Roles of Food Quality and Enemy-Free Space in Host Use by a Generalist Insect Herbivore

Abstract

The relative importance of food quality vs. enemy‐free space remains an unresolved but central issue in the evolutionary ecology of host use by phytophagous insects. In this study, we investigate their relative importance in determining host‐plant use by a generalist caterpillar, Estigmene acrea (Lepidoptera: Arctiidae). In nature, E. acrea late‐instar caterpillars preferred Senecio longilobus (Asteraceae), which contains pyrrolizidine alkaloids that the caterpillars sequester, over Viguiera dentata (Asteraceae), a natal host, and typically suffered a 28% mortality risk from parasitoids. We hypothesized that the natural, mixed diet of caterpillars provides high‐quality food via hosts like Viguiera as well as antiparasitoid defense via sequestered toxins from Senecio. We found that a pure Viguiera diet provides superior growth performance over a pure Senecio or mixed diet in the absence of parasitism. However, when parasitism risk is at least moderate, the mixed diet provides a survival advantage over the pure diets of Viguiera or Senecio. We therefore conclude that the balance between benefits of growth (food quality) and defense (enemy‐free space) maintains the use of a mixed diet in nature. Furthermore, the value of enemy‐free space supercedes the value of food quality in determining the host‐plant preference of late‐instar caterpillars.

Dealing with food shortage: larval dispersal behaviour and survival on non‐prey food of the hoverfly Episyrphus balteatus

“…Most of the decisions an insect makes directly influence the individual itself, but ovipositing females make decisions that influence their offspring. In most insect species, females oviposit on or close to larval food sources and often select oviposition sites that maximise larval survival (Thompson & Pellmyr, 1991;Ohsaki & Sato, 1994;Singer et al, 2004;Gripenberg et al, 2010). But unpredictability of food sources or trade-offs between female foraging and offspring performance (Thompson, 1988;Scheirs & De Bruyn, 2002) might lead the egg-laying female to make suboptimal decisions.…”

Oviposition preference of two hoverfly species in response to risk of intraguild predation

“…To enhance their fitness, for instance, females of insects tend to choose an oviposition site that provides suitable food as well as reduced risk of predation, as achieved by avoiding patches containing potential predators (e.g., Sadeghi and Gilbert, 2000a, b;Blaustein et al, 2004). These relationships have been studied mainly in several taxonomic groups of phytophagous insects (e.g., Yamaga and Ohgushi, 1999;Mira and Bernays, 2002;Singer et al, 2004), and predatory insects as well (e.g., Doumbia et al, 1998;Nakashima et al, 2006).…”

Effect of two solanaceous plants on developmental and population parameters of the tomato leaf miner, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae)

“…Different patterns of host-plant used by herbivorous insects are related to differences in physiology, morphology, chemical and physical defenses of the plants (Singer et al 2004), with subsequent differences in the herbivorous life history traits. Quality and quantity of food consumed by herbivores affect the growth, survival and fecundity of individuals, and hence their populational improvement (Scriber & Slansky 1981, Slansky 1993.…”