Pesticides detected in two urban areas have implications for local butterfly conservation

Human-managed green spaces in urban landscapes have become important focal points for insect conservation, partly because of the desirable insect diversity that these areas support, and also because exposure to nature is important for human health and wellbeing. An important issue in insect conservation is the extent to which nonpest insects are impacted by pesticide applications, but this has been relatively less examined outside of agricultural landscapes. Here, we investigated green spaces, including parks and private yards, in two urban areas (Sacramento, California, and Albuquerque, New Mexico, United States), asking if larval host plants for butterflies in the two regions contained herbicides, insecticides, and fungicides. We assayed 336 individual plants in 19 genera, including woody and herbaceous plants. Pesticide presence was ubiquitous: only 22 samples had no detectable levels of pesticides; the median number of compounds detected in the other 314 individual plants was three; and the maximum detected in any one plant was 18. Within Sacramento, azoxystrobin was detected in 84% of all samples, whereas atrazine was detected in 70% of samples within Albuquerque. Two compounds (azoxystrobin and chlorantraniliprole) were found to exceed concentrations that are known to cause lethal and sublethal effects in 71 out of 336 plants. Our results suggest that the effects of pesticides on nontarget species should be further explored in urban areas, and that nontarget effects on desirable insects are possible in these areas without thoughtful management and elimination of nonessential pesticide applications.