No 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...

No abstract

One of the defining features of the Anthropocene is eroding ecosystem services, decreases in biodiversity, and overall reductions in the abundance of once-common organisms, including many insects that play innumerable roles in natural communities and agricultural systems that support human society. It is now clear that the preservation of insects cannot rely solely on the legal protection of natural areas far removed from the densest areas of human habitation. Instead, a critical challenge moving forward is to intelligently manage areas that include intensively farmed landscapes, such as the Central Valley of California. Here we attempt to meet this challenge with a tool for modeling landscape connectivity for insects (with pollinators in particular in mind) that builds on available information including lethality of pesticides and expert opinion on insect movement. Despite the massive fragmentation of the Central Valley, we find that connectivity is possible, especially utilizing the restoration or improvement of agricultural margins, which (in their summed area) exceed natural areas. Our modeling approach is flexible and can be used to address a wide range of questions regarding both changes in land cover as well as changes in pesticide application rates. Finally, we highlight key steps that could be taken moving forward and the great many knowledge gaps that could be addressed in the field to improve future iterations of our modeling approach.

One of the defining features of the Anthropocene is eroding ecosystem services as a function of decreases in biodiversity and overall reductions in the abundance of once-common organisms, including many insects that play innumerable roles in natural communities and agricultural systems that support human society. It is now clear that the preservation of insects cannot rely solely on the legal protection of natural areas far removed from the densest areas of human habitation. Instead, a critical challenge moving forward is to intelligently manage areas that include intensively farmed landscapes, such as the Central Valley of California. Here we attempt to meet this challenge with a tool for modeling landscape connectivity for insects (with pollinators in particular in mind) that builds on available information including lethality of pesticides and expert opinion on insect movement. Despite the massive fragmentation of the Central Valley, we find that connectivity is possible, especially utilizing the restoration or improvement of agricultural margins which (in their summed area) exceed natural areas. Finally, we highlight steps moving forward and the great many knowledge gaps that could be addressed in the field to improve future iterations of our modeling approach.