Effects of fungicide and herbicide on a non-target butterfly performance

Agricultural intensification is one of the key drivers of biodiversity loss. Intensified agriculture is often associated with increased use of pesticides and the use of pesticides could negatively impact also non-target species living in the vicinity of agricultural lands. We exposed larvae of the Glanville fritillary butterfly (Melitaea cinxia) to a short-term exposure of a herbicide, a fungicide, or a mix of the two via their larval host plant (Plantago lanceolata). Survival and performance of the larvae was recorded and potential carry-over effects on adult butterfly fitness traits were assessed under semi-natural conditions in an outdoor enclosure. Our results showed significantly higher mortality of 60 % in the larvae exposed to the fungicide and 22 % mortality in the fungicide-herbicide mix treatment, with both treatments also impacting adult morphology. Adult female butterflies exposed to the mix of fungicide and herbicide treatment during their development also had lower lifetime reproductive success than the other treatment groups, suggesting that the combined chemical load had stronger carry-over effects into adulthood. Our results demonstrate clear negative impacts of a commonly used fungicide on a non-target butterfly species. The combined effect of two pesticides, while less lethal to larvae directly, seem to have a more profound carry-over impact on fitness of adult female butterflies. The mechanisms underlying the effects of a fungicide alone and in interaction with the herbicide, as well as the relatively minor impacts of herbicide alone on the specialist insect warrant further investigation in the role of pesticides in natural populations.