Exposed Neophasia terlooii (Lepidoptera: Pieridae) eggs are resistant to desiccation during quiescence

Authors: Halbritter, Dale

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/10/2020
Publication Date: 6/9/2020
Citation: Halbritter, D.A. 2020. Exposed Neophasia terlooii (Lepidoptera: Pieridae) eggs are resistant to desiccation during quiescence. Environmental Entomology. 49(4):918–923. https://doi.org/10.1093/ee/nvaa066.
DOI: https://doi.org/10.1093/ee/nvaa066

Interpretive Summary: Insects face the risk of dehydration due to their small size. Insect eggs that are laid on exposed surfaces are especially prone to extremes in temperature and dryness. The potential of butterfly egg clusters to absorb water from humidified air was investigated in this study. Butterflies in the genus Neophasia glue their eggs along live pine needles and they must survive long intervals without water while overwintering. After 2 days in a very dry environment, groups of Neophasia terlooii eggs were exposed to several different humidified air chambers for 8 days. The masses of the different egg groups were monitored over time. Eggs were able to absorb water from the air to get to their initial mass in chambers as low as 34.5% relative humidity. Humidity was recorded from within the pine needles of a live tree branch in the butterfly's natural habitat for 2 weeks at the start of the overwintering period. Daytime humidity among the pine needles dropped well below 34.5%, but frequently recovered to above 50% at night. In the absence of precipitation, N. terlooii eggs have the potential to rehydrate when humidity increases at night. The process by which water is absorbed from the air and the physical properties of the egg glue are discussed in the context of life in dry habitats.

Technical Abstract: Terrestrial insects face the risk of desiccation owing to their small size and high surface area to volume ratios. Insect eggs are essentially closed systems and those adhered to exposed substrates are especially prone to extremes in temperature and available moisture. The potential of butterfly egg clusters to absorb water from saturated and unsaturated atmospheres was investigated in this study. Butterflies in the genus Neophasia lay their eggs along live pine needles and they must survive long intervals without available liquid water while overwintering. After 2 days in a desiccating environment, groups of Neophasia terlooii eggs were exposed to several different humidified chambers for 8 days. Group masses were monitored over time and the change in mass was compared to the pre-desiccation mass using a repeated measures analysis. Eggs were able to recover water weight to at least their initial mass in conditions as low as 34.5% relative humidity. Ambient humidity was recorded from within the pine needles of a live tree branch in the natural habitat for 2 weeks at the start of the overwintering period. Daytime humidity among the pine needles dropped well below 34.5%, but frequently recovered to above 50% at night. In the absence of precipitation, N. terlooii eggs have the potential to rehydrate when humidity increases at night. The physiological mechanism of water uptake and the physical properties of the egg coating is discussed in the context of life in an arid environment.