Aggregative feeding of pipevine swallowtail larvae enhances hostplant suitability

Abstract

Many hypotheses have been proposed to explain the adaptive significance of aggregative feeding in the Lepidoptera. One hypothesis that has received little attention is how induced plant responses may be influenced by aggregative feeding, as compared to feeding by solitary larvae. This study investigated the role of aggregative feeding of the pipevine swallowtail, Battus philenor, in California with special emphasis on the induced responses to herbivory of its hostplant. Here, I show that first-instar larvae develop faster when feeding in a large aggregation compared to solitary or small groups of larvae. Furthermore, I show that this effect is mediated by a larval-density-dependent response in the plant and is independent of prior larval experience and direct interaction among larvae. These results indicate that large groups of larvae can effectively enhance hostplant suitability. A separate experiment showed that larvae feeding on previously damaged leaves had a reduced growth rate. Thus, following initial damage a plant first goes through a period of increased suitability, followed by induced resistance against subsequent herbivory. Aggregative feeding in this system may be an adaptive strategy for larvae to manipulate hostplant suitability, adding a new dimension to the role of aggregative feeding for the Lepidoptera.

Intraspecific Host Preferences of Mopane Moths (Imbrasia belina) in Mopane (Colophospermum mopane) Woodland

“…the production of enzymes in the gut or saliva, that reduce the detrimental effects of potentially damaging plant compounds such as tannins). The gregarious feeding behaviour of young mopane caterpillars may also enhance their ability to exploit their host plant (Fordyce 2003). Large groups are thought to either cause nutrient sinks or prevent induced defences in intact plants compared with smaller groups of caterpillars (Karban & Agrawal 2002).…”

Geographic Variation in Clutch Size and a Realized Benefit of Aggregative Feeding

“…Members of the genus Battus are restricted to host plants in the genus Aristolochia (Aristolochiaceae) and in California only one host plant species is available to B. philenor, the endemic A. californica (Racheli and Pariset 1992). The average clutch size observed in California populations, including the focal population at Stebbins Cold Canyon, is 13 eggs per cluster and larvae feed in dense aggregations following hatching (Fordyce 2003), whereas populations in eastern Texas using other Aristolochia species have an average clutch size of 2.5 (Rausher 1995). Geographic patterns of mtDNA variation suggest that B. philenor is a recent addition to the California fauna, indicating that the larger clutches observed in California appear to be a recent modification of this life-history trait (Fordyce and Nice 2003).…”

“…Alternatively, many adaptive hypotheses have been proposed for the evolution of aggregative feeding. Aggregative feeding may increase thermoregulatory ability (Bryant et al 2000), maximize resource use (Le Masurier 1994), circumvent structural plant defenses (Rathcke and Poole 1975), accelerate larval growth due to enhanced plant quality (Fordyce 2003), and function for defense, either through active group defense or enhanced aposematism (Fisher 1930;Stamp 1980). Two avenues of investigation have commonly been used to infer the adaptive significance and evolutionary history of aggregative feeding.…”

“…California females lay significantly larger egg clutches and larvae feed in larger groups compared to populations reported in Texas. We hypothesized that aggregative feeding exhibited by the California population of B. philenor represents an adaptation unique to the California host plant whereby groups of larvae effectively manipulate the plant quality so as to enhance its suitability for larval development (Fordyce 2003). Specifically we asked the following questions: Do plant characteristics explain the variation in clutch size observed within the California and Texas populations?…”

Use of volatiles of Aristolochia chilensis (Aristolochiaceae) in host searching by fourth-instar larvae and adults of Battus polydamas archidamas (Lepidoptera: Papilionidae: Troidini)

“…For example, females of Battus philenor lay clutches of eggs on the leaves of Aristolochia californica and the larvae feed gregariously until the late third instar, when they disperse and feed solitarily (Tatar, 1991;Rausher, 1995;Fordyce, 2003). This raises the questionhow do the dispersing larvae find new host-plants.…”