butterflies to maintain a proper directional orientation on their ∼4000 km migration, we grew swamp milkweed (Asclepias incarnata) in soil that was either untreated (0 ng g−1: control) or mixed with low (15 ng g−1 of soil) or high (25 ng g−1 of soil) levels of the neonicotinoid clothianidin. Monarch caterpillars were raised on control or clothianidin-treated milkweed and, after pupation, either tested for orientation in a static flight simulator or radio-tracked in the wild during the autumn migration period. Despite clothianidin being detectable in milkweed tissue consumed by caterpillars, there was no evidence that clothianidin influenced the orientation, vector strength (i.e. concentration of direction data around the mean) or rate of travel of adult butterflies, nor was there evidence that morphological traits (i.e. mass and forewing length), testing time, wind speed or temperature impacted directionality. Although sample sizes for both flight simulator and radio-tracking tests were limited, our preliminary results suggest that clothianidin exposure during early caterpillar development does not affect the directed flight of adult migratory monarch butterflies or influence their orientation at the beginning of migration.

Host Plant Species Mediates Impact of Neonicotinoid Exposure to Monarch Butterflies

“…Furthermore, our results concerning monarch flight ability also indicated that neonicotinoids might be less relevant to monarch migration than previously suspected, e.g., [40,69]. This conclusion was in agreement with recent findings from field-tracked monarchs that had been exposed to neonicotinoids [29]. Therefore, it is becoming clear that neonicotinoid exposure at concentrations typically found in milkweed does not hinder monarch flight and by extension, migration success.…”

“…While some evidence has suggested these declines stem from issues related to habitat loss during summer [20][21][22], other research points to problems faced during the fall migration [23][24][25][26]. In particular, neonicotinoids have been suggested as a potential cause of decreased monarch migration success [27][28][29]. Some studies cited the increasing use of neonicotinoids as a correlational factor with declines in eastern monarchs [28,30], and another found that western monarch declines were greater where pesticide use and habitat loss were higher [31].…”

Captive-reared migratory monarch butterflies show natural orientation when released in the wild

“…distilled water) with 4 plants per 1.68 L (6 square inch) pot in environmental chambers at the University of Guelph Phytotron. However, we found no evidence of any measurable effect of neonicotinoid exposure on orientation for monarchs with early-life (caterpillar) exposure to clothianidin compared to controls, either when they were tested in a flight simulator or radio tracked in the wild ( Wilcox et al, 2021 ).…”

“…This study was part of a larger project testing the effect of exposure to the neonicotinoid insecticide clothianidin on orientation of fall migratory monarch butterflies ( Wilcox et al, 2021 ). Swamp milkweed ( Asclepias incarnata ) was grown in commercial soil (LA4 Sunshine Loosefill, Sungro Horticulture, MA, USA) treated with either at 4, 8, 15 or 25 ng/g of clothianidin (neonicotinoid insecticide) or a control (i.e.…”

Insect Epigenetic Mechanisms Facing Anthropogenic-Derived Contamination, an Overview

“…In insects, this has been chiefly studied in managed bees Apis mellifera (Linnaeus, 1758) [ 187 ]. Nonetheless, there is also a growing body of evidence demonstrating adverse consequences on other managed as well as native insects [ 209 , 210 , 211 ].…”