Ana M. Vélez Arango
Date of this Version
Greiner, M. 2022. Monarch butterflies: Rearing methodologies and the impact of fungicide and insecticide exposures. M.S. thesis, University of Nebraska-Lincoln. 1-122.
The North American migratory monarch butterfly, Danaus plexippus L., populations has experienced a ca. 90% decline over the past two decades. The decline is attributed to climate change, loss and degradation of overwintering habitat, and the loss of milkweed plants in the midwestern United States. The remaining milkweed stands often occur close to agricultural fields, and efforts to establish additional milkweed on the landscape focus on agricultural systems. However, milkweed plants near agricultural fields are likely exposed to pesticides that could adversely impact monarch caterpillars. Effective management of milkweed habitat supporting monarch caterpillars requires knowledge about the toxicological impacts of pesticide exposure. This thesis includes two research chapters, one exploring monarch rearing on different diets and one investigating the impact of combinations of a fungicide and three commonly used insecticides on monarch caterpillar survival.
The second chapter of this thesis reports monarch butterfly rearing methodologies on an artificial diet and explores the differences in developmental time, survival, and pupal weight between monarch caterpillars reared on the Southland multi-species artificial diet (modified by replacing 15% (w/w) of the dry powder diet with tropical milkweed (Asclepias curassavica L.) powder and on a diet of tropical milkweed leaves. Monarchs reared on artificial diet had longer development at every life stage, 15% lower survival, and higher pupal weights relative to the diet consisting of tropical milkweed leaves.
The third chapter explores the impacts of combinations of the fungicide propiconazole and commonly used insecticides on monarch caterpillar survival. Propiconazole is an SBI fungicide and one of the most widely used fungicides in Nebraska soybean and corn fields. SBI fungicides can alter the toxicity of insecticides by interfering with the detoxification enzymes cytochrome P450s. We found that co-exposure to the SBI fungicide propiconazole with the neonicotinoid insecticide thiamethoxam and the organophosphate insecticide chlorpyrifos resulted in increased survival rates of monarch caterpillars. In contrast, we did not observe an interaction in the co-exposure between propiconazole and the pyrethroid insecticide bifenthrin. In this study, only antagonistic interactions were observed in monarchs co-exposed to propiconazole and insecticides, suggesting that SBI fungicides can alter the toxicity of insecticides in monarchs.
Advisor: Ana M. Vélez Arango