Facilitative Effects of Group Feeding on Performance of the Saddleback Caterpillar (Lepidoptera: Limacodidae)

Abstract

Gregarious feeding by insect herbivores is a widely observed, yet poorly understood, behavioral adaptation. Previous research has tested the importance of group feeding for predator deterrence, noting the ubiquity of aposematism among group-feeding insects, but few studies have examined the role of feeding facilitation for aggregates of insect herbivores. We tested the hypothesis that group feeding has facilitative effects on performance of the saddleback caterpillar, Acharia stimulea Clemens, a generalist herbivore of deciduous trees. In an understory forest setting, we reared caterpillars alone or in groups on two different host plants, white oak (Quercus alba L.) and American beech (Fagus grandifolia Ehrlich), and recorded multiple measures of insect performance during regular field censuses. As predicted, A. stimulea caterpillars feeding in groups on white oak had increased relative growth rates compared with caterpillars feeding alone, and the magnitude of this facilitative effect varied among censuses, conferring benefits both early and late in development. By contrast, no facilitative effects of group feeding were detected on beech, suggesting that the benefits of facilitative feeding may be host specific. On both hosts, caterpillar development time was slightly faster for group-feeding cohorts compared with their solitary counterparts. Because early instar caterpillars are particularly vulnerable to predation and parasitism, even modest increases in growth rates and reductions in development time may decrease exposure time to enemies during these vulnerable stages. On both hosts, group feeding also reduced the trade-off between individual development time and cocoon mass, suggesting that feeding efficiency is improved in group feeders relative to solitary caterpillars.

Adult facilitation becomes competition as juvenile soapberry bugs age

“…Studies of gregarious feeding behavior in caterpillars indicate that group feeding is beneficial during early development in some species (Denno & Benrey, 1997 ; Fiorentino et al., 2014 ; Fordyce, 2003 ; Inouye & Johnson, 2005 ). Aggregations typically break up in later developmental stages (Denno & Benrey, 1997 ; Fordyce, 2003 ; Inouye & Johnson, 2005 ), potentially as a result of increasing resource demand in older juveniles.…”

Integrating top‐down and bottom‐up effects of local density across scales and a complex life cycle

“…In insects, larval growth rates are important because they affect the amount of time individuals are vulnerable to predators and mass at pupation, which is typically correlated with fecundity (Honek 1993). In some species, larval aggregation is associated with higher per capita growth rates, as groups are better able to overcome physical plant defenses (e.g., trichomes) or otherwise mobilize resources than single larvae (Fordyce 2003, Inouye and Johnson 2005, Costa et al 2007, Fiorentino et al 2014). Because individuals must be in close proximity to have a mechanical advantage or create a localized nutrient sink (Karban and Agrawal 2002), this facilitative effect may depend on density at small scales (e.g., a single leaf).…”

Ontogenetic shift from aposematism and gregariousness to crypsis in a Romaleid grasshopper

“…By contrast, nymphs did exhibit synchronized feeding, suggesting density-dependent manipulation of host quality. Synchronized feeding has been shown to increase consumption rates in several gregarious folivorous insect species [53][54][55][56]. For example, Battus philenor (Lepidoptera) larvae gain more weight in groups than singly, even when prevented from interacting directly, suggesting that simultaneous feeding with others improves host suitability [40], via a form of induced susceptibility involving overcoming of chemical defenses or creation of a nutrient sink [57].…”

“…Conversely, being confined to a single host plant has been shown to increase efficacy of chemical defense in the polyphagous gregarious aposematic R. microptera [68]. The relative effectiveness of chemical defenses and aposematism in specialist vs generalist herbivorous insects is not clear: dietary specialization could enhance defense by increasing concentration of defensive compounds in the insect [54], or feeding from a diverse range of plants could allow synergies between plant compounds [35,69].…”