Exposed Neophasia terlooii (Lepidoptera: Pieridae) Eggs are Resistant to Desiccation During Quiescence

Abstract

Terrestrial insects face the risk of desiccation owing to their small size and high surface area to volume ratios. Insect eggs adhered to exposed substrates are especially prone to extremes in temperature and available moisture. The potential of butterfly egg clusters to withstand desiccation in saturated and unsaturated atmospheres was investigated in this study. Butterflies in the genus Neophasia (Lepidoptera: Pieridae) lay their eggs along live pine needles and they must survive long intervals without available liquid water while overwintering. After 2 d in a desiccating environment, groups of Neophasia terlooii Behr eggs were exposed to several different humidified chambers for 8 d at 5°C. Group masses were monitored over time and the change in mass was compared to the pre-desiccation mass. Changes in mass were minimal, ranging from a 3% increase in the saturated chamber (100% RH) to a 2% decrease in the driest chamber (<10% RH). Ambient humidity was recorded from among the pine needles of a live tree branch in the natural habitat for 2 wk at the start of the overwintering period. Daytime relative humidity among the pine needles dropped as low as 14.5% but rose as high as 92% at night. In the absence of precipitation, N. terlooii eggs can remain within 2% of their starting weight for 10 d at a constant RH of <10% at 5°C. The mechanism for avoiding desiccation and the physical properties of the egg coating are discussed in the context of life in an arid environment.

Keywords: desiccation; eggshell; humidity; survival.