Energetic cost of girdling in a notodontid caterpillar, Oedemasia leptinoides

In North America, notodontid caterpillars feed predominantly on hardwood trees; some cause significant economic damage with periodic outbreaks. The late instars of several species cut girdles around the petiole, rachis, or stem before feeding on distal leaf blades. Little is known about the benefits or costs of girdling for caterpillars. In this paper, we analyzed the energetic cost of girdling by comparing final instars of a girdling notodontid, Oedemasia leptinoides, with two non-girdling notodontids, Cecrita guttivitta and Lochmaeus manteo . Time allocated to four behaviors (girdling, feeding, walking, and inactive) was measured in the field with 3-h observations each day over three days. We also measured metabolic rates for the four behaviors using flow-through respirometry. The metabolic rate for each behavior was multiplied by the time spent over the 9 h of observation to estimate the total energetic cost of each behavior. In the field, O. leptinoides on black hickory ( Carya texana ) spent 4.6 ± 0.9% of their time girdling. They cut girdles primarily on the first day and fed on leaves mostly on days 2 and 3. Their metabolic rate during girdling was similar to feeding and walking, but greater than inactivity. Overall, the larvae utilized 6.4 ± 1.2% of their total energy while girdling. Relative to non-girdlers, O. leptinoides larvae spent significantly less time and energy feeding on leaves suggesting a trade-off between girdling and feeding. To our knowledge, this study is the first to quantify the energetic cost of an insect behavior for modifying host plants before feeding.