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First published online October 16, 2009
Journal of Experimental Biology 212, 3448-3454 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.033365

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Insect eggs protected from high temperatures by limited homeothermy of plant leaves

Kristen Potter^1,*, Goggy Davidowitz^1, and H. Arthur Woods²

¹ Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ 85721, USA
² Division of Biological Sciences, University of Montana, Missoula, MT 59812, USA

^* Author for correspondence (kap15{at}email.arizona.edu)

Accepted 28 July 2009

Virtually all aspects of insect biology are affected by body temperature, and many taxa have evolved sophisticated temperature-control mechanisms. All insects, however, begin life as eggs and lack the ability to thermoregulate. Eggs laid on leaves experience a thermal environment, and thus a body temperature, that is strongly influenced by the leaves themselves. Because plants can maintain leaf temperatures that differ from ambient, e.g. by evapotranspiration, plant hosts may protect eggs from extreme ambient temperatures. We examined the degree to which leaves buffer ambient thermal variation and whether that buffering benefits leaf-associated insect eggs. In particular, we: (1) measured temperature variation at oviposition sites in the field, (2) manipulated temperatures in the laboratory to determine the effect of different thermal conditions on embryo development time and survival, and (3) tested embryonic metabolic rates over increasing temperatures. Our results show that Datura wrightii leaves buffer Manduca sexta eggs from fatally high ambient temperatures in the southwestern USA. Moreover, small differences in temperature profiles among leaves can cause large variation in egg metabolic rate and development time. Specifically, large leaves were hotter than small leaves during the day, reaching temperatures that are stressfully high for eggs. This study provides the first mechanistic demonstration of how this type of leaf-constructed thermal refuge interacts with egg physiology.

Key words: microclimate, respirometry, leaf size, critical thermal maximum, Manduca sexta, Datura wrightii

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