Plant Quantity Affects Development and Survival of a Gregarious Insect Herbivore and Its Endoparasitoid Wasp

Abstract

Virtually all studies of plant-herbivore-natural enemy interactions focus on plant quality as the major constraint on development and survival. However, for many gregarious feeding insect herbivores that feed on small or ephemeral plants, the quantity of resources is much more limiting, yet this area has received virtually no attention. Here, in both lab and semi-field experiments using tents containing variably sized clusters of food plants, we studied the effects of periodic food deprivation in a tri-trophic system where quantitative constraints are profoundly important on insect performance. The large cabbage white Pieris brassicae, is a specialist herbivore of relatively small wild brassicaceous plants that grow in variable densities, with black mustard (Brassica nigra) being one of the most important. Larvae of P. brassicae are in turn attacked by a specialist endoparasitoid wasp, Cotesia glomerata. Increasing the length of food deprivation of newly molted final instar caterpillars significantly decreased herbivore and parasitoid survival and biomass, but shortened their development time. Moreover, the ability of caterpillars to recover when provided with food again was correlated with the length of the food deprivation period. In outdoor tents with natural vegetation, we created conditions similar to those faced by P. brassicae in nature by manipulating plant density. Low densities of B. nigra lead to potential starvation of P. brassicae broods and their parasitoids, replicating nutritional conditions of the lab experiments. The ability of both unparasitized and parasitized caterpillars to find corner plants was similar but decreased with central plant density. Survival of both the herbivore and parasitoid increased with plant density and was higher for unparasitized than for parasitized caterpillars. Our results, in comparison with previous studies, reveal that quantitative constraints are far more important that qualitative constraints on the performance of gregarious insect herbivores and their gregarious parasitoids in nature.

Responses of insect herbivores and their food plants to wind exposure and the importance of predation risk

“…The ability to exhibit developmental plasticity in response to resource limitation has been demonstrated in parasitoid wasps (Godfray, ), but little is thus far known about developmental plasticity in herbivorous insects, particularly as many species feed on plants that contain superabundant resources. In this situation, flexible larval growth due to food shortage is generally unnecessary except during heavy infestations (Fei, Gols, Zhu, & Harvey, ). Given that predation/parasitism risk is high for most insect herbivores, selection should favour development strategies that reduce the window of susceptibility of natural enemies but only to a certain point, given the known benefits of large body size in many insects, including P. brassicae (Boggs, ; García‐Barros, ; Honěk, ; Wiklund & Kaitala, ).…”

“…The ability to exhibit developmental plasticity in response to resource limitation has been demonstrated in parasitoid wasps (Godfray, 1994), but little is thus far known about developmental plasticity in herbivorous insects, particularly as many species feed on plants that contain superabundant resources. In this situation, flexible larval growth due to food shortage is generally unnecessary except during heavy infestations (Fei, Gols, Zhu, & Harvey, 2016).…”

Spatial and temporal diversity in hyperparasitoid communities of Cotesia glomerata on garlic mustard, Alliaria petiolata

“…The large cabbage white butterfly, P. brassicae L. is a multivoltine herbivore that has up to three generations per year in northern Europe and four in the south (Feltwell, 1982). It develops on several brassicaceous host plant species that are usually large and grow in dense, tightly packed assemblages, which is a prerequisite for survival because a brood may require at least several plants to sustain their complete larval development (Chew & Renwick, 1995;Fei et al, 2014Fei et al, , 2016. Because the food plants of P. brassicae are mostly ephemeral (fast-growing) annuals and biennials and are found in discrete parts of the growing season (April-October), the herbivore depends on multiple host plant species for its subsequent generations Heinen et al, 2016).…”

Geographical co-occurrence of butterfly species: The importance of niche filtering by host plant species

“…Given that the host specificity of butterflies is relatively high among herbivorous insects (Novotny et al 2010), butterflies that share a host plant are more likely to be potential competitors for each other than other less specialized herbivores are. Butterfly larvae often consume huge amounts of leaves in the larval stage, and even eat whole material of plants in some cases (Inouye and Johnson 2005; Fei et al 2016; Hashimoto and Ohgushi 2017). Moreover, it is suggested that not all plants or parts of a plant are suitable for butterfly larvae due to within- and among-individual variations in plant quality (e.g., nutritional status and defensive traits such as secondary metabolites) (Damman 1989; Dempster 1997; Van Zandt and Agrawal 2004).…”