Ecological consequences of shelter sharing by leaf‐tying caterpillars

Abstract

A wide variety of insect herbivores construct and inhabit leaf shelters (ties, rolls, folds, and webs). Shelter construction can lead to a high rate of secondary occupation by other arthropods, including other species of constructors. The consequences for the inhabitants of secondarily occupying these shelters are currently unknown. In this study, we conducted field experiments to examine the fitness consequences (survival and attack by natural enemies) for caterpillars that (i) occupy a shelter with conspecifics vs. occur singly; and (ii) establish a new shelter vs. colonize a pre-existing one. In addition, we conducted factorial laboratory experiments to test the hypothesis that caterpillars sharing shelters with conspecifics might have reduced construction costs (a potential benefit of shelter-sharing or secondary occupation). Larvae of Psilocorsis quercicella Clemens (Lepidoptera: Oecophoridae) placed in white oak [ Quercus alba L. (Fagaceae)] leaf ties alone or in groups of three had equal likelihood of survival from natural enemies. This same caterpillar species, however, had a higher disappearance rate when placed in pre-existing leaf ties than when placed in newly formed ones, suggesting a potential cost of secondary colonization. A similar experiment with a closely related species [ Psilocorsis cryptolechiella (Chambers)], however, failed to detect a cost of secondarily occupying shelters made on beech, Fagus grandifolia Ehrh. (Fagaceae). In the laboratory experiment, we found no evidence of shelter-sharing benefits; rather larvae reared in shelters in groups of three had lower pupal mass (and thus lower potential fecundity) than larvae reared singly, suggesting a cost of shelter sharing. Moreover, groups of larvae forced to repeatedly construct new shelters tended to have reduced survival relative to the other treatment, suggesting that energetic constraints are more likely to reduce fitness when larvae cohabit shelters. Taken together, these results indicate that the common phenomenon of shelter sharing by leaf-tying caterpillars has either neutral or negative effects for the occupants. The fact that these leaf-tying caterpillars actually share shelters may simply reflect limited availability of oviposition sites.

Why do leaf-tying caterpillars abandon their leaf ties?

“…However, previous studies have shown that new, unoccupied ties and damaged, occupied ties are equally attractive to colonizing herbivores (Lill, 2004; Lill & Marquis, 2004). This is despite the fact that caterpillars that are reared in groups within a single shelter achieve a lower pupal mass than those reared individually (Lill et al, 2007). This suggests that food resources are not the only limiting factor for site selection.…”

Native leaf‐tying caterpillars influence host plant use by the invasive Asiatic oak weevil through ecosystem engineering

“…No parasitism of C. castaneus has been observed by us or reported in the literature, although protection against parasitism is often a function of leaf shelters (e.g., LoPresti and Morse 2013). Ants facilitate the abundance of nonnative plant species by providing establishment sites of reduced competition (Farji-Brener et al 2010, Berg-Binder andSuarez 2012), but just the opposite may be the case in our system if multiple species use the same shelters, increasing competition (Sliwinski and Sigmon 2013) or parasitism (Lill et al 2007). …”

Vibratory territorial signals in caterpillars of the poplar lutestring, Tethea or (Lepidoptera: Drepanidae)

“…Shelters are also costly, requiring time, energy and material to build (Ruggiero & Merchant, 1986;Fitzgerald et al, 1991;Berenbaum et al, 1993;Cappuccino, 1993;Fitzgerald & Clark, 1994). Many caterpillars have evolved ways to maintain the use of their shelters while minimizing their costs, such as using empty shelters, attempting take over of occupied shelters, or by sharing them with con-and heterospecifics (Berenbaum et al, 1993;Cappuccino, 1993;Lill et al, 2007). Shelter sharing, however, often has associated costs and is not always favourable (Cappuccino, 1993;Lill et al, 2007).…”

“…Many caterpillars have evolved ways to maintain the use of their shelters while minimizing their costs, such as using empty shelters, attempting take over of occupied shelters, or by sharing them with con-and heterospecifics (Berenbaum et al, 1993;Cappuccino, 1993;Lill et al, 2007). Shelter sharing, however, often has associated costs and is not always favourable (Cappuccino, 1993;Lill et al, 2007). It is proposed that some caterpillars protect their energetic and time investments by defending their shelters from others using vibratory signals.…”

“…Leaf shelters are constructed by rolling, folding or tying leaves together with silk, or building webs or tents (Cappuccino, 1993;Lill et al, 2007) and are believed to provide many benefits, including a favorable microclimate, protection from natural enemies and dislodgement, and improved food quality (Fukui, 2001). As such, caterpillars that expend time, energy and material (silk) constructing their own shelters may be expected to defend these valuable commodities from intruding conand heterospecifics.…”