Prevalence of monarch (Danaus plexippus) and queen (Danaus gilippus) butterflies in West Texas during the fall of 2018

Abstract

Background: The monarch butterfly (Danaus plexippus) is a conspicuous insect that has experienced a drastic population decline over the past two decades. While there are several factors contributing to dwindling monarch populations, habitat loss is considered the most significant threat to monarchs. In the United States, loss of milkweed, particularly in the Midwest, has greatly reduced the available breeding habitat of monarchs. This has led to extensive efforts to conserve and restore milkweed resources throughout the Midwest. Recently, these research and conservation efforts have been expanded to include other important areas along the monarch's migratory path. Results: During the fall of 2018, we conducted surveys of monarch eggs and larvae through West Texas. We documented monarch and queen butterfly (Danaus gilippus) reproduction throughout the region and used the proportion of monarch and queen larva to estimate the number of monarch eggs. Peak egg densities for monarchs were as high as 0.78 per milkweed ramet after correction for the presence of queens. Despite our observations encompassing only a limited sample across one season, the peak monarch egg densities we observed exceeded published reports from when monarch populations were higher. Conclusions: To our knowledge, this is the first study to correct for the presence of queens when calculating the density of monarch eggs. This research also provides insight into monarch utilization of less well-known regions, such as West Texas, and highlights the need to expand the scope of monarch monitoring and conservation initiatives. While the importance of monarch research and conservation in the Midwest is unquestionable, more comprehensive efforts may identify new priorities in monarch conservation and lead to a more robust and effective overall strategy, particularly given the dynamic and rapidly changing global environment.

Distribution and phenology of monarch butterfly larvae and their milkweed hosts in the South Central US

“…capricornu, A. viridis, and A. oenotheroides are regarded as regionally important milkweed species for monarchs in Texas, Oklahoma, and Kansas by the USDA Natural Resource Conservation Service (2015c), and in Texas by USFWS (Tuggle 2014). Further support for the importance of A. latifolia as a late season monarch host in West Texas comes from Brym et al (2020; also unpublished data, D. Berman and K. Baum).…”

Distribution, phenology, and land cover preference risk assessments of four South-Central US milkweeds (Asclepias spp.) important for monarch butterflies

“…capricornu, A. oenotheroides, and A. latifolia (broadleaf milkweed) (Calvert 1999). Asclepias latifolia is also reported as a common host plant for the last generations of late summer/fall monarch larvae in west Texas (Brym et al 2020; also unpublished data, D.…”

Changes in landscape and climate in Mexico and Texas reveal small effects on migratory habitat of monarch butterflies (Danaus plexippus)

“…For example, climate conditions at various stages of the life cycle influence seasonal, annual, and possibly longer-term, trends 13 – 16 . Weather effects on spring recruitment (primarily in Texas) can influence overall annual population dynamics 13 , 17 while drought during the fall migration affects monarch lipid levels crucial for overwintering survival 6 , subsequent spring breeding 18 , 19 , and may influence overwintering population size 20 .…”