Pesticide contamination of milkweeds across the agricultural, urban, and open spaces of low elevation Northern California

Abstract

22Insects are facing multifaceted stressors in the Anthropocene and are in decline in many parts of 23 the world. The widespread use of pesticides is believed to be an important part of the problem. In 24 particular, the monarch butterfly is in sharp decline in the western United States. Here we show 25 that milkweeds in the Central Valley of California, a large urban and agricultural landscape that 26 is part of the monarch breeding and migration route, are contaminated with a diverse array of 27 pesticides. We found a few in high concentrations and many in trace amounts. We do not know 28 how these compounds act together and with other large-scale stressors to cause declines, but it is 29 clear that monarchs and other non-target insects are encountering these pesticides. These results 30 provide critical insight into the growing literature on the impact of pesticides on butterflies 31 specifically and non-target insects more broadly. We hope these field realistic concentrations 32 will aid in the design of further experiments in the field and the lab. 33 34 Abstract 35 Monarch butterflies (Danaus plexippus) are in decline in the western United States and are 36 encountering a range of anthropogenic stressors. Pesticides are among the factors that likely 37 contribute to this decline, though the concentrations of these chemicals in non-crop plants is not 38 well documented, especially in complex landscapes with a diversity of crop types and land uses.39In this study, we collected 227 milkweed (Asclepias spp.) leaf samples from 19 sites representing 40 different land use types across the Central Valley of California. We also sampled plants 41 purchased from two stores that sell to home gardeners. We found 64 pesticides (25 insecticides, 42 27 fungicides, and 11 herbicides, as well as 1 adjuvant) out of a possible 262 in our screen. 43Pesticides were detected in every sample, even at sites with little or no pesticide use based on 44 information from landowners. On average, approximately 9 compounds were detected per plant 45 across all sites, with a range of 1 to 25 compounds in any one sample. For the vast majority of 46 pesticides detected, we do not know the biological effects on monarch caterpillars that consume 47 these plants, however we did detect a few compounds for which effects on monarchs have been 48 experimentally investigated. Chlorantraniliprole in particular was identified in 91% of our 49 samples and found to exceed a tested LD50 for monarchs in 58 out of 227 samples. Our primary 50 conclusion is the ubiquity of pesticide presence in milkweeds in an early-summer window of 51 time that monarch larvae are likely to be present in the area. Thus, these results are consistent 52 with the hypothesis that pesticide exposure could be a contributing factor to monarch declines in 53 the western United States. This both highlights the need for a greater understanding of the lethal 54 and sublethal effects of these compounds (individually, additively, and synergistically) and 55 suggests the urgent need for s...

Larval pesticide exposure impacts monarch butterfly performance

“…Overall, our data point to several key messages. First, based on the results from this experiment combined with several other recently published studies 45,47,52,75 , it seems unlikely that neonicotinoids are one of the primary drivers of monarch declines. This is not to say that neonicotinoids are completely innocuous, but compared with other ongoing threats (e.g., loss of milkweed host-plants and overwintering habitat), they likely play a secondary role.…”

“…Although we did not directly test this compound, its toxicity to monarchs is comparable to clothianidin and several orders of magnitude less than more potent insecticides like beta-cyfluthrin (pyrethroid) and chlorantraniliprole (anthranilic diamide) 45 . A recent field survey of pesticide contamination in western US milkweeds similarly concluded that chlorantraniliprole was a far greater threat to monarchs than neonicotinoids 75 .…”

“…While neonicotinoids have received the lion’s share of attention, field surveys of pesticides residues on milkweed reveal a diversity of active ingredients that warrant additional toxicity testing for monarchs 52 , 75 . Our data specifically point to fungicides as a group that should be investigated more in the future.…”

The decline of butterflies in Europe: Problems, significance, and possible solutions

“…Little research has been done on the impact of neonicotinoids on butterflies. They are known to kill Monarch butterflies in the laboratory (42), and lethal quantities have been found in host plants in the field (43). Harmful effects have also been shown for predators of butterflies and other insects (44).…”

Butterfly Conservation in China: From Science to Action

“…Plant protection products (PPPs, e.g., pesticides and herbicides) associated with agriculture pose a second threat. Apart from imminent mortal effect after acute exposure, the larval performance, species richness, and abundance are also affected by chronical exposure [ 65 , 66 , 67 , 68 , 69 , 70 ]. Therefore, butterflies often suffer collateral damage under broad-spectrum pesticides in either agroecosystems or artificial green space in urban areas [ 2 , 71 , 72 , 73 ].…”